Plywood types, thickness and fiberglass reinforcement....??????

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C

CHFIII

Feeder Fish
MFK Member
Oct 4, 2012
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DFW
Hi All,

So I'm moving soon and the hatchery will be redone to maximize space and minimize the amount of labor I have to do. I'm going to be building racks of tanks and have played with the idea of Glass, Acrylic, or a Plywood and Glass build and I'm pretty well settled on the idea of plywood and glass for a number of reasons, mostly the flexibility it will give me. Since I am doing them three high I will probably do the top row 'shorter' with more divisions. So these are 8' long and either 24 or 36" wide and 12-16" tall for 120-180 Gallons per tank. They will be three high to maximize space so every inch counts as I am 5'8" and have recently gone the Lee Majors route getting bionics to repair my lower spine :-)

So... weight and thickness are both important factors. I play with the GARF build calculator but have figured out that it says 3/4" plywood is the best choice whether you are building a 10G or a 110G.

So I wandered around Home Depot tonight looking at plywood. The 3/4 Sheathing I have heard others recommend is so... what's the word? crappy looking? Yeah, that's it. I wondered whether the 1/2" hardwood ply would work. What about the 1/2" with Fiberglass reinforcement? I haven't seen any figures like "Adding 1 layer of fiberglass increases the strength by X and rigidity by Y". Anyone out there have a learned opinion???

As I looked at the various Plywoods I noticed that the cabinet grade 3/4" has FAR more 'Plys' than the others, I think it was like 9 versus 5 on the same thickness of hardwwod ply and the sheathing had less. From my reading on plywood, it is the alternating grain plys that give it strength and limit warping and flex, right? Price doesn't much matter here, I think the cabinet grade 3/4" was like $32 bucks for a 4x8 sheet so unless some fiberglass experts tell me that a couple layers of fiberglass makes 3/8 ply into a much stronger product than the 3/4 for half the weight I am inclined to go that route.

When does fiberglass reinforcement start to matter? 180 is a goldfish bowl compared to what some of you guys have built :-) If I can just Glue/Screw the 3/4 cabinet grade stuff together, seal it with pond armor or sweetwater epoxy paint (recommendations welcome) I may just not bother worrying about fiberglass reinforcement. 3/4" ply coated in epoxy seems pretty bomb proof given that my heights are low and I'm not dealing with the pressure that some of these monster builds have to worry about.

After I master the process with the utilitarian builds I want to make myself a row of show tanks on one wall. Say 36x36x96 ~525 Gallons and if I build two of those I'm going to be a lot more concerned about the engineering since the pressure will be MUCH greater due to the height. I'm assuming that when I do those I will be a lot more serious about overengineering the hell out of them but by then I will have built at least 15-18 of the more functional tanks.

If anyone can point me to a thread on plywood types, limits by thickness, the necessity and benefits of fiberglass etcetera I have not found a really in depth discussion.

Thanks in advance for the assistance. Once we move I hope to turn the project into a good, photo rich thread and already know that the collective wisdom of this group will save me many headaches, many dollars and improve upon what I design significantly :-)
 
Subscribed... looking for the same info. Thanks for asking in a much more verbose manner than I could come up with.
 
If you're only going 16" tall it really doesn't require 3/4" plywood. Theres so little pressure at that depth that manufactured fish tanks only use 3/8" thick glass. The only downside I can see with going to thinner plywood is more difficulty screwing into thinner material. You can certainly reinforce it with fiberglass. I always add fiberglass for strength and waterproofing since the resin soaks into the wood. I like to use MDF since it's cheap, straight and consistent. But it is heavy. I've found that the hardwood plywood is stronger but expensive. Do NOT use OSB! That's crap. It warps, splinters and flexes.
 
sashimimaster said:
If you're only going 16" tall it really doesn't require 3/4" plywood. Theres so little pressure at that depth that manufactured fish tanks only use 3/8" thick glass. The only downside I can see with going to thinner plywood is more difficulty screwing into thinner material. You can certainly reinforce it with fiberglass. I always add fiberglass for strength and waterproofing since the resin soaks into the wood. I like to use MDF since it's cheap, straight and consistent. But it is heavy. I've found that the hardwood plywood is stronger but expensive. Do NOT use OSB! That's crap. It warps, splinters and flexes.
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Thanks Sashimi,
I think I may go with the 3/4" cabinet grade just because it has so many more plys unless I can find a REALLY rigid 1/2" ply. The front panel will be extra strong becuse when I cut out the front ply I will leave vertical strips of wood where the stand supports will be blocking it any way. 1/2" would seem a lot easier to work with. What a pain in the butt that i used to be a powerlifter and now am under doctor's orders not to lift more than 20 pounds on my own until my back is completely rehabilitated! Time and gravity are ruthless fellas - take care of your lumbar spine :-)

Any thought on how 1/2" with a coat of fiberglass throughout and several layers of fiberglass tape at the seams compares to 3/4"? Taking 1/3 off the weight would be nice. Ain't like I am going to lift them anyway but handling the pieces as I build'm will be easier. I like your thinking on the resin soaking into the wood better than Epoxy. I use epoxy resins in another hobby (casting resins) and I think it would adhere to the fiberglass resin better than wood and likewise the resin would soak into wood better and make the waterprrofing much better. I want to build these once and forget about them so if I spend a little extra now or overbuild them that's fine. Will be nice to predrill everything and insert pipe during the build phase too. Like the glass, buying one bulkhead for $8 instead of building it with a $2 piece of threaded PVC is no big deal once but multiply by 48 and the difference is worth thinking about :-). Thinking I will run PVC to the bottom then stick a 'tee' on there with screen pipe on both sides to suck up fish poop and direct the returns to where the poop settles where the intake will be. Bare tanks and aesthetics are not primary - efficiency and water quality rule on this one. Tired ov vacuuming poop out of 50 tanks every day and I look forward to having a tank sale to get rid of my assortment of misfit tanks :-)

Next up is getting a good quote on glass.... I have two local dealers getting me quotes. The first quote I got on 94"x12" 1/4" glass was crazy high - like $96 each ($12/sqft). Glasscages.com lists 1/4" glass at $3/sqft so that local shop wasn't a little higher, they were FOUR TIMES higher. If I needed one piece, $70 would not bother me but when I need 12 of them! Glasscages offers 3/8" Starfire for $12/ft for crying out loud.

For those who buy glass rather than repurposing glass from old tanks, what do you typically pay? I've also noted some folks on Craigslist selling big shop windows (tempered but I ain't drillin the front) that I could have cut by a glass shop. Finding a good glass supplier who is reasonable is an absolute must if I'm going to make this work. I'm in the DFW Texas area if anyone knows a good glazier who can supply simple glass like I need at a reasonable price. If I had to drive a few hours to Houston or Autin or OKC or Tulsa I would not mind too much if it saves me a grand. ...but if glasscages can sell it $3/ft and that is a wholesale price I can't see paying four times that for the same thing. Advice welcome :-)

Trooper - yeah, verbosity is an issue with me. I type and think about 20 times faster than I can talk to I tend to create novellas rather than concise posts, lol :-)
 
OK, another question.....

I am looking at fiberglass supplies and see that there is a lot of types to choose from, like 1.5 ounce cloth to 10 ounce to 18-14 ounce 'roving'. Would seem like the heavier cloths would not be much harder to work with and cost is not substantial - site I am looking at has 5 gallon drums of resin for $199 and 25 yards of the 50" 24oz 'Roving' fiberglass mat for $135. I am a neophyte working with glass but am reasonably competent and it doesn't seem like rocket surgery to apply the stuff. I'm sure that multiple layers of thinner cloth is stronger but after 43 years of treating my body like a rental car I'd rather go 'one and done' on the fiberglass layup as that is sure to be quite a workout.

What do y'all use? I have no idea whether that heavy mat would mean "yeah, use a couple of coats of that and you should be OK" or "Holy crap, that thing will support a scyscraper". Anyone????
 
dogofwar said:
One way to cut down on glass cost is to use two 4' pieces vs. one 8' piece.

Thought about using drylok and hardiboard vs. plywood?

Matt
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Nope but I'm sure not opposed to it if it does the job. I'd assume it being 'inert' and not prone to splintering wood make it very easy to work with but I thought I read somewhere that it lacked the requisite rigidity? Is that not a concern at this size or not a concern if you glass the inside? If I can use something that would have cleaner lines like Hardiboard that would be preferable. Have you used it and did it work out OK? Does it also come in various thicknesses and if so, what would I need?
 
I've seen a nice DIY where you basically make a two by four frame and line it with hardiboard pieces...paint the inside with your favorite shade of drylok...and done. Only the bottom needs reinforcement with plywood under the hardiboard.

Hardi comes in 3'x5' and 4'x8' sheets and I think 1/4" and 1/2" with 1/2" preferable for this.

No experience of my own but I've thought about similar plans as you :)

Matt
 
Thanks Matt,

I think I read that Hardiboard/drylock could be used to line an already rigid wooden structure but that hardiboard on it's own would flex too much? I may be making that up... senility has been setting in due to lack of sleep since the baby was born in November ;-)

If it's lining a wooden frame I'm inclined to go with glass then epoxy (if glass is even required here given the short heights).... an extra 1/4" of hardiboard inside the wooden box seems like a lot of added weight? Assuming you seal the wood first then attach the hardiboard to it, then paint the inside with drylock and voila - waterprrof box? Can't wait to get moved so I can get to work on this. I'm actually scowling at breeding pairs for laying eggs right now because I'm adding 27 Gallon 'Tuff totes' all over the damned garage right now rather than buying tanks when I know I'm about to redo my whole system the way i want it. :-) Had an albino Pearlscale Angel whose mated with a gold and throws off 1000 eggs at a time breed last night and I just scowled at her and said "b-tch!". ...but yeah, I stuck the eggs in a hatching tank and will find somewhere to stick'm ;-)
 
I still think you only need 1/2" with some fiberglass. It would be plenty strong enough for the smaller tanks. The weight of the fiberglass determines how easily it conforms to shapes. If you were doing a lot of curves I would say use lighter weight. But since you're doing mostly straight flat areas any weight would be ok. Just remember the heavier the cloth the more difficult it is to work with and the more resin it takes to soak in. I would never use any heavier than a medium weight because it's a pain to work with when the cloth sticks to everything except where you intend it to. Don't ask me how I know....

btw I have slipped disk from moving a weight. I wasn't even doing a lift at the time. That split second changed my life. So I do a lot of hyperextensions and ab work to keep the core strengthened.
 
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