Downstairs floors, insulation, underfloor heating and screed

Now that the upstairs we liveable, it was time to start on the downstairs. First we had to remove the remaining screed from the back of the house. Then lay insulation. We put 125mm of insulation in the front rooms to bring it to roughly the same height as the back.

Next we had to put down a later of polythene and a foam expansion strip around the outside to allow for the screed to expand when heated by the underfloor pipes. Then we lay the 16mm Thermrite (pex-al-pex) underfloor heating pipes and clipped down onto the insulation. We had 7 zones in total.

The one big mistake we made was not too pressurise the system. We were told we only needed to fill the pipes with water. This is not correct, its important to pressurise the system up to about 6 bar and then let it drop and sit at 1.5 bar, otherwise the screed will crack. Because we didn't do this we had to cancel the screed delivery and go back into the queue. It meant that we had to move out for a month as we couldn't live in the house without a toilet or bath! The plumber from Clarity Heating came to connect the pipes to the manifold and pressurise the system. Another tip, was to place conduit around the pipes where they will pass through the screed to protect them. We used 22mm JG Conduit pipe.

Finally screed day had arrived! We opted for the more expensive CemFlor Therm, a concrete based liquid screed as opposed to the gypsum based (aka anhydrite or calcium sulphate) based flowing screeds. A cement based liquid screed is batched from cement, sand, water and a limestone powder-based binder containing additives to enhance flow, reduce shrinkage and stop bleed and segregation in the screed. Cement based screed has the advantages of the gypsum based ones but hopefully none of the disadvantages. The drying time is meant to be faster too. They can be used in wet areas, have no surface laitance and require no priming under any type of flooring adhesive. 

Finished floors at the back: