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

[John Ziebron]

Here's another possible idea for you.

A few months ago I made an alcove for my dog's outside water bowl to help keep out birds and leaves. I bought a product called GoBoard which is used primarily as an underlayment for tile. It is 1/2 inch thick and the sheet is 3 x 5 feet. It feels like a much denser foam than the styrofoam insulation board but is still very light weight and it has a gray layer on both sides. It cuts pretty easy with a utility knife but I ended up using my table saw to get straight, crisp edges. I used polyurethane glue only to hold the pieces together. I see no degradation in the months it's been outside in the sun and rain. I didn't paint it, although I did try spraying a scrap piece which seemed to absorb the thinner paint. If I had to paint it I would use a solid color stain.

[mike sato]

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.

Thanks for the info and confirmation. I'm going to try the primer as glue method with a modification to my previous post as follows:

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

The mod is in step-4 I'll use 100% acrylic paint instead of more primer. The acrylic paint should have more body and flexibility than primer which hopefully will add to the strength of the fabric reinforcement.

Thanks for the ideas,
Mike

[mike sato]

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

Oh, is that what he meant. That is a novel and nice idea indeed. Thanks.

[mike sato]

Here's another possible idea for you.

A few months ago I made an alcove for my dog's outside water bowl to help keep out birds and leaves. I bought a product called GoBoard which is used primarily as an underlayment for tile. It is 1/2 inch thick and the sheet is 3 x 5 feet. It feels like a much denser foam than the styrofoam insulation board but is still very light weight and it has a gray layer on both sides. It cuts pretty easy with a utility knife but I ended up using my table saw to get straight, crisp edges. I used polyurethane glue only to hold the pieces together. I see no degradation in the months it's been outside in the sun and rain. I didn't paint it, although I did try spraying a scrap piece which seemed to absorb the thinner paint. If I had to paint it I would use a solid color stain.

Where did you buy your GoBoard from? I searched HomeDepot and Lowes websites but did not have any hits.
What was the cost per 3x5x1/2" panel?
How stiff is the GoBoard? (Stiff like 1/2" plywood or 1/4" plywood, etc.)
When you used polyurethane glue to hold the pieces together, were there edges glued like in assembling a box?
What was your project?

Sorry for so many questions but you have gotten my attention to this product. May be helpful to others too.
Thanks,
Mike

[Jacques Gagnon]

Bill:

Thanks for bringing clarity to my suggestion.


J.

[mark mcfarlane]

... 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...

Painting over the mineral wool will change both its acoustic absorption characteristics (frequency dependent, largest impact of paint will be in the mid-higher frequencies) and its fire resistance (one of the benefits of rock wool, which is actually made from basalt and chalk). I don't know what kinds of temps you will be encountering, or what frequencies you are trying to attenuate, or how 'light' a spray you can achieve while still bonding the fibers but this is something to consider.

If the temps are not very high, the traditional approach to encapsulating mineral fiber in an acoustic application is with a cloth material. Flame resistant material is used in commercial applications. If you can breath through the material it won't have a significant impact on acoustic absorption. If you can't breathe through the surface coat, then higher frequencies will not be absorbed, they will be reflected.

A final note, Roxul is available in different densities which also effect its frequency absorption characteristics.

Food for thought.

[mike sato]

Painting over the mineral wool will change both its acoustic absorption characteristics (frequency dependent, largest impact of paint will be in the mid-higher frequencies) and its fire resistance (one of the benefits of rock wool, which is actually made from basalt and chalk). I don't know what kinds of temps you will be encountering, or what frequencies you are trying to attenuate, or how 'light' a spray you can achieve while still bonding the fibers but this is something to consider.

If the temps are not very high, the traditional approach to encapsulating mineral fiber in an acoustic application is with a cloth material. Flame resistant material is used in commercial applications. If you can breath through the material it won't have a significant impact on acoustic absorption. If you can't breathe through the surface coat, then higher frequencies will not be absorbed, they will be reflected.

A final note, Roxul is available in different densities which also effect its frequency absorption characteristics.

Food for thought.

I did agonize whether painting over the mineral wool would be too detrimental in my application. My current thought is that in an absorption scenario like panels on the walls and ceiling in a studio to absorb sound, it wouldn't be ideal and that fabric coverings are a far better solution. But to contain sound in a generator box, I don't think a thin coat of paint will make much difference in the sound reduction due to "transmission through" the mineral wool. I like using mineral wool for it's fire resistance and I'm going to use engine enamel as the paint in that regard.

>> A final note, Roxul is available in different densities which also effect its frequency absorption characteristics. <<
Yes, Roxul has looser "Safe-n-sound" and firmer Rockboard in various thicknesses and compressions. I did a pre test using Rockboard 60 with my generator alone and then enclosed completely with Rockboard60. The reduction in sound was dramatic. I estimate a 60% overall reduction. The reduction in higher frequencies was really dramatic so the end result was a low frequency muffled sound that was very tolerable. In my finished project there will be intake and exit ports for air so with baffling if I can end up with a 50% overall sound reduction I'll be very happy.

Thanks for your input,
Mike

[mark mcfarlane]

Sounds like you've thought it through Mike. If your paint layer just hits fibers and doesn't span the open pore space (i.e. you can blow through the paint layer) you should be fine. If the paint coat is continuous, and you can't blow through it, I don't think it will work as effectively on frequencies above a few hundred hertz.

Please let us know how it works out, I haven't seen anyone try to paint rock wool in this context :). There is the theory, and then there is the real world.

Sometimes you just need to try stuff. If the paint has too large an impact, you can always flip the panels so the paint is on the back side of the panels, against the plywood, then the paint won't have any significant impact.

I assume this will be outdoors.

[mike sato]

If the paint has too large an impact, you can always flip the panels so the paint is on the back side of the panels, against the plywood, then the paint won't have any significant impact.
..... Exactly what I planned to do if sound reduction is worse than my initial test enclosing my generator completely with RB60. I did make a video recording of that initial test so I can use it to compare sound levels. I'm pretty confident though that the paint will not affect reduction of sound level "transmission through" the Rockboard 60. With luck it may even help (one additional layer to go through) ... ;).


I assume this will be outdoors.

..... No, my generator will only be run in our carport during power outages so it will always be out of the rain. I'm using PT plywood because that's what I have left over from previous projects. Exhaust from the generator will be piped up above the roof of our carport (40 inches above roof level) so no chance of carbon monoxide poisoning by running the generator in the carport.

Thanks for the feedback,
Mike

[John Ziebron]

Mike, I bought the GoBoard at Menards. The 3x5x1/2" panel was $22.99. My local Lowes website shows it as currently unavailable but did show a price of over $42. I would say it is just as stiff as 1/2" plywood. It will break if stressed enough (I tried it with a scrap piece) but it does take quite a bit of force. Realize too that it is dense enough to put ceramic tile on it and be walked on. It is made by Johns Manville and their website shows other thicknesses as well although my Menards only stocked the 1/2" thickness.

No fancy joints, just put glue on an edge and stuck a panel piece on. I didn't take any pictures of it and it's dark now. But I'll take a couple tomorrow (if it doesn't rain all day) and post them for you.

[mike sato]

Mike, I bought the GoBoard at Menards. The 3x5x1/2" panel was $22.99. My local Lowes website shows it as currently unavailable but did show a price of over $42. I would say it is just as stiff as 1/2" plywood. It will break if stressed enough (I tried it with a scrap piece) but it does take quite a bit of force. Realize too that it is dense enough to put ceramic tile on it and be walked on. It is made by Johns Manville and their website shows other thicknesses as well although my Menards only stocked the 1/2" thickness.

No fancy joints, just put glue on an edge and stuck a panel piece on. I didn't take any pictures of it and it's dark now. But I'll take a couple tomorrow (if it doesn't rain all day) and post them for you.

Hi John,

Thanks for the info on the GoBoard. No Menards in our area, just HomeDepot and Lowes big box stores. The GoBoard may be hard to find here.
Whoa, $22.99 at Menards but $42+ at Lowes (if they stocked it). That's quite a difference!

I'll just use the plywood that I already have. Shouldn't be "too" heavy and the generator will only be used during power outages, so free (plywood) is good... :).

Thanks,
Mike

[Curt Harms]

If you're lining the inside of a plywood box, have you considered acoustic foam? I bought some on the bay for reline the motor cover of a Fein vac. One side was self adhesive and it makes a substantial difference even if I had to 'resaw' it to 3/8" to make the thickness work. It's surprising how well reasonably dense foam cuts on a bandsaw with fine toothed none-too-sharp blade.

[mike sato]

If you're lining the inside of a plywood box, have you considered acoustic foam? I bought some on the bay for reline the motor cover of a Fein vac. One side was self adhesive and it makes a substantial difference even if I had to 'resaw' it to 3/8" to make the thickness work. It's surprising how well reasonably dense foam cuts on a bandsaw with fine toothed none-too-sharp blade.

When researching the type of sound reduction material to use, I settled on the dense Roxul Rockboard instead of a foam. Consensus appears to be that density is what counts when trying to reduce sound transmission "through" the material. So I already got the Rockboard.

Thanks. Every idea counts,
Mike

[Curt Harms]

When researching the type of sound reduction material to use, I settled on the dense Roxul Rockboard instead of a foam. Consensus appears to be that density is what counts when trying to reduce sound transmission "through" the material. So I already got the Rockboard.

Thanks. Every idea counts,
Mike

Use what ya got, I'm the same way. I helped a guy move a couple hearing testing booths and learned a bit about sound transmission in the process. They used layers of dry wall with separators between, I don't remember the details there. Then lined the booth with acoustic foam. Not all foam is created equal, apparently. My experience with the Fein vac foam backs that up, huge difference made by a pretty thin layer of acoustic foam surrounding the motor/blower.

[mike sato]

Use what ya got, I'm the same way. I helped a guy move a couple hearing testing booths and learned a bit about sound transmission in the process. They used layers of dry wall with separators between, I don't remember the details there. Then lined the booth with acoustic foam. Not all foam is created equal, apparently. My experience with the Fein vac foam backs that up, huge difference made by a pretty thin layer of acoustic foam surrounding the motor/blower.

Thanks for sharing your info. It all helps in trying to understand sound reduction techniques.

Mike

[mike sato]

Sounds like you've thought it through Mike. If your paint layer just hits fibers and doesn't span the open pore space (i.e. you can blow through the paint layer) you should be fine. If the paint coat is continuous, and you can't blow through it, I don't think it will work as effectively on frequencies above a few hundred hertz.

Please let us know how it works out, I haven't seen anyone try to paint rock wool in this context :). There is the theory, and then there is the real world.

Sometimes you just need to try stuff. If the paint has too large an impact, you can always flip the panels so the paint is on the back side of the panels, against the plywood, then the paint won't have any significant impact.

I assume this will be outdoors.

Hi Mark,

Here's a follow up on painting the Rockboard in my generator's quiet box. The idea was to prevent loose fibers from being blown out of the box by the cooling air flow. I painted all of the exposed Rockboard inside of the quiet box and the paint is doing what I wanted. The paint formed a crust on the rock wool that prevents loose fibers from being blown out. The crust is stable as long as something doesn't hit it and break a piece off. In that case, just that small area will be damaged. Painting the Rockboard did not have any impact on the sound reduction.

Today, I published a youtube video about that sound reduction quiet box. When I shot the video, only the Rockboard in the intake end panel was painted (black) but the other panels were not painted yet. After shooting that video, I painted the rest of the panels since the paint on the test panel was holding up well.

The youtube video is titled "Generator or compressor sound reduction quiet box" and the thumbnail shows the compressor with the words "5X QUIETER" in red letters. It was published under the youtube name "Usefulgizmos".

Here's a link to make it more convenient for anyone who wants to view the video:
https://www.youtube.com/watch?v=_qPRIq-9U-4

View it in full screen to see the most detail,
Mike



(https://www.youtube.com/watch?v=_qPRIq-9U-4)

[Jacques Gagnon]

Mike,

Thanks for posting the results of your project. You have done a great job, from beginning to end! Good to know that paint can effectively be used on the insulation material.

I can see another project creeping onto my projects list! :D

Let's now hope you will not have to use that generator too often.

[mark mcfarlane]

Hi Mark,

Here's a follow up on painting the Rockboard in my generator's quiet box. ...
Mike



Nice job on the video Mike. Thanks for sharing this.

[michael langman]

Excellent video and sound reduction project Mike!
I look forward to the other videos on the scaffolding and saw stand.

[mike sato]

Jacques, Mark and Michael,

Thanks all for your kind feedback.
Yep, it is ironic that it was a build that I hope I never have to use .... ;).

Oh, I forgot to comment about gluing 1/8" plywood to the edge of 1/4" plywood. For the sound baffles in the video, I did that. Used Titebond III and wire brads. It turned out to be strong and secure so I did not have to reinforce the edges with fabric.

Mike