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07-17-2015, 10:53 AM

I'm a DIYer and will start by mentioning the issue that I'm having is very likely my fault. The reason I'm posting is I need some help in determining what the actual issue is and steps to remedy. This is the first time I've had any problems with a tile floor installation and it is the only place that I'm having trouble in the entire house. It's also the first time posting a forum.... I'm usually the lurker that soaks up other people's advice.

The problem is with our kitchen floor. The grout has been crumbling in many places. Not everywhere, but a large percentage of the floor has been affected. To me, this suggests floor movement, but I also considered the possibility that I improperly mixed the grout. Let me go on to a long boring description of our setup.

The kitchen is in the corner of the house and does not overlap the main support beam. Our floor joists are 2x10s. From memory, they span ~18 feet from the outer wall to the center support beam. We had a structural engineer come out prior to any floor installation to evaluate and ended up adding another support beam halfway between the center beam and outer basement wall.

The sub-floor above is 3/4" thick. It comprises of two layers of different thicknesses, though I do not recall which. The top layer seemed to be a particle board with some sort of glaze over it that did not seem to absorb water. It seemed liked it was in good shape, so we left it.

On top of the sub-floor, we added 1/4" hardiebacker board with thinset troweled between the two layers. It was taped with a mesh tape made for cement board application and held down by countless screws again made for the cement board. I do not recall if they were 1 1/4" or 1 5/8" screws, but I believe it was the later. As you all know, there are marks on the board indicating where the screws should be and we have at least that many. Although, I had some help with screwing the boards down and am concerned my help did not notice the tendency of the screws wanting to push the boards back up. I fixed as many of these spots as I could when I inspected it but who knows for sure if I caught them all. I'm always paranoid that I miss some myself.

The tile was held on by latex based thinset and cured for about a week before the grout was added. The grout was a sand based grout, but instead of mixing it with water a grout booster was used that was supposed to act as a sealer. This is where I believe I may have potentially made a misstep. I worked with the grout in small batches and think I screwed up the mix ratio with the booster, adding too much to make the grout more workable. Of course, no changes were made in mid-batch to disrupt the chemical process.

When the grout first started cracking, we used a grout saw and replaced some spots. My wife and I are in disagreement whether those places held or not.

Now, I am in the process of removing all of the grout to fix the problem. To my surprise, I have not found any of the tiles to have popped in the worst areas (which is where I started... I'm not done yet). This is what I would expect with a floor that we have used for a year if deflection was occurring... but regardless of how the grout was mix, it would seem to some sort of deflection would have to be occurring to disturb its steady state and make it crumble. But I also assume all floors deflect to some degree.

So, now I'm at a decision point. After the grout has been completely removed (which will happen no matter what), do I attempt to re-grout with something else (I have since had a lot of luck with the power grout 550 on other projects... no booster) and see how it does? Or tear up the floor and... replace... what? This is where I'm at a loss. I have no issue with doing it right, but in this case I'm not really sure what that is...

Please let me know if more information is needed.


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07-17-2015, 11:50 AM
Welcome, Henry. :)

What is the spacing of the floor joists?

The sub-floor above is 3/4" thick. It comprises of two layers of different thicknesses, though I do not recall which.I see no way for that to be at all suitable for a ceramic tile installation, but you'll need to determine exactly what you have and how it was installed to determine how unsuitable it might be.
The top layer seemed to be a particle board with some sort of glaze over it that did not seem to absorb water.That'll make it even less suitable.

The grout, presuming a Portland cement-based grout from your description, will be weaker than your tiles and the first place you'd expect to see cracking if your subfloor or/and CBU installation are substandard.

I would consider the use of the Grout Boost product unless it was recommended by the grout manufacturer and even then it would need to be mixed according to both manufacturer's recommendations.

My opinion; worth price charged.

07-17-2015, 12:27 PM
Thank you for the response.

I will measure my sub-floor thickness when I get home. There are places where I can still access this. I may be remembering incorrectly; it might have been the top boards was 3/4". I'll check regardless. The joists are 16" center.

From the sounds of it, leaving the particle board was not a wise decision. I read up on it a little more after your response and it makes sense why it took so long for this to pop up. The particle board is likely changing with the humidity, so it seems like that is what needs to go.

So, the solution is to tear up the particle board and replace with plywood (target sub-floor thickness is 1 1/4"), then rinse and repeat? Is there a method I can use to test the floor defelections prior to putting down more cement board after the particle board has been replaced?

07-17-2015, 01:00 PM
If it was really particle board, I think you know the answer. If it was OSB, you might not be in as much trouble, once you know the actual thickness and type of each layer.

07-19-2015, 06:29 AM
I was mistaken. The sub-floor is actually 1 1/4" thick, but the top sheet is a 3/4" type of particle board. Then my 1/4" backer board on top of that. I guess that means rip up. Before I do that, I just want to make sure there is nothing else I can do. Is there a more flexible grout that you guys could recommend that I try first?

07-19-2015, 10:01 AM
Henry, you might look into Fusion grout. I've heard that it stays a little flexible. That's the only thing I can think of. If you were to re-grout a small area in the main traffic area with Fusion and use it for a week or so just to see how it performs, might be an idea. I've only used it once so lets see what others think about that. Many here use it all the time.

07-19-2015, 01:25 PM
Thanks, that seems like something I would consider.

Posted pictures of the subfloor in an area where it can still be seen. You will not see the cement board here, but I think it's pretty clear the top-layer is particle board. If re-grouting with a somewhat flexible grout were not to work, I would just be pulling up this top layer and then glueing/screwing another sheet of plywood in its place. Probably screw down the initial sheet again first because I would guess it was nailed.

07-19-2015, 03:17 PM
That plywood layer is pretty worthless, too, Henry. I suppose it could be a three layer nominal 1/2" plywood of some sort, but I'm thinking it's more likely a rather unbelievable 3/8ths" plywood as a first subfloor layer.

You'll hafta determing all that when you get down there, I suppose.

My opinon; worth price charged.

07-19-2015, 08:23 PM
If the particle board is 3/4", then the plywood is likely 1/2", making up the total 1 1/4" that was mentioned earlier. The plywood looks to be about 2/3 the thickness of the particle board.

Either way, it's not worth much. You can invest in some grout that is flexible and possibly get by for a while. I think over time you're going to have a cracked tile or two.

Steve in Denver
07-19-2015, 10:14 PM
It probably doesn't make a difference to the situation, but I half-ass measured the layers in photoshop. The plywood layer is about 81 pixels, the particle board is about 102 pixels. Lets call it plywood 80% as thick as the particle board.

particle board=0.75" -> plywood=0.6"
particle board=23/32 -> plywood=9/16 to 19/32

Again, probably doesn't change much.

07-20-2015, 06:57 AM
I guess I'm going to forgo putting in a flexible grout and just rip it up and be done with it. There are cabinets in the kitchen already with installed counter tops. I do not want to add the counter top cost in again, so I thought I would try to do this with the cabinets in place.

Unfortunately, the cabinets sit on some tile as we tiled before installing the cabinets. We went back and forth for some time deciding which way to go. (I think I will forever choose the other way now, but aside from demonstrating a few new inventive combinations of curse words, little can be done about that choice now....)

My general approach is remove the cabinet toe kicks and then use a grinder wheel to cut the tile/backerboard just inside the toe kick line without destroying the cabinets. This means the cabinets will remain on the existing tile. The walkable area of the floor will be ripped up to the first layer of plywood so I'm certain everything sisters-up to a stud. Then the existing plywood will be screwed down everywhere I can to make sure it is snug. A new layer of plywood will then be glued/screwed down so that we get to 1 1/4". Then thinset, 1/4" backerboard, tile...

If you were called out to fix something like this, is that generally how you would handle it? Is there a better tool than a grinder to do what I'm suggesting?

07-20-2015, 07:20 AM
Is there a reason you cannot remove the cabinets and re-install them later?

At first that may sound like more work, but I'm betting that in the long run it's about the same, if not less. Just cutting the subfloor around them is going to be a royal [female dog].

This way, you will get good, proper sub-floor under the whole room. You may also get a chance to install some more joists once the entire subfloor is ripped out. If the first layer of plywood is not up to par, you will need to remove it anyway.

Plus, you will have them away from risks such as grinders, saws, subfloor sections (you know these awkward panel sections are going to try to get revenge on you by denting the cabinets), hammers, prybars, etc.

The cabinets aren't too hard to install again later, but I suppose that depends on how they are constructed. I'm thinking of standard box types here. If yours are built-in-place, it may be a very different story.

07-20-2015, 07:31 AM
I would like to remove them because I think it would make it a lot easier. But there are granite tops on the cabinets now and I'm not sure how to go about that without breaking them.

The island (one piece) can certainly be moved with the help of some very large friends and a couple furniture dollies, but I'm not sure how to get the cabinets along the wall. That's why I thought I would have to cut or break the tile.

07-20-2015, 07:49 AM
This is the general jist. The cabinets L around the floor, so there is one section on the left (where fridge is) that runs parallel with the floor joists. That's why if I do not remove the cabinets (which I can't figure out how I would), I do not want to cut out the bottom layer of plywood. The island, although impossibly difficult, can probably be moved because it was made as one cabinet. The fridge and dishwasher would obviously be removed.

After the toe kicks (3/4" thick) have been removed, tiles that do not make contact with the cabinet can be popped off. The ones use for weight support would need cut I think.

Then I think the most difficult piece of plywood to install (and where I would start) would be in the far back corner.

07-20-2015, 07:54 AM
That's a good explanation.

07-20-2015, 11:40 AM
That's a difficult one for sure, but not impossible. Fortunately, at least at this point, the particle board that's in place will break off fairly easily. It'll be a little jagged, but that can be cleaned up with a chisel and hammer.

Considering that the subfloor is only 1/2" or less, I think you're going to have to install some blocking between the joists to support the edges of the new subfloor. I don't think the subfloor is strong enough on its own to support it.

07-21-2015, 10:31 AM
Yes, thank you, Kevin. It took me a little bit to visualize what you meant because I was sure the stiffness of the second layer would take care of it. But that doesn't mean that second layer will end at a joist so the bottom layer could flex like a trampoline. I will drill a hole in the lower layer before I start so I can see where the second layer will end relative to a joist.

07-21-2015, 12:04 PM
I know particle board in not ideal...but it shouldn't affect the tile system if it doesn't get wet and the subfloor underneath is stable, right? I've torn out 30 year old floors that were thinsetted directly to particle board, that were holding up fine. I'm not advocating tiling over particle board, but since it's already been done I would try to make it work if possible.
I think the real issue is 1/2" plywood spanning 16 O.C. joists. Is there anyway you can get into the crawl space to add bracing in between the joists to stiffen up the floor? It just looks like tearing out the floor would be a huge pain. I would exhaust all options before doing that.
It also seems odd to me that the tiles haven't broken bond...usually when grout is cracking on floors it means tiles are loose.
Fusion grout does work great, its time consuming but leaves a very nice finish and you wont ever have to seal it.

07-21-2015, 02:37 PM
I wouldn't trust particle board. Maybe with a bit of luck it holds up, but humidity changes have to cause trouble, and it's not stable to begin with! Since the grout is cracking already, I don't think there are any band aids that are going to work.

07-21-2015, 02:46 PM
Then the existing plywood will be screwed down everywhere I can to make sure it is snug. A new layer of plywood will then be glued/screwed down so that we get to 1 1/4".Henry, there is no requirement that the subflooring be 1 1/4" thick.

What you don't wanna do is start that new subfloor with anything thinner than nominal 5/8ths" T&G material, and I personally would not start with anything less than nominal 3/4" material. What you elect to add above that is up to you, but cannot be less than nominal 3/8ths" plywood.

I don't believe your existing first layer qualifies, but I'm not there to measure it.

My opinion; worth price charged.

07-21-2015, 03:58 PM
Thanks for the replies.

Isaac, I would like to fix it without ripping it up, but I can't see a way to add any more bracing. The joists were already cross-braced (not sure if that's what it's called... the metal straps between each joist) and an additional support has already been added (kitchen is above joists in top left portion of picture). To sister the joists now, I would need to pull out a ton of electric (the load center is below the kitchen).

The way I am understanding it and visualizing it is that I have two problems. Please correct me if I'm wrong. The first problem is the thin layer of actual sub-floor I have (I can get a measurement of the layer of plywood but I think we agree that it's a moot point... it's not enough). It is not providing enough support and needs increased in thickness. The second problem, which I believe is to a lesser degree, is that the top-layer under the backboard is particle board. It is not guaranteed to cause problems and, had the plywood been thicker, may have never come-up as an issue. But it is a vulnerability due to spills that may seep through and cause it to expand or hump or possibly humidity. If the sub-floor were fine and the grout was not cracking, this would be a fix-as-needed.

So, my actual remedy is to thicken the sub-floor, right? I plan to glue and screw another layer of plywood onto it, without ripping up the existing plywood, so that it behaves as a thicker board. I suppose this may not be exactly what is recommended, but structurally it is the same right? Plywood is just layers of wood glued to layers of wood. And since it is necessary to get to this layer and the opportunity to eliminate the particle board presents itself, this vulnerability should get removed, too.

Since I'm not removing the cabinets along the wall, I need the sub-floor to be a greater or equal thickness to what I have now with the particle board in place. I'll get some measurements, but this should mean I need at least a 3/4" piece to throw on of the existing layer. So, assuming the lower layer is 3/8" - 1/2", I'll have a 1 1/8" sub-floor at minimum.

Moving the center cabinet without damaging it is going to be a big challenge. The others I guess I will cover with moving blankets and be very careful not to scuff them when I score the backerboard beneath or demo the floor. On top of that, removing all of that tile and backerboard screwed down in 9 million places with the thinset hiding the screws on top will probably take a while. Not looking forward to that...

But the painful part is this.... with the next few weekends already booked, I can't get to this right away so my wife wants to know if I can patch the grout (I cut out 40% of it already) until after our labor day party..............

Anyways, I really appreciate all of the help and advice. Please let me know if it still seems like I'm not getting it.

07-21-2015, 05:03 PM
Sounds like you have quite a project in front of you. Sorry to hear that but I think you are doing the right thing by investigating all the possibilities first.
I still do not understand why there are not any tiles that have broken bond. In almost every subfloor problem I have encountered, there are tiles in the traffic areas that have come loose. While modified thinset has more "flexibility" than grout, it definitely does not do well with substantial movement in the subfloor underneath it. Maybe some others can chime in on this.
There is a possibility that with a semi-flexible grout, you can at least buy some time (like when your ready to remodel the kitchen again, haha).
Again, I know we always want to "do it right", and if it were one of my customers I would recommend taking it all out. But, if I were in your shoes in my own house, I would spend the money for a couple units of Fusion and at least try that. Maybe just do it in the areas you've already removed the grout, and see how it performs over a couple months with traffic.

07-21-2015, 06:49 PM
I think the problem is that the two layers weren't screwed into the joists enough. That particle board is a no-no also, of course. It swells with humidity and contracts when it is cold. Screwing the subfloor to the joists is important. In the photo of the subfloor layers it does not look tight to the joist.

The single component grout might work if the tiles are not loose.