No. It can even be applied directly over polystyrene foam. Here is a link that might be useful: Edison Self Leveling Coatings

Hi everyone! Thanks for the feedback. The tile definitely wasn't ceramic. When we tried to pull it up, it just crumbled into tiny pieces. We didn't want to deal with the potential of asbestos (we don't know when the flooring was installed but the house is old enough where it was a concern) so we decided to cover it. Maybe that wasn't the smartest idea but that's what we did so we can only move forward! The "little mountains" aren't huge but definitely hurt when you step on them and range from just a little bump to extremely noticeable. This might be a stupid question, but can we just ground the lumps down so they're equal to the rest of the floor? If we go that route, is there something we need to do to afterwards before putting down the tile? And can someone explain why peel and stick tile in the laundry room is a bad idea? I've read mixed reviews about that type of tile, but my personal experience has always been positive (though I've never experienced it in a laundry room). Thanks for all of the feedback! I really, REALLY appreciate it.

its a misleading term self leveling :), you must use a spike roller to get results, did you scarify and prime the slab ? encapsulate mastic properly? ambient temps and improperly prepped slab, abnormal moisture readings etc..

How much of an issue is the puddle? Does it cause a hazard when walking to your car? Does it cause damage to your property (the stuff stored in the garage)? Do you 'need' perfection or is a DIY patch (and an obvious one) good enough for you? When it comes to leveling concrete it can be easy (assuming you have been taught some tricks of the trade AND have worked with the SLC product before) or it can be frustrating (none of the above). Technically you can rough up the concrete (give it a deep clean with detergents...then rinse, rinse, rinse and rinse again). You can prime it. Both of these are pretty easy. The tough part is the SLC. It is not self-leveling and it can be tricky to get the mixture right. Remember: SLC have MAXIMUM thicknesses as well as MINIMUM thicknesses. You have to choose the correct SLC AND IT'S OWN PRIMER to do the job properly. You have to know the max/min of the product and you have to leave an edge that you grind down later. As an aside, epoxy coating isn't going to do anything for the dip. Epoxy is a coating. It isn't a 'build up' product like SLC. To fix the dip, the epoxy professional STILL has to fix the dip with SLC.