The bath renovation goes on. I had to remove about 12 tiles today (because wife and I decided to make a change). The tiles were pretty well stuck on the walls and had to be pryed (sp?) off with a hammer and flat crowbar. After about 4 hard blows per tile, I was able to pry the tile off with the crowbar. Each came off intact and whole.
Tile is 12×12 porceline tile from Lowes. Thinset is Versabond.
Each tile was basically 99% free of any thinset. All of the thinset was tuck (pretty tenaciously) to the hardiebacker. I used a 1/4″ square notched trowel and each of the ridges were compressed by the tile (I could see the imprints of the ridges from the back of the tile on the thinset).
I mixed about a 1/3 of a 50lb bag using the proportions on the bag. The mix was creamy but stiff. I let it sit for 10 minutes (while I brought the tile to bathroom).
I applied the thinset to the wall with the trowel, set the tile, and gave it a slight wiggle. I know the tile was pretty well set and that the thinset was nicely adhered to the tile and hb. I know this because I had to pry one off the wall using a putty knife to reset it.
Why was there no thinset stuck to the back of the tile? There were some edges where the thinset was very well adhered and would need strong scraping to remove.
Was the thinset possibly too dry from the start?
Did I need to push harder on the tile to set it?
Should I apply the thinset to the wall and tile before setting the tile?
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It sounds like your thinset skimmed over while on the wall. if that was the case then you probably can not go off how well the tile that you had to pull off was stuck (reason if you had to pull it chances are that you did quite a bit of "adjusting" before you pulled it causing the mortar to stick better than the rest of the field)
Craig
After you let the thinset slake did you remix it? Remixing takes it from a fairly stiff mix to a very nice and easy to spread mix.
Other than that your techniques sounds fine.
The thinset could have skimmed over as was previously mentioned, or it could have just been the nature of the bond. When you broke the bond with your prybar, it's going to fail at the weakest point. Thinset-to-porous cement board is a pretty good bond. Thinset-to-thinset is homogenous and string in and of itself. Thinset-to-porcelain would be the weakest of the three.
The strength of bond also depends on how old the installtion is.
It can depend on the texture in the back of the tile, too. It sometimes helps to burn the thinset in on the back of the tile before setting it. "Burning in" means holding the tile in one hand and using the flat edge of the trowel to firmly apply a thin coat of thinset to the back of the tile. You're not looking for thickness, you're looking to sort of "wet" the back of the tile with thinset. A thin skim coat.
When burning in, everything else remains the same, you still use a notched trowel to apply thinset to the tile backer board.
I believe the term is "skinned" over.
Tu stultus esRebuilding my home in Cypress, CAAlso a CRX fanatic!
Look, just send me to my drawer. This whole talking-to-you thing is like double punishment.
"I believe the term is "skinned" over."
You sir, are correct.
I always spread a thin coat on the back of the tile. Use the flat edge of the trowel most of the time, sometimes I use the notch side if I need to build up a little thickness. Really doesn't need to be any thicker than like butter on cornbread.
"Put your creed in your deed." Emerson
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
I didn't remix the thinset after letting it slake. It was a bit thicker to work with than when I did my floor. That is what is causing me to think that I may have mixed it on the dry side.
How fast does thinset skin over after being applied to the wall? I only had 12 tiles on the wall and all were like this. For at least the first row, they were applied right after I applied the thinset.
The tile has been up on the shower walls for at least a week. It was not tiled completely. We have a plastic tarp around the whole shower so we can use it (our only shower). We did not use the shower in anyway for the first min 15 hours.
I think I will do both, mix a little looser (and re-mix after slaking) and back butter the tiles.
Sheesh...seems like a good thing that we decided to go with a different pattern for the tile. Would hate to think that someone could've been in the shower when a piece fell.
Thinset has a pretty good open time, so if you worked at a decent pace and didn't have something like hot halogen work lights shining on the thinsetted walls, it sounds like everything was fine. After allowing it to slake, you noticed that the mix was a lot stiffer than after the initial mxing, right? After the 10-minute slake give the mix a quick but thorough mix with a margin trowel (or low speed drill if you're using that), you'll see it go from a "stiff and grainy" mix back to a more "smooth and creamy" consistency. Then start spreading it on the walls.
I consider the smear of thinset on the back of the tiles to be the same idea as putting primer on new sheetrock befor epainting. "Put your creed in your deed." Emerson
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
Good analogy.
No hot lights but there was a fan and an open window. It's a small room and I sweat easily :-( Just wondering, would a stiff mix not adhere to the tile? I'll have to take some pics of the tile and the backer board. It just seems weird to not have adhered to the tile but yet kept a firm grip where I had to bang really hard with a crowbar and hammer to remove it.
again, if the tile were hard to remove, pay no attention to where the bond finally broke. they were fine and so was your thinset.
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I refuse to accept that there are limitations to what we can accomplish. Pete Draganic
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"Just wondering, would a stiff mix not adhere to the tile? I'll have to take some pics of the tile and the backer board. It just seems weird to not have adhered to the tile but yet kept a firm grip where I had to bang really hard with a crowbar and hammer to remove it."
No, a stiff mix is fine. Actually a stiff mix (less water) will give you a stronger bond than a loose watery mix. Don't over think this to much. You wrote that it took several whacks with a hammer and pry bar to dislodge the tile. So you had a good bond. It seems that you'd have been happier had the bond been broken mid-thickness of the thinset, ie, some thinset remaining on the wall and some thinset remaining on the tile.
Porcelain is non-porous, and the tile itself is quite strong, so the thinset-tile interface would be the logical point of bond failure. It doesn't mean your installation was inadequate, it's just the way it is. Had this installation been several months old, the bond still might have broken right at the thinset-tile interface, but due to the increased strength of the bond the tile probably would have broken into pieces instead of cleaving off in full tiles.
Remember, cementitious products like thinset cure over time. While the 24-hour, 7-day, and 14-day bond strengths are plenty strong, it still doesn't reach near full-strength until after about 28 days.
If your mix is too stiff, then the problem is that it won't easily conform to the nooks and crannies of the backer board or any texture on the back of the tile. Or it'll be so stiff that when you set the tile, the thinset ridges don't fully compress to fill the valleys and you end up with roughly 50%-70% thinset contact (the ridges) on the back of the tile.
Getting slightly off topic, the larger the tile, the more concerned you have to be with full coverage in terms of compressing the ridges. that's where back-buttering the tiles comes into play. 12" square can usually be set with no worries. If the tile has a texture or fired in pattern (like a waffle grid) on the back, or if the tiles aren't flat, like a pillow tile, then I might burn some thinset in on the back of the tile to fill the pattern.
If I'm working with large format tiles, tiles a lot larger than 12" squares, then I might go to a 1/2" notched trowel to spread thinset on the backer board and back-butter the tiles themselves with a slight thickness of thinset, maybe 1/8" or so.
If installing large formats in a wall, I might set them with a "dot" pattern instead of going for full thinset coverage. Different methods for different tile and different applications.
Thanks Mongo. I've only done 2 small floors as far as tiling (a 3x5 powder room and a small foyer). I'm good with finish carpentry, painting, some drywalling, etc. Tiling is a whole new world for me.--- It seems that you'd have been happier had the bond been broken mid-thickness of the thinset, ie, some thinset remaining on the wall and some thinset remaining on the tile. ----Well, I have to admit that I wouldn't have been so worried if that was the case. Your explanation helps to alleviate some anxiety (did I mention that I am an obsessive planner and worrywart?) I would feel horrible if a tile fell and hurt my wife or kids because I had made a mistake. I will make sure to back butter the tile as there is a waffle weave pattern on the back of the tile.
If you spend an extra couple bucks you can get "bonding mortar" that is real sticky. It will bond a whole lot better because it has an acrylic bonding agent in it. You can even step that up a notch to "flex" but don't ever plan to get that tile off.
What is bonding mortar? Can you provide a name of one? I thought Versabond being a modified thinset was stronger and stickier and than non-modified thinset. I've seen the flexbond but the data sheet didn't seem to imply that it was stronger bonding...just able to withstand slight movements in the underlayment. I'll admit that I don't fully understand all of the terms in the data sheet.
In the Custom line of thinset, CustomBlend is unmodified. VersaBond is lightly modified. FlexBond is highly modified. In a nutshell, the more modified, the stronger the bond.If you really wanna get wanky, then buy unmodified and modify it yourself with liquid latex admix. That'll give you a premuim bond, better than modified out of the bag. But in residential interior use, modified out of the bag is fine.If tiling over plywood or for exterior freeze/thaw installations, then dryset (unmodified) with a latex admix is your best bet.Custom's products are fine, they've never given me worry. But I'd say one of the stickier combinations is Mapei's Kerabond/Keralastic.
Edited 9/20/2009 10:44 pm ET by Mongo
One more question. Kerdi says to use unmodified thinset to adhere it to the cbu. In the current Fine Homebuilding, there is a user question on how to tile over existing tile. The answer was to use a modified thinset to adhere the Kerdi to the existing thinset. I assume modified was recommended so it would adhere to the existing tile. So, would it be OK to use Versabond or Flexbond to adhere the kerdi to the cbu? I know it may not be needed and a waste of money but would it be harmful in anyway?
You are speaking of the Schluter Kerdi fabric yes? The problem with this is that using a modified thinset with the fabric there will not be an opportunity for the thinset to dry by evaporation. Being a LATEX product. I have spoken to them regarding this and they will not warranty the product used in this fashion. However I spoke to an individual that works for them and used to work for one of the major suppliers of thinset and the like and a possible answer would be to allow the product an extended time for full cure. I would not be using this for larger format Por tile. Look to Laticrete for a few answers and you shall not be dissapointed.
Versabond is 'slightly' modified so you can use it with Kerdi. Flexibond is too modifiedd so no...you can't use that.
Kerdi calls for non modified but from all the pros I've talked to and from lots of personal experience I trust that slightly modified is OK to use.View Image
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"So, would it be OK to use Versabond or Flexbond to adhere the kerdi to the cbu?"I used Versabond (lightly modified) with Kerdi over cement board in this shower thread that I posted way back when. I've spoken to Schluter techies and was given the go-ahead.I wouldn't advocate a highly modified product like FlexBond.
Other than added cost, what is the problem with flexbond? It sure sticks that tile up there well. You can usually do without spacers if you have a good bed for the tile.
Flexbond over cbu can be used no problems. FlexBond only becomes an issue with Kerdi.Unmodified thinsets are simply portland cement based. Add water and they cure via a chemical reaction. Modified thinsets have a latex (latex = water) modifier in the mix. The portland cures via a chemical reaction, but the modifier cures via simple drying.Now envision a 12" square porcelain tile set over Kerdi membrane. Air can't pass through Kerdi. Air can't pass through porcelain. While the portland can cure via chemical hydration, the modifiers can't dry due to no free air. Make sense?An inadequate cure can lead to a weak bond. Now with smaller tiles, there are more grout lines, so the thinset behind the tiles is closer to "free air".So for me, I'll use a highly modified thinset whenever setting tile over CBU. For Custom thinset, that would be FlexBond. With Kerdi, if using tiles smaller than 12" squares, I feel quite comfortable using either an unmodified or a lightly modified (VersaBond) thinset. With large format tiles over Kerdi I'll use unmodified.
Funny how modified becomes a problem with Kerdi but doesn't seem to be a problem with Redgard and lots of other impervious membrane materials. Que pasa??
Exactly. There was talk from Schluter about dropping the restriction on modified when they come out big with Kerdi Board. We'll see. In the interim, I use what I use.
Mongo - great shower in that linked thread. My thinset was nowhere near as wet as the early pic of your thinset. Thanks for sharing the thread...I'm printing it out as a reference.
"Mongo - great shower in that linked thread. My thinset was nowhere near as wet as the early pic of your thinset. Thanks for sharing the thread...I'm printing it out as a reference."
Thanks, but for clarification, that thinset is a little looser because it's a Kerdi over cement board installation. If I was setting tile directly over CBU, the thinset would be thicker.
So for hanging the Kerdi I mix the thinset looser.
For setting tile I use a "standard" mix.
Edited 9/22/2009 12:08 am ET by Mongo
If it took considerable force to remove your tiles, then the bond was probably fine.
The separation finally occurred at the weakest point and I would think that with backer board the back of the tile was the least porous surface and therefore the weakest point.
I've removed plenty (I mean PLENTY) of tile and it almost always comes off with the tile being cleanest.
I refuse to accept that there are limitations to what we can accomplish. Pete Draganic
Take life as a test and shoot for a better score each day. Matt Garcia
You may be right, he may have had an adequate bond.
I always back-butter the tiles with just enough to fill the 'chambers' on the back of the tile and just leave the ribs showing, then set them in combed thinset. The combed thinset is never there more than a few minutes before a tile goes on. I have had one or two occasions to remove tiles I set this way, and it is damn near impossible. The tile shatters into a million pieces and/or some of the backerboard face tears off. Way, way, WAY harder than what he is describing.
Especially large tiles like 12x12 need back buttering. You can never go wrong spending the extra time it takes.
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Large tiles do not need buttering at all if done properly.
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I refuse to accept that there are limitations to what we can accomplish. Pete Draganic
Take life as a test and shoot for a better score each day. Matt Garcia
I didn't think it came in that flavor...lol
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Sometimes tiles won't adhere too well if there is a layer of dust or if some kind of release agent was used in the manufacturing process that is on the back of the tile. I always sponge the back of the tile to remove that stuff. It's also possible the tile absorbed a lot of the moisture from the thinset causing the thinset to be too dry so it could not cure properly.