This type of installation is used when installing underfloor heating on a first floor between joists. When using the dry sand & cement mix between the joists, the build-up is as follows – 2×1 battens screwed into joist and polyurethane insulation wedges between joists sitting on the battens 30mm from top of joist. Pipes are then clipped onto insulation and fed back to our underfloor heating manifold. A 4 to 1 sand and cement dry mix placed over the pipes up flush with top of the joist. This system can be polybonded to seal the sand and cement mix if you are laying the original floor boards back down. Otherwise 18mm plywood can be laid on top of the pipes and then your floor covering.
When using aluminium trays in this situation we use the same build up as before but this time the pipes sit in aluminium trays fixed onto the insulation and no dry mix is used. It is very important to make sure there is no air gap between the floor covering and the trays and pipes. In summary the plywood or original floor boards need to be pushed down on to the trays.