Tank Building

[Cichlabxr]

Hi,

Due to my research lately on building a plywood tank I now have one more dilemma.

I have noticed in both glass and plywood designs, some people advocate sitting the front ,back and sides on the base of the tank. The other school suggests having the base inside them.

I have a 4x2x2 which has the base inside but also have a standard 3footer with the sides standing on the base.

My instinct is to go with the latter.

Does anyone know which design the "often discussed tank builders" ie Extreme, St George use.

Thanks Martin

[dazza]

I believe the first option is stronger and easier to work with.

The trouble with the second option smaller surface area at the base and the sides tends to flex more.

I just fixed one of the second type with extra glass running on the edges of the base, so far so good.

[YAL05T]

Have a look at this guys "project".

http://www.monsterfishrescue.com/

[Eddie Salita]

My feeling and theory would be the first option also. With the sides flying past the base. Much of the basis for this theory would be that the adhesive is stronger in tension than in shear. You could in fact do both. By doing it with the base inside the sides, and then fixing a second base which the sides will touch. Then you will have a double thickness base also.

However, if you were relying on pure mechanical fixing (in this case you arent, or dont want to for good reasons) I would suggest the second method. Screwing/nailing into end grain or the edges of ply is not good. End grain/laminate will strip easily when fixed into. So in such an instance through the base into the sides would be stronger. This would put the screws into shear, which is where they are strongest. Just thought I would explain this also even though it is not terribly relevant, as it is part of the basis for my theory.

So, in summary, most adhesives are stronger in tension and mechanical fixings are stronger in shear. This is my experience of course. Specialist adhesives can be designed for specific purposes also. I am assuming you will be using silicone/sikaflex. I would also suggest you look into sikaflex (several types for different purposes) as far as aquarium safeness goes. Its strength especially with timer is superior. Being a polyurethane based thing, I imagine once cured it would be safe, but I dont have any experience with it in aquariums.

cheers,

Jason

[Cichlabxr]

Thanks for the replies.

Thanks Jason for the explanation of "mechanical fixing". You have given me the theory I knew must exist but had no idea how to ask.

I will look into sikaflex re; aquarium safety and post back what I find.

Thanks

Martin

[Ash]

My feeling and theory would be the first option also. With the sides flying past the base. Much of the basis for this theory would be that the adhesive is stronger in tension than in shear. You could in fact do both. By doing it with the base inside the sides, and then fixing a second base which the sides will touch. Then you will have a double thickness base also.

However, if you were relying on pure mechanical fixing (in this case you arent, or dont want to for good reasons) I would suggest the second method. Screwing/nailing into end grain or the edges of ply is not good. End grain/laminate will strip easily when fixed into. So in such an instance through the base into the sides would be stronger. This would put the screws into shear, which is where they are strongest. Just thought I would explain this also even though it is not terribly relevant, as it is part of the basis for my theory.

So, in summary, most adhesives are stronger in tension and mechanical fixings are stronger in shear. This is my experience of course. Specialist adhesives can be designed for specific purposes also. I am assuming you will be using silicone/sikaflex. I would also suggest you look into sikaflex (several types for different purposes) as far as aquarium safeness goes. Its strength especially with timer is superior. Being a polyurethane based thing, I imagine once cured it would be safe, but I dont have any experience with it in aquariums.

cheers,

Jason

I was about to post something similar after reading the first post but was pleasantly surprised to see this post saved me the trouble

I believe a lot of people use a construction adhesive like liquid nails for sticking the plywood together then rely on the epoxy coating on the inside of the wood to keep any toxic byproducts out of the water.

The non-toxic epoxy resin & fiberglass matting will also add strength to the joins, especially if you overlap the corners with sheets of woven matting rather than the random chop strand stuff.