Microcement substrate


New Member
Planning a wet room which will be finished floor to ceiling in Micro cement. I'll be getting in a pro to do the Micro cement itself but wondering if you could recommend a substrate for this to go on?

The walls are currently timber studs with Celotex between the rafters, the floor is a concrete slab with UFH. I have a Marmox 20mm shower-lay tray which has the gradient for the waste built in.

My thinking for the walls is either

1. Marmox 20mm plastered down to the floor - Waterproof but is it sturdy enough? Wall hung toilet and sink will be secured to the studwork.
2. Hardiebacker - Sturdy but the Micro cement would be responsible for all tanking.

For the floors:
1. Marmox 20mm throughout with a 5mm levelling screed to act as a smooth surface for the Micro cement
2. Lay the Marmox showerlay, coat with screed and use a liquid screed to the level of the finish before Micro cement.

Any tips on waterproofing the joints of whichever product you recommend gratefully received.

Picture of the drain showing the 10mm depth from the surface of the board to the drain itself attached



Well-Known Member
With the walls you can use hardie board or other but if using micro cement rather than tile you need to go onto a plastered finish. When I do them I board to floor with plaster board. Use a wet room system such as impey water guard. Comes with a waterproof internal corner for floor to wall. Screed your floor over this and up to your drain. Can't be too wet on your tray as you need to keep the tray shape for fall into drain. At drain you will need to leave 1 -2 mm for micro cement depending on coats, finish style and thickness. Plaster the walls going over the wall side of internal corner joint. Then you have a prepared surface for the micro cement for walls and floor.