Worksheet 6.1. C l a y p l a s t e r. Building with Clay.

Transcription

1 CLAY LEHMPUTZ PLASTER DIN C l a y p l a s t e r CLAYTEC e. K Viersen Issued Valid for 12 months, thereafter see Building with Clay.

2 Clay plaster products Mineral Clay Plaster Undercoat and topcoat plaster t = 5-20 mm as undercoat (t 10 mm on concrete) t = 5-10 mm as topcoat Granularity: earth 5 mm, sand mm Mineral Clay Plaster 20: naturally-moist, 1.2 t big-bag produces 700 litres Mineral Clay Plaster 16: dry, 30 kg sack produces 20 litres No Clay Undercoat Plaster with Straw Undercoat plaster t = 8-15 mm (up to 35 mm depending on substrate) Granularity: earth 5 mm, sand 0-2 mm, straw Naturally-moist, 1.2 t big-bag produces 700 litres Dry, 1.0 t big-bag produces 625 litres Dry, 25 kg sack produces 17 litres No Clay Topcoat Plaster with Straw Topcoat plaster t = 7-10 mm Granularity: earth 5 mm, sand 0-2 mm, straw Naturally-moist, 1.2 t big-bag produces 700 litres Dry, 1.0 t big-bag produces 625 litres Dry, 25 kg sack produces 17 litres No NEW Clay Plaster HW Undercoat and topcoat plaster t = 3-10 mm Granularity: mm Dry, 800 kg big-bag produces 544 litres Dry, 25 kg sack produces 17 litres NEW Clay Fine-Finish Topcoat Plaster 06 Topcoat or undercoat plaster for other fine-finish plasters t = 2-3 mm Granularity: mm, very fine fibres Dry, 800 kg big-bag produces 544 litres Dry, 25 kg sack produces 17 litres 2

3 Clay Fine-Finish Topcoat Plaster with Flax NEW Now also available in big-bags Topcoat or undercoat plaster for other fine-finish plasters t = 2-3 mm Granularity: mm, flax Dry, 800 kg big-bag produces 544 litres Dry, 30 kg sack produces 20 litres Clay Surface Filler Smoothing mortar For making surfaces of surface finish quality Q3 t 0.5 mm (for closing pores) 10 kg bucket produces 10 litres NEW "YELLOW" and "RED" primer Primer to improve adhesion of fine-finish (YELLOW) or coarse (RED) clay plaster mortars to smooth / low suction mineral-based substrates. Liquid, ready to use 10 litre and 5 litre buckets Reinforcement mesh To improve the stability of plaster layers on insulation, on surfaces with mixed backgrounds and material changes. Flax fabric: ecological, easy handling Jute: ecological Fibreglass fabric: easy handling Reed mat plaster base For improved adhesion on wood, light earth and mixed-material substrates 3

4 Coverage: plaster surface in m² for different plaster thicknesses Kind Supply form and weight Yield Mineral clay plaster 20 Big-bag, naturally-moist 1.2 t 700 l Mineral clay plaster 16 Sack 30 kg 20 l Clay undercoat plaster Big-bag, naturally-moist 1.2 t 700 l with straw Big-bag, dry 1.0 t 625 l Sack 25 kg 17 l Clay topcoat plaster, Big-bag, naturally-moist 1.2 t 700 l 70 coarse, with straw Big-bag, dry 1.0 t 625 l 63 Sack 25 kg 17 l 1.7 Clay plaster HW Big-bag, dry 800 kg 544 l Sack 25 kg 17 l Clay fine-finish Big-bag, dry 800 kg 544 l topcoat plaster 06 Sack 25 kg 17 l Clay fine-finish Big-bag, dry 800 kg 544 l topcoat plaster flax Sack 30 kg 20 l General notes on product choice and working method Naturally-moist plaster presents options that are not possible with dry plasters. The availability of ready-mixed clay plaster in 1.2 t big-bags is both environmentally-friendly and exceptionally cost-effective, and is only possible with clay plaster as all other plaster mortars would cure and harden. Clay plaster mortars can be processed using plastering machines comprising a mixer and a mortar pump. Naturally-moist plaster material must be protected against freezing in winter as its workability is diminished during the frost period. Dry plasters in 1.0 t big-bags or 25 kg sacks can also be processed using a plastering machine. Open systems (mixer and mortar pump) are well suited for naturally-moist material. Typical machines include a PFT MAXIMIX and ZP3, Closed systems (gypsum plastering machines) are only suitable for use with dry mortar material. Typical machines include a PFT G4, Coarse or fine grain plaster? Coarse-grain clay plaster mortars (granularity 1 mm) are suitable for masonry with mortar pockets or deep ridged surfaces, earth brick and earth block masonry, pumice brick masonry, coarsegrain concrete (primed), plaster bases, straw-clay, and historical clay plasters. Fine-grain clay plaster mortars (granularity 1 mm) are suitable for tight-fitting masonry blockwork with flush face and fine-grain priming, clay undercoat plaster, cement-, lime- and gypsumplasters, clayboards and other dry lining building boards. A special characteristic of clay plasters is that they only harden through drying and can therefore remain overnight or over the weekend in machinery and hoses. There is no mortar waste on site and spilt material can be scooped up and mixed back in. The standard plaster thickness values (shown in bold in the coverage table above) should be adhered to. The lowest value denotes the thinnest possible plaster thickness required to achieve a good professional result. The highest value is the maximum possible thickness achievable with the mortar, although its suitability for the respective substrate must always be tested (by conducting a trial) in each specific case. Ceilings should always be plastered as thin as possible. 4

5 Application Planning and preparations Plan sufficient time for clay plasters to dry. If required, mechanical forced drying can shorten the drying time considerably. When applying several base coats, the second coat can be undertaken as soon as the first coat has firmed up and is sufficiently stable. However, it is safer to allow each layer to dry before applying the next, and thinner layers dry faster than thicker layers. Before applying a top or finishing coat, base coats must have dried sufficiently so that no further shrinkage cracks arise. It is important that clay plasters dry in frost-free conditions. The surfaces of other adjacent building elements should be masked and protected against soiling. As clay plasters are water soluble, this is not as serious as with other plasters, but clay mortars can cause discoloration, particularly on exposed timber surfaces, etc. Preparation of the substrate Chases, holes and other missing sections of the substrate should be repaired in accordance with common practice with a mortar that corresponds to the material of substrate, applying reinforcement where necessary. The substrate should be stable, clean and sufficiently rough. Movement and shrinkage or warping of elements in the substrate must no longer occur. The substrate, along with any repairs undertaken, must be dry before applying a new coat of plaster, as residual moisture will otherwise hinder the drying of the plaster coat. That applies especially for concrete, or brickwork, lime-sandstone or aerated concrete blocks that may have become wet on site or in storage. The same applies for earth building elements that are slow to dry, e.g. light earth internal wall linings (see 3.1). Similarly, floor areas near the base of walls should also be dry. Surfaces that are regularly exposed to moisture, and may therefore also be contaminated with salts, are not suitable for plastering with earth mortar. An exception is the temporary use of clay mortars as a lost plaster (i.e. that is later removed) to draw out salts from an underlying substrate. The substrate should be free of staining substances (e.g. nicotine). Soot-contaminated surfaces (permeated by soot or tar) around old fireplaces and chimneys must be treated appropriately with a blocker in accordance with common practice. Highly alkaline substrates such as concrete (also aerated concrete or lime-sandstone) must be neutralised, especially when using strong and dark colours (e.g. YOSIMA clay design plasters or CLAYFIX Clay Direct clay coatings), to avoid an uneven end result with lighter patches. The suitability of the substrate and good adhesion of the plaster thickness should in all cases be tested by undertaking a suitably large trial surface. One or two coats? Two coats are necessary for substrates with holes and other irregularities for substrates with uneven suction characteristics when the required mortar thickness cannot be achieved in a single coat when reinforcement fabric needs to be incorporated. Single coat plasters are possible when applying coarse clay mortars to coarserough flat substrates applying fine clay mortars to fine-rough flat surfaces. Plaster bases are necessary on smooth surfaces on wood elements and surfaces whenever plaster adhesion is required independent of the substrate beneath. 3.1 Light earth internal wall linings Note Because earth does not react with water and bond chemically, there is not a risk of it setting too quickly. Plaster bases A commonly used plaster base for clay plasters and earth building is reed mat St70 (CLAY- TEC ), a plaster lath with 70 reeds per linear metre. When applied to a flat surface the 1 mm thick base wire is fixed with min. 16 mm long staples to the background. The base wire presses the reed stems against the substrate and must therefore be arranged outwards. The distance between staples is 5-7 cm. Reed plaster lath can be used to construct frame- Reed stem plaster base applied to the timber members of a half-timbered construction 5

6 works for receiving plaster on a supporting construction, spaced at max. 20 cm centres. The plaster base should then be additionally staple-fixed with a mm thick galvanized wire. Priming Claytec colourless deep penetrating primer and stabiliser (CLAYTEC and ) can be used to stabilise old plasters and other substrates with sandy surface. It can also be used to prepare surfaces for tiling (see below). Smooth surfaces and/or low-suction surfaces are primed with a primer. For high-suction or uneven-suction surfaces, the priming serves to reduce and equalise the degree of suction. Claytec YELLOW primer with a granularity of 0-1 mm (CLAYTEC and ) is used to prepare surfaces for fine-finish clay plasters (granularity < 1 mm) and YOSIMA clay design plasters. Claytec RED primer with a granularity of mm (CLATEC and ) is used to prepare surfaces for coarse clay plasters. Pre-wetting To bind dust on existing surfaces and to prolong the workability of plaster mortar, it can be advisable to pre-wet plaster substrates. This is best achieved with a fine moisture spray applied sparingly. A too liberal application of water closes the pores of the surface, inhibiting adhesion and extending the drying time unnecessarily. Mortar preparation and plaster application by hand or machine The addition of water determines the working consistency of the mortar, which should be similar to that of other plaster mortars, i.e. a malleable, workable mass. If the mortar is too stiff, it will not adhere well to the substrate; if too thin, it will contain too much mixing water causing shrinkage cracking as it dries. See the respective product datasheets / product labels for details on the amount of mixing water required. When applying plaster by hand, the mortar can be prepared with a trowel, motorised mixer drill or professional paddle-mixing machine. The mortar should be well mixed, but not excessively. Too intensive mixing can result in shrinkage cracks forming. CLAYTEC clay plaster mortar can be applied with a trowel or a smoothing trowel. In many cases it is spray-applied with a plastering machine or pump. Naturally-moist wares are processed with a compulsory mixer and mortar pump, dry wares with a continuous flow mixer (gypsum plastering machine, closed system). When processing with a gypsum plastering machine, the mortar should not be made too thin to benefit pumping. See com for further details on the use of plastering machines. The contact persons listed online have experience of using the respective machines in practice and can provide competent assistance. Contact us for silo delivery requirements. Once applied, the plaster is levelled with a smoother or plasterer s darby. The pressure applied compresses the mortar while still workable, especially when the plaster was applied by machine. This helps reduce the degree of shrinkage cracking and improves the hardening process as it dries. Information on suitable plastering machines 6

7 Plaster reinforcement Flax reinforcement mesh (CLAYTEC ,.033) is an ideal form of plaster reinforcement for clay plasters, combining optimal ecological qualities with good reliability and working properties. Jute (CLAYTEC ) and glass-fibre reinforcement fabric (CLAYTEC ) are also well suited. The reinforcement fabric or mesh is always applied to the still wet undercoat plaster and worked into the surface using a wooden float or rubbing board (for jute) or a smoothing trowel or similar utensil (flax and glass-fibre). Plastering tools and surface finishes Plaster reinforcement mesh is necessary on mixed-material substrates on soft substrates when board joints need reinforcing to bridge changes in materials in the substrate to counteract cracking resulting from thermal fluctuations (e.g. stoves, wall heating) to stabilise corners. Clay plasters can be applied and worked with the usual tools of the trade. Clay plaster surfaces are usually rubbed, either using a sponge, or a felt, plastic or wooden float. The surface texture depends on the mortar granularity and the tools used. The timing of the working of the surface specifically the dryness of the plaster has a major impact on the finish: the later the surface is worked, the finer the resulting surface finish. Clay plaster surfaces can also be smoothed with a trowel. We offer a range of CLAYTEC Japanese trowels that are an ideal choice for applying and smoothing clay plasters. When applying and working thin clay plasters, draughts produced by heating or ventilation (windows) should be avoided to prevent differential drying of the different parts of the wall. If the plaster hardens at different rates, it can produce an uneven surface appearance. Japanese trowels Corner profiles and plaster beads Plaster beads and profiles should be fixed well with a fixing compound (e.g. gypsum), with the fixing points arranged closer together than is usual for gypsum plasters: ~20 cm apart in the lower section of walls (e.g. up to ~1 m above finished floor level). Clay plaster external and internal corners are often rounded off to reduce the risk of denting and chipping. Special Japanese corner trowels and edgers are available with three different corner radii. Drying The drying time of clay plasters depends on the application thickness, the suction characteristics of the substrate and the building site conditions (ventilation, weather, any artificial drying), because the mixing water must dry out of the plaster. When drying is effective, this does not prolong the overall construction time: a 1 cm layer of plaster on a good-suction substrate can with good drying conditions be worked over after about a week. Thin layer applications of 2-3 mm dry in hours. Unlike other plasters, clay does not cure when drying and hardening and there is therefore no need to retain moisture in the plaster mortar to aid curing. As a consequence, artificial drying is more viable for clay plasters than for other plasters, although this should be undertaken gently to avoid shrinkage cracking. The CLAYTEC information sheet on artificial (forced) drying of clay plasters provides important information on how the drying process functions and the machines that can be Clay plasters, room climate and mould formation 7

8 used. Faster drying reduces the incidence of mould formation. For critical situations, the Technical Bulletin TM01 Requirements of clay plasters issued by the Dachverband Lehm e.v. (DVL German Association for Building with Earth) as well as DIN recommends the keeping of a drying monitoring protocol. Further information on clay plasters, room climate and mould is available online on Clay surface filler A clay surface filler (CLAYTEC ) is used to close the pores of clay adhesive plasters or clay fine-finish topcoat plasters and is applied very thin at 0.5 mm thick, if necessary several times. Once dry, the filler can be sanded. Clay surface filler can be used to achieve surface finish qualities of level Q3. Colour coatings, as described below, are usually sprayapplied to such finishes. YOSIMA clay design plaster, thin lime plaster YOSIMA clay design plasters are applied at a uniform thickness of 2 mm. The colours of this plaster range are derived from the earths used. They are not coloured but pure. YOSIMA plasters are available in a range of 140 colours and 8 textural variants. CLAYTEC thin lime plaster is a fine-grain lime finish for internal use. It is applied to CLAYTEC clay plasters and is used especially in historical building conservation projects. By comparison, the plasters described earlier on pages 2 and 3 are designed to be coated with a paint finish or similar. As such, they are made of normally sourced earths for clay plasters and can contain mineral impurities and colour variations. Paints and coatings The application of CLAYFIX Clay Direct clay paints and brushable plasters begins with the primer. For all clay and other similar plaster substrates, use WHITE primer without any granular component (CLAYTEC and ). It provides a good base coat and prevents the brown colour of the clay plaster from showing through light-coloured plaster surfaces. CLAYFIX Clay Direct is a coating that adheres through a combination of clay and organic binders. CLAYFIX Clay Direct brushable plasters have a slight granular component 0.5 mm, while CLAYFIX Clay Direct clay paints have none. They are used almost always for flat surfaces and are available in a choice of 12 selected colours. Further information is available in 6.3 CLAYFIX Clay Direct. CLAYFIX Lehm direkt Streichputz JADE-GRÜN 1.2 gut Ausgabe 08/2014 Wallpapers If clay plasters are to be wallpapered over at a later point in time, they must be sufficiently flat. Rough surfaces should be given a smoothing coat or pre-papered with a maculation 8

9 layer. If plaster surfaces are to be re-wallpapered, extreme care should be taken when removing old wallpaper before renovation to avoid detaching the clay plaster beneath. Tiling surfaces For tiling surfaces in showers and around bathtubs, a corresponding base plaster (e.g. a cement or lime-cement plaster) or a water-resistant (green) plasterboard panel should be used. For all other surfaces that may occasionally be splashed with water, tiles can also be bonded to clay plasters if this is easier than switching to a different underlying plaster material. Such surfaces should first be primed with deep penetrating primer (CLAYTEC and ). The primer should penetrate the clay plaster as much as possible, which can be achieved by applying the primer several times over wet in wet. The same approach can be taken when clay plasters are used as a background over occasionally exposed (no standing water!) water seals at the junction between wall and floor. Earth stoves Tile stoves and other stove or fireplaces can be given a clay plaster housing. The dense clay plaster retains the heat and radiates it at a slower rate over a longer period of time. The plaster can be applied to brick wire-mesh, which is commonly used for making stove housings. Galvanized wire mesh and metal plaster base are also suitable. It is important to assess whether the expected thermal stresses in the plaster surface may make it necessary to embed reinforcement fabric in the plaster. Reinforcement mesh or fabrics can likewise also be used to reinforce any projecting sections and edges. When plastering stoves or fireplaces, it is important to determine whether a plaster must be made of a non-combustible material of building material class A (DIN / DIN 4102). This is particularly important when planning to use clay plasters with straw. Wall heating systemsn Wall heating systems require thicker layers of clay plaster to cover the heating pipes mounted on the wall surface. The plaster, often several centimetres thick, is heated up by the heating register and radiates warmth into the room. The following work steps lead to reliable results: 1. Before plastering, the integrity of the heating system should be verified by conducting a pressure test. When plastering, the heating pipes should be under regular operating pressure. 2. Apply the first base coat layer when the heating is cold and level off flush with the surface of the heating pipes. 3. Raise the temperature to help dry out the first base coat of plaster. Alternatively, employ a temporary mobile heating apparatus, e.g. Laing S.O.S. Heizmobil EP 13 M. 4. After the first base coat layer has dried with the help of the heating, apply a second base coat of 5-10 mm while the wall heating is cold. 5. Embed a layer of reinforcement fabric in the surface of the second base coat. Adjacent 9

10 sections of reinforcement fabric should overlap sufficiently and the fabric should continue at least 25 cm beyond the edge of the heated surface into the adjacent plaster. 6. Allow the second base coat to dry fully, possibly with moderate help of the wall heating. 7. Apply the finish coat of plaster with the heating turned off! If the wall surface cannot be dried with the help of the wall heating register (e.g. when not yet operable), the thick layer of plaster must usually be force-dried. Thick plaster layers must also be properly dried right up to the edge of the surface. Technical information on wall heating systems Clay plasters for renovation and building conservation CLAYTEC clay plasters are commonly used to plaster straw-clay surfaces in historical halftimbered buildings, or to repair existing clay plaster surfaces. The use of similar materials ensures good adhesion between the existing surface and the new coat of plaster. The process begins with the removal of all loose material and usually also any previous repairs made with an inappropriate material. Holes and missing sections are then wetted and filled with clay mortar. Any timber members that are to be plastered over must be covered with a plaster base, ideally reed plaster base St70 (CLAYTEC ). The reed mat is cut into strips about as wide as the timber element and stapled securely to the wood. If using an undercoat plaster with straw, the reed plaster base may not be necessary if the timber members are < 8 cm wide and do not frame plastered surfaces. The reed plaster base provides a base for the plaster to adhere to. If a new plaster covers changes in materials (e.g. from timber to old plaster), the plaster is usually reinforced with reinforcement mesh, especially when the plaster mortar does not contain fibres. Timber elements do not need to be covered with foil or paper. Before beginning with plastering work, the old clay surface is brushed down with a soft brush and then the surface wetted to bind dust on the surface. To prepare the old clay plaster surface, a thin layer of not too stiff coarse clay plaster mortar is worked into the existing surfaces (by rubbing). This helps to improve the plaster bond and minimises differential tension in the surfaces. This preparatory step is particularly important when a fine-finish clay plaster is applied directly to an existing clay plaster that is in a good condition. In most cases, however, two coats of plaster are applied in order to incorporate plaster reinforcement over timber beams and chases, to level uneven surfaces or where the plaster covers different materials. Sometimes it is necessary to build-up the plaster on the existing wall surface in several layers to achieve an even surface. In such cases, each layer must be allowed to dry fully before the next is applied. Finishing plasters made of lime plaster are described in 6.9 Lime Plasters in Interiors. A further common area of application for clay plasters in renovation is the plastering of ceiling beams. Clay plasters are well suited to such applications due to their soft, malleable nature and in the past were traditionally used mixed with straw for all overhead plastering work or thicker plaster applications. The plaster was applied parallel to the beams with right-angle edges. Any holes and irregularities were evened out with straw-clay or a thick clay plaster. A thin lime plaster was then applied as finishing plaster. The Cologne ceiling, a special variant found in the Rhineland region, features rounded ends where the beams meet the wall. The corner is packed with a straw-clay mass to form a rounded corner of radius cm. When repairing or replacing plastered beams, the straight lines and sharp corners of the plaster can be produced by cutting and forming the reed plaster base mesh and working with boards screwed to the underside of the beams as 6.9 Lime Plasters in Interiors 10

11 guides. The vertical flanks of the beams are plastered first. Once dry, the underside of the ceiling and the beams can be plastered. Any necessary reinforcement mesh is worked into an additional layer of clay fine-finish topcoat plaster. In many cases, cross-beams beneath the ceiling beams as well as supporting columns were likewise plastered. The top coat is typically made of clay plaster, for example the white YOSIMA design plaster. The plastering of clay undercoat plasters with a thin finish of lime plaster is described in 6.9 Lime Plasters in Interiors. Full declaration and material characteristics (DIN 18947) Clay plaster Clay plaster Clay undercoat Clay undercoat Clay plaster Clay topcoat Clay topcoat mineral 20 mineral 16 plaster plaster, coarse HW plaster, fine 06 plaster, fine Full declaration of constituents Grain size group, Clay, sand Clay, sand Clay, sand, Clay, sand, Clay, sand, pumice, Clay, sand, Clay, sand, straw straw natural fibres natural fibres perlite, flax 0/4, < 5 mm 0/2, < 5 mm 0/4, < 8 mm 0/2, < 7 mm 0/2 0/1 0/1, < 2 mm oversize grain Fibres Barley straw Barley straw Natural fibres Natural fibres Flax - - < 30 mm < 10 mm < 3 mm < 15 mm Application thickness 5-20 mm 5-20 mm 8-15 mm 7-10 mm 3-10 mm 2-3 mm 2-3 mm Drying shrinkage Compression class Flexural strength Compression strength Adhesive strength Abrasion Bulk density class Thermal conductivity µ value Water vapour adsorption class Building material class 2 % 2 % 2 % 2 % < 2.0 % 3 % 4 % S ii s II S II S ii s ii s ii s II 1.0 N/mm N/mm N/mm N/mm N/mm N/mm N/mm N/mm N/mm N/mm N/mm N/mm N/mm N/mm N/mm N/mm N/mm N/mm N/mm N/mm N/mm g 0.1 g g 0.3 g 0.4 g 0.1 g W/m K 1.1 W/m K 0.91 W/m K 0.91 W/m K 0.73 W/m K 0.91 W/m K 0.91 W/m K 5/10 5/10 5/10 5/10 5/10 5/10 5/10 WS iii ws iii ws iii ws iii ws iii ws iii ws III A1 A1 B2* B2* A1 A1 A1 *A better fire classification is possible subject to additional fire performance testing (Lehmbau Regeln DVL 2009, p.97). DIN norms and certification DIN Since August 2013, clay plasters in Germany are certified by the DIN German Standards Organisation. CLAYTEC was one of the initiators of this development, which has helped to make clay plaster a modern building material. DIN certification also makes it possible to present a reliable and objective assessment of the technical and room-climatic qualities of CLAYTEC clay plasters. But our quality-consciousness does not end with the technical characteristics alone. Ecological qualities and health and safety are for us just as important and our products are therefore also certified in this respect by other relevant institutes included natureplus, the ECO Institut and the VDB Association of German Building Biologists. Our clay plasters come certified. C l a y p l a s t e r ID

12 Please note: The information provided in this worksheet is the product of extensive experience of earth building work and the use of our products. Nevertheless, this technical information cannot be regarded as legally binding. These notes assume a sufficient level of craftsmanship skills and experience, and knowledge of the relevant building trades. The most recent valid edition of this worksheet is always available from com. Reproduction and publication of these notes or parts thereof is not permitted. Copyright CLAYTEC e.k. WIKI = FAQs on using clay plaster CLAYTEC e. K. Nettetaler Straße 113 D Viersen-Boisheim Germany Tel: +49 (0)2153/918-0 Fax: +49 (0)2153/ service@claytec.com Sales and service in Austria: CLAYTEC Lehmbaustoffe GmbH Sackstraße 26 im Hof A-8010 Graz Austria Tel. and Fax +43 (0)316/ info@claytec.at 12