Need help with repair of spa cap

[JamesR]

I have these 4 sections of bluestone capping between the spa wall and the pool. One of them popped off during the winter and was laying in the bottom of the pool when I uncovered it in the spring. What is the best way to get this re-installed as far as prep of the existing surface and what to secure it with? It also has grout between the adjacent stone, but I think it is the same material as what is securing it. The first pic below is it just sitting on the wall, then second you can see it just lifts off. There is no existing adhesive material/mortar on the underneath of the stone. It is all smooth on the top of the wall.

 

[Arizonarob]

Hi James, hang tight, let me grab a couple of our construction guys to give ya some advice.
@jimmythegreek @bdavis466

 

[bdavis466]

A polymer modified thinset would probably be best

 

[jimmythegreek]

I agree but it's going to depend on if you have room to add mud underneath it or not. Some good adhesive like SRW or PL landscape would be choice B and a little grout between it to seal it up

 

[JamesR]

Not much room at all under it to lay a bed of thinset. It would all squish out at this point. Unless I were to grind some of it down. not looking to open up a can of worms either if i do not have to. That Loctite PL 500 stuff looks interesting and may work. Then i just have to find a small amount of grout to match the existing joints.

 

[jimmythegreek]

If you have access to an angle grinder you would help the bond by cutting some slots on both stone and beam so the glue has something more to bite to. We glue block with the SRW its strong stuff and flexes a tiny bit with weather change

 

[JamesR]

I do have an angle grinder. I will slice some grooves on both surfaces and try that adhesive. My local Home Depot stocks it. Any good recommendations for an outdoor grout that is swimming pool compatible? The grout width is probably around 3/8” wide.

 

[jimmythegreek]

Lowes Carrie's mapai and TEC they have a high end line that is outdoor rated. Could always use mortar and tint it even a sanded tile caulk would work but it will shrink so 2nd application will be necessary. Tape surfaces off if you caulk it first then peel wet

 

[JamesR]

I picked up the PL500 today. I will set the stone in place tomorrow then head on down to Lowes for some Mapai grout to see which color matches the best. Thanks for the help!

 

[bdavis466]

A little trick with that stuff - apply liberally to the spa and the cap, set the cap into place then pick the cap up completely separating it from the spa and then set it in place again. This makes a strong suction with the adhesive that should provide a good bond

 

[JamesR]

Well darn it, I did not read this little trick mentioned above last night before setting the cap in place today. I read the instructions and it said to apply in a zig zag to one of the bonding surfaces and set in place.
So that is what I did. Turns out that 3 of the 4 were loose so I popped them off, scored lines on the wall and the stones and then set them in place with weight on them. It has been a couple of hours so I do not want to pull them back up and redo. I hope they stay in place.