Questions about sealing a plywood tank

[apisto]

Hi all,

I finally managed to secure the room for a fish house. I have built plenty of glass tanks over the years but want to save costs by building all the tanks for the fish house from plywood. I'd rather spend the money on fish. I have plenty of sheets of 3/4'' of external plywood. The building trade in Ireland's in free fall and plenty of timber suppliers are having closing down sales or foreclosures...
The timber work is also not an issue.

I read plenty of threads and there are some very good looking tanks. However, nobody seems to mention how much epoxy resin or any other sealant they use. I had a look at the GARF site and they use 5 gallons for a 140 gallon tank. That seems rather a lot of epoxy for a small enough tank. Could somebody tell me how much epoxy is needed per square foot or yard?
This would make my costing a lot easier.

Secondly, there are so man resin on the market that I am somewhat confused. So far I found the following:
-Polyester Casting resin
-Isophthalic Polyester resin
-Plastidip
-Epoxy resins (several types)
-Epoxy pond sealer

Could somebody please shed some light on the issue?

And lastly, glass fibre cloth comes in several weights (anything from 300g upwards) that I have no idea which to use or if the use of fibre glass is strictly necessary. Any clues?

Thanks

 

[mannyhappy]

the fiber matte that is used is for strength only. You can get away without it, but i would recommend using it. It will mean you can get by with less tank bracing.

When the harden resin is cured, and bent, it WILL crack.

 

[mannyhappy]

also, i made a 196 gallon tank with gel coat and fiberglass matte.

gel coat is similar to fiberglass resin. You will be okay. Also, i used 1 gallon bucket. The fiberglass matte soaks it up pretty good. Two-three heavy even coats is what i did and it held water for 7 months before i had to tear it down to move. ( you will need a special roller that is used for matte applications that you use to push the air bubbles out. This is important.

 

[KLee79]

like manny said, fiberglass is only used for additional strength and it will soak up more resin than just on plywood. You cannot use polyester resin. in the long run, it is not safe for fish. it will eventually leach toxins out into the water. epoxy resin is the best. it offers more strength than polyester resin and is fish safe. 1 gallon on resin = approximately 250 sq ft. i'd coat the plywood at least 4-5 times. as far as the weight of fiberglass, its really up to your design. if your building a massive tank, then go with a higher weight. if you're building something like the on the garf page, 140g, then i wouldnt use fiberglass at all.

 

[CJH]

I read plenty of threads and there are some very good looking tanks. However, nobody seems to mention how much epoxy resin or any other sealant they use. I had a look at the GARF site and they use 5 gallons for a 140 gallon tank. That seems rather a lot of epoxy for a small enough tank. Could somebody tell me how much epoxy is needed per square foot or yard?

How much sealer is needed per square foot depends on the recommended dry mil thickness and this is not the same among the different choices. Not sure what system you use in Ireland for measuring the dry thickness of coatings but all companies I know of use mils, which is 0.001" or a thousandth of an inch.

So you basically take the recommended mil thickness and calculate the volume needed over the square footage. If the resin used is not 100% solids then you need to divide that volume by the percent solids.

I usually recommend at least 20% more than the calculated amount as there will always be some areas that are thicker than they need to be.

If you use fiberglass then the amount needed goes up. In general fiberglass mat is cheaper than fiberglass cloth but since the mat requires more resin the cost ends up being about the same.

I believe the ounce or gram rating of fiberglass cloth, roving or mat refers to the ounces of wet resin required to wet out that cloth, so you can factor that into your calculations.

Secondly, there are so man resin on the market that I am somewhat confused. So far I found the following:
-Polyester Casting resin
-Isophthalic Polyester resin
-Plastidip
-Epoxy resins (several types)
-Epoxy pond sealer

Could somebody please shed some light on the issue?

And lastly, glass fibre cloth comes in several weights (anything from 300g upwards) that I have no idea which to use or if the use of fibre glass is strictly necessary. Any clues?

Thanks

Of the options listed, I would only use the isophthalic polyester or a marine epoxy resin. I can't recommend the epoxy pond sealer since I don't know what it is exactly. But you should talk to the company and see what they say. Another choice that you can probably find is vinyl ester resin.

Here in the US we also have epoxy paints, at least for now until stricter VOC regulations go into effect. Sweetwater Epoxy Paint is the best example of an epoxy paint. Not sure if you have those in Ireland or elsewhere in the UK.

I'm positive that you can find polyurea in Ireland and I would look into that. Polyurea comes in a lot of blends so make sure you get one that is okay for fish and for sealing wood.

The use of fiberglass reinforcement depends partly on the size of the tank. I know of two epoxy companies here in the US that DO NOT recommend fiberglass reinforcement be used along with their products to seal plywood tanks. Moreover, if the tank needs it for structural reasons they suggest the fiberglass go on the outside of the tank and not interfere with the continuous waterproof layers of epoxy on the tank interior.

 

[apisto]

Ok, thanks for the replies. The biggest tank I am going to build will be roughly 7*2*2 or 210*60*60 cm in new money. This will have to be spot on first time around since I am planning to replace my current tank in the living room.
My wife would not be best pleased if 750 l of water would find it's way on the floor.
I had a look on the internet to see what is available around here. I came across this site http://www.sealsystems.ie/index.php?option=com_content&task=view&id=37&Itemid=75
The two products I would imagine would do the job are
-

Both are suitable for the food industry which should make them OK to use in aquaria​

The other product I found that I might look at is this http://cgi.ebay.ie/POND-PAINT-WATER...34.c0.m14.l1262&_trkparms=|301:1|293:1|294:30

All three products are fairly low in VOCs which would be an advantage.

Marine epoxy resin over here is sinfully expensive and there wouldn't be much of a difference building an all glass tank of which I have built many over the years.
PR water dispersible epoxy coating or PR solvent free epoxy coating

 

[mannyhappy]

just do it, and post pics.

Also remember, that no matter how daunting it may seem, it really isnt that hard to build an aquarium. Don't let people scare you off. you seem like a smart person and if you take your time you will be okay.

There is always a solution. (i.e. if you use a sealant that is toxic, you could always coat over it with something else.)

 

[apisto]

I am not overly concerned about toxicity. The timber work itself is no problem. My father-in-law was a carpenter before he retired and is bored since. Something for him to do. And even if I had to do it myself I wouldn't be worried. I have built all my aquarium stands and a new staircase in timber in my house so I am not entirely useless when it comes to wood working.
What bothers me is that the tanks could start leaking over time if I used the wrong sealant.

Most of the company's I rang have no idea what I was talking about. They've never heard about anybody building a fish tank from ply.

 

[mannyhappy]

Fiberglass matte and resin will never leak. (At least 2 coats of resin)

Yeah, just wait tilll you finish is and people see it in your house. They all gasp and then think your wierd.

The only way i'd use some of the other products is if i could not find a resin in the correct color.

(Also, the glass sticks to the cured resin with silicone very easily, i speak from experience here)

 

[apisto]

They think that I am weird as is

Ok, here's what I am playing around with now (so many options...)
Since the whole tank has to be made from the same timber as the rest of the furniture, I will have to clad it with oak veneer anyway.
-Basic plywood box set into a 3*1 frame to which I will attach the veneer later. I know that this is probably over engineering it somewhat but what the heck. The space between the tank and the veneer will also give me the space to mount the electronic ballasts for the T5 lights and keep the ballasts out of sight. I will add a small fan in the section where the ballast are to avoid any heat building up. The rest if the cavities between the 3*1 will be filled with insulation to keep heating costs down. The hood will have a couple of small fans built in to avoid heat building up on hot days.

So far so good. Still haven't decided what I am going to seal the inside with....