# HELP NEEDED FOR PLYWOOD TANK



## eric2683 (Sep 3, 2014)

hello guys am a new member on this forum hope you wiil help me out
am currently in the process of building a plywood aquarium seal with fibreglass consisting of two viewing panels of 90cm *57cm
the only problem i have is glass thickness?
what should i use?


http://imgur.com/z3hdeuO


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## joescaper1 (Feb 14, 2013)

http://saltaquarium.about.com/od/planas ... ulator.htm

Joe


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## Mcdaphnia (Dec 16, 2003)

Besides the glass, the problem i see first is that plywood flexes and Fiberglas will not be able to hold up to that much flexing. The outer walls should be supported, and a sump installed so that the water level in the tank stays the same all the time. http://www.customfishaquarium.com/glass ... ons-chart/


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## eric2683 (Sep 3, 2014)

Mcdaphnia said:


> Besides the glass, the problem i see first is that plywood flexes and Fiberglas will not be able to hold up to that much flexing. The outer walls should be supported, and a sump installed so that the water level in the tank stays the same all the time. http://www.customfishaquarium.com/glass ... ons-chart/


it will be difficult to flex because it has been reinforced on the back and bottom with beams


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## Mcdaphnia (Dec 16, 2003)

Water is powerful. It has tremendous hydraulic pressure. Unless the plywood is reinforced by solid concrete walls, it may flex more than the Fiberglas coating can. I know someone who built a sump for his fish room only 12 inches tall, less than a third of a meter. Cracks in the Fiberglas coating caused his plywood sump to fail. If it does leak, there are more flexible products like marine boat paint and rubber base paints that can seal over the Fiberglas. http://www.pondarmor.com/


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## eric2683 (Sep 3, 2014)

Mcdaphnia said:


> Water is powerful. It has tremendous hydraulic pressure. Unless the plywood is reinforced by solid concrete walls, it may flex more than the Fiberglas coating can. I know someone who built a sump for his fish room only 12 inches tall, less than a third of a meter. Cracks in the Fiberglas coating caused his plywood sump to fail. If it does leak, there are more flexible products like marine boat paint and rubber base paints that can seal over the Fiberglas. http://www.pondarmor.com/


i have followed this tutorial to built mine http://www.jonolavsakvarium.com/eng_diy ... itres.html
concerning pond armour its not available in my country the closest product i could found is the pekay t570 Damseal Bitumen Emulsion (non toxic)
For waterproofing of reservoirs, dams and fish ponds. Water-based


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## joescaper1 (Feb 14, 2013)

Eric,

Out of curiosity, how many layers of fiberglass were you going to apply? and what is the estimated final thickness?

Joe


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## BC in SK (Aug 11, 2012)

eric2683 said:


> the only problem i have is glass thickness


Should be using 1/2" glass (12mm) for a tank that size. I think with 2 panes in front you should have a strip of glass in the middle siliconed over top of the two panes to hold them together.
McDaphnia's link spells out the required thickness for the height and size of tank.

The important thing is that the top is braced well. It would be smart to fiberglass that as well. Adds strength and will prevent it from rotting over time.



Mcdaphnia said:


> I know someone who built a sump for his fish room only 12 inches tall, less than a third of a meter. Cracks in the Fiberglas coating caused his plywood sump to fail.


That is ridiculous! At that depth, 3/4" fiberglassed plywood does not even need any bracing. No idea what went wrong there :-? :-? 
My fiberglass tanks went about 30 years before they sprung a leak . And with out getting into too much detail, actually my fault they sprung leaks .... would have gone a lot longer, where it not for some things I did. Just as a comparison, my glass 125 gal. sprung a fast leak only 2 1/2 years after purchase. My 33 gal. had to be resealed twice over about a 20 year period. I believe even my 15 gal. did not go 30 years before needing to be resealed! In general, fiberglass tanks should be a lot stronger, sturdier and and last a lot longer before they need fixing.


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## OllieNZ (Apr 18, 2014)

Bc_in_sk said:


> Mcdaphnia said:
> 
> 
> > I know someone who built a sump for his fish room only 12 inches tall, less than a third of a meter. Cracks in the Fiberglas coating caused his plywood sump to fail.
> ...


Totally agree with this. Unless you get your resin to cloth ratio wrong (or you use an excessively thick layer) fiberglass should be just as flexible as 3/4 plywood. Resin type used will also effect long term usability, you need to use good quality epoxy or iso/npg polyester as the cheaper stuff won't last under water.


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## Mcdaphnia (Dec 16, 2003)

OllieNZ said:


> Bc_in_sk said:
> 
> 
> > Mcdaphnia said:
> ...


 You may be right about the kind of fiberglass resin they used or their skill at using it, but it must be that doing it right is rare, since every fiberglass sealed plywood tank I've seen was either brand new, leaking or had damp spots where the plywood was swelling and holding back the water. One inventive solution I saw to a leaking fiberglass/plywood tank was plastic rain gutter under the tank to catch the water and direct it to a barrel with a sump pump to put it back in the tank. I do have a 100 gallon fiberglass tank that is about 50 years old. However it is all fiberglass, no plywood, just layers of fiberglass. It's that light blue color popular in the 1960's so even though it holds water I am tempted to change it to black. I have yet to find anyone with a good fiberglass track record, so I have been holding off on that project for about 30 years and just using the tank as is. Most of the tanks I've seen just use the resin in several coats with no fabric.


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## OllieNZ (Apr 18, 2014)

If they haven't used the fabric then it's not fiberglass, just resin coated wood and without the reinforcement provided by the fabric the resin itself is very brittle and prone to cracking, so no surprise there. 
For your tank I'd find someone who could spray gelcoat it for you, the main issue with doing this is getting the gelcoat to a smooth finish again after spraying it's alot of sanding and polishing to get it back to a mirror finish.


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## Mcdaphnia (Dec 16, 2003)

OllieNZ said:


> If they haven't used the fabric then it's not fiberglass, just resin coated wood and without the reinforcement provided by the fabric the resin itself is very brittle and prone to cracking, so no surprise there.
> For your tank I'd find someone who could spray gelcoat it for you, the main issue with doing this is getting the gelcoat to a smooth finish again after spraying it's alot of sanding and polishing to get it back to a mirror finish.


You have it right. All the fiberglass plywood tanks that people made around here had no fabric, or a thin strip in the corners at most. The fiberglas coating crazed, like the cracking you see on the glaze of an old tea cup.


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## eric2683 (Sep 3, 2014)

BC in SK said:


> eric2683 said:
> 
> 
> > the only problem i have is glass thickness
> ...


 2 layers i think


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## eric2683 (Sep 3, 2014)

joescaper1 said:


> Eric,
> 
> Out of curiosity, how many layers of fiberglass were you going to apply? and what is the estimated final thickness?
> 
> Joe


 2 layers maybe three


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## eric2683 (Sep 3, 2014)

OllieNZ said:


> If they haven't used the fabric then it's not fiberglass, just resin coated wood and without the reinforcement provided by the fabric the resin itself is very brittle and prone to cracking, so no surprise there.
> For your tank I'd find someone who could spray gelcoat it for you, the main issue with doing this is getting the gelcoat to a smooth finish again after spraying it's alot of sanding and polishing to get it back to a mirror finish.


also bought 2 litres of gelcoat but did not applied yet


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## eric2683 (Sep 3, 2014)

i think ill give the 8mm a try coz 12 mm price is to high at my store and water level will be at 3/4 only


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## OllieNZ (Apr 18, 2014)

eric2683 said:


> OllieNZ said:
> 
> 
> > If they haven't used the fabric then it's not fiberglass, just resin coated wood and without the reinforcement provided by the fabric the resin itself is very brittle and prone to cracking, so no surprise there.
> ...


Did you get wax to mix in with it or is the gelcoat the flocoat type? If it's not the wax is essential to exclude air from the gelcoat to ensure it cures hard otherwise it will remain tacky for weeks, you can sand the tacky layer off but you'll clog a lot of sand paper doing it.
Also make sure you give the fibreglass a good wipe down with acetone no more than 15mins prior to gelcoating as this will ensure a good bond between the gelcoat and the fibreglass. I'd shoot for a thickness of 30-35 wet mil and do two coats, that should give you enough thickness to sand out brush marks.
The wax is a special type of liquid that you would mix in only with the final layer of the flocoat, not to be confused with the standard release wax used to prevent components sticking to moulds. I cant stress enough the wax is only for the final layer of the flocoat if you plan on putting any additional layers on top (either more gelcoat or fiberglass) the wax will prevent the correct chemical bond from occurring resulting in delamination.


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## eric2683 (Sep 3, 2014)

is it necessary to gelcoat it


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## freelanderuk (Jun 26, 2014)

fiberglass is porous, gel coat adds the waterproof protection


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## lilscoots (Mar 13, 2012)

It depends on the resin you use. If you use polyester resin, yes you need to gel coat, if you use marine epoxy resin, then you don't need to gel coat.


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## BC in SK (Aug 11, 2012)

lilscoots said:


> It depends on the resin you use. If you use polyester resin, yes you need to gel coat, if you use marine epoxy resin, then you don't need to gel coat.


As far as I know that is all anyone would use is marine epoxy resin. Weather it's fiber glassing boats or used in auto body it's always epoxy. 
Never even heard of polyester resin (?)----is it still even called "fiberglass", if polyester resin is used? Years ago, I worked briefly in a fiberglass plant and all that was ever used was epoxy.


eric2683 said:


> is it necessary to gelcoat it


No. It is basically for aesthetics. If you are fine with a somewhat rougher surface, definitely no need for a gel coat.


freelanderuk said:


> fiberglass is porous, gel coat adds the waterproof protection


No, fiberglass is not porous. :lol: It's plastic and VERY water proof!


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## eric2683 (Sep 3, 2014)

will add one more layer glassmat 450 tonight if not tired


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## OllieNZ (Apr 18, 2014)

Given the op is using chop strand mat (csm) I'd assume the resin being used is polyester, the styrene in the resin is required to break down the binder on the matting allowing it to wet out correctly. You can buy csm for use with epoxy but its not as common. 
Assuming the op is using general purpose polyester then yes it will require to be gelcoated for long tem submerged use.
Fyi most modern boats use polyester of the iso/npg type and all car body filler I've come across is polyester based. Its also used for a lot of aircraft parts especially in general aviation where the cost of epoxy makes its use unfeasible.
Just in case anyone is wondering I'm trained in the manufacture and repair of aerospace composites and the manufacture and repair of the tooling that goes with it. (moulds, plugs, etc)


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## freelanderuk (Jun 26, 2014)

freelanderuk said:


> fiberglass is porous, gel coat adds the waterproof protection


No, fiberglass is not porous. :lol: It's plastic and VERY water proof![/quote]

fiberglass is porous , i have had 3 boats that were all fiberglass and my last 25ft bayliner was fiberglass and had to have repairs where the fiberglass had become porous due to gel coat damage

http://www.insightmarinesurveyors.co.uk/blistersosmosis

Although often argued, all fibreglass hulls absorb water to some degree because the gel coat finish on the exterior, and the internal fibreglass reinforced plastic is porous. Even epoxies, the most waterproof resinous coatings available, are permeable. Since water is a solvent, it tends to react with the fibreglass, resulting in the water and solvents in the plastic mixing to create a weak solvent solution. Moisture continues to be absorbed through the gel coat and if resulting solutions are not able to escape by condensation on the interior, hydraulic pressure will be generated within the laminate, eventually leading to gel coat blistering.


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## BC in SK (Aug 11, 2012)

BC in SK said:


> lilscoots said:
> 
> 
> > It depends on the resin you use. If you use polyester resin, yes you need to gel coat, if you use marine epoxy resin, then you don't need to gel coat.
> ...


I guess I am serving to confuse in this thread, as I am not that well informed. Wasn't really aware that polyester resin ( and not marine epoxy) is what is commonly used as "fiber glass". May have been simply been calling polyester resin, "epoxy". 


OllieNZ said:


> Assuming the op is using general purpose polyester then yes it will require to be gelcoated for long tem submerged use.


I really thought it was primarily for aesthetic reasons and/or where a very smooth surface is required. 
Water tanks for industrial or agricultural use have no gel coat, and hold water just fine.
Unless I am still confused as to what is actually used to make these products?


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## eric2683 (Sep 3, 2014)

ok guys decided to go with 10mm glass just glued this morning will post pics later


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## eric2683 (Sep 3, 2014)

so far everything is right the tank is holding water just remain the stand and background to do


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## eric2683 (Sep 3, 2014)

tank finished


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