As some of you may know (or simply don’t care about – but know anyway) I actually do reply to every question I’m asked on this site. It may take a while for me to sober up enough get enough time away from work to answer it – but I do. As such I am frequently asked the same or similar questions a lot. I’m going to start turning these questions and answers into blog posts to leave myself more beer drinking time to help people with the same problems. So here’s my first one. If you have a suggestion for future posts like these just let me know and I’ll be more than happy to cobble together some similarly ridiculous advice for your problem. I will not share any names or other information with anyone else because – well, it’s none of their damn business – so no homeowners were harmed during the writing of this post.
Here’s the question:
My husband and I have recently tiled our kitchen and laundry room. It is a 35 year old house that had kitchen carpet in both areas. We removed the carpet and old linoleum was underneath. We installed backerboard thinset extra like you suggested on this site, which i read just now to make sure. Now we have something like a fault line running through our grout. We did remove the grout down to the thinset and cleaned out as much as we could then regrouted. Of course it cracked again within 2 weeks of the repair. I do suspect a tile is moving but is there any sure way to know if it is just that tile or more and if so what is the best way to fix it. Also I am not sure why it would move with backerboard under it could it be the floor itself?
My response to this all-too-common question is a bit complicated since it is rarely one specific reason and could be a number of things.
Hi (Name removed to protect people who actually ask me for advice),
The best way to determine what is moving (something is moving) is to go by layers. One of them is moving in an unusual manner or has not been properly addressed while preparing the floor for tile. We’ll start with the tile itself.
You stated that it appears to be a ‘fault line’ which says to me that it runs the length of several tiles in a row and down one grout joint. Is this correct? If so it means that your actual tile layer is more than likely not the problem – it’s below that. If a tile (or tiles) were moving the grout would be cracked along at least two sides of an individual tile and would not create the line you’ve described. UNLESS (you knew that was coming, right?) that line is the one you snapped a chalk line on or drew on the floor as a reference and did not get thinset completely up to it on the edges of the tile. This would cause voids (conveniently enough) under one edge of every one of those tiles in a straight line. That’s doubtful, though, and would also cause cracking in the grout joints running away from that line.
Your backerboard. Unfortunately this is where I believe the problem may be. You stated that you installed thinset beneath the backerboard – correct? You did not state that you taped the seams of the backerboard with thinset and an alkali-resistant mesh tape. I would be willing to bet (my wife doesn’t let me do that, by the way, so it isn’t binding) that the fault line you’ve described is either directly over or within about three inches of a seam in your backerboards. If they are not taped but are thinsetted down they are fully supported beneath but still move independently of one another. Simple things like walking on one side of the backerboard seam more than the other (completely normal with room layouts) will cause more stress on one sheet than the one next to it. If these two are not tied together with mesh tape and thinset they will move independently and crack your grout. The only remedy for this is to pull out enough tile to tape those joints.
Screwing the backerboard into the joists – this will cause uneven movement in your substrate layers as the area directly above the joist will move differently than the rest of your substrate. The joist will expand and contract moving the layers directly above it more than any areas between the joists. The area above it has direct pressure pushing up on it while the areas between the joist have no pressure below them but, instead, are simply being pulled along for the ride – at different speeds.
The linoleum – I doubt that is the problem but even with thinset beneath your backerboards it can still cause movement depending on the type of linoleum. You stated that your house was 35 years old so it’s possible that it was ‘cushioned’ linoleum. If so there is no way short of tearing it out that will eliminate all movement beneath your backerboards.
Your subfloor – another possibility beneath the linoleum. Since you did not remove the linoleum you do not know what shape the subfloor is in (unless you can see it between the joists from below) nor how the joints in the subfloor are staggered. You also do not know whether or not the linoleum has full contact with the subfloor or if there are voids. Another strong possibility is that the linoleum is installed to ‘luan’ which is a very thin laminated plywood commonly used beneath linoleum. If this is the case it is very likely that there are voids between the luan and the subfloor allowing movement of everything above it.
A joist – You did not state whether the area of the fault line is one on which you walk quite a bit or one that sees very little foot traffic. If the latter it may be a joist directly beneath that fault line which is expanding and contracting an unusual amount. It’s very rare but I have seen it. If this is the case (you’ve eliminated the above possibilities) you can ‘sister’ that joist with another joist screwed directly to it on either one or both sides of it. This will help stabilize that joist and possibly eliminate the problem.
The most likely cause (with walls as well as floors) is not taping the backerboard seams. This would require tearing out at least one or two rows of tile along that line (depending on where the seam is). The next strongest possibility is the layer of luan beneath your linoleum with voids beneath it. A fault line of cracking grout is a very distinctive problem with only a handful of causes and it’s usually the backerboard seams – in floors as well as walls.
Unfortunately anything other than the seams will require tearing out the installation at least down to the problem layer.
There you have it – quite anti-climactic, yes? That’s why I attempt to inject extremely bad humor in my posts – I don’t want you falling asleep on me . As I’ve stated before the only reason your grout would crack is due to movement (unless it is brand new, incorrectly mixed grout). The trick is to find what movement is causing the cracking. The best (only) way to prevent it is to make certain that your tile installation is properly constructed from the joists up or wall studs out. There will always be movement, the purpose of your preparation is to eliminate as much of that as possible and allowing for what is left.
If you have an idea or question which you feel may help out other people just let me know. You can simply leave in in the comments with something like ‘hey jackass, make this a post, willya…?’ or similar. Or you can shoot me an email at Roger@FloorElf.com – I’ll answer you, I’m pretty friendly. No, really…
Besides, I need all the help I can get.