# Acrylic tank with white seams



## gtownith (Jun 27, 2007)

i picked up this 110 gallon tank under 100 bux from clist should i be alarmed over these spots here? the tank was halfway full when i picked it up and there were no leaks.


----------



## djoneser (Mar 20, 2008)

Picture would help to answer the question. Are the white spots just mineral deposits? or ?? Mineral deposits can be cleaned relatively easily.


----------



## Malawidolphin (Dec 15, 2006)

Looks like separation of the seam to me. I'd be worried if it is in between the glass panes where it joins.


----------



## binro01 (Nov 25, 2008)

Was the seams visible prior to water being introduced into the tank? If not, and they showed up after some time with water in the tank I would be a bit concerned, because condensation takes time to show up. And if the color is from water condensation thaty means there is some sort of seperation at the seam.


----------



## t0rns0ul (Dec 27, 2008)

It's acrylic..

Get some acrylic "weld-on", run you about $5 with the application bottle and weld the seam just to be safe. It's a very simple process.

Video of how to weld acrylic





good luck!


----------



## gtownith (Jun 27, 2007)

it was there before addng water, i filled it today and yet there are no leaks.


----------



## Dragonetti (Mar 16, 2009)

You can try putting weld-on in there but it will not help if the seem has not separated. If it doesn't leak with water in it then the joint was stressed. Might hold and it might not, I wouldn't put in my house.


----------



## prov356 (Sep 20, 2006)

What you're seeing is called 'crazing' It happens over time with some joints. It could lead to leaks if it gets worse, but it may not. If you want to be safe, now is the time to repair.

You can't 'weldon' an existing joint like this. At least not with the solvent type watery Weldon. When a seam is made initially, you set it up so one piece sits on another with very thin wires in between to allow a very thin separation. No 8 guitar string works well.










You then run the watery weldon solvent along the seam where it gets drawn in by capillary action. The solvent itself evaporates in less than a minute, but melts the surfaces of the acrylic before it does. You then pull the wires and apply some pressure. The acrylic then hardens and the two pieces fuse together as if one. It's a lot like welding metal. Also think of melting the edges of two pieces of chocolate and then pressing them together and allowing it to cool. The reason I'm explaining all of this is to show that you obviously can't do this with an assembled joint. Running the watery weldon into it isn't a good idea.

There are some good instructional videos here.

There's a thicker weldon product that comes in a tube called Weldon 16 that you can use, but it can be really messy.

One possible method of repair. Get a piece of acrylic 1/4" square stock. Cut it to length, apply some weldon 16 along the inside corner that you're repairing and press the acyrlic piece into the joint. Hold it firmly along it's full length for about two minutes. It'll grab and hold tight at that point. Make sure you clean the joint really well with isopropyl alcohol first. This won't make a pretty joint, but it'll be no worse than the silicon joints on the glass tanks. You could also go ahead and do the other joints while you're at it, unless they look crystal clear. Why not just run a bead of this glue along the joint? Well, it's not like applying silicone or similar and I've not had good results with that method. It doesn't make a smooth bead like you'd think it would. And don't even try to smooth is with a finger like you'd do silicone. It starts to skin over quickly and will make a mess.

Protect all but the joint with cardboard or similar because if you get acrylic solvent of any kind where you don't want it, it'll make a premanent mark. It doesn't wipe off. It'll immediately and permanently deface any acrylic surface it touches. Be careful of getting some on your fingers when pressing and holding the acrylic. Wipe it off before touching the tank again.

You can try another method, if you really want to not mess up the appearance of the joint. I've used it and it works great. Get a small can of the watery weldon, Weldon 4. Also get a small piece of scrap acrylic. Make several cuts in the scrap acrylic on a table saw or similar, enough to get a small clump of acrylic shavings. Make sure they're not mixed in with wood shavings. Add enough of these shavings to the the can of solvent to thicken it up to the consistency of melted butter, not too thick. Add some and then let it sit overnight to melt. Check the consistency and add a little more if needed. It's easy to add too much, so be careful. You then set up the tank so it's sitting on the corner you want to repair.










Here I was sealing the seams of some newly bullt tanks. Not because there was a problem, but because I don't want a problem down the road. Run a thick bead along the edge of the joint using the dispenser bottle with a wide tube. See the link below. When the solvent evaporates, it leaves a thin seam of acrylic from the melted shavings that were added to the can. It's hardly noticeable at all. Let it sit for a couple of hours before moving the tank, and a few days before filling with water no matter which method you use.

Here are links to supplies that you'd need.

Ridout Plastics solvents

Applicator. Use the hypo 65 for syrupy glues. They're cheap, get at least two.

If you can find a local plastics shop, even better.

You may not need to do any of this, but if it leaks 12-18 months from now when it's full of adult fish, you'll wish you had. For future, when buying an acrylic tank, check the seams. If they're not crystal clear, but hazy in some spots, it's a flawed joint. Point it out and get some $$ knocked off the price or pass it by.

Just a note of interest. This crazing can be the result of the stresses and vibrations that the acrylic undergoes during fabrication. Professionals always place finished tanks in large ovens for a time at about 150 degrees. This reduces the risk of crazing down the road. Home hobbyist tank builders obviously can't do this, so when buyng a tank from someone who put it together themselves, take extra time to check the seams for crazing. Less than perfect seams are ok, and don't necessarliy indicate that a tank is going to fail. But crazing like you've got that goes the full width of the joint is a concern IMHO, even if it's not leaking now.


----------



## binro01 (Nov 25, 2008)

Wow! Very informitive post prov356! They should put that into the library!


----------



## gtownith (Jun 27, 2007)

wow, thats some good info thanks, now from what you see in my pic is there a possibility the previous owner tried to fix it? its been 24 hours with water in it and nothing yet i hope this holds. thanks again.


----------



## prov356 (Sep 20, 2006)

Thanks, but there are already some good articles in the forum library. I learned a lot from them when I got started. Anyone interested can check them out here.

I have a complete rundown of building an acrylic tank here. It was my first, and I look back at it and shake my head, but I learned a lot. The next 10 went easier, but still learning.


----------



## gtownith (Jun 27, 2007)

the white spot kinda looks like the rings on a tree stump up close


----------



## prov356 (Sep 20, 2006)

gtownith said:


> the white spot kinda looks like the rings on a tree stump up close


It can have a variety of appearances. Some crazing can happen in the faces of the tank, not just the seams. It looks like tiny scratches. Some crazing I've seen in joints reminds me of frost on a window.


----------



## pkut (Feb 3, 2005)

How deep into the thickness of the acrylic sheet do you have to sand and polish to get rid of crazing? I have an acrylic aquarium that I bought used and it has one area with some crazing. It appears to be near the surface of the material on the outside face. I am wondering how much material I will have to remove to eliminate it?


----------



## prov356 (Sep 20, 2006)

pkut said:


> How deep into the thickness of the acrylic sheet do you have to sand and polish to get rid of crazing? I have an acrylic aquarium that I bought used and it has one area with some crazing. It appears to be near the surface of the material on the outside face. I am wondering how much material I will have to remove to eliminate it?


The depth of the cracks can vary, so hard to say. If the scratches go very deep, then you'll end up with some optical distortion at that spot after removing the scratches. You can try some light sanding to see if they can be removed. Just go easy because acrylic sands down pretty easily. If you sand enough to feel the depression you're making then you'll likely get optical distortion. I would guess that most crazing cracks cannot be sanded out without ending up with optical distortion.


----------



## pkut (Feb 3, 2005)

Thank you for your help prov356. I am wet sanding by hand with 1500, 1800, 2400, 3200, 3800, 4000, 6000, 8000 and 12000 grit papers. I am going easy like you said and it seems to slowly be clearing up. I hope that I can clear the majority of it up without going very deep.

I'm not in any hurry, so I will just take my time and hope for the best.


----------



## Tiberian (Jun 14, 2009)

thanks for the info. I'm subscribing to this tread.


----------



## pkut (Feb 3, 2005)

Slowly but surely, the crazing on the face of my acrylic tank is disappearing. It takes a lot of work but I believe that doing this sanding by hand and feathering the damaged area with each finer grain sandpaper is working well. 
I would say that I have eliminated about 80% of the original damage. I'll keep working at it and post my final results.


----------

