plywood tank i dont get it
- Thread starter joedodge
- Start date
It all depends on how you build it as to if it's any good, but as for how it holds water, usually it is either fiberglassed or epoxied on the inside, then a gel coat is applied over that to make it water proof. Glass, or acrylic is siliconed in like normal. Read through some of the tank builds on here and you'll start to get a good idea. Depending on how you do it, and what size you need it can be more pratical, and less expensive than making an all glass or acrylic tank.
necro said it good, search through here and you'll see some good tanks. Necro's in the process of building a monster one himself that looks awesome....
Basically a membrane of some sort is applied to the plywood, therby making it waterproof. Usually the plywood provides structure against the forces of the water but in some cases the plywood does little more than to act as a form for the fiberglass structure.joedodge;2297283; said:
Methods that have been used to seal plywood tanks for the long term:
1) Polyester and Vinylester resin. Often called "fiberglass" but the fiberglass only refers to the fiberglass cloth, mat or roving that is embedded in the resin. Both of these resin types have been painted directly onto plywood without cloth/mat/roving and have held water.
Probably not the best idea since both of these resin types are a bit brittle. Stiff, but brittle.
It is often said that these need a topcoat to be watertight, but this is really not correct. They will absorb moisture but so will acrylic and it is used by itself to make tanks.
Both will probably be illegal by 2011 due to VOC regulations.
2) 100% solids Epoxy resins. Many types but probably best to lump them together. These can be used to wet out fiberglass or can be painted directly onto plywood.
Much more flexible and generally stronger than the resins in #1.
Many people avoid these due to reputation for being nasty. This is unfortunate as epoxy resins are VOC free. It's the epoxy paints that are really nasty. Epoxy resins will probably be one of our few choices after 2011.
I think it's important in threads like this to distinguish between epoxy resins and epoxy paints.
3) Solvent based epoxy paint, typically two-part pool paints. I have seen these painted direct to plywood or as a topcoat to polyester or epoxy resins. These tend to go on a bit thinner than resins so some feel they are cheaper because less is used. Very nasty to work with. Will be illegal by 2011.
I have never seen or heard of these being used to wet out fiberglass but that does not mean it has not been done.
The choices above are the three that I have seen the most, and I have seen a lot of plywood tanks and even built several. The oldest I saw was a marine holding tank coated with fiberglass and polyester resin. It had been holding water for 20 years when I saw it. It was a very shallow tank so the forces on the plywood were probably not that great.
I saw an entire wall of plywood tanks at a petstore that had been running for over ten years. They were painted with epoxy paint only.
Somebody used to teach a class every year at the fish club where I grew up. It was on building plywood tanks. He taught to use epoxy paint and had some tanks that were very old but I'm fairly certain they also had fiberglass. So not exactly the same as what he taught.
There are other products and methods that I know little about. Some of them sound promising provided silicone will stick to them.
So as you do your research, make sure to distinguish between "fiberglass" and polyester resin. Very common mistake. Also make sure to distinguish between "epoxy" and "epoxy paint". Very different.
I see mistakes in terminology all the time. And in this case the terminology is important.
For the record, if I were to build a plywood tank today I'd use 100% solids epoxy resin. I would not use any fiberglass cloth, mat or roving inside of the tank. If I needed the stuctural support of the fiberglass I would add it outside of the tank. I know of two epoxy companies that recommend this. In fact one of them sponsored a plywood tank build outlined in a thread right here on this forum.
