Don't use this, this product is like Flexseal rubberized sealer.
This is a reef safe insta set spray:
https://www.bulkreefsupply.com/inst...D=5032&indexName=brs_prod_m2_default_products
If your rock scape is glued up now, and has been allowed to cure, I don't believe you'd need the insta set spray at this point.
I would reinforce your 'scape using super glue and something like Poly-Fil, Cig butts, paper towel, baking soda, etc. You can also use a little sand or rock dust to hide those joints.
You can also use a variety of reef safe epoxies to reinforce your joints:
https://www.bulkreefsupply.com/catalogsearch/result?q=epoxy



