Bathroom floor tiling

[steve71]

I'm about to tile my bathroom floor with 600x600mm porcelain tiles. The floor is made of standard t+g softwood floorboards, over 9inch joists at 400mm spacing.

Question: do I rip up the floorboards and replace with 22mm wbp ply or leave the existing 20mm floorboards as is? My preference would be to replace with ply as I think it would give a flatter and more rigid surface to work with. Problem is that 22mm ply might be a bit too thick (see below), in which case, would something thinner be ok, say 18mm (if that size exisits)

Either way I'm planning to screw+glue 6mm hardie backer on top before tiling. I might also put electric underfloor heating (****) above the board, in which case I will probably put some self levelling over the top before tiling. Haven't decided on that yet, I guess it comes down to how much floor height I have left to avoid a step. The timber door threshold sits 23mm above the level of the floorboards, giving me about 43mm in total to play with.

This is my first floor tiling attempt and I want to get it right

Thanks in advance, and apologies if this the question has already been answered in another topic (I did look first).

[steve71]

Hi,
I just read this from the 'before you tile' thread...

"Floorboards
It is not advisable to tile straight onto floorboards as most wooden floors have too much flex in them and this causes the tiles to crack or debond from the substrate. If possible lift the original wooden floor, insert noggins at intervals, place adhesive such as pink grip onto the top of the joists and lay 25mm plywood onto this making sure that any joins in the plywood sheets are supported by the joists and the nogins underneath the screw these down making sure the screw heads are flush with the ply surface. next lay 6mm backerboards into a 6mm adhesive bed and screw down every 150mm in a grid pattern. Tape the joints in the backerboards with matching tape and seal these with rapid set adhesive."

... which does recommend replacing the floorboards. Problem is that 25mm ply is a bit thick. Would 20mm be ok, or even 18mm, given that I plan to fit the backerboards? I read elsewhere that 25mm is recommended before tiling but that was without backer board. I'm keen to fit underfloor heating and I think anything thicker than 20mm is going to rule that out.

Thanks

[wine~o]

remove floorboards, 18mm tongue and groove chipboard glued and screwed, overboard with either 6mm ply or better still "no more ply"

As a first time tiler you'll want a slow set bagged adhesive (3 hour open time) suitable for porkies. I think Topps do their own for not too much £££'s.

Larger format tiles will also need "back buttering"... Take your time to get the tiling level and evenly spaced.

[All The Gear]

You also need to be aware that if you use an electric UFH you are going to need to lay the cables on insulation boards which will add another 10mm to the depth, then SLC which will add another 4 or 5mm to bury the cables. If you don't use insulation boards you'll have a nice warm ceiling below your bathroom

[steve71]

Thanks the the advice there.

I read elsewhere that some kind of water proof/resistant ply should be used in the bathroom. Maybe that's if you don't use a backer board, so is that why chipboard would be ok here?

Unfortunately I've already been sold the adhesive by the guy in the porcelenosa shop that sold me (ie my wife) the large wall and floor tiles. Still, I like a challenge. On the plus side I'm doing both our bathrooms, so if I mess up the first one then at least I will have a second chance to fix my mistakes!

Looks like UFH isn't going to work, unless I can use insulation board instead of cement backer board?

If so, then I'd end up with 18 mm chipboard + 10mm insulation board + 5mm SLC + 5mm tile adhesive + 10mm tile = 48mm which is still too much

Would 6mm insulation board be ok?

Thanks again.

[wine~o]

Chip board with ply/backerboard over is fine. about UFH though. sorry.

[mike10]

I like Dukkaboard as a backing board for behind/under tiles.
Waterproof (tape the joints), lightweight, and easy to cut and handle.
You also get some insulation value with it so that's probably a bonus with UFH.

http://www.dukkaboard.com/

My kitchen floor is 18mm OSB on joists at 600 centres (not ideal I now know) with a layer of 10mm Dukkaboard on top (laid on adhesive and screwed through with the Dukkaboard washers).
Flooring is 400mm square porcelain tiles. Nothing has moved or cracked in the three years it has been down.

[steve71]

[quote="mike10"]I like Dukkaboard as a backing board for behind/under tiles.

Thanks Mike I'll take a look