How thick acylic for fixing top crack?

[hrdneglcry]

Hi so the top of my 180 acrylic has a crack. The LFS said because the whole tank depends of the reat of the tank for structural integrity I should patch the crack woth a 3/8" piece of acrylic. I ordered weldon 40. I was wondering if 3/8" is neccessary. The harwarde store doesn't have it that thick and my 3/8" thick piece is in the mail on its way. Can I use a thinner acrylic or do I need to stick with 3/8"?

 

[KrisReef]

Where are you going to apply the patch to correct the problem?

I think I would drain the tank, flip it upside down (on a saw horse or something similar) and place a new end cap inside the tank that was butted against the three sides of that end and was slightly wider so that it extends slightly past the original top peace, beyond those cracks in the top.

Once that dried in place I might flip the tank upright and add a perpendicular layer on top that covers the crack ends to remove any rough edges where the cracks are, but not necessarily.

The difficulty in patching the top is that it will be warped and not flat to allow placement of the patch with continuous contact between the old top and the patch.

Patching inside and the on top of the broken area would make the repair stronger but that will also shift stress points inside the tank when it is filled, which hopefully doesn’t cause a new crack elsewhere.

I have a large tank with a similar condition, I think someone else tried to lift it holding the tank top while the tank was partially filled and that broke the top? I have filled it about 3/4 full (18” water depth) for a holding tank and it has held up fine for over a year now. I don’t know if it would break if I filled it but I have not tried to fix/patch it either because of the warping around the break.

Good luck.

 

[KrisReef]

Also, when I do patch these kinds of breaks I drill an interceptor hole at/ near the end of the crack (tiny drill bit, maybe a 1/4 inch or less) so that the crack doesn’t expand after I patch and refill the tank. That crack ends scare me and I like to add a hole to create a round junction that isn’t cracked to prevent cracking.

The patch is then added to cover the hole if the crack is under water when filled or if I want to prevent salt creep.

It may be over kill with plastic since the application of solvent over the crack may bond the crack back together but I have never relied on that bonding to make the repair leak proof.

Patching can look ugly but I focus on service reliability in these situations. Otherwise I recommend buying a pretty new tank over patching.

 

[hrdneglcry]

I was going to add one piece approximately 6" by 24". I think I can get the cracks to be flush. Also I think this tank was lifted at the area at some point. The last owner swore that he ran the tank for years without fixing these cracks but I want to be safe. Did you you use an acrylic bit? I was just asking if I have to use 3/8" thick acrylic for the patch or could it be thinner?