Questions about tiling a floor.

[kimbers]

Hi,

We are having a new kitchen put in & deciding to replace the laminate flooring with porcelain tiles.

We have the interlocking ( tongue & groove? ) chipboard flooring rather than floorboards.

We've had some advice already from a tile shop who recommended we put down 6mm exterior plywood, screwed down with water resistant screws every 12" or so.

They also recommended treating the plywood before laying the tiles so that the water in the adhesive doesn't rot the plywood.

My question is really about what to treat it with, and whether to lay it first before treating.

We'll be looking at 60x30cm tiles over a total area of 11 metre square. They also recommended a flexible adhesive? Can anyone recommend one?

Thanks
Scott

 

[Maxsys]

I suggest you do a search and look at the wiki and sticky at the top of this page, been covered loads of times, but the upshot is chipboard is NOT a suitable substrate for tile, 6 mm ply is nowhere near thick enough, and you will need to know the size/pitch and span of the joists under the chipboard.

I would not use plywood, but would choose instead to replace the chipboard with plywood, and then go over this with a suitable tile backer board, however without information about what is under the chipboard i cannot give any recommendations.

 

[kimbers]

The advice was that we lay the plywood on top of the chipboard rather than replace so that we give the chipboard more strength.

What info do i need?

 

[kimbers]

The chipboard is floating on the floor joists. ( not sure how wide apart they are or how thick the chipboard is.) But the advice we've had so far is to put plywood down and screw to the chipboard flooring before tiling.

I'm not sure what thickness is correct, or whether ply is correct at all.

 

[Maxsys]

You need to know the size of each joist, the width and height, and what spacing there is between them, and the thickness of the chipboard, sorry but the advice you have been given is wrong, if you proceed with the advice from the tile shop the floor may fail due to excessive deflection, British standards state that 15mm ply is the minimum to use for over boarding, but if the subfloor has excessive bounce or deflection, then it won't matter if it's 6mm or 15mm (of course 15 would be better) but the floor is still likely to fail and you will end up with loose tiles, cracked grout and maybe cracked tiles.

Just trying to help.

 

[tpt]

maxsys is right. thats bad advice.

6mm is a complete waste of time.

 

[Richard C]

As already stated, the advice given by your tile shop is extremely bad & I would question if they have any idea what they are talking about; follow it & your tiles will almost certainly fail. 6mm ply is just a joke as is fixing at 300mm; fix every 150mm minimum & into the floor joists (check for pipes & cables), not just into the top of the original floor. Acrylic priming the underside & edges the ply is usual but not for the reason given which, again, is a total load of tosh; the water in the addy would never rot the ply & you should never prime the tile base unless the adhesive manufacturer recomends it. Sealing the underside is done to prevent moisture ingress into the underside which will warp the ply. You say the chip is floating on the joists, I doubt it but can you explain the floor construction & what is under the floor? It’s entirely possible you have a floating floor which won’t be suitable for tiling without a lot more work.

Chipboard is about the worst possible tile base you could imagine, I won’t overboard it & always replace with WBP ply 18-25mm thick; actual thickness you need will depend on the area being tiled & the size/pitch/span of your floor joists. In a light load/use area such as a bath/shower room, 18mm is often sufficient but in a heavy use/load area such as a kitchen I would advise 25mm as the minimum especially as you will need a flat tile base for those large format tiles. You will need a flexible powder cement adhesive but & it’s important to use only quality trade tilling materials; cheapo own brand & DIY stuff is mostly crap. What is your tile shop advising?

There are many things to catch you out particularly if you intend tiling a suspended timber floor. I would advise you read the Tiling Sticky & Forum Archive posts before doing any more work or buying materials, it could prevent you making disastrous & potentially expensive mistakes.

 

[gcol]

Only me; for a short time only. Get em while they're hot they're lovely.
Never really been a fan of trying to fix into the joists when overboarding - often not straight-forward to do and you run extra risk of piercing a pipe/cable. What you're trying to achieve by overboarding is to make the flooring sandwich rigid; does that matter then if it's welded bomb-proof to the joists? Hmmm not really, as long as the flooring is reasonably fixed then the flooring "sandwich" to be applied will keep things rigid and prevent the tiling bond (or tiles) from failing. Assuming your chipboard flooring is reasonably well fixed down and not like a trampoline, is sound and not resembling moist weetabix then overboard as already advised or as per the sticky I wrote. The idea is that the ply overboarding adds rigidity to the substrate to reduce flexing to a point the adhesive can cope with, thereby preventing the tiles coming loose or fracturing. The idea with fixing plenty of screws all over the floor is so the chipboard/ply sandwich holds "itself" together to form a rigid layer, not necessarily to the joists. Oooo don't you just love the word "rigid".... it's a tiling thing.
What I think we all agree on though is that the mush in the tile shop wants a slap.

 

[Richard C]

Never really been a fan of trying to fix into the joists when overboarding - often not straight-forward to do and you run extra risk of piercing a pipe/cable.

The possible problem with just fixing into the top of the floor rather than into the joists is there is a risk, albeit slight, the overboard can curl if the floorboards are not sound & adequately fixed, particularly if there is a moisture ingress problem. I recall at least one such problem on the forum a couple or so years ago when you posted on a daily basis; we debated & concluded (or at least I did) the problem had arisen due to “top fixing” which had allowed the edge of the ply overboard to curl with obvious results. Agreed you have to check for pipes & cables & that’s a possible “cock up” factor for inexperienced DIY but it’s what I do & always advise; all things being sound, it makes the tile base bomb proof &, as joe sometimes points out, it will last a lifetime; but it’s important to cover all the angles if you want it to last & even more so if you don’t want any customer complaints.

as per the sticky I wrote.

On the “sticky” , have you thought about updating it while you’re visiting? Although I’m not sure how many OP’s actually read it until I always advise them to do so, there are a number of things I think could be added (hopefully non-controversial ) which would be of benefit.

 

[gcol]

Hmmm, don't rember that conversation and as I said so long as the substrate is sound it should be fine. Adding fixings at such low centres is effectively "bonding" the ply (okay, bit of artistic license there) to the chipboard to form a solid foundation. Not gona get into an argument about it... you've said your peice, so have I. Lets keep that particular person away from anything to do with me or I'll scream, I swear (re: stricky coments). It's due to him that I haven't been around - can't be bothered with the hassle.
Regarding the sticky, what do you think wants updating. Put me something together (e-mail) and I'll have a look see and contact Admin to see about unlocking the thread. Don't expect me to quote BS in there, some of that is way overkill. Obviously I'll add that any additional comments are yours. Bear in mind that the post was only meant to be a "basic" guide, if you're thinking of adding anything a bit more involved then you may be as well creating your own "advanced" guide if you like. I never got round to it and to be fair, most advanced topcs were few and far between so it didn't really warrant it.

 

[Richard C]

Hmmm, don't rember that conversation

Well I'm sure I could find it but it's not really worth the time

Regarding the sticky, what do you think wants updating. Put me something together (e-mail) and I'll have a look see and contact Admin to see about unlocking the thread

I should have been more specific; it’s mostly additions than updating & I’ll work on it & advise but I’m (supposed to be ) going to Edinburgh on Saturday for a a week & a "very, very special date” so bear that in mind. Feel free to hold the "Tiling Forum" fort while I'm away but don't upset tictic

 

[gcol]

Any ideas you may have can be sent to me at any time using the email address you'll find if you have a look through my profile.
Sounds like you've a bit of fun ahead... good luck with that.

 

[Richard C]

Sounds like you've a bit of fun ahead... good luck with that.

 

[kimbers]

Thanks for the all the advice. Certainly gives me something to think about.

We now have part of the laminate flooring up & the chipboard seems very sound & well held down with no noticeable movement.

We have a slight issue in that we are intending on using 10mm tiles, and height is likely to be a problem if we go for thick board such as 18mm. Abit of a dilemma.

Unfortunately lifting the existing chipboard and replacing isn't an option due to a) the kitchen going in starting Monday, b) the additional cost.

 

[Richard C]

Unfortunately lifting the existing chipboard and replacing isn't an option due to
a) the kitchen going in starting Monday


b) the additional cost.

Will be nothing compared to the cost of your tiles failing