Flagstone Over Slab

paulbronson

Excellent website! I have a good one for you guys. We are installing approximately 20,000 sq. ft. of walk-on mortar set flagstone over a parking garage in Raleigh NC and are debating whether or not we should first seal the concrete slab.
Some background info--the slab is made of 6,000 reinforced psi concrete and is approximately six inches thick. There are five seperate buildings on top of the slab and our flagstone will serve as exterior flooring between the buildings.
The major concern here is the minor but constant freeze thaw cycling we encounter here. Would we be better sealing the slab to avoid potential peeling of the flagstone or would it be better to allow the slab to "breathe"? The slab is thick enough and close enough to heated buildings so that it shouldn't ever freeze solid (plus the cars in the garage will add heat underneath) but the flagstone/mortar certainly could freeze. We are coring 3" holes through the slab for drainage and our mortar bed will average about 1 1/2" thick.
If sealing the slab makes sense, should it be a dry-lock product or should it be a rubberized product like redguard? I would really appreciate your ideas on this one...

MarcD

I Def would not seal the concrete. Leave the mortar porous to the concrete
I would add a bonding additive when mixing it up though.


that sounds like a really cool job. take lots of pics.

olzo55

Call the architect or general for their recommendation.