"The X-Cubed" C.T.T.

[KCStudly]

If you have nice flush foam to wood frame you can roll a thin coat of TB2 on the foam and get a good bond between foam and wood. I have found that the trick to getting the glue to dry (the foam does not breath) is to only use enough glue that the wood can take all of the moisture. Big puddles or runs will not cure because the wood can only take so much before it is sealed, then the rest stays gooey for a very long time.

With a very thin coat of glue, the wood takes all of the moisture and you get a great bond, so long as you have nice uniform pressure... from something like a vacuum bag set up.

[absolutsnwbrdr]

Sounds like a good idea

I'll load up the wood framing with glue, then pour some on the insulation and spread it around evenly. I don't have anything that would work for an oversized vacuum bag though, so I'll just have to put some weight in the middle of the larger foam areas.

[capnTelescope]

I was concerned that with PL premium added on the side of the foam, that it would bulge a bit when skins were added. Am I worrying needlessly?

No, you're not. If you remember from by build thread, I had to knock my HD insulation down in thickness a little. Even then I had one area, that I didn't point out, that caused the interior ply to gap from my framing. I'd say check with a straight edge before you glue.

I don't have anything that would work for an oversized vacuum bag though,

Go to Target and get a couple of queen size air mattresses, turn them inside out, duct tape together, put in your wall and suck hard. I was trying to do that, and failed on 2 attempts to do it right, but it's "technically feasable." About $30 for the two, total.

good luck.

CapnVacuumBag

[KCStudly]

Read it again ^. I highly recommend against slobbering on the glue anywhere, even the wood frame portion. This will squeeze into the foam areas and create wet spots.

Use a paint roller and tray, and roll the glue on everything in a very thin coat; you might even call it a "dry" coat. Avoid lines of glue pushed up from consecutive rolls with the roller, that's too much glue!

Just a very thin even coat, transparent, no puddles, no lines, no drips; please. You will be rewarded.

Do a couple of tests for yourself using scrap. Slobber on, cut the back out after two days and you will find gummy goobers. Roll on very thin, allow normal time to dry (overnight), cut a chunk out of the back and you will find a veil of foam that can not be separated from the wood without mechanically scrapping. Using the roller method I found the bond between foam and wood using TB2 to be quite impressive.

[capnTelescope]

I'm gonna upset the apple cart and ask "Why glue the foam board in the first place?" I didn't and might be able to supply the answer eventually, but it's not going to rattle, is it? When you're going down the road, you won't hear it even if it does. When you're camped, the trailer isn't moving enough to create a rattle, IMHO. It's well captured, so it isn't going to escape.

It does seem like the thing to do, but is it really necessary?

Just askin'.

CapnHotAirBag

[Kharn]

I vote for not gluing the foam as well, or, just gluing one side of it. You also don't want it to pull the wall panels together and create an oil-canning-like effect.

[KCStudly]

By unitizing the skins with the foam the strength goes up tremendously. By stabilizing the outer skins they are much less prone to buckling (even minutely) under load.

Just like an I-beam, it is the outer fibers that do the work and will fail first. By attaching the two skins with a central core (like the web of an I-beam) you are essentially making one member with stable outer fibers that are further apart, instead of two unstable diaphragms with each of their own fibers relatively close together.

Sure, not gluing the foam may be good enough, but by gluing it you get more strength out of lighter materials. For the sake of a few dollars worth of glue, and a few extra minutes of time, IMO it is very worth doing.

[Martiangod]

when I glued my foam, used water based flooring adhesive, not thick like pl

[absolutsnwbrdr]

I like KC's method to create a SIP. Not because of the insulation panels moving around - they're all wedged very tight and are flush with the faces of the framing. And not because the trailer walls require the added strength - I'm sure it would be fine with just the 3/16" skins glued and brad nailed to the framing. But since I have the opportunity to do it, I might as well. It might cost a little bit more because of the additional adhesive used, but in the big picture the added cost (in labor and $) is a drop in the bucket. Since the insulation is flush with the framing there shouldn't be any oil-canning effect.

Another reason to glue the insulation that I just thought of - I have my wall frames designed to accommodate mounting the shelves & bulkhead, but that's it. Anything else added only has the 3/16" to attach to. If I decided I need to attach something else to the wall... like a cup holder, or rails across the interior shelf, or whatever... attaching with screws into the 3/16" skin would probably be ok. But the skin being glued to the foam behind it will make a big difference in the long term.

when I glued my foam, used water based flooring adhesive, not thick like pl

I'll have to look into that....

[KCStudly]

You can also drill holes and glue hardwood dowels in for mounting/screw locations. Provided whatever you are mounting will cover the foot print of the dowel, it would look fine. Even screwing in to the end grain of a dowel is better than just the thin ply. I suppose, if you are averse to screwing into end grain... the cheap dowel at big box is not truly hard... you could make thicker plywood plugs to glue into the drilled holes and screw into those.

I spent a great deal of time planning out blocking locations for light switches, light fixtures, coat hooks, pillow lights, fenders, side tables, etc. and even longer pocketing them out with a router, then gluing blocks in ahead of the skin, fairing, etc. It became quite tedious, but may have saved some weight in the end.

[capnTelescope]

You can also drill holes and glue hardwood dowels in for mounting/screw locations.

I like that idea. Actually a time-tested method of fixing a stripped screw hole. Works for both wood and foamie construction. Drill a pilot hole & don't worry about screwing into end grain, unless your cup holder weighs a ton. Then plan ahead. The foam isn't going to add any significant screw-holding power. Compare to screwing into drywall. Also, I think the skin-framing-skin construction is much like a torsion box anyway, so good and strong on its own. But in the end, do what you think is right. I didn't even let the cost of glue enter into my thinking.

I'm sure it would be fine with just the 3/16" skins glued and brad nailed to the framing.

Actually, the brads are there just to hold it together until the glue dries. Like me. Maybe that's why they call them "Brads."

[absolutsnwbrdr]

My friends wife let him come out and play again yesterday and we got quite a bit done! An extra pair of competent hands is always a huge help. We started by rough cutting the 3/16" plywood skins for the inside face of each side wall. Then using a 6" foam roller we spread glue over one section at a time and brad nailed the panels into place.



After letting the glue set up for a short time we took the router and trimmed out the door openings and around the edges.





Then we attached the side walls to the frame using (4) 2" carriage bolts for each side. I also through a couple 2-1/2" deck screws into the floor framing to draw the walls in tight in a couple places. Then double-checked that the angles at the front were correct.

After dinner I got to work on the lower bulkhead. Its essentially two rectangular frames that get skinned on each side. The void in the middle is a wire chase. The cabin-side is skinned in the picture, but the galley-side skin will have to wait to be attached until the galley shelf is installed. That way I can keep all the pocket holes hidden.



A little blurry, bit this the interior view. The 1x3 laid flat that resembles a small shelf is actually the bottom of a horizontal wire chase. You can also kind of see the rectangular cutout panel in the floor, at the base of the bulkhead, which gives access to the vertical wire chase.



I'll build some removable panels for the openings, but the openings serve a couple purposes: doggy door, air-conditioner location (only when needed), and i'll be able to slide my 10x10 canopy through there for transport.

Hope to get a little more done today!

[KCStudly]

Your prior planning is showing with each and every step. Good man!

[Martiangod]

The fun of the build is going to be over too fast, then you will have to go camping instead of building. Your setting quite a pace.
Looking good as ussual

[absolutsnwbrdr]

Thanks guys! Things are moving along pretty well right now, but eventually I'm going to reach a point where I can't really do too much more until I sell the X-II. All this wood is relatively inexpensive, but its all the big-ticket items that are going to hold me up.

This afternoon I shifted focus from the bulkhead to the front. The front area is definitely the toughest part of the whole build. Even with everything drawn up in AutoCAD, getting the compound miters just right slowed me down quite a bit. This is the first time I've ever had to make them, so its been a learning experience.

Started with the front wall....







Decided the angle corner sections needed to be built from the inside out, so I started with the skin instead of the framework.



But its starting to look like something inside!



Thats all for tonight. Need to get back to the season finale of Walking Dead....