Adhesive thickness

[jashton]

Hi

what thickness do most people assume for dry floor tile adhesive bed?

I'm replacing the subfloor so have the luxury of bringing the finished tiled floor up to the same height as the adjacent room.

What should I assume for the finished thickness of the adhesive, once bedded in and fully-cured?

Also - is 18mm WBP acceptable or should I go for 25mm? Joist centres are 400 or less.

ta

 

[tictic]

adhesive thickness..how big/thick are your tiles?

as for 18mm or 25mm wbp ply..what room is it? how much foot traffic is there likley to be going over it?

 

[jashton]

Oh, yeah. should have mentioned that info.

10mm porcelain tiles in a bathroom.

Room is 2.4x1.5 m with bath taking up 1600x700 plus WC and sink so the walkable area is small. Joists are 2.4m 4x2 and supported every 600mm by brick bearers. I've put noggins between the joists at 1/3 intervals, ie at roughly every 800mm, to make the floor more rigid.

I can easily replace what I have with 25mm WBP but I've already paid for and cut the 18mm so it's one less job/expense if it's not necessary.

Also, will have 10mm wedi board or similar above the ply. Not sure if it adds and rigidity but it' supposed to provide some dimensional stability right?

 

[Richard C]

4 x 2” is a pretty slender for joists but, if I’ve understood correctly, the joists are supported every 600mm along their length by brick piers? If that’s the case & at 400-450mm joist centres, you should not have any problems. Adding noggins won’t make the joists more rigid, they are in the opposite plane; noggins are only required to support any cross joints in the WBP, across the threshold or to provide support around the perimeter if absolutely necessary; only “sistering” the joists will make them more rigid.

From what you’ve said, I think 18mm WBP should be fine; but that’s just a remote opinion, I take no responsibility without jumping up & down on it! Personally I don’t see the point of over-boarding with “Wedi”; what you need is rigidity & I’m not sure you really understand what “dimensional stability” is but it doesn’t have much to do with tiling floors; it’s more to do with 3 dimensional flexing, perhaps in car chassis or aircraft design. IMO, over-boarding without bonding the two won’t add much more rigidity than a well fixed & correctly sized lump of WBP ply base; personally I don’t think you need them but if you’ve already bought them!

Floor tiles should always be laid on a thick, solid adhesive bed, flexi in this case. I use a 20mm wide x 10mm deep round (not square) notch trowel which will give an adhesive depth of 3-4mm; if the floor is level, this should be fine for anything other than tiles of paving slab dimensions. You can “butter up” to 2x for local levelling but don’t even think about going thick over the whole floor to make up the level; if you need to do that then you must find some other way of doing it.

 

[jashton]

nice one thanks. the backer board is actually thermal backer as there will be UFH. I'll stick with the 18mm WBP

out of curiousity - why round notch instead of square?

 

[Richard C]

the backer board is actually thermal backer as there will be UFH.

OK that’s fine; just something else you forgot to mention

out of curiousity - why round notch instead of square?

It’s all to do with the dynamics of what happens when you push a tile down into the adhesive ridges, with a slightly twisting motion of course A round notch adhesive ridge will (apparently) deform more uniformly than will a square notch into the solid adhesive bed essential for floor tiles; presumably tested by those that make the stuff but not by me