It’s not always easy to choose the right liquid screed application for a construction project. The difference between a new build and a renovation can be huge, and what works for one can cause a whole heap of problems on the other. This guide takes a closer look at the key differences in screed applications for new builds and renovations, covering everything from how the base is laid to how it’s heated and how long it takes to get it done.
Key Things to Keep in Mind
Liquid screed behaves in different ways depending on whether it’s being used in a brand new build or one that’s being renovated. New builds give you full control over the substrate, insulation, floor levels and underfloor heating design. Renovations on the other hand are limited by the existing floors, door thresholds, structural limitations and all sorts of legacy moisture issues. So it’s really important to decide on the right liquid screed application and liquid screed product early on in the building design process to avoid having to do costly rework.
In new builds, the optimal screed thickness can be easily achieved alongside the underfloor heating installation, and flowing calcium sulphate screeds can be used with ease. If it’s correctly specified from day one, then screed can make a huge difference to the thermal efficiency of the building, especially in residential environments. Underfloor heating design in a new build is also much easier to get right compared to doing a retrofit. In a retrofit, you often have to make compromises because of floor-to-ceiling height and existing thresholds.
Moisture control and damp proof membrane integrity are a lot easier to predict in new construction. Older properties can have missing or failed membranes, and you never really know what the substrate is like until you dig it up. There’s also often a lot of residual moisture that has to be sorted out before you can even think about laying a screed. The choice of screed type, mix, and the installation method – whether it’s bonded, unbonded or floating – all differs sharply between projects. At Ready2Pour we can advise on the right system for both new construction projects and older homes being modernised.
What is Liquid Screed and Where Does It Get Used?
Liquid screed, also known as flowing or self-compacting screed, is a pumpable, self-levelling mix. The liquid screeds we supply and install are BBA-approved Gyvlon calcium sulphate screeds made by Anhydritec, with a binder made from 98% recycled materials. It is a thin layer of material laid over a concrete base, insulation layer or underfloor heating system, and it can also cover underfloor pipes while creating a smooth surface for the final floor finish. Screed is primarily used to lay flooring materials like tile, LVT, timber and carpet.
Unlike traditional sand and cement screeds, at Ready2Pour we also provide applying screed as part of a supply-and-install service for domestic and commercial projects, with liquid screeds flowing around and fully encapsulating underfloor heating pipes without needing to be manually compacted, getting rid of the air voids that reduce heating efficiency in sand and cement screeds. They also achieve tighter level tolerances and can be laid at a much thinner section. Self-levelling screed is ideal for large areas and underfloor heating, allowing rapid installation over big spaces – Gyvlon screeds can be installed at up to 200 m² per hour, or 2,000 m² in a day, although that installation speed is separate from the later drying process.
Typical applications in the UK from 2024-2026 include new housing developments, apartment blocks with underfloor heating, residential extensions and the refurbishment of large open-plan commercial spaces. This article focuses on comparing the screed applications in new builds and renovations, rather than covering screeding theory from scratch. Screed can also support thermal and acoustic insulation, helping reduce noise transmission when used with insulation layers or underfloor heating systems.
Different Types of Screed and What Works Best
The main types of screed – bonded, unbonded, floating and wearing – are used in both new builds and renovations, but the selection criteria shift significantly depending on project constraints, including thickness and composition to suit load bearing capacity in industrial settings.
Bonded screed is laid directly onto the structural base and stuck down with a bonding agent or mechanical key, adhering straight to the concrete subfloor. Its thickness usually ranges from 25 to 40 mm and is especially suitable for thinner applications where heavy loading is expected over a good quality concrete substrate.
Unbonded screed is separated from the concrete subfloor by a slip layer or membrane and is laid unbonded over a suitable damp proof membrane on the concrete slab. The typical thickness for traditional unbonded screeds is 50 to 75 mm because the screed is separated by that membrane, but liquid screed can be laid much thinner – from 30 mm with Gyvlon ECO or XTR, and as little as 15 mm with Gyvlon FINIO across up to 30% of the floor area. It is common in new builds where a membrane or insulation layer sits between the slab and screed layer.
Floating screed is laid over acoustic or thermal insulation boards and is the standard choice for new builds with underfloor heating. With liquid screed, Gyvlon ECO needs a minimum of 35 mm in domestic applications and 40 mm in commercial ones, while Gyvlon FINIO can go down to 30 mm on suitable insulation. Traditional floating screed generally requires a minimum thickness of 65 mm, and at least 65 mm is needed where heavier loads are expected.
Flowing screed (liquid screed) is a self-levelling, pumpable mix that is usually calcium sulfate based and is commonly used with underfloor heating systems that have cast-in water pipes, though product-specific guidance should always be checked for suitability. Bonded applications start at 25 mm, and floating liquid screeds over insulation start from 30 to 40 mm depending on the product and whether it’s a domestic or commercial build – much thinner than traditional screed mixes. Screed flooring can give you a really durable, level surface in commercial spaces, and self-levelling screed is your go-to where you need to level things out because the floor is all wonky.
Traditional sand-and-cement screed is still a versatile option for various applications. A standard screed mix is a 1:3 or 1:4.5 cement to sharp sand ratio – which gives screed a bit of a higher sand-to-cement ratio than concrete.
Wearing screed is the way to go when you’re looking for a screed that can take a pounding in industrial settings and commercial buildings like warehouses, factories and power stations, designed for maximum wear as the finished floor, and with thicker sections it helps improve structural performance too. Heavy-duty screeds make a great exposed final floor surface when you’re expecting heavy traffic and heavy loads – all day long.
And then there are screeds with added strength – fibre-reinforced or reinforced screed using polypropylene fibres, glass fibres, fine metal mesh or fine glass mesh – often used in new builds where structural depth is limited or thinner applications are needed, but also in heritage refurbishments. Gyvlon liquid screeds, on the other hand, don’t need any reinforcement at all.
Base Conditions: New Concrete Slabs vs Existing Floors
The state of the base largely determines which type of screed and screed thickness you can use – and new builds have a clear advantage in this area.
In the UK in 2026, when you’re building a new home, the base is usually a fresh in-situ slab or concrete subfloor that’s been cast to a C28/35 strength class with a flat finish and an integrated damp proof membrane. The concrete is used for the structural elements like foundations and walls and has a coarser texture than screed because it’s got bigger aggregates like gravel and sand in it. The predictable condition of the new slab makes it straightforward to choose between bonded and unbonded screed.
But if you’re renovating, things can be a lot more complicated. Often you’re dealing with old concrete, timber, quarry tiles, cracked slabs or properties from the 1950s to the 90s. Uneven surfaces, contamination from oil, bitumen or old adhesive and uncertain structural integrity all mean you need to do some extra investigation before you can make any decisions. The substrate needs to be clean, level and structurally sound before any screed goes down, but once that’s confirmed, flowing screed can be installed quickly.
Checking if there’s a damp proof membrane in place in older properties is key. If the membrane is missing or failed, then a screed over a new membrane is usually needed to avoid problems with moisture causing failures in the screed layer and the floor finishes above. Where damp presents as a serious issue, separating the screed from the substrate with a membrane can also help protect the floor build-up from moisture-related damage. Contamination removal is also far more common and difficult in renovation projects, even where you only need mechanical preparation to get the surface ready for the screed.
Damp Proof Membranes and Moisture Control
Moisture control is critical for screed performance, especially when you’re using calcium sulphate flowing screed or laying floor finishes that are sensitive like LVT, engineered timber or vinyl in 2026. Where damp is a risk, using the wrong screed can lead to adhesives failing, staining and delamination.
New builds usually have a damp proof membrane below the structural slab, which gives you the flexibility to choose between bonded screed or thinner unbonded screed build-ups. Because you can control the moisture conditions when you’re dealing with a new slab that’s been cast and cured under controlled conditions.
But renovation projects are a whole different ball game – you’re dealing with rising damp, the lack of an original membrane or high residual moisture in older slabs. Surface-applied DPMs and thicker unbonded screed constructions are often needed, and you need to be sure to prepare the screed properly, protect the new floor from footfall and vehicle traffic while it’s drying and let it dry completely before you’re ready to install the final floor layer or any other floor finishes. Gyvlon screeds can usually take light foot traffic after 16 hours to two days, but full drying takes much longer – around 1 mm per day up to 40 mm, and 0.5 mm per day beyond that. The building needs to be properly ventilated after 48 hours, and underfloor heating can be used to help bring the drying time down. If the programme is tight, Gyvlon ECO FD E2C gets floor coverings down at least twice as fast.
You should never use calcium sulphate screeds in situations where long term wetting is likely, such as in basements or wet rooms without proper tanking, because these screeds don’t like moisture. In these cases, cement based screeds or alternative systems are a better option.
Moisture testing is different depending on the situation – in a brand new slab you might only need one reading once it’s cured, but if you’re refurbishing a 1970s slab, you’ll need multiple tests over time. Either way, liquid screed is generally ready for floor coverings once its residual moisture falls below 0.5% CM, which usually takes 4 to 6 weeks depending on thickness and conditions.
Underfloor Heating: New Build vs Retrofit
Liquid screed is the go-to choice for underfloor heating today. Screed is used in residential homes for underfloor heating and its design can be much easier to get right in new builds where every layer can be planned out from scratch.
In new builds, underfloor heating pipes or electric cables are fixed to thermal insulation boards, pressure-tested and then covered by a floating screed. With a screed made specifically for underfloor heating, like Gyvlon THERMIO MAX, you only need around 15 mm of screed above the pipes, with a minimum total thickness of 30 mm in residential builds and 35 mm in commercial ones. The insulating materials and damp proof membrane are integrated into the slab design, giving you excellent thermal insulation and minimising downward heat loss while helping to achieve a smooth finish over the heating installation. This all enables efficient heat distribution across the entire floor. THERMIO MAX has a thermal conductivity of 2.5 W/mK, which is 40% higher than a standard cement screed, and independent testing shows heating bill savings of up to 20%.
And this build-up can also help with sound insulation by limiting sound transfer between floors.
In retrofits, the existing floor-to-ceiling height, door thresholds and stairs can all limit how deep you can go with underfloor heating systems. Low-profile underfloor heating systems are often a better option in these situations because they take up much less depth. Thin, lightweight screeds help here too – Gyvlon FINIO is designed for renovations where ceiling heights and floor weights matter, and is up to 60% thinner and lighter than traditional screed when unbonded. Where the screed is bonded to the existing base, THERMIO MAX needs just 10 mm above the pipes, with a minimum total thickness of 20 mm in residential builds.
Ready to choose the perfect liquid screed solution for your new build or renovation? Contact Ready2Pour today for expert advice and professional installation services tailored to your project needs.