Patching acrylic aquarium with Weld On 4?

mesopelagic · May 15, 2024

First, thank you all in advance for reading and offering any advice. I'm a PhD student on a shoestring budget without any experiences in this (thrown to the wolves...) trying to build a large, shallow tank for research, size 77 x 105 x 30cm. I had 8mm transparent acrylic cut to the dimensions I need, leaving room for the pieces to slot together (decided on the 8mm based on this: http://www.plasticgenius.com/2009/05/calculate-aquarium-thickness.html). I called the company to ask but don't know what type of acrylic it is (cast or extruded, any specifics about grade etc), just that it's Perspex. The company polished the edges before shipping to us.

After several stupid failures (I'll comment below), we tried using Weld On 4, which we were scared to use to begin with because the research animals are highly sensitive invertebrates. This is the only Weld On type easily available in the UK. Today we tried water in the bottom of the tank after letting the Weld On 4 sit for 36 hours. There are several places where the seams have bubbles all the way across, and it's possible to run your fingernail between the panes (see pictures). It obviously leaked. At this point, I'm wondering what can be done to save this. I'm out of money and paying for everything myself and honestly about to just give up.

Should I apply more Weld On 4 to the edges where there's an issue, and hope that it reseals properly? There's conflicting advice about whether this works, or if the seam will be weakened but it will work, or if it won't work at all.

Alternatively, should I get clear acrylic triangles to wedge into the seams and bond those in place to try to remake the seam? i.e. https://www.clearplastictube.co.uk/clear-acrylic-triangle-right-angle-4mm-1000mm

mesopelagic · May 15, 2024

Comment re: all of my mistakes and how I screwed up this badly in the first place:

The first time we tried to assemble the tank, we used Everbuild Stixall to put it together, let everything cure for 24 hours, then added Bond It HA6 RTV silicone sealant to seal the internal joints. After 3 days of curing, that failed the leak test. We re-sealed the internal joints plus the external joints, let it cure again for 3 days, and it failed the leak test again. We pulled the entire thing apart, used a boxcutter and some ethanol to remove the silicone, and tried again. This time the tank held water for about 5 days before failing. Went back to the drawing board, everybody recommends Weld On for acrylic tanks. Alright. We pulled everything apart and removed the silicone again, added Weld On 4 (the ONLY stuff we can seem to get in the UK due to chemical regulations), and let that sit.

Please don't tell me how stupid I was with all of this. I know. There are a lot of other things going on right now that are making me seriously consider quitting the PhD as a whole, and this is just the cherry on top. This post (cross posted to Reef Central) is my hail mary to beg the community to help me, if there is any way I can be helped. Or... do I just give up, at least on this tank? I would want to save the acrylic, maybe cut everything down by a few centimeters and try again with a slightly smaller version of the tank, but I have no access to cutting or polishing tools.

mfinn · May 15, 2024

@Troylee might be able to offer some advice.

Troylee · May 15, 2024

Yeah you got some bad joints… what I would do is squirt some Weldon 4 in the voids and let it soak for about 30 seconds then clamp it with a squeeze grip or something of that nature.. let it cure over night and come back with Weldon 16 and lay a bead inside to fill any voids.. Weldon 40 would be best if you can your hands on that over there?

Lowell Lemon · May 15, 2024

The attempts to use other bonding agents and silicone and then trying to clean up using alcohol to clean up the joints have damaged the acrylic and the materials should be scrapped. That along with Perspex being an extruded or continuous cast acrylic lead to failure. Sorry for you in this frustrating experience. Find someone who can donate the correct tank for your research in the UK.

Troylee · May 15, 2024

Lowell Lemon said:
The attempts to use other bonding agents and silicone and then trying to clean up using alcohol to clean up the joints have damaged the acrylic and the materials should be scrapped. That along with Perspex being an extruded or continuous cast acrylic lead to failure. Sorry for you in this frustrating experience. Find someone who can donate the correct tank for your research in the UK.

The good thing is silicone don’t stick at all so it should be easy to remove lol… I don’t think it would leave any residue.. I don’t know what he’s cleaned it with

mesopelagic · May 15, 2024

Troylee said:
The good thing is silicone don’t stick at all so it should be easy to remove lol… I don’t think it would leave any residue.. I don’t know what he’s cleaned it with

The silicone still left a very thin layer behind, so we cleaned it off with a razor blade, but to remove the remaining residue we used a scrub brush and ethanol. There are still gaps about 1-2mm thick where the WeldOn 4 didn't connect things properly.

Troylee · May 15, 2024

The only chance you have of saving it is laying a bead of Weldon 40 inside… 16 isn’t the greatest.. being that it’s small you might get away it but as Lowell mentioned you have compromised the plastic already..