Between six and twelve months ago, we poured four separate 250 sq. ft. quadrants of self-leveling cement (a.k.a. self-leveling mortar, or self-leveling underlayment) onto our basement concrete slab. We selected LevelQuik ES for the job and followed the instructions to the letter… Or so we thought…
Much to my dismay, last week I noticed that a small 3 foot x 8 foot area of the underlayment had an issue. The top 1/16″ of the self leveler was partially crumbling and delaminating from the surface. There was a significant amount of dust in the area and loose cement bits. The issue isn’t systematic across the whole floor. In fact, this section is in the most recent quadrant poured, while other areas over 12 months old are working out just perfectly. We’re getting ready to insulate the basement and soon after, lay Schluter Ditra and stone tile.
What Causes Self-leveler to Fail?
Before we started the project, we googled extensively for advice on using self leveler on a concrete slab, unfortunately finding little. We’ve subsequently written a great deal about our own experience with self leveler (much of it at that link). Even though information was a bit sparse, we heard repeatedly from tile experts that you must follow subfloor preparation instructions, you must mix the self leveler to the consistency on the package, and you must follow application instructions. We did all that, so what caused the issue?
Unfortunately, we’re not sure. Perhaps one of the last batches of self leveler wasn’t completely mixed, or some contaminate got into the batch, or the water/powder ratio wasn’t quite right. Any of these could have caused the problem. We’re pretty sure the subfloor isn’t part of the problem, since the delamination is limited to the top 1/16″ layer.
Our Solution: Prime the Area with LevelQuik Primer
LevelQuik Primer is a latex-based primer designed to prepare a surface for pouring LevelQuik on top. We noticed in using this primer on other sections of the subfloor and existing SLU that it tends to bind up any loose dust on the LevelQuik and create a smoother surface. We applied full strength primer to the 24 square foot area and, for now, all is well. This solution seems to have worked. The surface layer appears to be stable, and we’ve noticed no further delamination.
Other Self Leveler Problems & Solutions
We’re lucky that this problem isn’t systematic across the floor, or all the way to the slab. If that were the case, the only solution would be to remove the SLU as much as possible, correct the issue (if it is subfloor related), and re-pour the area. Since we’ve got radiant heating wire in the way, that would prove very, very difficult.
For those of you out there considering this project, remember: subfloor preparation and following application instructions is absolutely essential.
What do you think? Ever had a problem with self-leveler, or looking for advice on working with the material? Leave a comment here, and don’t forget to use the site’s search function. There’s a lot of good information available.