My uncle and I are getting set to put down the floor/foundation for a sauna in my basement. Since my house is only about a year old and I'm not sure if there was any sort of sealant treatment on the floor, would I have any trouble have the mortar blocks and mix adhere to the basement floor if there is any sort of treatment? If so, is there an additive I could get to help the mortar mix cure?

I would wash the area with a good acid mix made for etching concrete. Gravity is going to be your best friend with this installation.

I would not use an acid to etch the floor. One is is a mess. Two is it takes a muriatic acid to etch concrete and its very caustic as well as a Shure Kleen High Detergent. Either or it has to be rinsed and so on to be neutralized and if there is a sealer there already it may react to that and turns into a mess. The worst enemy is the surface is very smooth.

When ever you lay block on smooth concrete no matter if there is a sealant or not the mortar doesn't stick well to begin with. If you want it to stick snap a chalk line where the block is going to go and just take a 1" chisel and nick the concrete behind the chalk line (in sided block wall part) and just where the block webs touch the concrete floor. You don;t want to put acid on the floor as all. This can be left as a residue and effect the fresh mortar you are putting down. Any how that how we masons do it. The other method is lay out the block and drill a 3/8"thick pin and 1" deep or so hole in and put a 4" pin in the hole where the block web is and lay block fill some mortar in that pinned web hole and now its pinned.

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