Using screws to hold plywood/foam construction together while gluing?

[ReluctantTraveler]

I'm planning to build my rig on top of a flatbed using marine-grade plywood and rigid foam board insulation, with a wood frame (similar to what IdaSHO has done with his camper).

I'll be gluing the whole thing together with SikaFlex or something similar. Is there any reason not to use screws at the edges and corners to hold things in place while the glue sets up?

I planned to glass or silicone over them before painting to seal the holes up. As an alternative I could use brad nails, but "glue and screw" seems a bit more sturdy.

 

[billiebob]

screws are the better choice

 

[NatersXJ6]

Having built a lot of various stuff out of various stuff…. I will say that brads or maybe other nail gun driven fasteners are much less likely to move while connecting. If screws are your answer, clamping while putting in screws will create much higher precision joins… however, screws will be much stronger and can pull joints together in a way that nails won’t really do as well. The best overall might be gluing, brad nailing, then screwing, but it really depends on your desired level of finish quality.

 

[ReluctantTraveler]

Having built a lot of various stuff out of various stuff…. I will say that brads or maybe other nail gun driven fasteners are much less likely to move while connecting. If screws are your answer, clamping while putting in screws will create much higher precision joins… however, screws will be much stronger and can pull joints together in a way that nails won’t really do as well. The best overall might be gluing, brad nailing, then screwing, but it really depends on your desired level of finish quality.

as in, the wood is more likely to shift while being screwed together if it is not already held together in some other way?

 

[IdaSHO]

FYI, I used stainless 18GA brads for all of my skin to framing connections. (framing to framing was done with pocket hole screws)
Wont rust, will never split the material its fastening together, and assuming you apply enough pressure when nailing, will hold the panel to the framing just fine while the glue cures.
If you build things correctly, you shouldnt NEED to pull panels together. They should line up to begin with. So take your time and do it right.

As mentioned, screws do have a tendency to shift materials. And it does, as a screw is far more likely to follow grain patterns than a small brad.
Brads are also easier to sand, create MUCH smaller holes to fill, and wont damage a router bit if you are rounding corners after assembly.
Also, when dealing with thin panels/ply, a bunch of small fasteners is considerably more effective than a few large fasteners.
Large fasteners will create waves, with brads you will be able to hold things flat.

 

[ReluctantTraveler]

FYI, I used stainless 18GA brads for all of my skin to framing connections. (framing to framing was done with pocket hole screws)
Wont rust, will never split the material its fastening together, and assuming you apply enough pressure when nailing, will hold the panel to the framing just fine while the glue cures.
If you build things correctly, you shouldnt NEED to pull panels together. They should line up to begin with. So take your time and do it right.

As mentioned, screws do have a tendency to shift materials. And it does, as a screw is far more likely to follow grain patterns than a small brad.
Brads are also easier to sand, create MUCH smaller holes to fill, and wont damage a router bit if you are rounding corners after assembly.
Also, when dealing with thin panels/ply, a bunch of small fasteners is considerably more effective than a few large fasteners.
Large fasteners will create waves, with brads you will be able to hold things flat.

As always, Kenny, thank you for the constant advice! How "off road" do you get with your rig? I'm a bit worried about things falling apart while on jacks.

My wife is really keen on removing it from the truck if we'll be staying in one spot for a week.

I know you have a steel frame inside yours. I'd planned to build entirely with wood.

 

[NatersXJ6]

as in, the wood is more likely to shift while being screwed together if it is not already held together in some other way?

Yes, as @IdaSHO mentioned, screws can pick up and follow tough grain patterns, even with pre drilling, and in a typical “holding by hand” situation, this can torque your joint out of position by 1/32 or maybe even 1/16 if the world hates you. Adding glue lubricates the joint and makes this effect harder to control.

If a brad Hits a knot or tough grain, it can bend, change path, and blow out, but it is usually easier to deal with than a misplaced screw. When I build furniture using pocket screws, I’m especially careful to put attention to these types of issues, or I just touch everything up with a small hand plane and assume I’m the only one that will notice.

To the point made above, you shouldn’t HAVE to pull joints into alignment, but wood is not metal and doesn’t hold the same precision, especially if being built with varying temperature or humidity over time. I’ve also noticed that the most common sources of lumber seem to be dropping severely in quality and storage methods, so you are likely to work with at least some compromised material.

If you are buying all kiln-dried and rough sawn hardwoods and planing and jointing your own stuff, essentially building high-end furniture techniques, maybe you won’t ever have to pull a joint. It will be a very expensive build and waste a lot of material though!

It sounds like fun. Enjoy the journey!

 

[ReluctantTraveler]

Yes, as @IdaSHO mentioned, screws can pick up and follow tough grain patterns, even with pre drilling, and in a typical “holding by hand” situation, this can torque your joint out of position by 1/32 or maybe even 1/16 if the world hates you. Adding glue lubricates the joint and makes this effect harder to control.

If a brad Hits a knot or tough grain, it can bend, change path, and blow out, but it is usually easier to deal with than a misplaced screw. When I build furniture using pocket screws, I’m especially careful to put attention to these types of issues, or I just touch everything up with a small hand plane and assume I’m the only one that will notice.

To the point made above, you shouldn’t HAVE to pull joints into alignment, but wood is not metal and doesn’t hold the same precision, especially if being built with varying temperature or humidity over time. I’ve also noticed that the most common sources of lumber seem to be dropping severely in quality and storage methods, so you are likely to work with at least some compromised material.

If you are buying all kiln-dried and rough sawn hardwoods and planing and jointing your own stuff, essentially building high-end furniture techniques, maybe you won’t ever have to pull a joint. It will be a very expensive build and east a lot of material though!

It sounds like fun. Enjoy the journey!

Thanks for all of this!

A few folks here recommended Boulter Plywood as a good source of quality marine-grade plywood. I know with COVID, supply and quality of everything is kind of a mess, but hopefully choosing a good supplier will make a bit of difference.

 

[jwiereng]

I wonder why more homebuilds not built like IdaSHO. Simply tools, simple materials, excellent and durable results.

I also wonder why commercial RV trailers/campers are not made this way?
It is just because it takes too long, and not enough craftsman available to work in commercial production?

 

[ripperj]

Didn’t IdaSho fiberglass glass his whole camper? Very time intensive and expensive


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[ReluctantTraveler]

Didn’t IdaSho fiberglass glass his whole camper? Very time intensive and expensive


Sent from my iPhone using Tapatalk Pro

No, just the seams and joints. He later used MonstaLiner on the whole thing.

 

[IdaSHO]

No, just the seams and joints. He later used MonstaLiner on the whole thing.

Correct. Though to get away with just doing the seams you must use the proper plywood. Mine is done entirely in 6mm bs1088 Okoume, and completely saturated with marine epoxy. The ply is spendy stuff, but worth it. Anything less and without glass the surface will check and fail.

 

[ReluctantTraveler]

Correct. Though to get away with just doing the seams you must use the proper plywood. Mine is done entirely in 6mm bs1088 Okoume, and completely saturated with marine epoxy. The ply is spendy stuff, but worth it. Anything less and without glass the surface will check and fail.

Safe to assume that's a marine-grade plywood? That'd been my plan.

 

[IdaSHO]

Safe to assume that's a marine-grade plywood? That'd been my plan.

Yes, though never assume a “marine plywood” is actually marine ply. If it is not BS1088, its not true marine grade ply.

 

[ReluctantTraveler]

Yes, though never assume a “marine plywood” is actually marine ply. If it is not BS1088, its not true marine grade ply.

TIL. Thanks Kenny!