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

[Alloy]

Moisture, and not trapping it is the key. Aluminum would trap it, yes, but just as bad is that it would also likely be a surface for moisture to condense on.

Air sealing (not allowing water vapor into the wall) is far more importand than allowing it to (evaporate) escape.

 

[IdaSHO]

Air sealing (not allowing water vapor into the wall) is far more importand than allowing it to (evaporate) escape.

Important yes, but no structure is perfectly sealed.
If you allow moisture in, you MUST allow it a way out. This is of the most important rules with wood construction, be it a camper or a multimillion dollar home. Its referred to as moisture management. And is often overlooked and IMO is right at the root if all “OMG WOOD” issues.

Unless your interior wall surfaces are 100% moisture impermeable, you will have moisture inside the walls. Cooking, bathing, even just breathing dumps moisture into the air.

A wood structure with a moisture impermeable skin like aluminum is about the best (or worst) way to test this. The only reason why older aluminum sided campers survive as well as they do as they are far from sealed. Plenty of leaks to allow whatever moisture gets in, a way out.

 

[ReluctantTraveler]

Important yes, but no structure is perfectly sealed.
If you allow moisture in, you MUST allow it a way out. This is of the most important rules with wood construction, be it a camper or a multimillion dollar home. Its referred to as moisture management. And is often overlooked and IMO is right at the root if all “OMG WOOD” issues.

Unless your interior wall surfaces are 100% moisture impermeable, you will have moisture inside the walls. Cooking, bathing, even just breathing dumps moisture into the air.

A wood structure with a moisture impermeable skin like aluminum is about the best (or worst) way to test this. The only reason why older aluminum sided campers survive as well as they do as they are far from sealed. Plenty of leaks to allow whatever moisture gets in, a way out.

How do you achieve this in yours, Kenny? I know you mentioned that moisture does build up, particularly with winter camping.

 

[Alloy]

Important yes, but no structure is perfectly sealed.
If you allow moisture in, you MUST allow it a way out. This is of the most important rules with wood construction, be it a camper or a multimillion dollar home. Its referred to as moisture management. And is often overlooked and IMO is right at the root if all “OMG WOOD” issues.

Unless your interior wall surfaces are 100% moisture impermeable, you will have moisture inside the walls. Cooking, bathing, even just breathing dumps moisture into the air.

A wood structure with a moisture impermeable skin like aluminum is about the best (or worst) way to test this. The only reason why older aluminum sided campers survive as well as they do as they are far from sealed. Plenty of leaks to allow whatever moisture gets in, a way out.

The purpose of air sealing is to limit the amount of water vapor entering the wall so it doesn't do any damage.

It doesn't matter if the outside wall is plywood, glass, FRP or aluminum water vapor will condense on the first cool surface.

 

[givemethewillys]

Along those lines... is there any world in which its easier/simpler to use an aluminum exterior shell instead of plywood and epoxy?

I could imagine using a wooden frame and rigid foam, just like you have, but gluing aluminum panels and sealing the joints with silicone or something like that.

I could VERY MUCH be hand-waving over some serious complications, though.

I think the biggest problem with that is that the materials expand and contract at different rates, making it difficult to bond and not have waves.

 

[IdaSHO]

I think the biggest problem with that is that the materials expand and contract at different rates, making it difficult to bond and not have waves.

Waves are the least of your problems. That difference in expansion and contraction is just one reason that no DIYer have a chance of bonding aluminum to ply without any gaps.

This is why Ill always advocate a coating over a skin. A coating is bonded in such a way that it moves with the ply as it moves, never allowing a surface for moisture to condense (like between the ply and skin)

Plywood with a coating is also what Id consider thermally stable or consistent. Aluminum is incredibly conductive, thermally and otherwise. Just more reason attempting to bond them together with good/reliable results is not likely.

 

[IdaSHO]

How do you achieve this in yours, Kenny? I know you mentioned that moisture does build up, particularly with winter camping.

Ill dig up some photos when I have a chance, to help explain. But the basics are as such…

*Ply is bonded to all (wood) framing.
*Exterior of ply is glassed/epoxy coated/painted
*Interior of plywood, framing, each and every wall cavity is epoxy coated.
*Then the walls are insulated from the inside (xps foam)
*Finally, interior skins (that have been painted/sealed are applied.

Done this way, by design, moisture condenses within the wall cavity on the epoxy, then uses the path of least resistance to dry… to the interior. Never does is even try to penetrate the exterior ply skin.

 

[ReluctantTraveler]

Ill dig up some photos when I have a chance, to help explain. But the basics are as such…

*Ply is bonded to all (wood) framing.
*Exterior of ply is glassed/epoxy coated/painted
*Interior of plywood, framing, each and every wall cavity is epoxy coated.
*Then the walls are insulated from the inside (xps foam)
*Finally, interior skins (that have been painted/sealed are applied.

Done this way, by design, moisture condenses within the wall cavity on the epoxy, then uses the path of least resistance to dry… to the interior. Never does is even try to penetrate the exterior ply skin.

Nod nod, so that part makes sense. Once the moisture is inside your rig, are you cracking a window or running AC to let it vent out?

 

[ITTOG]

Ill dig up some photos when I have a chance, to help explain. But the basics are as such…

*Ply is bonded to all (wood) framing.
*Exterior of ply is glassed/epoxy coated/painted
*Interior of plywood, framing, each and every wall cavity is epoxy coated.
*Then the walls are insulated from the inside (xps foam)
*Finally, interior skins (that have been painted/sealed are applied.

Done this way, by design, moisture condenses within the wall cavity on the epoxy, then uses the path of least resistance to dry… to the interior. Never does is even try to penetrate the exterior ply skin.

I don't beleive I knew you epoxied the interior side of the plywood and the framing. Did you just brush it on?

 

[ReluctantTraveler]

I don't beleive I knew you epoxied the interior side of the plywood and the framing. Did you just brush it on?

I believe it was brushed and rolled on. I only knew this because I have his Flickr album bookmarked and look at it for reference constantly.

 

[IdaSHO]

Yes, just brushed and rolled.

I had a few white and clear garage floor epoxy kits (solvent based) that I used to encapsulate the framing and 6mm skin
Here is another shot showing the wall cavities prior to insulating

 

[IdaSHO]

Nod nod, so that part makes sense. Once the moisture is inside your rig, are you cracking a window or running AC to let it vent out?

Pretty much. In the cold where moisture can really become a problem we always have a window or two cracked anyhow.
Two dogs and two adult humanoids alone are enough to keep it above 65 if its above 40 degrees outside.
The furnace is a 6kBTU, and has never come up short. Windows cracked all the way down to -20F and its plenty to maintain 65 degrees.

 

[ReluctantTraveler]

Yes, just brushed and rolled.

I had a few white and clear garage floor epoxy kits (solvent based) that I used to encapsulate the framing and 6mm skin
Here is another shot showing the wall cavities prior to insulating

did you epoxy the framing before or after putting on the exterior?

 

[IdaSHO]

did you epoxy the framing before or after putting on the exterior?

After