lightweight or underbuilt? your opinions, please

[Artificer]

regarding foam, does pink come in 3/4" thick? I went with white foam with foil on both sides (tuff-R or high-R?) to get the 3/4" I wanted....

h/d only has pink in 2" thick, at least that I could find.

I never checked around and don't know which foam is the most rigid and the best to use to strengthen sandwich walls.

I think the pink stuff (Owens Corning Foamular 150) at HD is in 1", 1.5", 2", and possibly 3/8" fanfold. You might be able to get Foamular 250 (NOT at HD) and that comes in 3/4" thickness. The 250 is 66% stronger than the standard 150.

For walls, any foam that has a good glue bond to the skins will be fine.

Is the white foam isocyanurate? (sp?) If it is, then the strength is just a little less than the extruded polystyrene (pink or blue insulation)

[jmtk]

For walls, any foam that has a good glue bond to the skins will be fine.

So how much glue constitutes a "good glue bond"? This is what I did before putting the insulation in. I ran some glue beads all over the surface, then trowled it out:

And this is the glue I used:

Would it be better to put even more adhesive down? Leave it thicker? I'd imagine the more bonded surface area the better.

Jeanette

[Artificer]

So how much glue constitutes a "good glue bond"? This is what I did before putting the insulation in. I ran some glue beads all over the surface, then trowled it out:
...
Would it be better to put even more adhesive down? Leave it thicker? I'd imagine the more bonded surface area the better.

Jeanette

From a quick glance, I would estimate you have 10%-20%coverage. On the walls, thats probably enough. On the floors... it might be, but more is better in this case. If you want to maximize strength, then maximize the coverage. (100%) I'm fond of Elmer's brand polyurethane glue in a bottle. It flows out well, and gives a good bond. Since its has a honey like viscosity, it trowels out very nicely.

Coverage is more important than thickness. You only have to have it thick enough to form a bond. Anything extra is a waste. (or insurance of bonding) After a certain point, it gets silly, like 1/8" thick bead of glue. I used a V-notched trowel with my tile adhesive. If I remember corectly, it had 1/16" notches.

I'm going to do an insulated panel strength test in the next few days, and I'll probably make up a special trowel. Pour the glue on, trowel it out to .020-.040" thick. Just a guestimate for now.

My test is going to be a bunch of 4" wide pieces of 1/8" birch ply, 48" long, glued to both sides of 1", 2" EPS, 2" bead board, and possibly 1" isocyanurate (if I still have some scraps left). I was going to use the Elmers Poly, buy I might throw in a 2" EPS with the vinyl floor adhesive. Hmmm... might have to wait a week for that stuff to cure properly. I'll let you know how the tests turn out. I'm going to look at deflection under load, and see how much load they take before they break. Should be usefull information for the ultralight trailer thread.

[asianflava]

Try to concentrate on putting glue near the edges. If the panel delaminates, it will start there first.

[Arne]

Artificer... thank you for the foam information... I went with the white/foil because of the thickness..... still thinking about what to do with the next one.

[Steve Frederick]

Jeanette! Your idea is just right!
I've built three T/D's so-far and currently on #'s 3 and 4..Just that way!
Very sturdy! Just make the laminations tight, use good materials, and share the pics!!

[jmtk]

Steve,

It's good to know you've done the same! If I remember right, though, in your shop manual (which is great, by the way) you specified 1/4" skins inside and out on your sidewalls, and 1/4" roof. Seems to me you also had a 1/2" floor (I'm doing this from memory, rather than looking at your CD, so sorry if I remembered wrong). So you've apparently gone thinner on other builds.

I'm going to be using your inside-out method. It just makes so much sense to do it that way.

Jeanette

[Mitheral]

regarding foam, does pink come in 3/4" thick? I went with white foam with foil on both sides (tuff-R or high-R?) to get the 3/4" I wanted....

h/d only has pink in 2" thick, at least that I could find.

Model RRers use this stuff for bases for terrain. From what I've seen on RR forums whether the local borg carries extruded or not has a lot to do with how much below zero your climate experiences and for how long every year. Here in Canada it's a year round item in thicknesses from 3/4" to 2"s. You can usually get it ordered in though.

Besides the lower strength there is another big drawback to the white expanded foam aka bead board. It sucks up water like a sponge. A tiny leak in a wall sandwich using bead board is going to be more of a problem than a sandwich using pink/blue extruded foam. This is because with the white expanded foam the water will wick all over and keep your wood damp leading to rot.

[Artificer]

regarding foam, does pink come in 3/4" thick? I went with white foam with foil on both sides (tuff-R or high-R?) to get the 3/4" I wanted....

h/d only has pink in 2" thick, at least that I could find.

...
Besides the lower strength there is another big drawback to the white expanded foam aka bead board. It sucks up water like a sponge. A tiny leak in a wall sandwich using bead board is going to be more of a problem than a sandwich using pink/blue extruded foam. This is because with the white expanded foam the water will wick all over and keep your wood damp leading to rot.

If he has Tuff-R, its an isocyanurate insulation. Just about as strong as Foamular 150, if my reading between the lines is correct. Its easy to tell... if its got covering layers of aluminum or fiberglass, its probably isocyanurate. If it little balls stuck together, get something else.