Sub Floor Preparation
It is vital that prior to screeding the correct preparation of the sub floor area has been completed. The sub floor must be scraped off to ensure the removal of an mortor splashes and then swept thoroughly to remove any dust and debris. This will allow the insulation to sit flat with no rocking.
Begin by laying the insulation sheets ensuring that they are positioned tightly together with no gaps. To position the insulation around pipework, cut the holes before laying and then bring the pipework through. On occasion it may not be possible to notch out your insulation around the pipe, in these instances, ensure that the insulation is fitted around the pipework as tightly as possible, using dry sand to fill in any gaps, making sure that your filler is level with the insulation surface. Dry sand can also be used to eliminate gaps between boards or along the walls.
Using polythene that is a minimum of 500 Gauge, cover the entire surface of the insulation making sure that it is flat and overlays (joins) are 100 mm and then taped using a suitable tape. It is important that non foil based tapes are used for this when using calcium sulphite screeds. This is because the the foil component of the tape causes a chemical reaction with the screed resulting in many air bubbles forming. Standard Duct Tape is a good alternative. Around the edges of the room, the polythene needs a lip of 100mm, making sure that it is pushed tightly into the corners and then stapled or tacked onto the wall.
When combining calcium sulphate screeds with underfloor heating, a perimeter expansion edging strip should be put in place along all walls. The strip has a self adhesive foam section which is adhered to the wall and then a polythene lip which needs to be laid out and taped to the floor.
(If no insulation is required, simply follow the directions for the membrane after preparing your sub floor. It is imperative that a polythene barrier is created around the room. This is firstly to contain the screed and prevent it from flowing freely out of the room and secondly to prevent a reaction from occurring between the concrete and the calcium sulphate screed.)
Under Floor Heating
Once the floor has been prepped and polythened, the underfloor heating pipes can be put in place. These must be positioned carefully, a plan is made in advance, and then they must be clipped every 400mm. Once in place, the system must be pressure tested and filled with water prior to screeding. This is to ensure that the system is working and that there are no leaks as changes cannot be made once the screed has been poured.
It is important that anything protruding from the floor eg pipework should have perimeter expansion edging foam wrapped around them which is taped to the floor using appropriate tape. (See membrane above for details.)
Expansion Joints should be installed in doorways.