Asked on Dec 2, 2011

I'm looking for help on using self-leveling mortar.

KMS WoodworksWoodbridge Environmental


I am going to tile my very small bathroom floor and it isn't level so I bought self-leveling mortar to use first over the cement board. I worked with someone before that used it and it really helped, but I now find out I should use some kind of primer first (according to the "instructions" on the bag). I want to know if that's necessary since I'm pouring it on cement board. The "instructions" on the bag aren't very detailed so I'm looking for some advice from anyone that has used it before. I want to do the job correctly, but I don't want to do an extra step if it's not really needed with this particular application.
2 answers
  • The self leveling cement should be put on first, then the cement board. This is the ideal method of using this product. The primary reason for the self leveling primer is to bond to the older cement floor or wood floor that you may be covering. With new cement board its not as important. However I would suggest that you do use it as dependence of this product and its warranty relies on the use of the primer. I would use it. If you can remove the cement board before you use the leveling cement I would suggest you do this. As the cement board offers better crack resistance then does the leveling compound and if there is any flex in the floor the cement board would resist this better then the leveling compound. I know its a pain in the backside to do it this way, but if you want your project to last you need to start out right.

  • KMS Woodworks
    on Dec 3, 2011

    I've done it both ways with out any trouble., the cracking woodbridge hints about may be due to subfloor flex which should have been taken care of before the cement board went down. If your cement board was installed properly with some thinset / mastic and well screwed or nailed it will help with the flexing. I have done a good number of installs with the leveler used as cover for electric heating elements...these tend to be deeper applications so the flex / crack issue is less of a concern. my product of choice is from custom building products and called "Level quick"

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