Silicone Not Working On Lava Rocks?

I bought a bag of those small red "lava" rocks from Lowes because I wanted to try making my own decoration. I also bought a tube of GE all purpose 100% silicone which I read is good for this and safe in the aquarium. But after gluing the rocks together and waiting about 24 hours, the silicone is extremely flexible and easily peels off from the rocks.

Is it just a matter of waiting longer for it to cure? It has been rather hot and kinda humid here lately. Or is there another product better suited for doing this?

 

Silicone will always be flexible. If you want a hard set adhesive, use thick super glue gel. Just ensure it only contains cyanoacrylate.

If the rocks are very clean and they don't stay bonded after 48 hours, try super glue. Silicone needs a pretty flawlessly clean surface. The lava rock may be too dusty. I don't mean you didn't rinse it, I mean the lava is easily crumbled so it kind of works against having a strong skin to bond to.

 

Silicone will always be flexible. If you want a hard set adhesive, use thick super glue gel. Just ensure it only contains cyanoacrylate.

If the rocks are very clean and they don't stay bonded after 48 hours, try super glue. Silicone needs a pretty flawlessly clean surface. The lava rock may be too dusty. I don't mean you didn't rinse it, I mean the lava is easily crumbled so it kind of works against having a strong skin to bond to.

Well I did rinse them first, forgot to say that. I'm basing the rigidness on this video where the guy can pick up the piece no problem,

Also I did buy some super glue before buying the silicone since I've used glue in the past. But I quickly realized I would need a massive amount of super glue to keep these rocks together since there are so many gaps, so that won't really work.

 

Well I did rinse them first, forgot to say that. I'm basing the rigidness on this video where the guy can pick up the piece no problem,

Also I did buy some super glue before buying the silicone since I've used glue in the past. But I quickly realized I would need a massive amount of super glue to keep these rocks together since there are so many gaps, so that won't really work.

Bulk reef supply sells super thick super glue in large tubes for like 14 bucks.

Also, silicone needs to cure from the outside in. What this means is if you use too thick of a glob, the inside will actually never cure since it doesn't get exposed to the air. Really smush the rocks together and leave them for 48 hours

 

Bulk reef supply sells super thick super glue in large tubes for like 14 bucks.

Also, silicone needs to cure from the outside in. What this means is if you use too thick of a glob, the inside will actually never cure since it doesn't get exposed to the air. Really smush the rocks together and leave them for 48 hours

that makes sense, I did kinda glob it on. I'll give it a shot, thanks.

 

I think everyone is pretty spot on with their observation, and the tips!

Just wanted to say that most lava rock you buy for landscaping purposes is extremely dusty, and even a good rinse doesn't exactly remove it all. I'd try soaking for a while and you're apt to see the rocks change the water to the color of the stone still in a day or two, and shorter if you use an air stone to move the water around the rocks.

Whenever I need to glue pieces together for whatever purpose I almost always use a combination of superglue and silicone. Often times I dot with silicone several areas of the surface on larger pieces with strong and tight contact to the surface I want it to adhere, then fill empty space between the stone or wood with smaller pieces, bonding these with superglue. The superglue and small pieces are there to prevent the structure from moving as the silicone cures.

Overworking pieces, or trying to manipulate them after the silicone has began it's drying process (often a skin forms) will often create very weak bonds that peel away from the surfaces.

I think it's most important to align pieces needing to be glue in a way they will sit without stressing the bonds. For example, you don't want to glue a pyrimid shaped piece upside down on its smallest point and it's weight off balance. Obviously said example piece won't hold long-term or very well.

If you glue pieces that seem to naturally fit together you'll have much better luck.