Epoxy Sealant on Plywood: a cautionary tale

[waynes world]

When I constructed this tank I was quite heavy into GRP fabrication projects like automotive panels and whatnot. I can assure you it would have been more than just a few hours worth of work to fiberglass the whole tank. Every DIY aquarist I could find at the time also (wrongly) assured me that the polyester resin I wanted to use with glass cloth would be fish toxic even when cured.

Ovbiously the lesson has been learned, and I know better now, which is why I'm sharing this experience. At the time I built the tank, the best sources I could find on the internet indicated that sealing with epoxy resin alone should be plenty. It also took at least a year before this epoxy became hard and brittle. Even a month after painting it on you could put a mark in it with a sharp object - I naively assumed this was the nature of the cured product.

Anyway, hindsight is 20/20. I'm sharing this now because I couldn't find info like this then. I hope it helps someone avoid the same mistake.

I wasnt having a go mate, sorry if i came across that way, i did underexagerate on the time a little it would take to lay it up LOL, but worth the time and affort i think.

I posted for the folk reading this to help along with ideas.

 

[cvermeulen]

No offense taken, I guess that sounded a bit defensive. I guess more than anything I'm a bit miffed with everyone who told me that A) polyester wouldn't work, and B) Epoxy resin alone would work, and would last for years. In retrospect it's obvious to me, too that the epoxy resin alone was a poor choice.

There is a major lack of data from people who have OLD plywood tanks. I think this is because people do not like to post about the failure of their projects, and/or people are on to bigger and better things by the time a tank might have failed. I am personally hoping to have positive updates on my 600g tank in a few years, but then again, I might have built something larger by then

For now, I've got a year of service from my $300 600g tank build so far. Hopefully I'm not writing a post like this about it someday.

 

[pengu13]

in my build the epoxy failed with fiberglass reinforcement from the flex of the tank, more problems then one. zavlar came through to save it i just sanded and re-coated it with a lot of liquid rubber

 

[nes999]

but you have to admit plywood tanks are not meant to be moved. i here many many issus with all plywood tanks after a move.

 

[sashimimaster]

in my build the epoxy failed with fiberglass reinforcement from the flex of the tank, more problems then one. zavlar came through to save it i just sanded and re-coated it with a lot of liquid rubber

How much did it flex? How high was your tank?

 

[Muni]

Good info. I followed your 600 gallon build. Still love the one gold fish in there.


I think the new trend is to use a layer of hardi-backer or tile backing board over plywood then seal it. It's much stiffer and resists flexing. But in your case the epoxy still would have been an issue.

 

[greenterra]

but you have to admit plywood tanks are not meant to be moved. i here many many issus with all plywood tanks after a move.

Not meant to be moved? While some may agree with you? This to me is a sign of poor construction to start with. I flipped mine all over the place during construction and after and will not hesitate to move it in the future should the need arrive. Do people honestly think that epoxy/timber boats don't flex? Even FRP/GRP boats flex and twist. The biggest problems I generally see with people constructing ply tanks with epoxy are

a. The failure to use fibreglass reinforcing.

b. The use of a cheap non 100% solids epoxy that is not specifically designed for timber boat building.

c. Failure to use a dilutant in the 1st coat to ensure a proper soak of the resin deep into the ply.

d. No sanding in between cured coats to ensure no blistering or delamination between the layers. This is a must for correct adhesion.

Lastly, there is the ability or lack of to use the materials correctly. Something that is unfortunately out of all product manufactures hands.

 

[pengu13]

How much did it flex? How high was your tank?

Not to much flex that was noticeable but i have it all in my build thread the epoxy failing was my fault. the flex and i think it may of bubbled under the pressure of the 36" tank but only 32" of water.
http://www.monsterfishkeepers.com/forums/showthread.php?t=348524
that being said i would try epoxy again for another build. you learn as you go

but you have to admit plywood tanks are not meant to be moved. i here many many issues with all plywood tanks after a move.

I wouldn't say that, a guy i knew (the first big tank i saw) bought a used plywood fiberglass tank it was moved to his house then it was set up it the living room, the garage, the basement and moved to a new house with no problems

greenterra i agree with 100%

 

[cvermeulen]

but you have to admit plywood tanks are not meant to be moved. i here many many issus with all plywood tanks after a move.

You won't get much support on that one.

1) My tank failed without ever having been moved. The flex was from waterchanges, and wood moving with humidity changes, age, etc.

2) Who is to say what a custom built tank is "meant" for? If it's built right for what is going to be done with it, there shouldn't be any problems.

 

[cvermeulen]

Not meant to be moved? While some may agree with you? This to me is a sign of poor construction to start with. I flipped mine all over the place during construction and after and will not hesitate to move it in the future should the need arrive. Do people honestly think that epoxy/timber boats don't flex? Even FRP/GRP boats flex and twist. The biggest problems I generally see with people constructing ply tanks with epoxy are

a. The failure to use fibreglass reinforcing.

b. The use of a cheap non 100% solids epoxy that is not specifically designed for timber boat building.

c. Failure to use a dilutant in the 1st coat to ensure a proper soak of the resin deep into the ply.

d. No sanding in between cured coats to ensure no blistering or delamination between the layers. This is a must for correct adhesion.

Lastly, there is the ability or lack of to use the materials correctly. Something that is unfortunately out of all product manufactures hands.

All good points. A and C applied to my problems, as well as maybe a lack of experience with the material. The epoxy I used was supposedly quite high quality, but was just not intended to be used this way. It was also not compatible with any available dilutants I knew of at the time.