Spa stone cap repair


New member
Mar 16, 2021
Good Morning. Does anyone have recommendations on how to repair the "seal" between a stone cap and a fiberglass hot tub? Also, I need to repair the grout on the stone cap.

I found an old thread that recommended MAPEI outdoor pre-mixed grout, but all the install videos I see recommend putting a foam backer for the grout and the cap seal. Is that necessary to keep the grout/sealant in place?

Finally, the old seal material is as hard as a brick and I cannot chip it out. I'm guessing a cutting wheel/grinder?

Photos attached.

Thanks for any input you have. 20210309_162608_resized.jpg20210309_162631_resized.jpg


Gold Supporter
TFP Guide
Jul 21, 2013
Northern NJ
Pool Size
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Welcome to TFP.

It looks to me like either your spa dropped a bit or you have expansive soil that raised the stone and created that gap. It looks like some things are moving with the gap and cracking mortar between the stones.

I would use a flexible mastic between the tub and stone. Hard grout will likely crack again with more movement. Sikaflex or Deck-O-Seal.


Gold Supporter
LifeTime Supporter
TFP Guide
Jul 3, 2013
Southern OK
Welcome to TFP :)

The tool: You will need a multi tool with a grout blade, should make fast work of the grout... Between the spa and the coping will be 100% pool silicone caulk and that can be cut out with the multi tool or knife.. Be careful of the fiberglass as it can get away from you..

Here is the tool you want

here are some blades

Between the top of the fiberglass and below the coping I am not sure if they used caulk or mastic
pick a color any color

As for grout you really want an outdoor pool grout and they may seem scary but that is what you need.. Mix a cup at a time and that should get about 4 to 6 feet of grout and get it cleaned up before it sets...

Not pool coping but he is using the tool and new grout :)
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