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what is the best way to fix cracks in self-leveling underlayment before I begin tiling?

I spread self-leveling underlayment in my bathroom to prepare a sub floor for tiling.  It began to crack within a few days so I would like to fix it before proceeding to tiling.  Do you have suggestions for fixing these small crack networks?



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Posted 2013-10-26T01:50:02+0000  by loomise loomise

Quickest fix for this if the cracks are 1/2 inch and under would just fill in with mortar as you tile.  Any issues why the self levelor cracked? i.e. subfloor issues?

Posted 2013-10-27T23:10:32+0000  by TheSwede

Hey loomise,


Thanks for your question and welcome to the community!


I'd have to disagree withTheSwede and say that it would be better for a foundation for your new tiles to remove the existing cracked underlayment. It's more of removal, than wouldn't want to build a house on loose rocks would you? That's why starting with a solid surface with no cracks will help.


Did you happen to use the primer rated for the self leveling compound? Failure to do so generally leaves cracks and makes the compound not adhere properly to the surface. Regardless if this is a concrete slab subfloor, primer HAS to be placed first before using the self leveling compound.


Shown below, we carry both brands alongside their respected leveling compounds in our flooring department.

Once you apply the primer and then leveling compound properly, you should have no problems with your subfloor.


As an added measure, you can apply a sealant and crack prevention membrane called RedGard that works well for giving a great moisture barrier and sealer for the subfloor. It's optional to do, but it can greatly assist your tiles in the long run.


Let me know if you have any additional questions,


Posted 2013-10-30T19:49:16+0000  by Joseph_HD_ATL



Thanks for responding.  That is indeed what happened.  I did not know primer was required until too late so a portion of the central part of the skim coated floor began to rise.  I put some crack patch on it, but in the end I removed the portion that was rising and loose (about 4"x3" area) and filled it in with thin set mortar and began tiling.  This was probably not the best solution and I will probably pay for it in the long run.  For the moment the tile appears solid.  Good lesson for next time.



Posted 2013-10-31T01:24:43+0000  by loomise

Hey again loomsie,


You are very welcome. I'm glad you at least removed the loose area. Even with filling it with thin-set mortar is better than nothing at all. As long you own the home, just periodically check the grout lines for any cracking, but you should be fine.


While you are at this stage, make sure you are sealing your tiles and grout as well. This will ensure that it will be protected from the top.


Let me know if you have any additional questions.




Posted 2013-11-02T19:36:01+0000  by Joseph_HD_ATL
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