Sandwich everything - talk me out of it.

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Re: Sandwich everything - talk me out of it.

Postby Philip » Thu Aug 15, 2019 9:19 am

If your going with any foam. Most likely you will need a foam hot knife. Most all foam will need trimed some where. A razor knife will handle sizing. It will not handle any over size thickness problems. All foam sold as half inch is actually around 5/8" thick.

If you use fiberglass. The outside ply could go down to 1/8". All the outside ply is doing is forming a mold to build the hard shell on. I would have used 1/8" ply on my build if I could have gotten it local. All I could get was 1/4" without driving 100 miles one way.

The down side to fiberglass is the sanding to get a smooth finish. If you can glass the walls before assembly makes its a lot easyer to glass smooth with little to no sanding.
Here is my build.

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Re: Sandwich everything - talk me out of it.

Postby Squigie » Fri Aug 16, 2019 12:38 am

I know this isn't quite the right place for this, but I also didn't think a new thread was warranted. ...And I'm not starting my 'Build Journal' until I have a design set.

Anyway...
I tested a minor assembly today. I did not like what I saw.
Afterward, I did a high-dive into the depths of the interweb (in the few additional moments when I had the time), which prompted me to do some examination and testing.

The "Poplar" that I've been buying is actually Cottonwood (one piece) and Quaking Aspen (the rest of it)!
Too soft. Too rot-prone. Too wrong for longevity.

I do not see myself using "Poplar" in this trailer, now, unless I can trust the source (which I can't, yet). I'd rather use pine. I have a lot of experience with the above wood families and I no longer trust "poplar" for this application.
I think I'll be turning to oak where it matters (attachment/mount points, etc.) and possibly pine where ultimate strength and screw-holding ability aren't terribly important.

We'll see how that plays out over the planning stages... :thinking:

In other news, I found supplier of 4x8' 1/8" plywood (rather than 5x5). They even let me play with their product. There was the traditional Baltic Birch. But also "Oak". It didn't look like oak, smell like oak, or feel like oak to me, and had a 'Made in China' label on it. I'm not sure that I trust the oak; but at least there's another supplier on the table.

We'll see how things work out.

If I do go with Oak in any fashion, that will make weight an even bigger factor to keep in mind. (Oak's weight penalty, vs "Poplar" is about 50%.)
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Re: Sandwich everything - talk me out of it.

Postby S. Heisley » Fri Aug 16, 2019 6:57 pm

Both Quaking Aspen and Cottonwood are members of the Poplar family, Populus. It is the wood used by cabinet makers for structural skeletal strength. As you already know, it is lightweight; however, when choosing your poplar boards, try to stay away from any with large amounts of green or brown coloring as they tend to weigh more. Poplar wood harvested from higher, cooler areas grows faster and lives longer than in the hot areas, where it grows slower and has a shorter life. (Supposedly, the faster a tree grows, the softer the wood.) However, it's anybody's guess where your wood is coming from. I used poplar in my build and did not have any problems with it. (I am also happy with my sandwiched walls.) Most of the strength of your build comes from the whole unit, not from a few pieces of wood.
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Re: Sandwich everything - talk me out of it.

Postby Pmullen503 » Fri Aug 16, 2019 7:14 pm

Nothing except perhaps treated wood will hold up in trailer construction if it gets wet and stays wet. The prevention of water intrusion, and the draining and drying in areas where it's unavoidable like around doors and hatches is more important than which species of wood you use.
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Re: Sandwich everything - talk me out of it.

Postby tony.latham » Fri Aug 16, 2019 9:57 pm

Too rot-prone.


C'mon! When was the last time you saw wood rot in Idaho Falls that wasn't sitting on the ground? Sure, it might blow into the next county, but it doesn't rot.

:oops:

T
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Re: Sandwich everything - talk me out of it.

Postby Squigie » Fri Aug 16, 2019 10:21 pm

tony.latham wrote:
Too rot-prone.


C'mon! When was the last time you saw wood rot in Idaho Falls that wasn't sitting on the ground? Sure, it might blow into the next county, but it doesn't rot.

:oops:

T

WHAT?!
Can't hear you through this wind!
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Re: Sandwich everything - talk me out of it.

Postby QueticoBill » Sat Aug 17, 2019 7:27 am

I bought a lot of poplar from these folks: https://www.bellforestproducts.com/ - like a 1000 bf - for some custom trim. Good people, great product. Very straight and clear and not at all prone to twist, and mills so nice. A fraction of the cost of local stores and loved being able to plane to precise thickness, and certainly worth having the planer. 10' pieces by UPS.
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Re: Sandwich everything - talk me out of it.

Postby Squigie » Thu Aug 29, 2019 11:15 am

tony.latham wrote:Why the 1" skeleton in the walls? Why not 3/4" (CDX)? (And by the way, 3/4" foam is sometimes hard to find. But there's a pile up here in Salmon.)

Thankfully, there's no need to drive to Salmon.
I finally tracked down some 3/4" foam. It had to be ordered, but not as a full (or half) unit. The company already has a truck coming from Boise tomorrow, so there's no charge for shipping.

That was my last chance for something local - a garage / overhead door company, which I just remembered to check with this morning. (A couple of their trucks have Corning pink panthers on them, even though they don't advertise insulation. Worth a shot, right?...)
Otherwise, the next place that "thought" they could get some was in Salt Lake City, but I'm rarely in SLC with the means to transport building materials.
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Re: Sandwich everything - talk me out of it.

Postby friz » Thu Aug 29, 2019 3:53 pm

Mines kind of an open face sandwich. Starting from the outside: fiberglass and resin, 1/4 marine ply, resin, glue, 1/4 fan fold foam, fake suede headliner. The foam and headliner do a good job of insulating. As long as we are pulling air through the camper the suede stays cool to the touch.Image

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