Floating screed thickness – how thin can you go?
I’m Andy Parkin, Managing Director of the Multi-Award Winning Speed Screed.
Whenever we are talking about floating screed thickness, and generally we tend to be talking how thin a screed can go down to, we have got to look and examine what the substrate is, and in this case it is a floating construction.
When we say floating, it can be an acoustic insulation, or it can be thermal insulation. If you imagine the screed, it appears for all intents and purposes to be floating, sat on top of the insulation. The insulation may have a membrane over the top, it would always be recommended, and even more so if it has a silver foil backing to the insulation.
You have a number of generic type products, and there are certain manufacturers making those products.
Flowing screed, calcium sulphate flowing screed is 35mm domestically and at 40mm commercially minimum depths onto insulation. The maximum depth would be 80mm for a calcium sulphate flowing screed. At 80mm you are likely to get a lot of bleed water, which can then lead to a weak and friable surface that needs to be sanded down.
Modified Sand and Cement Screed
The next product is a sand and cement screed, but a modified version. This is an add mixture based modified sand and cement that actually gives you rapid strength. If you are looking for something where you need to traffic the screed early, or looking to load it and you don’t want to damage the screed, you need high strength very quickly, and this is the perfect product.
- 35mm minimum on top of insulation (floating construction)
The maximum? Well there isn’t a maximum per se, providing that the screed is always well compact and it’s compact in layers, but you would question the thickness of the screed in terms of why wouldn’t you use a little bit more of the insulation in the floating construction to reduce the depth of the screed.
Depending what the loading is going to be, you might need to speak to the designer to talk about what the strength of the insulation needs to be to withstand the loading of the screed. To reduce the depth of the screed using void formers will help. As a by-product of that, you get better thermal performance from the project as well.
There are obvious benefits, sometimes there are cost savings, sometimes no immediate cost savings, but the longevity of the product will offer longterm cost savings through the increased thermal performance that you will get.
Hydraulic Binders – Fast Drying Screed
Sand and cement screed with hydraulic binders in can go down to 40mm floating. This is a fast drying product, and is ideal is you need to if you need to get your floor coverings on very quickly.
Again no specified maximum, but you would always look at ways of reducing the depth if possible, can I put void formers in there?
Traditional Sand And Cement Screed
A traditional sand and cement screed, as defined by the British Standard BS8204-1:2003 would be 65mm for domestic, 75mm for commercial floating construction.
No upper limits but look at the viability, and think about the long drying time due to the depth. The thicker the screed, the longer it is going to take to dry.
If you have any further questions about floating screed thickness then please contact us.