Epoxy question - what's your favorite?

[driftwoodhunter]

I'm going to experiment with repairing something on my tank - so what epoxy do you think will be strongest for a metal to plastic bond? There are so many to choose from...

Thanks!

[UDGags]

What plastic?

[Sake]

Have you tried JB weld? Also sanding the surface or adding a screw in the mix to give the epoxy something to bite on could help. I know sometimes when setting marble or granite slabs, we'll use 3 second epoxy (what tile setters call it) this stuff holds up 500lbs plus with just 5 spots. The only problem is that it sets up so quickly you don't have alot of wiggle room. You can add more or less of the mix together to give you a bit more leeway but then you risk weakening the epoxy.

[dmagerl]

I think the rule of thumb is the longer it takes to set, the stronger the bond is. 24hour epoxy is stronger than 5min epoxy.

Otherwise, they're all pretty much the same.

[driftwoodhunter]

Thanks for all the fast replies! I was heading out to Lowes anyhow, so while there I grabbed the original JB Weld. I never used it before but it had the longest drying time, the highest PSI, and it was good for metal, pvc, and plastic. I'll be adhering (or trying to - lol) a metal T brace to the plastic rim of my tank, where one of the top braces broke.

Thanks for all your help!

[Sake]

I know alot of epoxy products are incredibly strong. I use to do foundation repair and did epoxy injection. Sometimes I would have to go back because the crack started leaking again...only thing is, not 1 time did it leak from the spot I patched. What happened is the house settled a bit more and a new crack opened up right next to the epoxy. My point is, if some epoxies can hold up to that kind of force, I'm sure you can find one that works for you.

I think the rule of thumb is the longer it takes to set, the stronger the bond is. 24hour epoxy is stronger than 5min epoxy

I'm going to disagree with that statement, I have used many quick drying epoxies for some heavy duty applications, and never have I seen the difference between that and longer drying epoxies. I will agree that if you add more of the hardener it weakens the epoxy, but as long as you follow the directions quick drying epoxies are just as strong.

[DarkCobra]

JB Weld's my favorite too.

But with an adhesive, a good quality join depends on surface prep. Rough up the mating surfaces with sandpaper to give it something to grip.

[driftwoodhunter]

Originally Posted by DarkCobra

JB Weld's my favorite too.

But with an adhesive, a good quality join depends on surface prep. Rough up the mating surfaces with sandpaper to give it something to grip.

yep, will do!

Thanks everyone for the advice - please continue to add any that comes to mind, epoxys and such are new to me & I know nothing about them. Good stuff to learn...

[R.sok]

make sure you use a course grit sandpaper to make the scratches! Sometimes when I don't have any on hand I just take a file & use it to make scratches

[driftwoodhunter]

Well, now I'm having serious second thoughts. If anyone wants to see my project, please look at the link I have below my signature for the 125 dirt tank (I hope some of you will!). There is a member here who has a ton of experience with tanks and he says it will not work. One option I thought of was to get a metal U shaped piece made to slip over the existing rim (from front to back, over the broken brace). I might simply keep using the clamp I have on the tank to prevent bowing until I can get the U shaped part made...

[m00se]

I was just going to tell you - the greasy plastic that they make bracing and rims out of will probably not adhere to epoxy, or any other adhesive. The metal U shape brace is probably the only practical way to replace that brace.

[trgiboney]

Have you looked into getting a new rim. I had a marineland tank that did the same thing and it was not expensive or hard to replace. The old rim is held on with a little silicone and should come of after running one of those flexable break off razor knife around the outer and inner edge. If you dont know the brand of the tank look at the bottom outside of the tank for a sticker. If you don't have one start sending pictures of the tank front and top to the major manufacture customer service asking for their help. Also ask here maybe someone will know what brand it is.

[ER9]

its hard to say from pic what type of plastic that is. there are some types, nylon, polyethelene/propylene based plastics that cant be easily glued back together, some not gluable at all with glues and adhesives you will be able to buy. if you have a tube of superglue. put a drop on the plastic, let it dry and try to pry it off. if it pops off your lid is most likely one of these plastics and trying to glue it will be useless. in that case mechanical fix is needed.

i would recomend a mechanical fix/brace even if it is gluable. that looks like a cross brace on top of tank which has a ton of stress from water in tank. i personally wouldn't trust any glue to hold that kind of stress. i worked for a company that manufactured epoxy adhesives for years and we also made acrylic aquariums in our fabrication shop. if it was my tank i would get new lid or mechanical brace.

[m00se]

Generally what happens is that a light fixture is propped right over the brace, and the heat degrades the plastic and it cracks eventually. De-rimming and re-installing a new top piece would require a new silicone to old silicone attachment, which has limited to no chance of staying water tight. Then it becomes a question of whether re-siliconing the entire tank is worth the risk of failure. I'd opt for the new clamp type brace if it were me.

[driftwoodhunter]

Yes, it's one of the top braces on a 125 tank - I think I will play it safe and wait until I get a metal "U" shaped brace made to cover the broken brace and bent to overlap the back & front of the rim. Then I'll be making a canopy for the tank (notched to accommodate the metal brace) so looks aren't an issue now.