Wood/deck screws VS bolts VS lag bolts strongest ?

[dangerhack]

Basic wood glue joints are very strong when gluing up wood face grain to face grain, face grain to edge grain or edge grain to edge grain. Once end grain is involved a standard glue joint is not very strong.

How this applies to plywood is a bit tricky since the veneers are mostly rotorary sawn and because grain direction alternates between layers. The upshot being that when joining plywood in the typical 90* edge joint as typically used in plywood aquaria, standard wood glue does not provide a very strong joint. At least not as strong as in the typical wood glue-up.

Also, glue joints rely on a near perfect junction between adjoining pieces of wood. When dealing with typical plywood and dimensional lumber you rarely get this so one needs an adhesive that has gap filling properties. So construction adhesive, polyurethane glue if the gaps are minimal or maybe even thickened epoxy.

My point being is that in the typical plywood tank there would not be much of a need for standard wood glue. I would use epoxy at the plywood to plywood joints since I would personally choose that for sealing the tank as well.

If my tank required external framing I'd likely use some sort of contruction adhesive for the junction between lumber and plywood.

Now, onto fasteners. For attaching plywood to plywood, I would use stainless wood screws. I don't believe there are lag bolts small enough in diameter for this and obviously bolts and washers wouldn't work here. I might also consider pocket screws.

For attaching the plywood to the framing, I would use either pocket holes in the lumber so there would be no screw holes inside of the tank or I'd use counter-sunk wood screws inside so there would be minimal patching.

The only place lag bolts or bolts and washers would be useful would be joining the external framing at the corners. And in this case I think I'd just use lag bolts over washers.

I suppose once could also use lag bolts to attach vertical framing members to the bottom framing plate since this is where some of the greatest stresses are on the tank. You'd have to take care to pre-drill with a large enough bit and to counter sink the heads.

Thanks for the detailed response.. Very useful info


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[dangerhack]

First off what are you using this item for. The right tool for the job is best. For the frame? Plywood sheeting?


Modify I see now. Screws are super strong the key is using the proper screw length and material.
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I'm asking for both... Building the wood Contstruction for the stand... And also for connecting the wood framing to the Sheetrock


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[MFK2009]

On my build I used the same Liquid Rubber (Zavlar) that I was using as tank sealant, saw no reason to use something different.
The LR is a very strong Glue.

Used Std off shelf #10x2inch wood screws, on glued edges, and then on exterior corners and bottom edges [ fastened again with the LR ] pieces of 90 degree metal cladding that goes around wood framing on house or garage doors. Its thin pre-finished steel
This made perfect straight corners, covered up all the screw heads, and the 7 to 2 inch bonded surfaces on two sides makes a super strong corner (and it was free left overs from someones house build) Had to do a little cutting of it with jigsaw & snips.
I had no worries about corner strength after adding.

 

[CJH]

I'm asking for both... Building the wood Contstruction for the stand... And also for connecting the wood framing to the Sheetrock


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I didn't realize you also meant for the stand. In the case of stands you really don't even want the shear strength of a fastener holding up the tank. With a lumber built stand you always have the downward force of the tank distributed to framing members. Sure a screw may hold that framing member in place but it shouldn't be the strength of the fastener itself holding the tank up.

To me the most important joint to consider in a plywood build, at least when it comes to fasteners, is the vertical joints where plywood is joined at a 90* angle. Here you have the force of the water acting both perpendicular and parallel to the fasteners. Water is both trying to force that screw straight out (parallel) and also trying to snap that screw in half (perpendicular).

I assume you meant plywood above when you wrote sheetrock? If so I think the most important thing here is to use a stainless screw. The water will be trying the push the plywood towards the outside framing so the strength of this fastener is not tested to the same degree. Technically it doesn't even need to be stainless as in a properly built plywood tank water would never get to these screws. But even if enough moisture gets in to cause corrosion but not necessarily a leak the corrosion resistance would be a good thing to have.

 

[dangerhack]

On my build I used the same Liquid Rubber (Zavlar) that I was using as tank sealant, saw no reason to use something different.
The LR is a very strong Glue.

Used Std off shelf #10x2inch wood screws, on glued edges, and then on exterior corners and bottom edges [ fastened again with the LR ] pieces of 90 degree metal cladding that goes around wood framing on house or garage doors. Its thin pre-finished steel
This made perfect straight corners, covered up all the screw heads, and the 7 to 2 inch bonded surfaces on two sides makes a super strong corner (and it was free left overs from someones house build) Had to do a little cutting of it with jigsaw & snips.
I had no worries about corner strength after adding.


View attachment 836946

Thanks for the info never thought of using liquid rubber as a glue for the wood ... I'm def gonna brace my plywood an stand with metal i already had that in mind


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[dangerhack]

I didn't realize you also meant for the stand. In the case of stands you really don't even want the shear strength of a fastener holding up the tank. With a lumber built stand you always have the downward force of the tank distributed to framing members. Sure a screw may hold that framing member in place but it shouldn't be the strength of the fastener itself holding the tank up.

To me the most important joint to consider in a plywood build, at least when it comes to fasteners, is the vertical joints where plywood is joined at a 90* angle. Here you have the force of the water acting both perpendicular and parallel to the fasteners. Water is both trying to force that screw straight out (parallel) and also trying to snap that screw in half (perpendicular).

I assume you meant plywood above when you wrote sheetrock? If so I think the most important thing here is to use a stainless screw. The water will be trying the push the plywood towards the outside framing so the strength of this fastener is not tested to the same degree. Technically it doesn't even need to be stainless as in a properly built plywood tank water would never get to these screws. But even if enough moisture gets in to cause corrosion but not necessarily a leak the corrosion resistance would be a good thing to have.

Lol yea I ment plywood.. All this talk about wood framing made me think of sheet rock because I'm redoing so in my house lol... Some very good points I will def built this stand overkill anyway but I appreciate all the tips very good things to consider when building a quality tank build


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