I’m Andy Parkin, Managing Director of the Multi Award-Winning Speed Screed – Biscuit Screed
Biscuit Screed? It is an unusual term, not often will you come across this as it is generally only relating to underfloor heating, and underfloor heating in between joists.
There are other certain circumstances where a biscuit screed is used, however 99% of the time you are looking at underfloor heating. On the first floor it is often a wooden joisted system. You either leave the heating pipes surrounded by just air under the floor boards (not a very effective way of conducting the heat), use reflective plates on top of the joists, but this is still not as effective as using the heat storage capacity of screed.
The floor construction is joists, and in between you have the underfloor heating pipes that may be clipped onto insulation or directly onto the boards.
In between the joints the biscuit screed goes over the heating pipes, and the screed is literally only acting as a storage heater for the screed (thermal mass).
It serves no real other purpose, it is not there as a wearing element. It’s not there to have floor covering attached to it, and it doesn’t really need a any great strength. It does need its density so it can be thermally conductive, and it just needs to be sticking together (cement bounded).
Typically, a traditional screed is a one to four (cement – sand ratio). A biscuit screed ratio would one to eight, and that would be a sufficient strength.
The cement is just there just to hold the screed together. You don’t have to worry about what the coverage over the pipes is, even if you do get any induced cracking it is not a major problem at all. The biscuit screed will be covered with the floor boards, and thus protecting the screed. No need to worry about any delamination of the floor coverings.
That is a biscuit screed, use it in between joists over underfloor heating.