Can't Glue Acrylic Baffles In A Glass Tank?!

[TaylorPilot]

I get told all the time that you can't glue acrylic baffles in a glass tank because they won't hold. While I agree that you can't butt two pieces of acrylic and silicone them together like you would two panels when you build a glass tank, they work fine when sandwiching a piece of acrylic between two beads of acrylic. Fast forward to today, and I am designing a new sump kit and wanted to remove some older baffles from a 55 I built years ago. I figured I would film pulling them out to show how well they stick. Only problem is I couldn't get them out. This is 1/4" cast acrylic in an Aqueon 55 gallon. I used GE Silicone 1 just like you get at Lowe's to install. The baffles were installed years ago. If this panel was made out of glass, it would have shattered from me pulling on it this hard. Also, note that even though I have installed braces, they are supporting the other side. In other words, I am pulling as hard as I can against the baffles weakest side. If I have been pulling in the same direction the water would be pushing, it would have been even more secure. These baffles are almost impossible to get out once installed. It took me about 30 minutes with a razor blade to get them out. The silicone actually came off the glass panels easier because they are hard and the razor slid against them. When I tried to run it down the acrylic, the razor dug into the soft acrylic, making it impossible to get all the silicone off them.

No one should be scared of installing acrylic panels in a glass tank to build a DIY sump!

 

[DesertReefT4r]

Umm 2 of my diy sumps with acrylic baffles siliconed in, my old one lasted for like 5 years with no issues. First 2 pics are my old sump from my old tanks, used it on 2 tanks. I ues AGA silicon on the first one and it held very well my new sump I used GE II and its is working fine but not as good of a bond to the acrylic. Is using aquarium silicon or GE II ideal or the best choice? No. There are better options for this use. Dow 795 or GE 1200 are much better choices and are made to bond both acrylic and glass and a must if you need the bond to hold back pressure or weight. However these are much harder to find and normally need to be ordered online and are more expensive.

 

[ca1ore]

Certainly acrylic panels can be used in a glass sump as long as you account for expansion; personally I find them inferior to glass but YMMV.

 

[User1]

Certainly acrylic panels can be used in a glass sump as long as you account for expansion; personally I find them inferior to glass but YMMV.

I've heard they can or do expand breaking the glass. I personally would only recommend using glass if on a glass tank. Note - I've personally never had this happen but then again I only have an acrylic sump.

 

[TaylorPilot]

I've heard they can or do expand breaking the glass. I personally would only recommend using glass if on a glass tank. Note - I've personally never had this happen but then again I only have an acrylic sump.

That is true if it is a super tight fit, although I have never seen or met anyone that it happened to. It is imperative that you have a little slack so that when you silicone the panel in, that there is a little space. That way when it absorbs a little water, the silicone will absorb the expansion. With that said, I remember reading that when fully submerged that it will expand .3%. For an 18" wide panel(widest panels I make), that is 0.054" of expansion. I typically build them so there is 3/16" (0.1875") on each side. Another thing I have noticed concerning glass tank with silicone seams. If the tanks are filled, the silicone stretches. Take an off the shelf 120 for example. The cross brace has allot of slack in it when the tank is empty. Fill it up and the brace becomes very tight. Obviously the glass isn't bowing. It has to be the silicone seams stretching. So even if the panel was installed tight, I would imagine the silicone would stretch more from the water pressure than the acrylic would expand. Add any bit of slack, and it becomes a non issue. IMHO expansion, like the silicone adhesion is completely overblown when you take a few things into consideration when installing.

 

[ca1ore]

I actually think it is the glass bowing rather than stretched silicone. My rimless glass frag tank, for example, bows out 1/4" in the middle of the long axis. There's not much silicone between panels to actually stretch.

 

[erk]

I have always siliconed acrylic panels in my glass sumps. I leave a .125 inch of gap on either side for silicone and expansion. I see no bowing at all. And the reason there is any expansion isn't so much because of water absorption, its thermal expansion.

Glass and acrylic have very different coefficients of thermal expansion. Acrylic expands faster than glass. To account for this, you add a gap and fill that gap with a compound that can give.

This concept is used extensively in systems where two different materials are placed in contact with one another. The best example is lens systems, especially weather sealed ones. For systems where the individual lenses must be removable for service, a seal material is placed between the glass and housing, that effectively "matches" the CTE of each material. Silicone can be a good material for this with it's high temperature resistance, resistance to an enormous range of chemicals, and it's ability to retain flexibility for the entire life of the product. Just don't expect it to work well for high precision since it is very flexible.

 

[ca1ore]

Acrylic generally doesn't warp if both sides are exposed to the same conditions (i.e. when submerged).

 

[erk]

Acrylic generally doesn't warp if both sides are exposed to the same conditions (i.e. when submerged).

This applies to all materials. Glass cracks if one side is substantially warmer than the other and it isn't tempered. Metals and plastics will bow and deflect. It will be more noticeable with plastics since they typically have a higher CTE.

 

[TherealplexiG]

Yall pretty ugly with silicone work.

 

[Ratsinmyhead]

Yall pretty ugly with silicone work.

Sad face. I wouldn’t care too much about the cleanliness of the silicone in a sump unless it was on display. In that case I would be using an acrylic sump.

 

[TaylorPilot]

Yall pretty ugly with silicone work.

Guilty as charged....I don't have the patience for making it pretty.

 

[redfishbluefish]

The OP has had good luck with GE I, but there is another silicone specifically made for plastics. It can be found at HD, but not with the other silicones in the paint department, but in the department where they sell acrylic sheets....for my, in the window department. Here is the silicone I'm talking about:

This stuff sticks like grim death to acrylic (and glass). So for those who say acrylic baffles can't be used in glass sumps have never used this silicone.

I've used in multiple sumps without issue....great stuff.

 

[Glenner’sreef]

I’ve got an Aqueon 40 g breeder with a Fiji Cube sump baffle kit to fit it. $125 I believe and would highly recommend it. Solid and does exactly what it’s supposed to. It has 3-4” sock holders and comes with three socks. I use 2 and use the other for the new Red Sea 4” media basket. It fits perfectly.

 

[TherealplexiG]

Hi taylor,
Long time bruh.
How's you?

 

[Forsaken77]

The OP has had good luck with GE I, but there is another silicone specifically made for plastics. It can be found at HD, but not with the other silicones in the paint department, but in the department where they sell acrylic sheets....for my, in the window department. Here is the silicone I'm talking about:

This stuff sticks like grim death to acrylic (and glass). So for those who say acrylic baffles can't be used in glass sumps have never used this silicone.

I've used in multiple sumps without issue....great stuff.

That silicone is safe to use in aquariums? I forget why, but the GE-2 is also 100% silicone but shouldn't be used.

 

[TherealplexiG]

That silicone is safe to use in aquariums? I forget why, but the GE-2 is also 100% silicone but shouldn't be used.

Silicone is a type of synthetic rubber. We use this term for caulk aka sealant. There are various types of sealant available, some especially for plastics. I'm skeptical about use of PU sealants, or any other composition than silicone coz it may have toxicity at miniscule levels. Silicone has good resistance to saltwater. Hence I'd go with aquarium safe silicone commonly available. Watch out for mold and mildew mentioned on the package if you're using something else, it wouldn't be safe at all.

Forsaken'
I'll try to find msds and tds for the brand you asked and post it later.
I use rtv 100 series for most of the stuff, it's by momentive.

 

[klp]

I used regular aquarium silicone from LFS years ago in a 90 when I built a refugium into the tank itself. Just braced against the flow. Used it for several years with no issues.

 

[redfishbluefish]

That silicone is safe to use in aquariums? I forget why, but the GE-2 is also 100% silicone but shouldn't be used.

I have used it multiple times without issue. One time was a emergency use with it seeing water within 30 minutes, and again, no noted problems.

I'll also state that whatever silicone you use, let it cure for as long as you can.....at least three days, but prefer a week. I'll be making another sump in a couple of weeks using this stuff.

 

[ca1ore]

This applies to all materials. Glass cracks if one side is substantially warmer than the other and it isn't tempered. Metals and plastics will bow and deflect. It will be more noticeable with plastics since they typically have a higher CTE.

Yes, I know that. My point was that if somebody uses acrylic as a baffle it probably won't bow; used as a tank cover it will bow like crazy.