Fixing leak in acrylic aquarium seam with Weld On 4?

[mesopelagic]

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: Calculate Aquarium Thickness - How THICK must the Plexiglas be?). 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. 4mm x 1000mm Clear Acrylic TRIANGLE Right-Angle Bar

 

[mesopelagic]

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 Reef2Reef) 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.

 

[kharmaguru]

Your double go at this probable made your weldon process less than ideal. I would say at this point if there is enough bond to hold the structure then just focus on making it leak proof. Can you get weldon 16? It's a thicker adhesive rather than solvent and could possible fill all the voids. Another option could be a good quality silicone spread wide on all internal joints.

 

[Vinny Kreyling]

I was under the impression that silicone does NOT adhere to acrylic well enough to be used as an adhesive.

 

[mesopelagic]

I was under the impression that silicone does NOT adhere to acrylic well enough to be used as an adhesive.

It doesn't, learned this the hard and expensive way. I'm looking into Weld On 16 right now, but after shipping, the cost for a single container is prohibitive because there's only one vendor in the UK that sells it. It's not looking good for me at the moment.

 

[kharmaguru]

I was under the impression that silicone does NOT adhere to acrylic well enough to be used as an adhesive.

100%. My suggestion was to use as a sealant not as an adhesive based on the structure being sufficient from the weldon 4.

 

[Vinny Kreyling]

There has to be a substitute used in Europe for Weldon.

 

[griss]

There has to be a substitute used in Europe for Weldon.

Acrylic Adhesives Products - Ellsworth Adhesives

Acrylic adhesives are structural adhesives which are capable of bonding a broad range of substrates, including most types of plastic and metals when minimally prepared and unprepared. Two-part catalyst cure or one part UV/heat cure are available. Acrylic adhesives have good to excellent...

ellsworthadhesives.eu

 

[Timfish]

If you can find Weldon #40 it is a two part "self polymerizing" that will fill in the gaps much better and is much stronger than #3, #4 or #16. Alternately you can get thin acrylic rod and use that the reinforce the joints with any of the four glues. Once dried or cured your tank should be safe for any inverts. It comes in cartridges but those require a special cartridge "gun" or applicator you'll need to buy or borrow.

I've used super glue gel (cyanoacrylate) to glue acrylic also and that should work with rods for a shallow tank like yours.


A note on using #40, a small scale can be used to mix the two parts, I use paper cups and wood stirrer sticks to gently mix the two then let it sit a couple minutes for bubbles to float to the surface, the pot life is about 10 minutes and takes about 20 minutes to set up and 24 hours to cure, surfaces should be sanded lightly with 220 - 320 grit sand paper. it was the viscosity of thick oil so if rods are used they may need to be taped to stay in place while the adhesive sets.

 

[shred5]

I fixed a acrylic seam that was splitting once. I cut a square rod put in the corner of the tank. I used weld-on to fix it in place.. This reinforced the seam and sealed it. Does it look great no but it certainly worked. It actually is probably even stronger than the original seam this way.

You can buy square acrylic rods too I think even eBay and Amazon have some if you don't have the acrylic or tools to make them.

 

[Hong Kong]

DO NOT use silicon and acrylic ever. Try also to use ARALDITE glue 2 component after dry is transparent. Japanese subcontractors in China 1997 when i was first time used Araldite for glueing acrylic pipes and filter internal panels that keep filtration sponges ect. If yo cant find Araldite use one of the best glue Acrifix acrylic adhesive. Bear in mind that I glued a metal plate on engine block cracked 12 cm crack with Araldite can get high temperature as well once is dry. Never leaked again. Araldite need 12-24 h to dry no movement. Heating with heat gun will help dry sooner.