Gluing 1/8" plywood to edge of 1/4" plywood

[mike sato]

Project is a box to be as light as possible. The box will be lined with 3" thick mineral wool insulation for sound proofing. The box will be subject to loud sound vibrations for about 2-3 days (is a sound proofing box) maybe once a year. I want the box to be as light as possible because in use it may be lifted and removed, then placed back several times a day.

The dimensions of the box will be about 27" long x 24" wide x 12" high. It will have 4 plywood sides and a plywood top. The bottom of the box will be open.

The two 24" sides will be 1/2" pressure treated plywood.
The two 27" sides will be 1/4" pressure treated plywood. (1/4" to minimize the weight)
The top cover will be 1/8" plywood that is 24" x 27". (1/8" to minimize the weight)

My plan is to first assemble the sides. Then apply Titebond III to the top edges of the 1/4" and 1/2" plywood sides and let that soak in and dry for about 15 minutes. Then apply more Titebond to the top edge of the plywood sides and to the perimeter of the 1/8" plywood cover that will mate with the plywood sides. I'll use 2 penny galvanized finishing nails to nail the cover to the 1/2" sides but my guess is I'll have to use wire brads to nail the cover to the 1/4" sides. This box is strictly for sound proofing so does not have to look nice. It will not be painted.

My question is will the joint between the 1/4" sides and the 1/8" top cover be strong and last if assembled as described?

[Adam Herman]

can you put a 1/2 or 3/4 triangle shape in the corners and glue? this will stiffen up the whole structure. what is the purpose of this box? the 1/4 ply could create vibration problems if it is subjected to low frequencies. Speakers and sound proofing are very heavy and extremely rigid for good reason. are you mitigating a loud thing inside the box or are you protecting something in the box from sound?

[mike sato]

can you put a 1/2 or 3/4 triangle shape in the corners and glue? this will stiffen up the whole structure. what is the purpose of this box? the 1/4 ply could create vibration problems if it is subjected to low frequencies. Speakers and sound proofing are very heavy and extremely rigid for good reason. are you mitigating a loud thing inside the box or are you protecting something in the box from sound?

Actually this box will go on top of another bigger box for our generator. It will act somewhat as an exit air sound baffle so it will take exit air from the bottom, have some internal baffles and have a hole in one of the sides for the air to exit. (The exhaust from the engine is piped out of the main generator box so is not a consideration for this smaller box.) I don't think there's a need for triangular braces at the corners since the top of the box is affixed to the sides so will hold the sides square.

I'm hoping that someone who has used 1/4" plywood to make a box can let me know how strong 1/4" edge joints can be if they are glued. Also whether Titebond III glue will work for this project.

Thanks,
Mike

[Adam Herman]

i think the 1/4 to 1/8th ply joint will not hold up much, and would use something to increase the glue area. I think that thin ply is likely to delaminate on the edge where the veneer is glued to the end of the other sheet. you could keep it light by using a strip of fabric folded in the corner, either outside or inside and glue, this will strengthen it significantly with very little weight, similar to fiberglass, but you can use muslin or similar fabric. TB3 should be fine.

[Jacques Gagnon]

Mike:

Ready for a potential "outside the box" idea? How about building a box with blue or pink styrofoam? Lightweight, waterproof, insulation factor.

I love wood, but if your primary concerns are weight and water resistance, this could do the work.

[mike sato]

i think the 1/4 to 1/8th ply joint will not hold up much, and would use something to increase the glue area. I think that thin ply is likely to delaminate on the edge where the veneer is glued to the end of the other sheet. you could keep it light by using a strip of fabric folded in the corner, either outside or inside and glue, this will strengthen it significantly with very little weight, similar to fiberglass, but you can use muslin or similar fabric. TB3 should be fine.

Now that is a really great idea! A fabric strip on the outside down the length of the plywood joint would provide all the strength needed and also protect the edges of the 1/8" plywood. Weight gain and increase in box size would be negligible. I already have some fabric that is normally used at joints in the roof when applying Hydrostop elastomeric roof coating.

Do you think latex primer (which I already have) would be sufficient as the bonding agent for the fabric?

[Bill Adamsen]

I like the cloth reinforcing idea. I think I'd use glass and epoxy. I think we're all wondering, what is the box for?

[mike sato]

Mike:

Ready for a potential "outside the box" idea? How about building a box with blue or pink styrofoam? Lightweight, waterproof, insulation factor.

I love wood, but if your primary concerns are weight and water resistance, this could do the work.

Nice idea. However I already have some Roxul Rockboard 60 (mineral wool) to use for this project. Rockboard 60 does provide substantially better sound proofing than Styrofoam. The wood cover primarily acts as an exoskeleton for the RB60 and very importantly to contain small fibers from irritating the skin like fiberglass does. I plan to spray the exposed areas of the RB60 inside of the box with a light coat of automotive engine enamel to minimize fibers from being expelled from the box. I'm also going to install a handle on the 1/2" plywood to make it easier to transport the box.

Thanks. Every idea counts,
Mike

[mike sato]

I like the cloth reinforcing idea. I think I'd use glass and epoxy. I think we're all wondering, what is the box for?

I recently purchased two gallons of epoxy resin (1 gallon resin, 1 gallon hardener) but if using latex primer will be sufficient, that would be a lot easier and less messy. Also I'm thinking that the latex primer should have some flexibility.

The purpose of the box was explained in post #3.

Thanks for the the feedback. Every idea counts,
Mike

[Mel Fulks]

Use of cloth for such strengththening goes back hundreds of years. It can turn cheap plywood into a product as durable as
MDO. I've used glue but your idea of using primer as glue might work if done quickly and applied to both surfaces. I've seen mentions of Glidden "The Gripper" primer used as glue.

[Jacques Gagnon]

Thanks for the additional background.

Using the automotive enamel over the RB60 is an interesting approach; let us know the results. I could see using the same approach inside the dust collector enclosure (inside walls lined with fiberboard).

Jacques

[mike sato]

Use of cloth for such strengththening goes back hundreds of years. It can turn cheap plywood into a product as durable as
MDO. I've used glue but your idea of using primer as glue might work if done quickly and applied to both surfaces. I've seen mentions of Glidden "The Gripper" primer used as glue.

I'm thinking about priming the wood and letting it dry somewhat to allow the primer to soak into the wood. Then applying another coat of primer and quickly laying a strip of 2" wide fabric over the joint with 1" per side. Then immediately applying more primer to soak through the fabric. After it dries sufficiently, applying another coat of primer to fill the weave of the fabric.

Any concerns about this not being strong enough and why will be appreciated,
Mike

[mike sato]

Thanks for the additional background.

Using the automotive enamel over the RB60 is an interesting approach; let us know the results. I could see using the same approach inside the dust collector enclosure (inside walls lined with fiberboard).

Jacques

Sure, will post results of the effectiveness of the automotive enamel. It will be a while since I have to buy the materials for my generator box and since the frame will be made out of pressure treated lumber (not plywood), I'll have to give it about a week or two for the lumber to dry before beginning construction. As you know, PT lumber is always wet/damp when purchased.

[Mel Fulks]

Mike, in earlier days they did routinely use paint for glue ...and paint. So that should work. I have only used glue for adhesion, then acrylic primer thinned with a little water. Then full coat of primer. Then paint.

[Bill Space]

Nice idea. However I already have some Roxul Rockboard 60 (mineral wool) to use for this project. Rockboard 60 does provide substantially better sound proofing than Styrofoam...
Mike

Mike, I think you may have missed Jacques’ point. I think he was suggesting using styrofoam or similar insulation board in place of plywood, to hold the insulation you already have and plan to use.

Seemed like an interesting and workable alternative idea to me.

Bill