A bump in the middle of the cement board

Reply

  #1  
Old 09-01-09, 02:36 PM
Member
Thread Starter
Join Date: Apr 2009
Location: Chicago
Posts: 69
A bump in the middle of the cement board

Hi,

I found a bump in the middle of the cement board when I did a dry-run for my 13"x13" ceramic floor tiles. The board is 1/4" thick. I installed it on top of 3/4" plywood with modified thinset and screws a week ago. The bump is about 1/8" high. It isn't a screw head. It's right under the center of one of the tile. Is it a problem? Is it okay to even it out with thinset when I install the tile? Or, should I remove the high spot first? If so, how can I do it? I don't want to remove the whole sheet of cement board if possible.

Thanks,

Keith
 
Sponsored Links
  #2  
Old 09-01-09, 03:44 PM
HotxxxxxxxOKC's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2006
Location: USA
Posts: 8,044
You may find it difficult to make sure the remaining tiles are flat with no lippage if you leave it as is. Is this hump under the board or on a tape seam?
 
  #3  
Old 09-01-09, 08:27 PM
Member
Thread Starter
Join Date: Apr 2009
Location: Chicago
Posts: 69
Hi HotinOKC, thanks for your quick response. The high spot is not on a tape seam. I haven't taped the seams yet. The hump is almost in the middle of a full sheet of cement board (3'x5'). It's under the board. I guess I didn't comb the thinset evenly or the subfloor is not even. What can I do?

-- Keith
 
  #4  
Old 09-02-09, 07:03 AM
Member
Join Date: Jan 2006
Location: USA
Posts: 3,493
Keith

Can you tell if the hump lines up with a plywood seam from the subfloor? Does it go clear accross the cement board?
 
  #5  
Old 09-02-09, 07:55 AM
Member
Thread Starter
Join Date: Apr 2009
Location: Chicago
Posts: 69
If the hump isn't right on top of the plywood seam, it will be very close to it. The hump may go accross the cement board but only one small spot, around 4"x4" is high enough (1/8") to make me concern. The height of the rest of the hump is negligible and doesn't cause any problem.
 
  #6  
Old 09-02-09, 08:22 AM
Member
Join Date: Jan 2006
Location: USA
Posts: 3,493
Keith

It could be that the plywood panels are installed too tight, such that the seam is raising up. If thats the case, it'll continue to move vertically and will cause the tile to crack. Your best bet would be to remove the cement board, cut a relief kerf in the plywood seam and reinstall the cement board. You should be able to back the screws out of the cement board easy enough. Removing the cement board may be a pia however, specially if you used a modified thinset under it. Check the floor carefully to make sure you do not have other high spots at any other plywood seams.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes