Anhydrite Floor Screeding
What is an anhydrite screed?
Anhydrite screed, also referred to as a calcium sulphate screed or gypsum screed, is the most commonly recognised liquid screed on the market and has been around for roughly twenty years in the UK. Instead of using a cement binder which is used in traditional sand and cement and cementitious flowing screeds, the screed is composed of an anhydrous (dry) calcium sulphate binder in addition to aggregates and water. When the components are mixed the water starts a reaction and calcium sulphate dihydrate is formed – which is more commonly referred to as gypsum (the same material found in plasters and plasterboard). This reaction can last up to a week until all the calcium sulphate has been used up, leaving any remaining water to evaporate up through the surface. The end result is an extremely solid, level and flat subfloor on which you can lay your final floor finish whether it be carpet, tiles, vinyl or wood flooring.
What are the advantages of an anhydrite screed?
The performance of the screed:
- Due to its fluid nature, it is nearly completely self-levelling, easily achieving an SR2 standard for flatness (plus or minus 5mm over a 2m straight edge).
- It has low shrinkage compared with cement-based screeds, which means that the screed is much less prone to cracking and fewer control joints are required.
- The screed can be laid at thinner depths – 25mm bonded, 30mm unbonded, 35mm floating over insulation and 25mm cover to underfloor heating pipework.
- Due to the thinner applications, drying times are reduced – dries at 1mm per day up to 40mm and 0.5mm per day thereafter.
- Quality control is improved as tests are carried out on the screed both at the plant after it is batched and on site by the installation team. The suppliers will also only supply to approved installers who have undertaken proper training and invested in the necessary equipment to carry out the works.
Productivity can be dramatically improved:
- Anhydrite screeds can be laid up to ten times faster than traditional screeds with areas exceeding 1000m2 achievable per day. Not only will this help reduce the overall build time of your project, but it will also result in extra savings on labour costs.
- After installation the screed will have gained enough strength after just 24-48 hours to allow for foot traffic, so trades can get back to work sooner.
It is far less labour-intensive:
- The screed is delivered ready-mixed at a local concrete plant and delivered to site on a concrete mixer where it is pumped into place, removing the need for labour-intensive mixing and manual handling on site.
- Once the screed is poured it is self-levelling and self-compacting, so there is no requirement for tradesmen to level and compact the screed on their hands and knees as is the case with traditional screed.
It has superior performance with underfloor heating:
- As well as having a greater density than sand and cement screed, due to its fluid nature the screed fully encapsulates the pipework leaving no voids around the pipes.
- Thinner applications – just 25mm over pipework – means better heating efficiency as the screed is quicker to heat up and cool down.
- Improved heating efficiency means a saving on heating bills.
It is eco-friendly:
- The binder is made up of 98% recycled content.
- The floor has a reduced carbon footprint as the processes involved in the production of cement produces much higher carbon emissions in relation to an anhydrite screed.
Are there different types of anhydrite screed?
Yes, there are variants of anhydrite screeds which have been adapted to suit different applications and requirements such as:
- Fast-drying screeds for earlier trafficking and shortened build times.
- Thin-section screeds for thinner applications over solid substrates
- Energy efficient screeds for further improved performance with underfloor heating
- Heavy duty screeds for floors which will be subjected to increased loadings
Who supplies anhydrite screeds?
- The two major players are Gypsol and Gyvlon who provide their anhydrite binders to ready-mix concrete plants.
- The ready-mix concrete plants mix the binder with water and aggregates to batch the screed prior to delivery via concrete mixers.
- National ready-mix suppliers include Tarmac, Cemex, Marshall’s and Aggregate Industries.