Acrylic to Glass Silicone Bonding

DirtDiggler2823 · Dec 10, 2020

Stumbled upon this video which highlights which silicones bond well to acrylic, but the top two seem to be fungus and mold resistant, which means poison in the reef(?) Reason for the ask, is that I'm building a new sump out of a 40B and plan on using acrylic baffles. The GE silicone in the red tube that is made for plastics is a nightmare to work with as it seems every tube I come across is bad.

brandon clow · Dec 11, 2020

I built a 55 gallon sump with 1/4in acrylic sheets I had laying around and used the GE blue silicone tube. Four months in without issues and all chambers are fairly tall. I leak tested it for a couple of days with progressing each chamber after a duration of time without leaks and not a lot of warp at all.

mfinn · Dec 11, 2020

I've made a couple sumps out of glass tanks and acrylic baffles and used momentive rtv 108.
The last one I made about 4 years ago ( I used momentive rtv 103 because I had it on hand ) and the new owner hasn't said anything to me about it failing.
I'm sure he would.

JPG@CFI · Feb 5, 2021

I’d go with E6000 as it cures much faster.

Greg P · Feb 5, 2021

Hate to beat a dead horse here, but why wouldn't you just use glass and silicone?

Silicone and acrylic just don't bond

DirtDiggler2823 · Feb 9, 2021

Greg P said:
Hate to beat a dead horse here, but why wouldn't you just use glass and silicone?

Silicone and acrylic just don't bond

Sometimes its just easier to work with acrylic. For instance, my hands are big and clumsy, so I'd probably crack the glass or hurt myself making some of the cuts or holes, not to mention I'm not sure I could drill a 4 hole in glass without ruining things. I was able to make the acrylic on glass with silicone thing work though. Pretty confident it will hold indefinately.

NeonRabbit221B · Feb 9, 2021

I made mine with GE1 and it held up fine. Make sure the acrylic baffles have a 1/32" gap so the glass doesn't crack.

DirtDiggler2823 · Feb 9, 2021

NeonRabbit221B said:
I made mine with GE1 and it held up fine. Make sure the acrylic baffles have a 1/32" gap so the glass doesn't crack.

Yeah, I did something similar. I also used 1/4 inch thick acrylic which really cuts down on bowing.

14 foot reef · Feb 9, 2021

If you sand the acrylic with a 100 grit sand paper where the Silicone will come in contact with the acrylic, the bond will be way greater than not roughing the surface up. It's a trick I've used for 30 years.

DirtDiggler2823 · Feb 10, 2021

14 foot reef said:
If you sand the acrylic with a 100 grit sand paper where the Silicone will come in contact with the acrylic, the bond will be way greater than not roughing the surface up. It's a trick I've used for 30 years.

I did the same thing. I sanded all the sides actually. One reason was silicone adhesion, the other was to help diffuse light from the refugium.

Greg P · Feb 12, 2021

DirtDiggler2823 said:
Sometimes its just easier to work with acrylic. For instance, my hands are big and clumsy, so I'd probably crack the glass or hurt myself making some of the cuts or holes, not to mention I'm not sure I could drill a 4 hole in glass without ruining things. I was able to make the acrylic on glass with silicone thing work though. Pretty confident it will hold indefinately.

If it lasts long-term for you then have at it. Cheap and easy to use.
Just wanted to point out that for many, acrylic/silicone seals don't last

Greg P · Feb 12, 2021

DirtDiggler2823 said:
I did the same thing. I sanded all the sides actually. One reason was silicone adhesion, the other was to help diffuse light from the refugium.

Acrylic will absorb water and swell
Acrylic baffles can/will swell and change size/burst sump walls
Just sayin ...
Long-term it's something to research before you build your unit

DirtDiggler2823 · Feb 16, 2021

Greg P said:
Acrylic will absorb water and swell
Acrylic baffles can/will swell and change size/burst sump walls
Just sayin ...
Long-term it's something to research before you build your unit

Ran acrylic baffles for 3 years on my last sump build, never had any issues. I think it all factors into how you build it.

X-37B · Feb 16, 2021

Greg P said:
Hate to beat a dead horse here, but why wouldn't you just use glass and silicone?

Silicone and acrylic just don't bond

?????? 95% of the glass aquariums that use acrylic overflows use silicone to bond with no issues or they would not use them.

DirtDiggler2823 · Feb 16, 2021

90's reefer said:
?????? 95% of the glass aquariums that use acrylic overflows use silicone to bond with no issues or they would not use them.

This is true

Greg P · Feb 16, 2021

90's reefer said:
?????? 95% of the glass aquariums that use acrylic overflows use silicone to bond with no issues or they would not use them.

My reasoning is because;
Acrylic overflows are being pushed against the glass by in-tank water pressure, such as with the Aqueon MegaFlow units.
Baffles are resisting a sideways force so are pulling against the silicone, and as I stated previously, can swell.
There is info on the web about acrylic absorbing water, and there are cases out there where acrylic baffles installed too tight-fitting can break the glass walls of tanks.

Just putting it out there for everyone's benefit.

danzig · Feb 16, 2021

Greg P said:
My reasoning is because;
Acrylic overflows are being pushed against the glass by in-tank water pressure, such as with the Aqueon MegaFlow units.
Baffles are resisting a sideways force so are pulling against the silicone, and as I stated previously, can swell.
There is info on the web about acrylic absorbing water, and there are cases out there where acrylic baffles installed too tight-fitting can break the glass walls of tanks.

Just putting it out there for everyone's benefit.

This 100%. Also if you are going to do it, scuff the acrylic with sandpaper, and a utility blade to make scratches where it will be contacting the silicone, it makes it way stronger and adds more surface area and better for adhesion.