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In most cases, these grates are simply a friction fit into the recessed hole and are bedded onto whatever drainage or aggregate sits beneath them @neal. Once they are sitting flat and the surrounding area is finished, they generally don’t go anywhere and don’t need to be mechanically fixed or heavily glued in place.
If you do want to positively adhere the grate to the concrete recess, a flexible polyurethane sealant adhesive such as Sikaflex 11FC or similar is a good option. It bonds well to concrete and to the underside of the plastic grate, while still allowing a little movement without cracking. You can apply a bead around the base of the recess, press the grate into position, and clean up any squeeze-out before it skins over. The same product can also be used around the top edge to seal the perimeter if needed.
That said, if the waterproof sealant you already have is rated as both a sealant and an adhesive, not just a surface gap filler, it will likely do the job just fine. As long as it is compatible with concrete and plastic and has good adhesion properties, there’s no real need to buy a different product. Once set, the grate should be well seated and secure for long-term use.
Please let me know if you have any questions.
Mitchell
Thankyou. Makes sense. I guess the main thing is so it’s waterproof around the sides of the grate. I’ve attached a couple of photos. If there’s a more appropriate sealant/adhesive let me know. It’s so I can flush the patio out and get rid of the water and dog hair.
I'd definitely go with Sikaflex over wet-area silicone, @neal. Bed the grate in with it and then caulk the gap between the grate and the concrete. Go to the effort of taping off the top of the grate and the concrete so you can smooth the Sikaflex off with a wet finger and not get it on the grate or concrete.
Mitchell
