Cracks in Decking and Mildew in "Foam Lining" Next to House Wall and Decking


New member
May 22, 2020
Fulshear, TX
Hello. Our in group pool is only 3 years old but it appears due to settling, we have cracking happening on the cool decking AND in the "grout" line going around the pool between the decking and the coping. We also are experiencing some mildew "rot" on the "foam lining" next to our house slab/wall and the decking shown in the attached pictures. I have reached out to our pool builder but no response and I am getting quoted around $1k to fix these issues from a separate pool company (which he also said this mildew rot is something he hasn't seen before)...any thoughts or feedback appreciated!!



Gold Supporter
TFP Guide
Jul 21, 2013
Northern NJ
Welcome to TFP.

The "grout" line going around the pool between the decking and the coping is your pool expansion joint. It is a key part of keeping your coping and tile from cracking and is filled with flexible mastic. Depending on your ground movement between the two structures may be normal. Expansion Joints and Coping - Further Reading

It looks like you have some shrinkage int he flexible mastic but to repair it properly means scraping out the old mastic and installing new material. DECK-O-SEAL - Polysulfide-Based Joint Sealant is typically used.

I have not seen mildew rot before. But foam left exposed to the sun will be broken down by the suns UV. I would put something like Deck-O-Seal or Sealants | SIKA in that joint.