QUESTIONWe have a 1600 sq. foot second floor exposed deck. Surface slope is 1/4" per foot. Wood frame, plywood subfloor, covered by 18" squares of porcelain tile. Grout has minimal cracking, but enough to cause water to enter and drip into the screen porch below the deck. porch ceiling is finished compounding the problem. Is there any sort of elastomeric sealer that we could apply over the grout joints that are cracked that is viscous enough that it would seal the cracks in the grout and keep the water out??
ANSWERANSWER - The leaking of deck causing damages in the ceiling below is the symptom of the cause of the problem. Treating the symptom will not remediate the cause of the problem.
If the deck is leaking then it hasn't been properly waterproofed below the tile over the substrate. If there wasn't a waterproof membrane installed when it was constructed, then that is the cause of the problem. If there was a waterproof membrane installed when it was constructed, then it was installed incorrectly or something damaged it after it was installed.
If there is a waterproof membrane under the tile assembly then maybe you can try to find the leak and then make the appropriate repairs.
There isn't any type of sealer that you can apply over the grout to seal the grout joints. If the tile is impervious, so water can't migrate through it, you could remove all of the grout and then install a sealant foam backer rod in the joints and install an ASTM C920 sealant over it filling the grout joints. Also all transition joints from floor to walls or to other materials should be filled with the sealant too. This type of sealant is generally a full strength silicone sealant or a urethane sealant. Always follow the manufacturers' directions of the sealant for how to use and apply it.
This repair is not considered a legitimate way to waterproof a tile installation, but in theory it could work.