The previous owner of my house tiled all the bedrooms on the second floor. I would like to remove all the tile and lay down hardwood flooring. So far I have removed the tile and now have all the thin set underneath. My question is whether it needs to be completely removed with a grinder or if we can use a very thin layer of self leveling cement to fill in all the grooves and make a level surface on which to lay the hardwood flooring? On the first floor there is a concrete slab and I used an industrial concrete grinder to remove all the thinnest. That worked great but I am concerned that this type of machine will just rip through the subfloor. And the idea of grinding off all the thinnest with a hand grinder seems like it will take forever. Any suggestions on the self leveling compound and if so which product would be recommended? Thank you
Yes you must remove all of the thinset - FOR SURE. Thinset is not meant to be exposed and a leveler on top of it will not protect it enough. From walking and moving furniture you will end up with chunks of thinset/leveler and it will just be a mess.
You either have backer board or plywood under the thinset. You have would really grind off thinset in this scenario but you can:
pry up the first layer of subfloor and redo it.
try to hit it with a heavy scraper.
and what I would try first... pound it out. Most thinset will disengage with heavy vibration. Try a hammer or mallet on a small area. Strike the thinset repetitively pretty hard in a circle pattern. See if you get some chunks disengaging after the first few minutes. If this works it get much easier after you start.
If the thinset is sound and without damaged or loose sections than it would be perfectly acceptable to leave it in place. Floating-off the floor to level the surface before the finish floor gets installed is the accepted industry standard.
Conversely, if you find the thin-set floor had received more damage than anticipated, it should be removed. It sounds as if the industrial grinder worked well on the first floor. Also consider that if the thin-set is over a plywood sub-floor it should break apart fairly easy with a sledge hammer. If used cautiously, it will fracture the floor into pieces and produce very little dust.
Lastly, if you do remove the thin-set and now have a wooden sub-floor you will have to be sure it is level and secured tightly to the floor joists.
If the thin set is clean the self leveling cement should bond well and hold up for a hardwood floor on top. I have used an adhesion promoter (similar to add mix) to increase the bond strength. The brand I remember was moose milk, it was less than 15.00 per gallon. There are others I just remember that name.