Help with tiling please

[Brew]

My new kitchen extention has had a floor laid with green waterproof T&G chipboards laid over 65mm screed and wet underfloor heating. The screed is level with the joists. All the tilers I have asked say tiles cannot be laid directly to this and it needs A - relaying with a proper tile backing board. B - Lay a 3mm membrane and tiling to that, C - Floor sanding through the green finish. Different tilers are saying diferent things and I'm not sure whos advice to follow. The cost is likely to about £1000 so I want to get it right. Anyone have experience of laying tiles to this type of flooring?

Many thanks

Brew

[A.Lee]

You probably could fix direct to the board using flexi adhesive, but it would be better to do it onto concrete boards. 6'x4' boards are only around £7, so it shouldnt cost too much to do it. They will give a more stable surface for the tiles, and will not damage the sub-floor if you ever want to gett he tiles up.

Alan.

[Jim K]

both? are the cement boards not strong enough alone? how thick are they? vs floor level change including tiles/adhesive??

Jim K

[Brew]

Thanks for the advice, the most popular idea is to overboard it with concrete based boards but the only problem with that is the UFH. The boards would need setting on some sort of adhesive to maintain a good contact for heat transfer. Not really a problem but it does raise the finished height more than I would like so the green chipboard is coming up and 12.5mm Aquapanel boards replacing them. Expensive but not as expensive as having to do it all again sometime in the near future.

Cheers

Brew

[Jim K]

mmm so that's 8mm plus tiles 10mm min, plus adhesive =3D ? more than 3/4 inch floor height difference? could be fun/obvious....

Jim K

[stuart noble]

I know of several cases where floor tiles have been laid directly on to green chipboard without incident. Adhesive sticks very well to waterproof surfaces, as we know from tiling on to old ceramic or vinyl flooring. Suck it and see. If there are any chipboard offcuts, lay a single tile, and see if you can move it after 24 hours. I doubt it somehow.

[stuart noble]

I know of several cases where floor tiles have been laid directly on to green chipboard without incident. Adhesive sticks very well to waterproof surfaces, as we know from tiling on to old ceramic or vinyl flooring. Suck it and see. If there are any chipboard offcuts, lay a single tile, and see if you can move it after 24 hours. I doubt it somehow.

[Roger Mills]

I'm not sure that's a fair test because it won't simulate the flexing which occurs when the floor is walked on.

[stuart noble]

I doubt there would be much flexing on a 60mm concrete base. It sounds like the tilers are anticipating an adhesion problem rather than one of flexibility

[Jim K]

come again?

[Jim K]

erm still not with you I'm on about height from adjacent floors... wot you on about adhesion???

Jim K

[stuart noble]

Height wouldn't be an issue if tiles went on to the chip. IIRC that's what I was on about

[Man at B&Q]

The OP talks about joists, not a concrete base.

MBQ