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Unread 11-26-2022, 01:59 PM   #1
Turnip
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First floor tile job--failure?

Hello everyone. Long time reader, first time poster. This forum is excellent and has been a huge help to me--it even works on our mountain (dial-up!) internet connection. Thanks to everyone for your contributions.

I did my first tiling last night and this morning am thinking I need to pull it all up and start over. Would appreciate any help or tips, thanks!

I am building a tile hearth (and wall surround) for a wood stove install. I have prepped the sub-floor per Hardie specs: (on top of our 2" T&G plank flooring, I installed 5/8" birch exterior plywood (solid!), then thinset with 1/4" X 1/4" trowel, then 1/4" Hardie Backer, taped & sealed seams with thinset, screwed backer into plywood with 1 1/4" backer screws. Tough job (for me) but all of that went well. The thinset seemed really thick but adhered to Hardie just fine.

FYI We are using Laticrete 253 Gold thinset. I selected it because I am chemically sensitive and it is zero VOC. I had no issues with any chemical odor, which is great!

However, I mixed the entire 50# bag (rookie mistake) with the exact amount of water specified on bag (water first, then thinset), it took a REALLY long time for my husband and I to mix, lots of little dry lumps to work out. We used a power drill with beater and also a 2" trim board to scrape it off the bottom. Other sites had warned me not to alter the mixing ratio which is why I chose to mix the whole bag at once. (I do have a kitchen scale and will mix 1/4 to 1/2 bags from now on...) Is it possible to overmix it?

All that said, even when we first mixed it the mixture was quite thick, did not look like the thinset in videos I've seen (I watch industry videos or videos from professional tile setters only), but I was determined to not alter the chemistry with more water (even though we live in a dry climate). It went under the Hardie OK, and the first couple rows of tiles, but then it was harder and harder to work with. My ridges were smooth and even and I could hear the air bubbles pressing out when I slid side to side, so I figured it was OK. I used 8X8 tiles with backbuttering. Pulled up tiles every so often and had good coverage--at first. Later tiles had poorer coverage--should have just stopped there and mixed new thinset? I read that you can remix your thinset 1-2 times to loosen it up (no additional water ever), so did that, and kept backbuttering, re-ridging, and slogging through. Then I started to notice lippage (newer tiles higher than first rows) and that's when I decided to call it a day. Could barely sleep last night, thinking at 2am I should jump out of bed and pull up all the tiles...

My roughly 4X5' hearth floor is half done and now I'm wondering if I need to pull everything up and start over. I fortunately have extra tiles so if I have to sacrifice some--well, not great, but doable. It is imperative that the floor not fail under our heavy wood stove. Also, the floor needs to be level (no lippage) so that our fancy EPA wood stove functions properly. The lippage I have so far will not fall under the stove feet so it is not perfect looking (if you look close enough) but won't affect the stove leveling.

I suspect that the thinset was drying out, or that I over-mixed it?

SO, questions are, if the mortar is drying out, but you are still getting 80-100% coverage, will it still fail, simply because the mortar was too dry and thick? I suspect so.

Other question--how can I tell if a tile is adhered properly next day? I have read people tap with a hammer? Is this a rubber mallet, or?

Also, if i do need to demo last night's work and start over, what is the best way of doing that? Just pull the tiles up with a screwdriver or pry bar? Is there any chance of saving them (without hours of work removing thinset?). I really only "lost" one box if I do have to demo them. Not too bad.

Lastly, would I need to pull up the Hardie Backer (I have extra) and re-fit? Or just scrape the thinset of the Hardie backer? If I do need to remove Hardie and start over, will I need an angle grinder to remove the thinset from the plywood even though it's been less than 24 hours? Or?

Any help is appreciated. Sorry for the long winded post! Thank you so much for making this such a useful forum!
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Unread 11-26-2022, 03:37 PM   #2
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Welcome, Heidi,

Mortar does have a "pot" life, or working time; the time from when it is first mixed to when it becomes too stiff and dry (it is actually curing in the bucket) to be useable. Some mortars have longer pot life than others. To complicate matters, Hardie tile backer is very thirsty, it will draw moisture out of the mortar. If your mortar was mixed much thicker than, say, the consistency of peanut butter that, combined with the type of tile you installed (some absorb more moisture than others), how long the mortar had been in the bucket, and the Hardie might mean there isn't enough moisture in the mortar to properly cure. That you mention the tiles you installed later are higher than the ones you installed earlier does suggest the mortar was stiffening up.

You probably don't want to tap them with a hammer. You can tap them with the plastic end of, say, a screw driver. Tap around on the tile you first installed, then on the later ones. If any of them sound hollow that could be an indication that they aren't bonded well.

At this point you might consider trying to remove one or two of the last ones you installed. For that I'd suggest a flat pry bar. If they pop off with little effort you'll have your answer. If they come right off just use a putty knife to scrape off the mortar still on the Hardie. If the mortar was too dry it should come off pretty easily. If you decide to go that route, the sooner you do the easier it'll be. You might not need to remove them all, perhaps the first ones will be fine.
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Unread 11-26-2022, 04:01 PM   #3
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Generally, birch plywood may not be a great substrate for your tile. It depends on what glue was used to hold it together. Generally, a softwood plywood made with an exterior rated glue is what is called for. If the ply doesn't delaminate because of the moisture, it should be okay.

What can cause problems mixing thinset is using a drill motor that spins too fast...that can entrain air in the mix sort of like when whipping eggs, but just mixing it, other than eating into your pot life, isn't an issue.
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Unread 11-26-2022, 04:10 PM   #4
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Thank you so much, Dan! That explains things very well. Thirsty Hardiebacker + thirsty tile + dry climate = stiff, dry thinset. I will pry up a couple tiles to investigate and go from there.

I was working within the pot time (4 hours on my bag) but given our dry climate I think pot time must be more like 1 or 2 hours! I will mix smaller batches when I retile/lay the rest.

One more question, please: immediately after mixing, the thinset was stiff and dry. It just didn't feel right to me from the start. My first ridges were ragged so I keyed in more thinset which produced better ridges. After installing the first panel of Hardie backer I lifted & checked the coverage and it was not great, so I re-keyed, and re-notched on the plywood and then back buttered both Hardie panels before fitting. Hardie only calls for 1/4" X 1/4" trowel on this step so my hope is that, even though I started with thick/dry mortar, that the back buttering of backer board will provide adequate adhesion.

Thoughts? I am scared to try and remove the backer board (would likely have to replace the plywood underneath, too?), but far more scared that my tile will fail!

FYI we had to use Hardie on this hearth project because of fire codes. Hope to try an uncoupling membrane when I tile our bathrooms (if I ever want to tile again after this project! ha ha!).

Thanks SO much for your help, and on a Saturday! Very appreciated!
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Last edited by Turnip; 11-26-2022 at 04:11 PM. Reason: had name wrong
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Unread 11-26-2022, 04:18 PM   #5
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Thank you Jim! We are going to buy a professional mixer today instead of using our corded drill. We did use a slow speed, and also mixed a lot by hand, but something was not right. I think smaller batches will help in the future.

As for the plywood--shoot! I was told that the birch would be the best for this job. It was VERY heavy and sure hard to pilot & screw through into the sub floor planks! It is definitely exterior grade plywood, made by Roseburg I believe. I got it from a specialty wood shop who advised me this would be the best for this project. The only other 5/8" they had was marine. Should I have gotten that?

Well, if you think I have made a mess of this, and need different plywood, please let me know. I really want to make this right, even if it means a day or two of demo and rebuild.

Thanks so much!
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Unread 11-26-2022, 04:51 PM   #6
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The marine grade ply won't hurt anything in this application, Heidi, but wasn't necessary. And I wouldn't be concerned about the mortar between the ply and the Hardie, for the mortar's primary purpose is to fill any shallow voids between the Hardie and the ply. As has been said here, the mortar holds the Hardie up, the screws hold it down. Leave the Hardie alone.

FWIW, and from the perspective of a DIY'er, I always mix small batches of mortar, primarily because I am mind numbingly slooooow. I don't ever measure. I add a few cups of water into the bucket, then scoop in mortar so that it creates a mountain in the middle of the water. Then I start mixing using my drill. I can pretty quickly tell if I need more mortar and I scoop a bit in at a time and continue mixing. I'm looking for consistency; when I pull the mixer out of the bucket the resulting stalagmites (for lack of a better descriptor) should fall down/droop over, but not dissolve/disappear. Once you get the consistency you want remember to let the mortar slake, then re-mix.

You can also help matters by giving your Hardie a sponge bath prior to combing out your mortar. You want it just damp, but not wet.
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Unread 11-26-2022, 04:59 PM   #7
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FWIW, there are some modified mortars that just do not look like they're wet enough until you've got them mixed for a while so adding water earlier than that can disrupt the mix, possibly considerably. Using the same mortar, you'll get a hang for what it looks like if you wing it, but for the DIY'er, it's better to measure and weigh. Doing that, I rarely have to make any fine adjustments which might be a little more water (usually less than a cup) or maybe a handful of mortar. They warned us about that in one class at Laticrete, and it became obvious when we were mixing the stuff...looked way too dry, then poof, it turned smooth and soft.
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Unread 11-26-2022, 05:05 PM   #8
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Great, thanks for the mortar mixing tips Dan and Jim! Less air and smaller batches!

Sounds like the exterior birch plywood is OK as underlayment atop our T&G planks. Overkill, but not going to bungle the job?

I'm thinking that when I re-tile I will run a low humidifier since it's so dry here. I did damp sponge the Hardie (as in the Hardie videos) but it dried very quickly--bone dry by the time I mortared just minutes later! I will sponge it a bit more next time, and perhaps re-sponge each area just before I key in my mortar.

Getting ready to pull some tiles now. Fingers crossed it goes smoothly and I only have to pull one row! I'll let you know how it goes as soon as possible.

Thank you, thank you, thank you!!!! I am so grateful for this forum and for your valuable time and insights.
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Unread 11-26-2022, 05:21 PM   #9
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I really have comparatively little experience with mortar mixing, Jim, but I feel like if it hasn't become smooth and creamy/soft by the end if the initial mix/slake/final mix process it probably isn't going to.

I have experienced what you described, though it was mixing a batch of grout. The stuff looked way too dry for the first 2 or 3 minutes then magically changed.
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Unread 11-26-2022, 06:08 PM   #10
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Yep--tiles popping off with a little elbow grease. It is obvious that the mortar is WAY too high/thick.

It's a bummer I have to demo and redo my work, but it is such a comfort and relief to have this resource and be able to get support here! Thanks again very much for your help and time today! OK, back to the grind!
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Unread 11-26-2022, 06:42 PM   #11
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oops! A 2" triangle shaped layer (about 1/8" thick) of Hardie backer came up with one of the edge tiles. Assuming I can patch it in with tape & thinset when I am ready to re-tile?
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Unread 11-26-2022, 07:00 PM   #12
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Most thinset can handle that extra depth. Since that chunk came off, that seems to indicate your bond was good to the tile. HB can come apart in layers, which is usually a bit different than a board made mostly with cement and without the fibers in it.
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Unread 11-26-2022, 07:58 PM   #13
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Thanks for your reply! I am done removing the tiles, but still have thinset to scrape off of hardiebacker.

Another small layer of Hardie just came up, about 8" X 3", 1/16-1/8" thick (second photo). The layers that came up were attached to tile from the very first row I had set. In hindsight, I probably could have left that first row in place, but the subsequent rows I had set were so terrible (first photo) that I decided to remove all of the tile and start from scratch. And even though the coverage looked pretty good on that first row I set, the tiles slid right off the thinset with a putty knife. That didn't seem right, so I decided to remove everything. Everything slid right off but the 8th and 9th tiles I had set took up some of the Hardie backer at the back corner.

So, now I am wondering if I can tape & patch the Hardie backer when I re-tile or if I should remove everything down to the plywood. Does anyone know if it is easier to remove thinset from Hardiebacker or from plywood? Or maybe I pull everything, get new plywood, and start from scratch? I have all the supplies except the plywood. Of course, it would mean more holes in my T&G planks.
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Unread 11-26-2022, 08:28 PM   #14
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after some research it looks like I can repair the HB and that this will be easier than removing it completely down to the plywood. If anyone thinks this is a mistake, please let me know. thanks!
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Unread 11-26-2022, 10:07 PM   #15
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Where you can see the trowel notches, that means that the tile was not set well. It could be from several reasons:
- the thinset was too stiff to flow when you tried to set the tile
- you did not move the tile across the notches so that they were flattened enough
- you did not press hard enough...this gets harder the larger the tile as the pressure you can exert is spread across the tile

I'm a fan of slant-notched trowels...the notches are taller, but because they're slanted, after the trowel passes over, they fall over, creating a flatter surface making it easier to fully embed the tile. On a floor, you want 100% of the edges and ideally at least 95% of the rest of the tile embedded. 100% of the whole thing is ideal, but not required.
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