Science behind using rock dust w/ glue to help join rocks together?

[saltyfish24]

I've been watching BRS's old rock aquascape videos, where they use the dust to hide joints. That makes sense to me. But then I watched this Jag Aquatics video where he is saying to use the dust along with the glue to help hold the joint - not just as a cosmetic tool.

What's the science behind this? I thought you'd want the glue to be in contact with the solid pieces of each piece of rock to get a solid joint. Wouldn't the rock dust be preventing that? I was actually thinking of cleaning the joining surfaces before gluing so they're less dusty before joining them with glue.

But I believe the video, I just struggle with the logic. Maybe he's using glue that works differently than cyano-acrylate super glue and I shouldn't take his method if I'm using regular super glue?

 

[mook1178]

I don't know for sure, but the only thing I can come up with is that there is several points now to spread the pressure of the joint out.

 

[UncommonSense]

It’s analogous to cement vs. concrete:

Cement is the binding agent, concrete is the binding agent with rock, sand, and other additives; usually more than tripling the strength vs. raw cement!

 

[exnisstech]

I use mortar (e Marco 400) to bond rock together and just sprinkle sand or rock dust on the joints while tye mortar is wet. I don't trust super glue alone to bond rock to rock even with dust mixed in. Maybe it works I dunno. I know it's pretty easy to pop plugs off that are super glued to rock. I know the motar holds because I dropped a structure on the concrete and it was fine. A good mortar joint is usually stronger than the material being bonded.

 

[UncommonSense]

I don't trust super glue alone to bond rock to rock even with dust mixed in.

I used fiberglass plus Bob Smith (good) superglue, making a composite to anchor each rock on my pillars together in at least three points of contact… around half of the joints have broken free already!

 

[MDahms]

Regular super glue is thin and flows right through the sand/rock chips and then binds them together and to the rock. Then you can build upon that first layer to make a strong join. It works quite well as long as all materials are dry.

 

[saltyfish24]

Regular super glue is thin and flows right through the sand/rock chips and then binds them together and to the rock. Then you can build upon that first layer to make a strong join. It works quite well as long as all materials are dry.

So instead of using gel super glue, I should be using the runny stuff when filling joints with rock powder?

 

[Marc G-L]

The thin CA glue reacts on dry rock with moisture in the air in a very exothermic reaction. The thin CA literally wicks against all the surfaces it touches. My method was to use generous amounts of thin CA on rock powder and tiny crushed coral. While it was still curing, ie seconds later wearing gloves I put more power on that wet mixture and then pushed in down while supporting the joint. 10 seconds later a strong bond is secured.
On further research, several chemical manufacturing sites stated saltwater and UV light from tank LED's can break the CA down.

I never heard of a saltwater boaters using CA to mend broken boat parts, With that in mind I followed up with very moist E-Marco 400 cement pushed into the underside of the joints. Why? Because who wants structural failures when your tank and corals have grown out 2-3 years later. It's basically an insurance policy in case the BRS team reverses their claims, as they have learned to do, when experience changed their adamate statements to the contrary.

 

[MDahms]

So instead of using gel super glue, I should be using the runny stuff when filling joints with rock powder?

I had a lot more luck using the runny superglue for the initial bonds. The gel just doesn’t penetrate through the sand and into the rock well enough. The gel is useful for the last coat if you want to get dry sand to stick to any joints you want to hide or materials like epoxy.

 

[Marc G-L]

I agree, when I ran out of thin stuff and didn't want to buy another 30oz bottle, I used the smaller gel I purchased. Not as easy to work with, the sand and larger rubble don't stick as well to it, and lastly it takes a while to cure completely.

 

[John Neuzil]

So instead of using gel super glue, I should be using the runny stuff when filling joints with rock powder?

Yes

 

[painter1982]

BRS also has a video of them testing the strength of various methods of gluing the rocks together. The gel with epoxy is strongest with the thin glue and dust used to hide that joint.

 

[Marc G-L]

Strongest if you drop it 3 ft. The Mortar has polymer to allow the bond to have a small amount of flexibility without cracking/ breaking. I believe either offer a more secure attachment over CA alone. Some people complain the epoxy never quite matures in saltwater and becomes mealy and break off.