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Question:

We are thinking of installing engineered flooring on a concrete slab. Must the concrete be prefectly level?

The slab can vary in depth from -1inch to 0inch over a 10 foot range.we tried self leveling concrete. some parts of our initial pour,when we just learning did not turn out so well. now there are small areas that are as much as +.75inches.Can we shave/grind the high spots down. Do you recommend that we grind these spots down before installing the flooring?

Answer:

I do highly reccomend doing a job right. If you want a good job, either do a level set or rent a grinder and level the floor.
There is an easier way: fill the low spots with an epoxy cement, and level out the floor. Minor variations won't bite you, but three quarters of an inch is not minor.
The easiest and correct thing to do is to relevel the floor. Tear up all the old thinset, the floor leveling compound, and repour. This material is typically pretty brital and should come right up. It will be a little more tediuos over a concrete slab than a crawl space floor. For a crawl space floor, just beat hell out of it with a sledge hammer. About 1/3 to 1/2 of your force should do the trick. You don't want holes in the subfloor. No need to worry about damaged particle subfloor as this will fill with the new self leveling compound. For a concrete slab, you want to do the same thing but be sure to start in a corner and chip away a small area. You can then continue to chip away into the thicker portion working your way accross the floor. Or you can get some kind of chipping tool under the edge of the compound. Just don't wack it hard enough to break your slab. No need to get 100% of everything. Just the high side stuff. The leveling compound will cover the boogers. Be sure to mix your leveling compound a little thinner. This is one job you really do want to leave to the pros. It works great with a concrete truck with premix and a small pumper truck. God Bless
If this is glue down installation, you need to grind and fill. This could take a professional 3-4 different coatings to get it exact. It is easier to fill than grind. I would error on the side of caution. If it is rolling, you may chase it around the room the first couple of times. If it is a floating floor I would do nearly the same thing, except it does not have to be quite as prefect. I would take a level, the longer the better and grid out the floor marking with a crayon marking highs and lows. Screed from high point to high point. Let it dry. Sand. Screed again. Keep repeating until you meet the specifications in the instructions for the flooring.

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