Sandwich wall frames

[Andrew Herrick]

While we're on this, does the thickness of XPS - I think a full 3/4" but not sure - work OK with nominal 3/4" ply, usually a thirty second under 3/4"? I was afraid it could cause ply to bulge ever so slightly.

My first teardrop was stick-framed with an XPS foam core like you're talking about. I don't build that way any more, but that's another story! Yes, the foam does bulge a bit. You won't be easily able to glue the skins to the frame. You'll have to use fasteners (plus glue, if you want). But once the skins were assembled, you couldn't visually see any bulges or discontinuities.

[tony.latham]

While we're on this, does the thickness of XPS - I think a full 3/4" but not sure - work OK with nominal 3/4" ply, usually a thirty second under 3/4"? I was afraid it could cause ply to bulge ever so slightly.

I ran into that with my second build. A little 4 x 8' to get my sister off the ground and out of tent.



I put 60 grit on my random orbital sander and ran it over the foam for two or three minutes. Kept checking it with a straight edge. It's easy to do.

Tony

[QueticoBill]

I wonder how a planer deals with foam.

[capnTelescope]

I wonder how a planer deals with foam.

A power planer gets foam dust all over everywhere, but does the job. Do it outdoors.

[QueticoBill]

I wonder how a planer deals with foam.

A power planer gets foam dust all over everywhere, but does the job. Do it outdoors.

I can only imagine and a dust collector connected to the planer is probably marginally effective at most. Still, sanding xps seems not without a lot of dust and harder to control. Would have to cut it to 1' x 8' but not too bad. Maybe 160 or so sq ft and I finished 1000 be ft of rough poplar last year over several weekends. A couple hours. I wonder if a 64th from each side would remove any files or release agents and help glue bond.

[QueticoBill]

Another follow up. When I use xps in houses, I deliberately undercut it - leaving 3/16 of an inch gap or so all around, and then filling gap with foam in a can. Admittedly, preventing convection in a house is more important than in a tear drop but it would seem to add to the strength and lower stress on the skin to foam bond. I think bob in another thread we do overbuild, but just wondered.

[yrock87]

While we're on this, does the thickness of XPS - I think a full 3/4" but not sure - work OK with nominal 3/4" ply, usually a thirty second under 3/4"? I was afraid it could cause ply to bulge ever so slightly.

this is another reason I chose to rip my own lumber and stick build. I set the table saw to cut exactly the thickness of the foam. which was right at one inch. after the first cut I compared to the foam, made a small adjustment and was ready to rock. no bulging, sanding, planning, ext required. since the foam-ply bond was imperative to the strength of the whole assembly, I didn't want to sacrifice and get "close enough" and then try to get a quality bond with 1/32 gaps on either the wood or the foam.

[QueticoBill]

While we're on this, does the thickness of XPS - I think a full 3/4" but not sure - work OK with nominal 3/4" ply, usually a thirty second under 3/4"? I was afraid it could cause ply to bulge ever so slightly.

this is another reason I chose to rip my own lumber and stick build. I set the table saw to cut exactly the thickness of the foam. which was right at one inch. after the first cut I compared to the foam, made a small adjustment and was ready to rock. no bulging, sanding, planning, ext required. since the foam-ply bond was imperative to the strength of the whole assembly, I didn't want to sacrifice and get "close enough" and then try to get a quality bond with 1/32 gaps on either the wood or the foam.

So are you resawing rough or thicker lumber? I would like to use ply for the frame, and the thickness of that is a little more predetermined. Though I could use poplar like I did for a house project where I wanted to match the profile of 110 years ago and bought a stack of rough cut.

[yrock87]

I ripped select 2x6 (1.5x5x5) down to the thickness I needed, 1 inch. That game me 1 inch thick by 1.5inch wide framing.

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