grout keeps cracking, problem seems to be with backerboard seam

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Old 03-14-06, 02:12 PM
DVUKELIC
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grout keeps cracking, problem seems to be with backerboard seam

we installed ceramic tile over 1/2" backerboard, we needed to cut 2 pieces to fit in our bathroom. Since the tile was installed we have had to re-grout 2x, the first time we thought it was either defective grout or mixed wrong, the second time we took out the grout, we lifted some tiles and put more screws in the backerboard and re-grouted. There is still a problem however where the tile is installed over the seam in the 2 pieces of backerboard. (where they butt together). Is there any way to fix this without having to lift the entire job up and start all over? The problem with the grout seems to stem from movement in the backerboard right where the seam is. please help, just want to be done with this!
 
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Old 03-14-06, 02:39 PM
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Did you use thinset under the backer board? Backerboard tape over the seam? Should have been a 1/8" gap between the backer sheets, filled with thinset and taped as you tile. Maybe pop the tiles along the seam and use a carbide scoring tool to make a gap that can be filled and taped. What's everything under the backer and di this seam fall on a joist (was it fastened through the subfloor to the joists) or over a seam in the subfloor panels?
 
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Old 03-14-06, 02:50 PM
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did not use thinset, just screwed it to the floor, left 1/8" gap but did not fill with thinset or tape, plywood under the backer, not sure what thickness, did not fasten through the subfloor, just to the subfloor, did not fall on a seam in the subfloor but not sure if on a joist. how can you tell?
 
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Old 03-14-06, 03:49 PM
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You have at least two problems and maybe more. You should have used an unmodified thinset under the backerboard. This fills any voids between the plywood and the backerboard. You also should have taped and mudded the seams with alkalai resistant mesh tape and thinset. If this is not corrected you will continue to have the problems that you are having. I don't know any quick fixes for this other than to do it over and do it right.

You may also have other problems. What's under the backerboard? How many layers of plywood and how thick. What are the size of the joists, spacing beween them and the unsupported span from below?
 
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Old 03-14-06, 04:01 PM
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Originally Posted by HeresJohnny
I don't know any quick fixes for this other than to do it over and do it right.
Exactly!


As long as there is no thinset under the backer, there will be movement. Lucky for you (in the short term) it was not under a tile or your tile would keep cracking. Long term, the floor just won't last. Expect more cracked grout, loose or cracked tile. Short term, you could fill the grout line with a color/texture matched caulk until the rest of the floor falls apart. Then you can redo it correctly.
 
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Old 03-15-06, 10:44 AM
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When you finally redo the whole floor keep in mind that ALL backerboard manufacturers want their products set into a fresh bed of thinset. Some say unmodified and some say modified but at any rate they all want you to use thinset. Depending on which backerboard you choose they also all come with installation instructions available but you may have to ask the supplier for the printed documents of instructions.

Your only problem may be the lack of thinset under the backer and no seam tape, but obviously 'movement' is the real culprit. Before re-doing the floor you should investigate further to determine where this movement is in fact coming from. If it is structural movement or flex in the underlayment additional action will be required to stop the movement before any tile installation can be sucessful.
 
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Old 03-17-06, 12:13 PM
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thank you all for the helpful info...back to the drawing board, will let you know how it turns out
 
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