Would you lay a damp proof membrane?

[KeRa]

I am laying tiles onto 6mm plyboard fixed down to a concrete floor with wooded access panels that allow access to underfloor heating pipes in my downstairs cloakroom.

I plan to seal the edges and the faces of the plywood.

I see that it is possible to buy a 3m x 4mm 1000 gauge damp proof membrane for around £5. Is there any point in fitting such a membrane under the plyboard?

 

[Softus]

Are the panels there for essential maintenance?

If so, and if you tile the floor, how will you gain access to the wooden panels?

Aside from that, there's no need for a DPM between concrete and wood/tiles. In fact, there's a need not to have a DPM, because it would reduce the transfer of heat into the living space.

 

[KeRa]

The panels just allow access to pipes under the fllor that connect to wall radiators. In the normal run of events there should be no needto get to them.

This is not an underfloor heating system, it is just the pipes supplying the radiators on the wall.

 

[Softus]

The panels just allow access to pipes under the fllor that connect to wall radiators. In the normal run of events there should be no needto get to them.

So why were the panels put there?

This is not an underfloor heating system, it is just the pipes supplying the radiators on the wall.

Well that makes my point about heat transfer irrelevant, but you still don't need a DPC, and I still don't see how you're going to get to the pipes after tiling over them.

 

[KeRa]

The panels were put there so that the pipes could run in the air rather than through the concrete floor.

If I screw the panels down I would have to take the tiles up to get at the pipes (not that there should be any reason to anyway).

Else I could just lay the plywood and rely on the weight of the tiles and the toilet to hold it in place which would allow the whole floor to be lifted if I removed the skirting.

 

[Softus]

The panels were put there so that the pipes could run in the air rather than through the concrete floor.

Oh, OK.

If I screw the panels down I would have to take the tiles up to get at the pipes (not that there should be any reason to anyway).

If you don't screw them down it will be a disaster.

Else I could just lay the plywood and rely on the weight of the tiles and the toilet to hold it in place which would allow the whole floor to be lifted if I removed the skirting.

Don't even consider doing that, for even the briefest moment. You'd regret it.

When tiling, it's impossible to make the substrate too rigid. The more movement there is, the quicker the grout will crack and the tiles will lift.

Unless your floor is already solid, I wouldn't use plywood that's as thin as 6mm - it won't add any rigidity.

Consider a minimum plywood thickness of 18mm, even it means having a small step or a ramp at the threshold.

 

[KeRa]

That was the same feeling I had about reducing movement. I already have the wood cut, so I am sort of tied to 6mm board, but I plan to screw it down every 30cm and 20 cm at edges and corners. It is a small room and there is a toilet pan bolted to it too.