We’ve had porcelain tile demo’ed off our concrete slab and contractor was about to install vinyl planks, but found moisture between slab & tiles in many areas. Plumber confirmed no leaks and slab shows no signs of moisture after 1 day uncovered. Based on info on other posts it seems likely to be natural seepage through the concrete. It hasn’t been a problem or even noticeable over the 25-yr life of the tiles, probably due to our arid climate + good landscape drainage against the house + transpiration through the grout around the 12” tiles. So now floors are dry and contractor is recommending leveling w/waterproof Titebond 531. We chose Smartcore Ultra vinyl planks due to their attached waterproof underlayment so Titebond seems redundant & raises the cost of the work significantly. What do you think?