Tips for perfect screed and underfloor heating
Tips for perfect screed and underfloor heating Understanding guidelines and standard procedures specific to the floor screeding industry is critical if you want to boost productivity, reduce project timelines, cut down operating costs, minimise risks, and deliver optimal flooring for your residential or commercial projects. Why this guide? Because it provides all the information you need to know to understand how a well planned and laid screed can make a difference to your building project. By following our tips, you will be able to make an informed decision about the right screeding contractor for your project and get a perfect floor, regardless of whether the final purpose of your screeding project is regular ceramic tile or linoleum flooring, luxurious wood flooring alternatives, or a soft carpet that feet sink into. Here are six practical steps to getting a perfect screed and under-floor heating system.
Project Planning In screeding, there are two approaches to project planning: 1) setting project timescales based on screed drying times; 2) determining what the area will be used for along with through traffic and final floor finish. While the second point can be easily established by asking the project initiator about the purpose of the area, for the first point, the screeding contractor must possess extensive knowledge about optimum drying times for different types of screeds. The British Standards recommend drying times of 1 day per mm for the first 40mm of screed and 2 days per mm over 40mm. For a standard 75mm depth screed, this can mean a drying time of 110 days in perfect conditions. If your project also includes under-floor heating (UFH), screeds deliver a cost-effective, simple sub-floor, and one of the best performing heat conductors, enhancing the efficiency of UFH systems. Combined with various admixtures, fast-drying and self-levelling screeds can help drive down project timescales, facilitating project delivery within set time frames. Besides drying times, project scheduling should include agreed time frame for special flooring requirements, UFH pipework, and screed testing. All screeds come with instructions that should be strictly followed in order to allow mixtures to dry out completely to achieve the best results. For cement screeds this means natural conditions with no external heat source to accelerate the drying process. Anhydrite screeds on the other hand can be force dried after seven days If you plan to add a UFH system to your construction project, the best decision you can make is to subcontract your screeding project to a professional with extensive knowledge and experience in both screeding and UFH.
Screed System: Design and Specifications Getting the perfect screed for your project depends on getting the right information about project timelines, floor use, foot traffic, square meterage, type of floor coverings, and UFH systems. For the best results, the screed surface should be finished according to the type of flooring that will be installed on top. Additionally, screeders should take into account the surface regularity (SR), the compressive and flexural strength and, in the case of underfloor heating, the screed s ability to expand and contract sufficiently through the heating cycles. Aggregates and admixtures used in screeds affect the compressive (C) and flexural (F) strength of screeds. Typically, screeds with high C and F values are appropriate for heavy duty projects, whilst screeds with low C and F values are more suitable for lighter duty operations. Fast Drying screeds have a reduced amount of available water, making them less prone to the cracking, curling and shrinking that can be seen when traditional screeds are used with UFH. They have the added benefit of reducing project timelines. For textile coverings, solid wood, engineered wood or hardwood flooring, and asphalt, the best choice is a non-slip finish. For tile or linoleum flooring, a smoother surface should be considered.
Screed Mixing Mixing screeds correctly is one of the most critical parts of getting a robust, flat, durable screed layer. Site-mixed screeds are superior in terms of quality, flexibility, and costs compared to ready-mixed screeds, especially when the project is undertaken by a skilled, experienced contractor. The reason for this is that the site-mixed screeds give complete control over the types of admixtures, mixing techniques, and equipment used, allowing screeders to achieve great results and adjust the amount of screed they need according to project specifications. Forced action mixers ensure efficient distribution of cement and admixtures throughout the aggregates, yielding an evenly mixed, high-quality screed. Many fast-drying screeds allow foot traffic to proceed as early as 12 hours, considerably reducing project timelines. Calculating water-tocement ratios correctly is very important; whilst low amounts of water or cement may prevent the screed from developing the required strength, excessive amounts can make screed more prone to curling or cracking. Although most ready-mixed screeds comply with the latest British and European Standards, ensuring a certain level of quality and delivering great convenience, they are more expensive than site-mixed alternatives and come premixed with certain admixtures, which dictate curing, drying, and hardening times, greatly affecting project timescales and budgets. Slips in project timelines can result in wasted batches of ready mix screed and additional expense of sourcing more screed. Whilst ready mixed screed may seem more convenient, it does not guarantee a quality finish as compaction, levels, and surface regularity can only achieved by the individual installer. Whilst hand mixing screeds would appear to be an option for small spaces, it is to be avoided at all costs. Insufficient mixing, batch to batch variations, and contamination from mixing on the ground lead to inconsistent results. Screed failure often occurs with hand mixed screed when small pockets of unmixed aggregates reduce the screed strength. Conversely, forced action screed mixers allow screeds to be mixed quickly, efficiently, and consistently; distributing aggregates evenly through the mixture. Under no circumstances should cement mixers be used for mixing screeds. Since these mixers cannot distribute cement and admixtures efficiently throughout the aggregates, parts of the mixture may contain very low or very high amounts of cement and admixtures. This may negatively affect the force transfer in screeds, which typically results from aggregate-cement interaction, facilitating screed failure. Most screed types are appropriate for the installation of UFH systems. Regardless of whether they are site or ready mixed, it is still important to ensure that the screed is dry completely before the installation of the final floor.
The Right Process for Installing Screeds Laying screed is not an easy job. The first thing a professional should do is to ensure that there have been no changes to the project specifications or timelines that may change the type of screed required. Using crack inducement joints at key places such as at door thresholds reduces the incidence of screed cracking as the screed drys. To avoid damage to freshly poured screed, always adhere to the walk on times and ensure that the screed is protected from any external water. General site traffic proceed on screed 5-7 days after laying. However, advice should be sought on when it is permissible to allow heavy site traffic, such as MEWPs and scaffolding on the screed. The surface of the screed should be protected from direct wear until final floor finishes are to be installed. Additionally, the builder must make sure that the concrete base is well prepared for the installation of screed. The slab must have been cast at least six weeks prior to screeding and there may be further preparation such as removing laitance in the event of bonded applications. Also, the builder must check entrances and exists, removing obstacles so that the screed installation process goes as smoothly as possible. The screeding contractor must inspect the entire area, make sure that it is watertight, and establish the datum level, recording measurements for further reference regarding maximum allowable deviation from master datum. Then, the screeder must ensure that potable water is available close to the mixing plant and a waste facility is within easy reach. For the best results, the screeder must mix the screed correctly, complying with the recommended cement-aggregates-water ratios and using the right mixing techniques. To enhance screed performance and extend its durability, the screeder should apply consecutive layers of screeds, avoiding dry joints. Polythene sheets may be required to cure the screed and stop a fast surface evaporation which can lead to a weaker construction. Some proprietary screed systems have a controlled drying process and do not require polythene cure. Stress Relief Joint Time to Dry Protection
Inspection and Testing Screed failure is a common and costly issue these days. It can happen when screeders use inadequate materials and mixing techniques, and also when screeds are laid without appropriate supervision and inspection. As a result, specific screed issues, such as non-uniform compaction around pipes, remain undetected until the floor is in use. Unfortunately, most builders do not know that screed failure can be easily prevented by performing timely inspections and tests, which should focus on moisture, surface regularity, and screed strength. Since the actual drying time for screeds depends on the ambient conditions, screed depth, and screed formulation, performing a moisture test is very important to ensure that the screed is completely dry before installing the final floor. Calcium Carbide Test The most accurate and efficient method to determine and measure moisture in screeds is the calcium carbide test. To perform this test, screeders must remove a small sample of screed, which is crushed into a powder and placed into a vacuum flask. Calcium carbide is then added, and the flask is sealed and shaken until the reagent mixes completely with the screed powder. The moisture within the screed sample reacts with the calcium carbide, producing acetylene gas. The pressure released by the gas and measured with a pressure gauge is directly proportional with the percentage of moisture by weight contained within the screed. This can help avoid a series of issues relating to residual moisture, which may damage the final floor along with the under-floor and promote mould formation. Hardness Test How do professionals get perfectly level screeds? That is quite simple: by using modern electronic devices, such as laser levels. Unlike a spirit level, these instruments will accurately assess the level and depth of screed required to obtain a flat plane for a perfect floor. continued...
...continued The BRE Drop Hammer test delivers one of the best methods to identify areas that may fail to withstand expected loads and stresses. This test consists in dropping a hammer that falls 1m on to a circular area of contact of 500sq. mm. After a minimum of three tests per 25sq. m, the screeder must use a special gauge to measure the depth of indentation. To get the best possible screed, all the operations mentioned in this guide should be carried out by specialists. BRE Drop Hammer Test To avoid any issues, screeders and clients should agree project timetable and specifications in detail, including moisture and flatness, before the installation of the screed. Fast-drying screeds will reduce waiting times and uncertainty related to screed moisture content. A BRE Drop Hammer test should always be performed, but especially when there are doubts regarding the mix proportions, mixing techniques, and screed installation methods used. A surface regularity test should be performed after the screed is installed. The results from this coupled with the departure from datum test values, will give an indication of the flatness of the floor and, if required, will allow any corrective action to be taken. Most screeds crack at random intervals, as they dry and shrink; the use of fast-drying screeds can help mitigate the risks of cracking due to sudden drying and shrinking. If cracks are observed during on-site inspections, they should be assessed in relation to the purpose of the area and future structural settlement. While fine cracks are not usually detrimental, wider cracks require appropriate corrective measures, such as filling with cement-based products, injecting epoxy resins, or sawing, removing and re-laying, in order to prevent screed fracturing under loading.
Finding the Right Screeding Contractor The right screeding contractor should have extensive knowledge and experience, the latest technology, skilled workforce, and strong references to back up claims. Additionally, he must be able to successfully manage any screeding project, from planning, screed choice, mixing techniques, and screed laying through project delivery on time and within budget. The easiest way to find proficient, reputable screeders is to approach professional bodies, such as the Construction Products Association (CPA), Federation of Master Builders (FMB), and Trustmark. All these organisations assess the financial status of contractors, verify their references, and make site visits before granting membership. Never go with the cheapest alternative; usually, the contractors who take low-paying jobs are unable to deliver the quality expected. Hiring one contractor capable of taking care of any screeding, UFH, and testing tasks will consolidate the decision-making process, and help you avoid errors and mitigate their effects when they do occur. To find a reliable, experienced contractor, seek references, check forums, and even speak to previous customers. The contractor should be licensed for all the work he agrees to perform. If you want to design and install UFH and screed systems, for instance, the contractor must hold the necessary licenses and permits for each phase of the project. Always ask for written quotes and contracts; unlike oral agreements, written contracts offer real protection if something goes wrong, and a fixed quote will protect you from budget creep.
As an investor in quality management systems, BuilderScreed ensures that all of its professionals are able to manage screed projects of any size and type across South East England. Furthermore, by combining superior workmanship with the latest screeding technologies, top products, and rigorous quality control, the experienced, skilled, and competent screeders working at BuilderScreed can deliver high-quality screeds, just perfect for a perfect floor. Contact BuilderScreed today for free expert advice, no-obligation quotes, or estimates, and you will benefit from the best service offered by one of the most reputable UK screeding contractors. BuilderScreed is a division of: CSC Screeding Ltd Chancery Court Business Centre Lincolns Inn, Lincoln Road High Wycombe, Bucks. HP12 3RE Tel: 0845 500 4055 Email: info@cscscreeding.co.uk Web: builderscreed.co.uk Endorsed by the Screed Scientist