Tiling to Calcium Sulfate Based Screeds

Transcription

1 Tiling to Calcium Sulfate Based Screeds Published by The Tile Association The Tile Association The Mount, 43 Stafford Road, Stone, Staffordshire ST15 0HG Tel Website: Page 1 of 20 The Tile Association

2 1 FOREWORD A Technical Working Group of The Tile Association has prepared the paper Tiling to Calcium Sulfate based Screeds. The Paper has been written with the aim of providing advice for all parties involved in the process of designing and using calcium sulfate based screeds primarily for use with ceramic and natural stone tiling, and should be used in conjunction with current and forthcoming British, European and International Standards on tiles, tile related products and tile fixing. The guidance can also apply to other rigid tiles. The Tile Association gratefully acknowledges the support given by members of the Association, together with invaluable assistance offered by Lafarge Gyvlon Ltd, Cemex Ltd and Neil Beningfield & Associates Ltd. 2 DEFINITIONS Calcium Sulfate CaSO 4 Coefficient of thermal expansion DPM Ettringite RH (Relative Humidity) SR C F Chemical Name (International spelling) Chemical formula Mathematical value used for calculating thermal expansion Damp proof membrane A mineral produced as a result of a chemical reaction between calcium sulfate and cement in the presence of moisture Atmospheric moisture content Surface regularity Characteristic compressive strength Characteristic flexural strength 3 PRODUCT DESCRIPTION This document covers the pump-applied self-smoothing screeds based on a binder of calcium sulfate. The document does not include hand-applied screeds and reference should be made to manufacturers of hand-applied screeds when using such products. The British Standard regarding the application of this type of screed is Part 7 of BS8204:2003 Pumpable self-smoothing screeds Code of practice. This standard specifies requirements such as soundness and level tolerances. These screed materials are also referred to in BS EN13813:2002 Screed material and floor screeds. Screed material. Properties and requirements and BS EN Methods of tests for screed material. NBS Publication Section M13 also applies in the installation of such screeds. 3.1 Uses As a levelling screed in domestic and commercial projects, to provide a suitable surface for the application of floor coverings, tiles and other specialist finishes and toppings. As with all screeds calcium sulfate screeds should be laid in a weather tight building envelope. Page 2 of 20

3 Calcium sulfate based screeds can be laid on bases suitable to receive conventional cement based screeds. They can be laid bonded to the base, unbonded (laid on a membrane) or floating (laid on insulation for thermal or sound insulation). They are not suitable as a wearing surface or for external or internal locations where they can become damp, frequently wet or saturated areas. By their nature, flow-applied screeds cannot be laid to any significant falls. 3.2 Characteristics Minimal shrinkage, negligible cracking and curling Infrequent construction joints Self compacting High characteristic strength (in situ strengths of 20 to 35N/mm 2 ) BRE Screed Test Category A unbonded, Categories B & C floating, to BS No reinforcement required, even for unbonded or floating screeds Can incorporate underfloor heating Unsuitable for damp, wet and saturated locations Drying rate dependent on screed thickness and site conditions Requires low moisture content prior to tiling Requires sealing by protective primer where Portland cementitious bedding systems are used Normal expectation would be to achieve SR2. SR1 can be achieved with care and attention. Pre-treatment, for example, sanding the surface may be necessary to remove laitance. 3.3 Materials The screed will consist of: Anhydrite or alpha (α) hemi-hydrate calcium sulfate binder A well graded sharp sand and/or inorganic filler Additives and admixtures depending on screed manufacturer Clean water The binder will be one of the chemical forms of calcium sulfate. CaSO 4 is the anhydrous form of calcium sulfate, known as anhydrite CaSO 4. ½ H 2 O is known as hemi-hydrate. There are various forms of hemi-hydrate, in particular alpha hemi-hydrate that may be used in screed formulations. Whichever form of anhydrite or hemi-hydrate is used as the screed binder, it will, when mixed with water, crystallise to form gypsum, CaSO 4.2H 2 O. All hardened calcium sulfate screeds will be similar gypsum materials. Calcium sulfate screeds are proprietary formulations. They may be delivered to site in one of the following ways: a) Fully batched and mixed off site at a screed batching plant and delivered in mixing vehicles. b) In silos or transmix. The dry-mix ingredients will be mixed with water in a continuous mixer-pump unit for delivery to the working area. c) In bags. The bags will be emptied into the dry powder hopper of a continuous mixerpump unit for delivery to the working area. Page 3 of 20

4 On site quality control should be carried out by the screeding contractor with a simple flow test to verify the consistency of the mix. In all areas these surfaces will require adequate surface preparation prior to tiling (see clause 5.1). 3.4 Typical Physical Properties Wet density (approx) 2,200kg/m 3 Dry density (approx) 2,000kg/m 3 BRE Test (BS8204-1) Time to foot traffic Drying time before laying ceramic tiles Categories A, B or C hrs (depending on ambient temperature and humidity). (in good ventilation 1 & ambient conditions, e.g. 20 o C and 65%RH) - Up to 40mm thickness 1 day/mm - Over 40mm thickness See Table 2 Coefficient of Thermal expansion 12x10-6 mm/mm/ o C (See BS EN ISO ) Fire rating (BS476-4) Dimensional change on setting /drying Characteristic strength (28 days) Thermal conductivity 3.5 Product Recognition Non-combustible ±0.2mm per linear metre C20-F3 to C35-F Watt/m o C. See manufacturer s data sheet The main contractor and/or client should inform the tiling contractor of the nature of the screed, and the tiling contractor should ask for this information. Information on the nature of the screed should be detailed in the Operation and Maintenance Manual kept by the building owner. Calcium sulfate based screeds are a mix of fine and coarse aggregates with a calcium sulfate binder, and therefore look similar to a cement sand screed. It is not always obvious that a screed is, or is not, a calcium sulfate based screed. Often a light colour, almost white, will indicate that the screed is likely to be calcium sulfate based. However calcium sulfate screeds are not always white and can be much the same colour as the aggregate they contain. In addition, where refurbishment work is being undertaken any previous floor finishes, adhesives or smoothing compounds will hide the nature of the screed beneath. A definitive determination of the nature of the screed will require a chemical analysis of a sample of the screed. A calcium sulfate screed will be characterised by high calcium oxide and sulfate content. 4 DESIGN CONSIDERATIONS FOR SCREED The choice of floor tiles on this type of screed is an area which demands careful consideration at the design stage. Contact with specialist tiling contractors and tile manufacturers/suppliers should be considered at this stage. Calcium sulphate screeds may not be suitable for certain heavy duty installations and advice should be sought on their suitability. 1 Poor ventilation will increase drying times Page 4 of 20

5 4.1 Forms of Screed Construction Any concrete or base should be constructed in accordance with BS8204-1:2003 +A1:2009 and the screed finished to SR1, with the appropriate soundness category Bonded construction The screed may be laid onto a mechanically prepared concrete base that is protected from rising damp. This will permit the minimum screed thickness but is seldom used because, for a small increase in thickness, an unbonded screed can be laid without the need for preparation Unbonded construction on a separating membrane The screed may be laid on a separating membrane as an unbonded screed. The separating membrane is typically a polyethylene sheet of minimum 500 gauge thickness. This will obviate the need for base preparation and can prevent wet screed from flowing down holes and gaps in a base, particularly a precast plank or beam and block base. For bases without protection against rise of ground water, a DPM should be provided under the screed Floating construction - unheated The screed may be laid on insulation to provide thermal insulation or impact sound insulation or a combination of these. A polyethylene sheet membrane should be laid over the insulation to prevent the screed mortar flowing under the insulation. This sheet can be of DPM grade if a damp proof membrane is required Floating construction incorporating underfloor heating Pump-applied self-levelling calcium sulfate screeds are suitable for underfloor heating applications laid with a minimum 25mm cover over the pipes or wires, although due consideration should be given to the screed and underfloor heating manufacturers guidelines. There must be an effective damp proof membrane between the screed and the substrate, ideally underneath any insulation. A slip membrane may or may not be required. Consult underfloor heating manufacturer. Pump-applied self-levelling calcium sulfate screeds are suitable for the incorporation of under-tile heating systems. 4.2 Thickness The minimum thickness recommended in BS will typically be as shown in the table below Page 5 of 20

6 Table 1 Typical minimum thickness Bonded Unbonded over a solid base Floating over thermal or sound insulation Cover over conduits and heating pipes 25mm 30mm 40mm (or 35mm in purely domestic applications depending on the load bearing capacity of the insulation) 25mm (dependent on the underfloor heating system) The maximum thickness is typically some 80mm, however the thicker the screed the longer it will take to dry. Abrupt changes in thickness, which can lead to formation of screed cracks, should be avoided. 4.3 Movement Accommodation For floors 2 m or more between restraining surfaces such as perimeter walls, columns or steps, joints should extend through the full depth of the screed and finish to allow for small thermal and moisture movements. The screed should be further divided up as discussed in Section 7. At the design stage provision should be made for the thermal expansion of the screed and the applied flooring. See Clause Heated and unheated sections of screed, regardless of shape, must be separated by means of a joint. Movement joints should be inserted in the doorways where the surfaces have separate heating circuits which are likely to be heated in different ways. Account should be taken of the shape of the floor area (e.g. L-shaped screed) to avoid cracking. This is best achieved by dividing such areas into rectangular panels separated by movement joints. 4.4 Setting out of Tiling Setting out may have to be related to the siting of movement joints which are usually detailed on working drawings but it is sometimes necessary for their positioning to be left to the discretion of the tiling contractor and formed as the tiling works progress. If this is not practicable because of construction programme restraints e.g. crack inducement joints may need to be formed in calcium sulfate base screed without underfloor heating before tiling works are carried out then it is very important that the tiling contractor or specifier sets out exactly where joints are to be cut into the screed so as to ensure they will coincide precisely with the tiling layout, falling directly underneath joints formed between full tiles or cut tile units to a pre-determined design layout. Careful measurement or a gauge rod should be made indicating the overall measurement of a given number of units with specified joint widths; with this the tiling contractor will determine the best method of setting out to avoid unsightly cut units. Whole units should be used to the greatest possible extent. If cutting is necessary then cut tiles should be fixed as unobtrusively as possible and should achieve symmetry with regard to cut tiles in the total area. Page 6 of 20

7 5 SCREED INSTALLATION 5.1 Surface Preparation Bonded Screeds Totally enclosed medium/heavy shot blasting or other mechanised preparation should be used to expose clean aggregate in the concrete base. All residues must be removed by vacuum to provide a dry, dust free surface free from laitance or other contamination. The base should be primed with an acrylic polymer primer, polyurethane or water dispersed epoxy primer or such other primer as may be recommended, which is allowed to dry before application of the screed. Note: The concrete base should be sufficiently dry and the moisture level should be tested. See Clause Unbonded and Floating Screeds The base should be sufficiently level to ensure that any membrane will be flat to the floor without risk of puncture. The base should be level enough to ensure insulation boards are fully supported and cannot rock on high points. Alternatively, if insulation boards will not be fully supported, they may be laid into a grout or weak screed mix or similar to ensure full support. The insulation boards must be of sufficient density to avoid compression from the weight of the screed and tiling system. Prior to installation of insulation boards the base should be cleaned to remove loose residue. Due consideration should be given to substrate moisture. See clause Application Application should be to the manufacturer s instructions by a suitably trained and qualified applicator. The designer and main contractor are responsible for determining the position of a DPM, where appropriate. In all cases ground bearing concrete slabs should include a DPM to protect against rising damp. Note that damp concrete bases (e.g. with residual construction moisture) in direct contact with the screed can result in considerably extended drying times for a screed laid bonded or not isolated from that base. This may have a detrimental effect on the adhesion of the installed floor finish. The ambient conditions must be suitable for the drying of the screed. Adequate temperature will also be necessary. As with all screeds, it is the responsibility of the main contractor to ensure that the base and screed are sufficiently dry prior to laying floor tiles. Levels must be accurate to meet the requirements of the specification for the floor tiles being installed. Table 4 of British Standard BS defines three classes of Surface Regularity - SR1, SR2 and SR3. If SR1 is not achieved, further work, by the use of a suitable levelling compound, may be required before tiling installation can be undertaken. (See clause 9.2) Very large pours of unbonded or floating construction, with a dimension exceeding 40m without interruption (such as dividing walls), should have suitably formed bay joint of Page 7 of 20

8 compressible material. This may be formed by a crack inducer or a full depth saw cut as soon as the screed has hardened, to form a bay joint. This must be carried through overlaid tiling and will affect the setting out and location of cut tiles. (See clause 7) 6 SURFACE TREATMENT, DRYING AND TESTING OF THE SCREEDS 6.1 Surface Treatment Where required, removal of loose friable skin must be carried out at a suitable time after screeding, usually 4-6 days after application using appropriate equipment. This will also assist the drying of the screed. 6.2 Drying Screed drying time is approximately 1mm/day up to 40 mm thickness in adequate temperatures and drying conditions. This will increase for screeds thicker than 40 mm and in poor drying conditions. In common with other screeds, it is very important that good drying conditions are provided for as soon as the screed is laid. The screed should be protected from very rapid drying or draughts on the first day, but thereafter atmospheric humidity must be low, i.e. not greater than 65 o RH, and the air temperature must be adequate (e.g. 20 o C) so that moisture can evaporate. Good ventilation or the use of dehumidifiers can assist in reducing the atmospheric humidity. Table 2 Sample drying times: Screed thickness 40mm 50mm 60mm Drying time in ideal drying conditions 40 days 60 days 80 days Drying times will increase in adverse conditions when temperatures are lower and/or relative humidity is higher. The drying rate of a calcium sulfate based screed can be improved by increasing the room temperature and or lowering the relative humidity in accordance with the manufacturer s advice. Drying can also be improved by using heaters and dehumidifiers and any underfloor heating must be commissioned in accordance with the manufacturer s advice and slowly brought up to temperature. Heaters and dehumidifiers should not be directed at the screed. Underfloor heating should be commissioned in accordance with the instructions of the manufacturer, and may be used to speed drying of the screed 7 days after laying of the screed. If it is desired to force dry or accelerate the screed drying, and the floor contains heating pipes the following should be adopted: Step 1 Allow seven days drying Page 8 of 20

9 Step 2 Increase the heating system temperature by 5 o C per day until the planned maximum input temperature is reached. Step 3 Keep the planned input temperature constant for a minimum 7 days without reduction. Step 4 Reduce the screed temperature by 10 o C per day until the screed surface reaches room temperature or not less than 15 o C. The screed must be checked for dryness by the floor layer prior to tiling. Similar procedures applied to electric-based heating systems. 6.3 Testing Residual Moisture Levels Before ceramic floor finishes are laid, the moisture content of the screed should be checked to ensure that it is adequately dry. Three different tests for determining moisture levels are described below. This responsibility is in the hands of the main contractor or other party. The British Standard BS8203-1:2001 method for measuring the moisture condition of a base to receive a floor covering is to use an electronic meter or hair hygrometer. This non-destructive test method for sand: cement screeds may also be used for pumped calcium sulfate based screeds. This figure equates approximately to 75% relative humidity (the required limit for floor finishes). For correct results, the BS8203 method must be strictly adhered to, including the use of a correctly sized and insulated box sealed to the floor, a sufficiently long test for equilibrium to be reached, typically hours, and the use (where appropriate) of an impervious sheet around the instrument The European Standard for testing calcium sulfate screeds recommends the CM (Carbide Method) of testing. A carbide moisture tester may be used, preferably a model which has an appropriate scale reading on the recording dial. Typical requirements will be 0.5% water by weight for moisture sensitive floor coverings (e.g. ceramics and adhesives). This figure equates approximately to 75% relative humidity. At a thickness of 30mm, with ambient temperature of 20 o C and with good ventilation, the screed should reach a moisture content of 0.5% in approximately 30 days. The moisture content of the screed may be determined by drying a sample of the screed in an oven. The sample is weighed before and after the oven drying to determine the weight loss as a percentage of the dry weight. The oven temperature should be 40 o C (higher temperatures will give false results). Samples should be of full screed depth and are to be wrapped in plastic immediately after sampling to prevent them drying during transport to the testing laboratory. Electronic meters may be useful in determining where wetter and drier areas of screed are located, but one of the above methods should be used to determine whether a screed is dry enough to receive the flooring Soundness Testing Page 9 of 20

10 Soundness testing of the pumped calcium sulfate screed is the responsibility of the main contractor. Where required bonded and unbonded pumped calcium sulfate based screeds, when tested using the BRE Screed Tester should achieve Category A, B or C as described in the Annexe to BS8204-1:2001 depending on the final service conditions and load. Floating calcium sulfate screeds (i.e. on insulation) cannot be tested by this means Departure from datum The maximum permissible departure of the level of the screed from a specified or agreed datum plane should be specified taking into account the area of the floor and its use. For large areas for normal purposes a departure of ±15mm from datum may be found to be satisfactory. Greater accuracy to datum may be required in small rooms, along the line of partition walls, in the vicinity of door openings and where specialised equipment is to be installed directly on the floor Surface Regularity Test The surface should be tested in accordance with British Standard BS with A The class of local surface regularity of the screed should be selected from those given in Table 1 according to the use of the floor. In making this selection, account should be taken of the type and thickness of the flooring to be applied and the standard of surface regularity required of the finished floor. The highest standard (SR1) should be used where ceramic floor tiles are bedded in adhesives when any irregularities in the screed surface cannot be accommodated within the adhesive bed and where the minimum irregularity is required of the finished floor. The medium standard (SR2) of surface regularity can be selected where the regularity of the finished floor tiling is not a significant factor or when provision is made for the screed surface to be pre-smoothed before the installation of the ceramic floor tiles. The lowest standard (SR3) can be selected where an unbonded semi-dry cement and sand bed is applied over a separating membrane as described in clause 24.2 of BS Insistence on higher standards of surface regularity than are necessary will result in higher costs. Pumpable self-smoothing screeds do not self-level. SR2 is a typical expectation. SR1 may be achieved with care. The designer should specify the maximum permitted abrupt change in level across joints in screeds taking into account the type and thickness of the flooring to be applied. Where unbonded semi-dry bedding is used, a maximum of 2 mm would be acceptable, taking into account the surface preparation necessary to receive flooring. For ceramic floor tiles bedded directly on the prepared screed surface it would be appropriate not to have any changes in level across screed joints unless provision is made for pre-smoothing the screed. Table 3 Classification of surface regularity of pumped self-smoothing screeds to receive rigid tiling Page 10 of 20

11 Class SR1 SR2 SR3 Maximum permissible departure from a 2m straightedge resting in contact with the floor 3 mm 5 mm 10 mm Application Ceramic floor tiles bedded in adhesives directly to the prepared and primed screed. Ceramic floor tiles bedded after pre-smoothing the screed Ceramic floor tiles bedded in an unbonded semi-dry cement and sand bed Check surface levels against datum using normal surveying methods. Check surface regularity by using a 2m long straight edge laid in contact with the floor surface and resting under its own weight. Measure the deviations of the surface from the underside of the straight edge between points of contact by means of a slip gauge or other suitable measuring device. The number of measurements required to check levels and surface regularity should be agreed between the parties concerned, bearing in mind the accuracy required and the likely time and cost involved. 7 JOINTS IN SCREED 7.1 General Any movement joints, or joints likely to be subject to movement, in the calcium sulfate screed should coincide with movement joints in the tile bed. Such movement joints should be designed to accommodate differential movement between the separated sections of screed, i.e. of sufficient width to accommodate the anticipated movement. Wherever possible movement joints in the screed should be formed as straight joints and should intersect with other movement joints at right angles to assist the setting out of the floor tiling. In addition to these locations, intermediate or stress relieving joints, spaced and formed as recommended in BS5385-3, should be incorporated in the tile bed and where necessary in the screed. 7.2 Movement Joints Movement joints in unheated calcium sulfate floor screeds In unheated calcium sulfate floor screeds, movement joints should be detailed: - Over structural joints in the underlying construction. These movement joints through the screed and tile bed should coincide with and be designed to accommodate the same movement of the underlying structural joints. At day joints in unbonded or floating calcium sulfate screeds which are likely to be subject to movement. At perimeters of floors where the screed abuts walls and upstands. At doorway thresholds between separate areas of use. At junctions between heated and unheated sections of the screed. As a bay, generally with a side length 40 m or in accordance with the instructions of the screed manufacturer. Page 11 of 20

12 The width and spacing of movement joints should be sufficient to accommodate anticipated movement. The provision and detailing of movement joints should be considered at the design stage and the thermal movement of the calcium sulfate screed (caused for example by exposure to sunlight) should also be taken into consideration. Note that, although pumped calcium sulfate based screeds can be laid in large areas without joints, where joints are required in unheated screeds, they may be formed by either crack inducers or saw cuts through the hardened screed or formed during the laying of the screed. In the latter case, this will require the use of the formwork or proprietary pre-formed movement joint profiles designed for these screeds Movement joints in heated calcium sulfate floor screeds In heated calcium sulfate floor screeds, movement joints should be detailed: Over structural joints in the underlying construction. These movement joints through the screed and tile bed should coincide with and be designed to accommodate the same movement of the underlying structural joints. At perimeters of floors where the screed abuts walls and upstands. As a movement joint through both the screed and tile bed dividing the tiling into areas not greater than 40sqm. The areas bounded by movement joints should be square to rectangular with the width to length ratio not exceeding 5 to 8. As movement joints at significant changes of width of the screed surface and in doorways. As a bay joint isolating areas of screed with separately controlled heating circuits. At doorway thresholds between separate areas of use. At junctions between heated and unheated sections of the screed. The width and spacing of movement joints should be sufficient to accommodate anticipated thermal movement of the screed between the maximum operating temperature and expected lowest temperature of the screed. The coefficient of thermal expansion of the pumped calcium sulfate screed should be taken to be 12 x 10-6 mm/mm/ C. If the detail provided by the screed manufacturer states that there might be changes in length during installation (expansion), these must also be taken into account when calculating the necessary width of movement joints. Note that, although pumped calcium sulfate based screeds can be laid in large areas without joints, where joints are required in heated screed they will have to be formed during the application of the calcium sulfate screed. This will require the use of formwork or the use of proprietary pre-formed movement joint profiles designed for this purpose. Note that where heated water pipes are used, BS EN :2009 Water based surface embedded heating and cooling systems Part 4:Installation- recommends that movement joints and perimeter joints shall only be crossed by connecting pipes (flow pipes and return pipes of the circuit) and solely in one level. In this case, the connecting pipes should be covered with a flexible insulation tube of some 0.3m in length. Table 4 Indicative values of hard flooring materials. Type of Hard Flooring C.T.E x 10-6 o C -1 Comparison with Concrete (10) Group Blb floor tiles 5 to 9 Medium Group Bla floor tiles 6 to 7 Medium Agglomerate tiles 20 to 30 Very high, greater than most Page 12 of 20

13 bases Granite & Basalt 6 to 9 Medium Marble 3.5 to 7 Low to medium Limestone & Dolomite 6 to 10 Medium Sandstone 11 to 12 Medium Quartzite 11 to 13 Medium Glass tiles & mosaics Approximately 8 Medium Terrazzo 7 to 13 Medium Slate 3 to 9 Low to medium (Note C.T.E. = Coefficient of Thermal Expansion) Table 5 Indicative values for some materials used on building sites. Building Materials C.T.E. x 10-6 o C -1 Comparison with Concrete Concrete 7 to 13 Medium Lightweight concrete 7 to 8 Medium Cement and sand screed 11 to 13 Medium Calcium sulfate based 10 to 12 Medium screeds Mild steel 11 to 13 Medium Aluminium 24 High Brass 19 Medium to high Rigid PVC panels 76 Very high Wood (across grain) 30 to 35 High Wood (along grain) 4 to 6 Low Cement board 7 Medium Plywood 3 to 5 Low UPVC 60 Very high Acrylic plastics 70 to 80 Very high Glass fibre reinforced 25 to 40 High to very high polyester Proprietary tile backer boards Vary with composition 7.3 Intermediate or Stress Relieving Joints Medium (restrained by composite structure) Intermediate or stress relieving joints, spaced and formed as recommended in BS , should be incorporated in the tile bed and, where necessary, in the screed. The need and the spacing of intermediate/stress relieving joints should be considered at the design stage and these should be installed as described in clause 9.5 of this document Intermediate/stress relieving joints in ceramic tiling on unheated calcium sulfate floor screeds Where the dimensions of the tiled floor exceed 8 to 10 metres between perimeter joints, intermediate/stress relieving joints should be inserted to divide the tiled floor into bays of 8-10 metres. The area of tiling bounded by such joints should be kept as square as possible to ensure that any stresses are equal in each direction. Additional intermediate/stress relieving joints should be inserted in suspended floors where stresses can develop where deflection may occur, e.g. over supporting walls or beams. Page 13 of 20

14 With large areas of ceramic floor tiling it is advisable to divide the floor tiling into bays by incorporating movement joints at not more than 30 metre intervals, each bay being subdivided into smaller bays by stress relieving joints not greater than 10m apart Intermediate joints in heated floor structures Heated screeds are already divided into 40 m 2 maximum bays; therefore intermediate joints should not be required. However some tile types with a higher coefficient of thermal expansion (see Table 4) may require to be laid in smaller bay sizes. 8 SURFACE PREPARATION AND REPAIR OF THE SCREED 8.1 General Avoid water ingress to completed screeds, and arrange to dry out accidental spillages as soon as possible. 8.2 Surface Regularity Normal expectation would be to achieve SR2. SR1 can be achieved with care and attention. Where required use an appropriate smoothing/levelling compound to achieve surface regularity SR1. Before an appropriate smoothing/levelling compound is laid on the calcium sulfate based screed, the screed should be dry and primed with a suitable primer recommended by the manufacturer of the product being applied. 8.3 Cracks It is normal for their cause to be identified and repaired. 8.4 Surface Damage Surface damage can be made good with a smoothing/levelling compound, either cement based, latex based or calcium sulfate based. A primer will be needed before application of these products. (See clause 9.2) 8.5 Other Surface Defects Refer to manufacturer for advice. 9 TILING SYSTEMS British Standard BS5385 is the Code of Practice for Wall and Floor Tiling. This document should be viewed in conjunction with this British Standard. 9.1 Assessment of Substrate The calcium sulfate based screed should have been allowed to dry. The moisture content should have been checked by appropriate means. Confirmation should have been obtained that the residual moisture content should be lower than 0.5% water by weight or 75% relative humidity before the application of primer. (See clause 6.3) The main contractor, Page 14 of 20

15 project manager or responsible person should ensure that the surface of the screed has been correctly prepared to ensure removal of all laitance and loosely bound particles. This can be achieved by using abrasive sanding equipment and vacuum cleaning or for a more effective, dust free and environmentally friendly technique then contained shot blasting equipment with vacuum extraction is recommended. The tiling contractor should ensure this has been carried out before tiling begins. Laitance is the loose or weakly cohesive fines present on the surface of a screed so surface preparation should be used to remove it. The screed should be swept and vacuumed by the tiling contractor to remove all dust and friable material such that the surface to be tiled is clean, dry and sound. 9.2 Priming and Levelling To ensure maximum adhesion, and to avoid an adverse chemical reaction e.g. ettringite formation between the sulfate in the screed and cementitious adhesives or levelling compounds, the screed must be primed with a primer compatible with the tile adhesive (e.g. acrylic polymer, polyurethane or water dispersed epoxy primer). The primer application should provide complete coverage and shall be adequately absorbed in the calcium sulfate surface in accordance with the instructions of the manufacturer of the adhesive or levelling compound. The applied primer should then be allowed to dry out. 9.3 Tanking on Pumped Calcium Sulfate Screeds Background Information Calcium sulfate screed should not be used in damp, frequently wet or saturated areas. If there are cases where occasional spillages may occur, tanking should be used as a safeguard to prevent the calcium sulfate screed becoming wet. To ensure adequate protection, the tanking should be brought up the walls to a sufficient height. The calcium sulfate based screed must be dried to a residual moisture content of lower than 0.5%. The main contractor, project manager or responsible person should ensure that the surface of the screed has been correctly prepared to ensure removal of all laitance and loosely bound particles. This can be achieved by using abrasive sanding equipment and vacuum cleaning or for a more effective, dust free and environmentally free technique then contained shot blasting equipment with vacuum extraction is recommended. The tiling contractor should ensure this has been carried out before tiling begins Priming To ensure maximum adhesion of the tanking system the screed must be primed with a suitable primer if recommended by the tanking system manufacturer. A continuous film must be obtained. The primer should be allowed to fully dry Tanking The tanking membrane should be impervious to liquid water and have a low moisture vapour transmission rate. Page 15 of 20

16 The tanking is usually applied to the primed surface as a paint applied membrane or as a mat system in accordance with manufacturer s recommendations. Surface treatment such as blinding with fine aggregate to provide a key and improve adhesion of subsequently applied tiling may be adopted with some systems. 9.4 Adhesive Selection The most suitable adhesive for tiling over primed calcium sulfate screeds is a suitable polymer modified cementitious adhesive having a C2 classification in the European Standard, BSEN12004:2007. Both normal and rapid-setting types should be suitable but the adhesive manufacturer s advice must also be sought to confirm suitability. The selection of a suitable adhesive (BS EN 12004:2007) will depend on several factors, the most common being: The type of tiles being fixed. If the calcium sulfate screed is unheated or heated. If the use of a rapid hardening (class F) adhesive is required. Type C adhesive of class 2 or class 2F (C2 or C2F) should be used: If the tiles being fixed are vitrified tiles (porcelain and similar dense, non-absorbent tiles). If the calcium sulfate screed is heated. Type C adhesive of class 1 or 1F (C1 or C1F) may also be used: If the tiles being fixed are quarry tiles or ceramic floor tiles of similar absorbency. If the calcium sulfate screed is unheated. Other specialised proprietary adhesives outside the scope of the current Standard classification may be suitable. The use of a pourable or fluid bed adhesive will be advantageous when fixing large format floor tiles. In all cases the adhesive manufacturer s advice should also be sought to confirm suitability. With natural stone tiles or agglomerated tiles the selection of the adhesive should follow the recommendations of BS as well as being compatible with the characteristics of the tiles being fixed. 9.5 Movement Joints in the Screed General Forming movement joints in calcium sulfate screeds requires the use of proprietary joint profiles or other suitable materials and these should be spaced in the required positions to carry through the joints that will appear in the tiling, where applicable. Attention must be paid to the siting of these to ensure compatibility with the tiling. It is advisable therefore to form intermediate movement joints in non-heated screeds by mechanical saw cutting through the screed as the tiling is being laid and precise positioning of the movement joints can be set out. Page 16 of 20

17 For calcium sulfate screeds, this sawing will need to be carried out by means of a dry cut floor saw with vacuum attachment in order to ensure that the screed remains dry Movement joints in the tiling and the screed Movement joints should be located in the screeding as required by the structure beneath and the subsequently applied tile finish in accordance with BS and BS Such joints have to be brought through the tile and bed. These will normally be around the perimeter of the floor and where the tiling abuts columns, curbs, steps and plant fixed to the base. Any structural joints in the building should be carried through the screed and tile bed to the face of the tiling. See Section 6.2 Movement Joints Other Standards may apply. To facilitate the installation of the movement joints in the floor tiling the joints in the screed can be part filled with a suitable back-up material and the movement joints installation as recommended in BS Ceramic Tile and Natural Stone Movement Joints The design and installation is covered in BS and BS Movement joint cavities should extend through the tiling, tile bed and screed and should be completely filled and sealed after grouting of the tile joints. Where separating layers are incorporated the movement joint should extend to this layer only. The minimum movement joint width should be 6 mm. For joint widths of 10mm or over pre-fabricated profiles should be included which are metal edge protected. Structural movement joints in the bed and tiling should be sited immediately over and be continuous with structural movement joints in the base. Perimeter movement joints should be inserted where tiling abuts restraining surfaces, e.g. perimeter walls, columns, steps and fixed plant, etc. Intermediate movement joints should be inserted where required, see Clause 7.2. The tile field should be kept as square as possible to ensure that stresses are equal in each direction. Additional movement joints should be inserted in suspended floors where flexing may occur, e.g. over supporting walls or beams. Movement joints should be inserted over joints within the screed, at doorways. Where large thermal movements or vibrations are expected, the movement joint spacing should be closer together. For movement joints in heated calcium sulfate based screeds see clause The tiles must be fixed and the adhesive or bedding allowed to cure before joints are sealed. Where a sealant type joint is being used, the joints must be cut or formed with parallel edges and must be free from contamination e.g. grout, dust, etc. For sealant type joints it is normal to partially fill the joint cavity with a compressible material e.g. cellular polyethylene, before topping up the joint to the finished level with sealant. The choice of sealant will depend upon the environment of the tiled application, e.g. resistance to chemicals, rolling loads, mechanical cleaning, etc. The sealant manufacturers advice should be sought for selection of the correct sealant in each application. Page 17 of 20

18 For areas with high pedestrian traffic or where wheeled loads are being transported, preformed movement joint profiles manufactured from metal or PVC should be considered. These types of profile will reduce the likelihood of tile or joint damage. Information regarding the correct selection and use of pre-formed movement joint profiles should be obtained from the manufacturer. 9.6 Tile Installation The tiles should be fixed using a solid bed method of application, ensuring as far as is practically possible, a void-free bed beneath the tiles as defined in BS This will involve the use of a notched trowel, designed specifically to produce a solid bed when the ribs of adhesive are forced together under the weight of the tile as it is pressed down. In certain circumstances it may be necessary to butter the back of the tile. When fixing large format floor tiles (e.g. longer than 600mm on one side), use of a pourable i.e. lower viscosity adhesive will be advantageous in achieving a solid bed. Further advice however should be sought from the manufacturer to confirm their suitability. Care should be taken not to damage the previously applied primed coating with the notched trowel. NB: Where underfloor heating is incorporated this should have been thoroughly checked and tested prior to tiling. This will involve the gradual heating and cooling sequence allowing the floor to cool down to room temperature but above 15 C before tiling commences. (See Clause 6.2 heating schedule) 9.7 Grout Selection The adhesive should be allowed to harden and dry for the time recommended by the manufacturer, prior to the start of grouting. Sufficient time should be allowed to elapse to ensure adequate setting of the bed to preclude disturbance of the tiles during the grouting operation. For the majority of installations a cementitious grout, preferably polymer modified, is recommended, ideally from the CG2 classification in BSEN For hygiene purposes, where routine aggressive cleaning products are used and nonabsorbent joints are required a grout based on a reaction resin (e.g. epoxide), of BSEN13888 classification, RG1, may be used. The grout should be mixed in accordance with the manufacturer s instructions and then worked into the joint cavities with a grout float or rubber squeegee, until they are filled solidly. Grouting machines can be used with advantage on large floors. The minimum width of floor tile joints is 3mm and the minimum depth 6 mm unless the tile thickness is less. For more details please refer to the relevant clauses in British Standard BS The grout finish should be, as near as is practicable, flush with the tile surface. Surplus grout should be removed from the tile face within the working time of the grout mortar. After removing excess grout and after the grout in the joints has hardened sufficiently, the tiled surface should be wiped over and left clean. Page 18 of 20

19 Where reaction resin grouts are used the manufacturer s recommendations should be followed regarding application and cleaning off. 10 CLEANING & MAINTENANCE OF TILES Ceramic floor finishes need little maintenance and can be kept clean by regular sweeping, then washing with warm water to which a neutral or nearly neutral detergent has been added. Final thorough rinsing with clean water is essential. Large areas of plain or textured floor tiles are more readily cleaned with rotary mechanical scrubbing machines. The regular use of scrub and rinse cleaning machines fitted with abrasive pads may damage the tiled surface and result in gradual loss of thickness in the wear layer. When using such machines care should be taken to ensure that the final rinse is with clean water only. The Tile Association has produced the document The cleaning and maintenance of tiles which gives detailed advice on cleaning and maintenance. 11 SOURCES OF REFERENCE/BIBLIOGRAPHY Building Research Establishment (BRE), Watford British Standards: BS EN Water based surface embedded heating and cooling systems Part 4: Installation BS476 Fire tests on building materials and structures BS5385 Wall and floor tiling BS8000 Workmanship on building sites BS8203 Code of practice for installation of resilient floor coverings BS8204 Screeds, bases and in-situ floorings BS EN ISO Ceramic Tiles BS EN Adhesives for tiles Definitions and specifications BS EN 13813:2002 Screed material and floor screeds. Screed material. Properties and requirements BS EN Grouts for tiles - Definitions and specification BS EN Methods of test for screed materials BS EN Liquid applied water impermeable products for use beneath ceramic tiling bonded with adhesives. Requirements, test methods, evaluation of conformity, classification and designation DIN German Standard Building Lime-Part 1: Definitions, specifications, control NBS Publication, National Building Specifications The Tile Association documents: Adhesives and Grouts in Internal Tiling Movement Joints in Internal Tiling The Cleaning and Maintenance of Tiles Tiling to Heated Floors Screeds Flooring & Finishes ISBN , published by CIRIA Merkblatt Keramische Fliesen und Platten, Naturwerkstein und Betonwerkstein auf calciumsulfatgebundenen Estrichen Published in January 2000 by the Fachverband des Page 19 of 20

20 deutschen fliesengewerbes, Zentralverband des deutschem baugewerbes and Deutsches Baugewerbe. Members of the Working Group Neil Beningfield Paul Dawtrey Lesley Day Andy Hone Alan Jackson Andy Nevitt Brian Newell Cyril Potter Colin Stanyard David Wilson Page 20 of 20