Underfloor heating systems (UFH) are a modern and energy-efficient way to heat your home. A typical system works by pumping heated water through flexible piping in the floor. This radiates heat upwards into the immediate environment. When installed correctly with the appropriate type of screed, UFH can heat a single room, such as a bathroom, or an entire home. UFH is an easy to install and eco-friendly heating method that has gained in popularity over the last 10 to 15 years. In fact, many new build homes now come with underfloor heating as standard.
There are many benefits to underfloor heating systems, not least greater energy efficiency, and lower running costs once the system is installed. In comparison to traditional radiators, UFH distributes heat more evenly and reduces the chance of lost heat, should a window or door be opened. The system does not take up wall space, meaning there is more room for additional furnishings. There are no noises from water-filling radiators and less chance of burns from hot radiator surfaces. UFH is also good for allergy sufferers and effective at reducing the growth of mould.
What Is Screed Floor?
Screed is a type of mortar, commonly used for flooring, and has a smooth texture. It is less course than concrete and can be used for numerous tasks, including installing underfloor heating systems. Screed is often made from fine grains of sand and typically sits above a solid concentrate base. The purpose of screed is to provide a smooth top surface so that tiles, carpet, laminate, or wood flooring can be installed.
Screed’s smooth properties make it ideal for use as the upper section of flooring. In many floor installations, screed is placed above a concrete slab. The final top layer of flooring, such as laminate, or carpet, can then be situated above. Concrete is made from stronger aggregates and this makes it more durable. Screed is less durable but has a more suitable consistency. This makes it ideal for underfloor heating systems. There are various types of screed available on the market. But the most common types can be categorised as semi-dry screed and liquid screed.
You can use this article to find the costs of floor screeding.
Different Types Of Screed Flooring
It is recommended that you choose the type of screed floor at the same time as the type of underfloor heating system. Planning and ensuring you have the right materials and components can reduce the possibility of problems in the future. Making changes after installation can problematic and costly. Part of this preparation is selecting the right type of screed to use for securing the underfloor heating pipework. This will ensure the heat can travel through the floor and warm the room effectively.
The two main types of screed are semi-dry and liquid:
- Semi-dry screed – Often known as the ‘traditional’ method, semi-dry screed is the most popular and is made from a mixture of sand and cement. The ratio of the mix is usually 3:1 or 4:1, depending on the requirements of the project. Water is applied to create a smooth consistency. The mixture can then be applied by hand using a trowel or other flat-edged tool and levelling boards. Good accuracy and results can be achieved, but an experienced installer is vital to ensure consistency and quality of the final design. Polypropylene fibres can be added to improve the strength of the mixture.
- Liquid screed – This type of screed is sometimes referred to as ‘self-leveling’ screed or ‘flowing screed’. It does not require the use of levelling boards and flat-edged instruments. Rather than being prepared on-site or delivered, liquid screen is directly poured onto a concrete surface to the required amount of depth. The mixture fills the surface more quickly than with traditional methods, enabling a fill of up to 1500 m2 to 2000 m2 in a single day. With fast-drying, liquid screed allows the installation of surface carpets, tiles, wood, or laminate more quickly, allowing the project to be completed sooner.
What Is The Best Screed For Underfloor Heating?
Semi-dry screed is the most common type of screed used for most underfloor heating projects. But this does not mean it is the best. There are times when liquid screed may be more appropriate. It all depends on the nature of your build and the requirements of the development. Semi-dry screeds are typically better for smaller floor surface areas, where a trowel or flat edge tool can be used to smooth the surface. Fast-drying mixtures are available from some manufacturers and allow semi-dry screeds to be applied to more urgent build projects.
Liquid screeds are faster to apply because they can be easily poured directly onto the specified surface area. They do not need pre-mixing with water, unlike semi-dry screeds. The free-flowing nature of liquid screeds means that larger surface areas can be covered in a faster amount of time, and with greater accuracy. And because liquid screed dries faster and is less likely to crack, the underfloor heating system can be used sooner to help dry the flooring. This is useful when manpower is limited and the project must progress to remain on schedule. A liquid screed is also stronger than semi-dry screed, especially when proprietary mixtures are used in construction.
How Do You Screed Over Underfloor Heating?
An underfloor heating system is effectively ‘planted’ inside a screed. The installation of underfloor heating should not be attempted before the room is protected from external elements. It is crucial to install underfloor heating systems and screed correctly. Otherwise, problems can occur, such as cracks in the upper surface. This is especially the case with stone or tiled surfaces.
Other issues to avoid include inconsistent surface levels. Although it is possible to install UFH and screed on a DIY basis, if you are unsure, it is always best to secure the services of a professional underfloor heating systems specialist. Mistakes and substandard heating issues are invariably expensive to remedy.
Before installation of underfloor heating pipework and associated movement joints, it is important to make sure the surface is completely smooth to accommodate the screed. Be sure to select the most appropriate type of screed (semi-dry or liquid) and have a clear idea of the height necessary to maximise heat efficiency.
The underfloor heating piping or cables should not be wound too tightly so that it restricts the flow of water. Instead, popular layouts should be considered, such as linear, serpentine, and spiral. Insulation is equally important and keeps the efficiency of the system high to prevent lost warmth.
Once the screed has been applied over the UFH piping, the ‘commissioning process’ can begin. Do not attempt to walk on the screed until it has completely dried. Instead, wait for the screed to cure before turning on the heating. After the curing process, the UFH system can be switched on to further assist with drying. Once the screed has completely dried and set, floor finishes can be installed, such as tiling, laminate, hardwood boards, and carpets.
How Long Does Screed Floor Take To Dry?
Screed floor varies in the amount of time it takes to dry. The type of screed, the size and layout of the flooring, and the commissioning process are all factors to consider. Semi-dry screed takes longer to dry than a liquid screed, which can be walked on within 48 to 72 hours. Often 3 to 4 weeks is the total required drying time. A useful measurement is 1 day’s worth of drying time per every 40 millimetres of height. Keep windows and doors fully closed to keep out the elements until the solidifying process has been completed. You should ensure you do not turn on the underfloor heating system for over one month. This prevents unnecessary cracks from forming. Super fast-drying screeds are available if you are short on time.
Summary
This article has provided an overview of underfloor heating systems, the types of screed available, and the installation and potential issues you may encounter. Underfloor heating has many advantages over traditional heating methods. It is more energy-efficient, cheaper to run, and is a good practical alternative to radiators. But there is a higher initial cost to purchase and install an underfloor heating system. The correct UFH installation and the right type of screed must be used for maximum effect.
The size of your property or room, your budget, and the complexity of the layout are key factors in determining the design and type of screed for the project. It is certainly possible to install underfloor heating if you are DIY savvy. With the correct screed mixture, an underfloor heating system is relatively straightforward for anyone with basic building knowledge.
Having said that, problems can occur if the underfloor heating system and screed are incorrectly installed. A common problem is cracks forming in the screed or in the upper floor. This is especially common when tiles or stone is used for the floor walking surface. So be sure to thoroughly read your underfloor heating installation documentation to minimise the potential for these issues.
