Traditional screed mix applied to floor

Day 31: Floor Screeded and Windows Finished

Tuesday 3rd September

Worked recommenced after a week off for holidays. Today the screed was applied to the floor. Both builders were fed concrete screed, made on site, by the 2 labourers. Before the screeding started a base plate (forget the proper name) was placed along the bottom of the French doors and the old French doors were removed so that they could screed up to the current height of screed in the house. It now looks more like a proper room than it has so far.

What is Screed?

Screed is a levelled layer of cement that is applied to a floor. In our case it was a “dry cement” that was poured onto the Celutex insulation boards (that sat on the suspended block and beam floor) and was levelled by hand using wooden batons and a level.

The official term for what we had done is that we had screed applied as a floating finish over a layer of rigid insulation material. The screed was about 75mm thick.

Screeds can be pumped, these are “runnier” and are anhydrite compounds based on a calcium sulphite binder. They produce smoother finishes. Most old school builders will prefer to mix their own and bring it in by wheelbarrow. Our screed was very coarse – lots of little stones in it. No idea if this is “normal”, certainly looks coarser than the screed Barratt Homes did.

Guidance can be found in BS 8204, which covers screeds, bases and in situ floorings.

Traditional screed mix

A traditional screed mix is 3 to 5 parts sand mixed with 1 part cement. Usually a ratio of 4 to 1 is used.

Drying time

Screed dries within one day for walking on, and within a few days it is dry enough to move in on. However, for three months it will continue to dry so you cannot install any solid flooring on it. Carpet is OK (we moved the old living room carpet in, see next blog or two).

The basic calculation for total drying is either one month per inch, or one day per millimeter. So 75 mm is 75 days, or about 2.95 inch (I know, decimal inches!). Either way, three months ensures it is well dry. Although some calculate a 75 mm screed as 110 days drying time, because the first 40mm dries a 1 mm per day, and he remaining slower (about 0.5 mm per day).

We eventually had Karndean flooring in the living room. This was done in December, three months after screeding.

Karndean floor required a second screed, a very thin layer (about 3 mm) of self levelling (well, almost) screed. Very runny/ The floorer called it a Latex screed, but pointed out that there is no Latex in it! See update here.

Curing time

Some screeds should be allowed to “cure”, which involves covering them in a plastic sheet to slow down the drying of the top layer to prevent cracking and curling. This is usually 5-7 days. We did not do this, I think because it was a traditional screed mix.