Hairline Crack in Floor Tiles

[WaveyDave]

Hello

I had my bathroom tiled about 6/7 months back. We used a polished travertine tile on the floor (30.5x45.7). I overboarded the floorboards with 12mm WBP first, screwing down every 4". Last night I noticed that the light was reflecting strangely along an (almost) straight line. This line runs exactly where two sheets of ply meet.

Upon further investigation, I noticed a thin line running right along the width of about 5 tiles (exactly where the boards below would meet), and that in parts there was a hairline crack (some areas you can just about feel with a fingernail).

Has anyone come across this before? The ply was securely fastened down, but it seems that one of the sheets must have lifted or dropped slightly, and the resulting difference in height has put undue pressure on the tile. However, the crack runs along areas where we wouldn't usually walk (eg right next to the basin). I'm guessing the tiles will have to come up? Strangely enough, there is no damage to the grout!

Thanks

Dave

 

[Richard C]

If it's been done professionally, call them back but it could be any number of reasons;

• Was the join in the WBP supported over a joist
• Did you screw THROUGH the floorboards into the joists of just screw into the floorboards?
• Depending on the size of the room & span of the joists, over boarding with 12mm can be marginal & may not be thick enough under some circumstances; many recommend 15mm as a minimum!
• What tile adhesive/grout was used?
• Is there any flex in the floor.
It’s almost certainly going to have to come up if you want to rectify it; my advice would be to remove the lot, including floor boards, & replace with it with properly secured WBP; I regularly use18mm but this is a minimum. Use 25mm if it’s a large room, the joist spans are wide or if the floor flexes unduly; screw it down properly, use quality trade flexible adhesive/grout & follow the manufacturers’ instructions for preparation & it should be fine next time!

 

[WaveyDave]

Many thanks for your reply Richard. To answer your points -

It was done by a professional tiler.

The join wasn't over a joist, it was simply butted where the sheet finished, and screwed about an inch from the edge (on each board).

Didn't screw through the floorboards, only into the boards themselves, but the boards had been securely fastend to the joists.

Don't know what adhesive/grout they used, as they supplied and took any leftover with them. It was flexible, but that's all I know.

No flex in the floor that I can detect, and I did bounce around on it after I boarded it. I followed the tilers instructions carefully to minimise any comeback on myself.

To be honest, taking it all up would be a nightmare, as the bathroom suite has all been fitted, and that means the WC is on top of the tiles, the shower base overlaps the edges, and the skirting is on!

The room is no more than 9m2 (fairly square approx 3x3, probably a little less).

I plan on getting back in touch with the tiler after Christmas. This whole renovation has been a nightmare and I want Christmas without any mess or hassle!

 

[Richard C]

It was done by a professional tiler.

If he’s a pro, IMO he should have done the prep work himself or given you better guidance. Personally, I will never accept a customer doing any crucial prep work weather its plastering, tiling or whatever work I’m doing. It’s all or nothing as it’s the only way I can guarantee it’s going to be right; avoids any future arguments & if the job goes wrong, it can only be my fault!

The join wasn't over a joist, it was simply butted where the sheet finished, and screwed about an inch from the edge (on each board).

That could be the first mistake; if the over joint runs in the same direction as the joist (at right angles to the boards) it should be laid so the join is securely fixed along the centre line of the joist & the fixings run through the boards into the joist, not just fixed to the boards on top. When the join runs across the joists, some of the fixings should coincide with the joists where they occur; all the intermediate fixings should have been through the boards & into the joists. The edge of the boards has obviously curled & lifted slightly away from the floor boards or the underlying board itself may even have lifted with the ply if the run in the same direction. The action of the ply fully drying over the following weeks & even months can exert a huge force & it will curl if not sufficiently secure, cracking the adhesive/grout &, in your case, even the tiles.

Didn't screw through the floorboards, only into the boards themselves, but the boards had been securely fastend to the joists.

Another mistake; if the ply had been fixed through into the joists you may have got away with it even considering the comment above. Personally, I will always choose to take up the existing f/boards & replace with WBP, either 18mm or even 25mm where considered necessary.

Don't know what adhesive/grout they used, as they supplied and took any leftover with them. It was flexible, but that's all I know.

The choice of adhesive & grout products is critical to the success & longevity of the job & the best ones aren’t cheap. I only ever use BAL products & would never touch the stuff sold in DIY sheds; it’s cheaper but could prove to be much more expensive in the long run.

No flex in the floor that I can detect, and I did bounce around on it after I boarded it. I followed the tilers instructions carefully to minimise any comeback on myself.

Maybe the floor was sufficiently rigid but the problem looks like it was caused by the ply curling as I‘ve explained above.

To be honest, taking it all up would be a nightmare, as the bathroom suite has all been fitted, and that means the WC is on top of the tiles, the shower base overlaps the edges, and the skirting is on!

Raking out & re-grouting may fix the grout lines but you won’t be able to fix the cracked tiles, they will have to be removed & replaced but, personally, I don’t think any such repair will last, the problem lies with an insecure base.

The room is no more than 9m2 (fairly square approx 3x3, probably a little less).
I plan on getting back in touch with the tiler after Christmas. This whole renovation has been a nightmare and I want Christmas without any mess or hassle!

That’s a reasonably sized room but it depends on supporting walls (below) & the floor joist span; difficult to say without actually seeing it. Renovation work is never easy if your living with it but good luck, I hope he’s sympathetic towards you.

 

[WaveyDave]

Thanks again Richard

As I said, I'll hopefully get him back after Christmas.

Do you think the remainder of the tiles will be saved (ie can you generally pop a tile up without breaking it)?

The line that's showing runs parallel with the floorboards, so across the joists. As I said, the odd thing is, the grout doesn't have any damage to it at all, not even a minor crack - only the tiles![/quote]

 

[Richard C]

Do you think the remainder of the tiles will be saved (ie can you generally pop a tile up without breaking it)?

I’ve never really tried to salvage tiles but I suppose it rather depends on how good a job the tiller did with the adhesive bed & how good the adhesive is. I only use BAL cement powder adhesive on ply floors & I wouldn’t give much hope of “popping” tiles fixed with that stuff off once it’s cured. A chepo adhesive might fare better & I don’t know if judicious use of a steamer would help but I wouldn’t hold out any hopes.

The line that's showing runs parallel with the floorboards, so across the joists. As I said, the odd thing is, the grout doesn't have any damage to it at all, not even a minor crack - only the tiles!

That’s interesting; I would have expected it to have been the other way around! What that says to me is that there may well be some flex in the floor over the span of the floor joists & because the join in the ply runs across the them, all the movement is occurring at the joint which will be the weakest point; is the join roughly in the centre of supporting walls below the room?

As the grout is showing no signs of distress, it may well be the tiller has used some decent stuff & it’s doing its job quiet well. Tiles, on the other hand (certainly ceramic or porcelain) wont flex at all (natural Travertine may be slightly better but I don’t know) & if the join in the ply is roughly though the centre of the tiles then it’s gonna crack!

 

[gcol]

If the edge of the ply sheet runs along the edge of a floorboard you're potentially going to have problems.
From what you have said, the tiler has advised you correctly about preparation materials and methods, it just seems that you have slipped up in where you positioned your ply sheets. Your tiler will not have been able to see this error as it would have been covered up by the ply. By all means call the tiler, but be prepared to have to pay for remedial work.
You'll be able to get the individual tiles up so you won't have to make too much mess - assuming you have/can get the same tiles.

 

[WaveyDave]

If the edge of the ply sheet runs along the edge of a floorboard you're potentially going to have problems.
From what you have said, the tiler has advised you correctly about preparation materials and methods, it just seems that you have slipped up in where you positioned your ply sheets. Your tiler will not have been able to see this error as it would have been covered up by the ply. By all means call the tiler, but be prepared to have to pay for remedial work.
You'll be able to get the individual tiles up so you won't have to make too much mess - assuming you have/can get the same tiles.

Thanks gcol. Didn't mean to imply that the tiler was at fault, as he's been a pretty decent guy.

This particular bit doesn't hang over a gap in the floorboards, but overlaps (from memory) by an inch or so.

Would it be reasonable to either try to refix that area of the board, or plane it a little to even it off again?

Luckily, I have about 18 spare tiles, so can afford to replace them. I had to order them from stonehouse tiles, so wouldn't want to pay for pallet delivery again!

 

[gcol]

This particular bit doesn't hang over a gap in the floorboards, but overlaps (from memory) by an inch or so.

An inch or so? Wouldn't that be just about where your screw would be going? Sounds like you have fixed the ply down with screws on (or very close) to the edge of the floorboard. It's perfectly possible that they didn't get a good grip or the board could have split.

Would it be reasonable to either try to refix that area of the board, or plane it a little to even it off again?

Remove the offending tiles, clean off the adhesive as best as you can and put plenty of screws all around the area you think has come adrift. If your floorboards are not securely fixed to your joists, you'll need to drive screws through to firm them up.

 

[Richard C]

Would it be reasonable to either try to refix that area of the board, or plane it a little to even it off again?

I think your biggest problem is that you’ve got a join in the ply that appears to be at or near the centre of the room running across the joists instead of along the centre line of one of them. Any flexing in the floor &/or differential movement between the sheets of ply overlay will occur at this join as it’s the weakest point; it’s moved once & even with additional fixings it may well move again. The ply flooring or overlay should be laid so that any joins near the centre of the room run along the centre of a joist (across the boards) & not running with them. If you can get the tiles up fairly easily without damage I would bite the bullet, take the lot up & start again; done properly it should easily last 10 years or more.