Possible woody wall for foamie??

[R. W. Alexander]

Ok, these are the changes I made for the foam wall. I got some 1/8" ply for both sides of the side walls. I will make a SPS panel, and then I will glue the
cedar strips to the 1/8" wall. This should make a very lightweight and strong wall.

[OP827]

Here is the components for "the mix" I used: spar varnish(polyurethane based) and/or Minvax polyurethane and oil paint solvents like mineral spirit and/or recordsol(same stuff). I did the same test as GPW did above here. The photo below shows that the foam does NOT dissolve by these solvents, minvax or spar varnish mix within half an hour or so as the mix and solvent dry:



But when I had used this very same mix on the trailer build last year, the mix apparently remained wet for an extended period of time as I put some generous amounts on the surface of the internal compartment made of baltic birch. Some of the mix had leaked from one compartment towards the foam. It hapenned only in one out of three compartments and within a few days the foam started to soften in the area outside of that compartment bottom. It must be noted that the foam did NOT dissolve like if it would be by an acetone. It just started to loose its rigidity and became "spongy" and structurally unsound to the point that I decided to remove the damaged soft foam area and replace it with the great stuff foam. See below the finished repair area already covered with fiberglass:



Since we started this discussion I decided to look up the XPS chemical resistance properties of XPS foam online and found one refence where it has a table of chemical resistance of Polysterene foam against various hydrocarbons, not exactly mineral spirits, but petrol and diesel are close enough to it, see it on Page 3 of this document - http://www2.basf.de/basf2/img/produkte/kunststoffe/styrodur/downloads2/en/styrodur_chemical_resistance.pdf

Looks like the XPS foam may not get the effects of mineral solvent exposure immediately, but when, like in my case, the exposure was long enough, the damage in a form of softening can appear.

Hope this information will help others on this forum.

Cheers everyone!

[OP827]

Ok, these are the changes I made for the foam wall. I got some 1/8" ply for both sides of the side walls. I will make a SPS panel, and then I will glue the
cedar strips to the 1/8" wall. This should make a very lightweight and strong wall.

If glued properly, this will produce a substantially stronger than a present day commercial trailers filon+foam+luan typical sandwich wall. It may not be lighter though.

Back to protection from weather, I would personally still protect the wood with epoxy and glass cloth like they do on wood canoes. I just got the feeling that w/o fiberglass or canvas any wood with any paint cover, no matter how good it is, the expansion and contraction of wood would eventually manifest small cracks on the surface. Subject to weather exposure, of course, and YMMV.

[GPW]

If you have all that wood , you really don’t need the foam then eh ???

[OP827]

If you have all that wood , you really don’t need the foam then eh ???

Oh No , I do need foam GPW, but I am open to hear your and all others ideas on this board about how a trailer build could be made ligher and stronger, please do share. That is why I am still here. The thickness of wood you see in the picture is only 1.5 inch deep to attach access doors. After that it is 3mm or 4.5mm think plywood for compartments that hold items inside as batteries and gas bottle, so that bumping them into the wall will not create a hole in the foam.

[OP827]

Tested just now ... Four different foams ... First coat of pure Mineral Spirits , then a dab of pure Poly ..... Although you can see pooling of the poly there is no signs of any melting ...

GPW, may I ask you to do the same test, but cover the pools of your solvent and the mix with polyethylene for about a day or os and then and report the results?
In my tests from yesterday I noticed slight caving in from dried out mix. It is nowhere close to acetone damange which would just it the whole peace, it is like some heat was melting the foam, but left the foam softer than before. I would like to find out why we now have different results.

[GPW]

“ so that bumping them into the wall will not create a hole in the foam. “ ... You know , in these many years we’ve never ever heard of that happening , even with Eagle’s grand kid who was a “kicker” ...
Why do so many people underestimate the strength of Foam ? ... Must be some erroneous preconceived notion ... certainly testing and experience proves otherwise ... except for Bears and flying Frozen turkeys of course ...

I’d suggest if YOU are getting negative results from your testing , then you should change your Materials , or methods ... No use in me testing it over again ... I know my stuff Works !!! Used on 3 trailer builds already ...

[OP827]

Below are my test results of the XPS foam chemical resistance from
1) Undiluted Minwax polyurethane,
2) Recordsol paint thinner for oil based paints,
3) Mineral Spirits.

All the chemicals were put on the same piece of foam and then covered with polyethylene film. After two or three hours of such exposure, the XPS foam started to dissolve from Mineral Spirits and Recordsol, while MInwax did not visibly affect the foam. See the photo below.

[KCStudly]

Seek out the SDS (MSDS) for the Recordsol and I bet you will find that it includes some sort of chemical solvent.

[OP827]

Recordsol amount was bigger than Mineral Spirits, but the damage is only slightly bigger comparing to Mineral Spirits. Recordsol seems to be little bit more agressive to XPS foam.

[OP827]

Seek out the SDS (MSDS) for the Recordsol and I bet you will find that it includes some sort of chemical solvent.

Yes, you are right about that KC, Recordsol has 10 times more Aromatics, here is the difference between Recordsol and Mineral Spirits explained - http://www.recochem.com/us/products/cleaners_degreasers/odorless_mineral_spirits

[GPW]

At the store , there’s always the choice between the Pure Mineral Spirits , and “paint thinner” which contains Mineral Spirits , and something else ( and is cheaper ) ...
I always pay the extra for the Pure MS , because I also use it for my Oil Paintings ...

[R. W. Alexander]

I did a test piece on some foam for a possible woodie wall. I did canvas on foam with a 3/16" thick wood exterior, using titebond II.
And another piece without the canvas. Both test pieces were good, and strong
The wood to foam is more than strong enough for my build, plus I can save weight by not using the 10oz. per yard canvas on the outside.