ultra compact slide in / sleeper

[rruff]

Maybe I'm not seeing it well in that photo? What I see is a very thin layer on both sides, with a thick filler center.

No, I just pulled one apart and measured. Each layer is 1mm of the same wood, the center is just turned 90 deg. Compared to the luan I have which is a thick center and paper thin faces.

The ply is very nice and light is fine too, but the glue that bonds the plies doesn't seem to be waterproof, and the poor bonding to one of the core faces is certainly unacceptable.

 

[IdaSHO]

Yeah, finding such problems with a material is never fun. And I agree, it is 100% unacceptable.

Assuming you are pushing the way of epoxy and glass, one could argue that waterproof glue isnt needed.

But the adhesion problems between the core and the ply is hard to swallow.

 

[rruff]

rruff, if you have the inclination and the supplies handy, I'd be curious to see how a luan panel with a single layer of fiberglass (6 oz cloth say) would fair against the full fiberglass panel in screwdriver test.

Done! I happened to have some very old epoxy and some Bondo cloth (~5.5oz), so I laid that on the 2.7mm luan with 15psi XPS underneath. Bomber. I can't ram a screwdriver through that either.

I also laid 3 layers of cloth and epoxy right on the XPS. That was easier to penetrate than I expected. I think what is happening is that the weak foam does not support the fiberglass very well. Either the fiberglass over the honeycomb core, or fiberglass over wood over foam is better. Still the 3 layers of fiberglass over cheap foam was significantly better than just luan over the same foam.

I'm still undecided on how I want to do this. The fiberglass-honeycomb panels from Carbon-Core should be quite durable, but the panels alone would cost $3500 with shipping. And I'd have to do a lot of fiberglass cutting and scarfing and bonding, and reinforce the panels for attachments. And I'd have fiberglass interior, which I don't really want. Option 2 would be their PVC or PE foam which would cost about half that (but ultimately no cost savings), and I do the exterior fiberglass and interior plywood myself. It might be more work but not a lot, because I'd build the window and door frames and hard points, plus a wood perimeter frame in the panels. Just screw and glue the floor, roof, and walls together when I get them done, and go over the edges with fiberglass. The upside is that I wouldn't need to do any fiberglass cutting, and I'd get the plywood interior.

My original idea was to build with cheap foam and redwood stringers in the core, with plywood face sheets, and an outer layer of fiberglass. This is similar to option 2 above except I'm using cheap foam (vs structural foam) and exterior plywood+fiberglass skin instead of just fiberglass. The downside is that the outer ply will be susceptible to rot if I get leaks. But I know this will be strong and tough otherwise. There is a big cost variation depending on what plywood I use. 3mm Okoume would end up almost as costly as the Carbon-Core options, while luan would be about $1200 cheaper. One advantage to this approach is that I can build the panels in my cold garage using PL Premium to bond everything together. I only need warmer temperatures for the outer fiberglass layer.

Decisions...

 

[Gunner207]

Only separation from the core. The strongest and lightest exterior would be vacuum bagged one price exterior of glass or more expensive reinforcement in epoxy.

 

[Gunner207]

Try to find 3mm meranti plywood, sometimes under the trade name hydrotec. Much less then okoume and when encapsulated in glass it is just as good. . This boat was cold molded with 3mm meranti 7 years ago, only the bottom is glassed, the sides are epoxy primer and one part paint.

 

[rruff]

Try to find 3mm meranti plywood, sometimes under the trade name hydrotec.

Funny you mention that, I just spent a couple hours looking for 3mm meranti online. Still none whatsoever. The thinnest is 4mm, which weighs 18-21 lb/sheet. 3mm Okoume weighs only ~8 lb/sheet.

 

[IdaSHO]

I dont thin kIve ever seen a 3mm Merranti


4mm Okoume is just 12# per sheet

I use the 6mm Okoume for exterior skins. Its just 18# per sheet.


And you can find some 3mm here:

http://boulterplywood.com/MarinePlywood_4.htm


Lots of fun info on that page as well. :ylsmoke:

 

[rruff]

Yes, thin Okoume is easy to find, but I can't find Meranti in less than 4mm. It isn't a big deal though. Meranti is stiffer, stronger, cheaper, and more rot resistant, but also heavier than Okoume.

 

[The Artisan]

2.7 work for ya?
https://www.ctscabinetsupplies.com/...mcode=3BB18&category=&department=37&class=37P
Kevin

 

[rruff]

2.7 work for ya?

Have you seen it? Obviously not marine ply. I've seen cheap 2.7mm Meranti listed elsewhere too, but I suspect it's the same as the luan sold at HD. Thick core and very thin faces.

 

[Gunner207]

Just realized what I typed. Sorry that I sent you on wild goose chase, I meant 6mm. My point is that strength of the panel comes from several factors. Such as skin stiffness as well as the thickness of the core that separates the two skins. Think of the web of an I beam as the core. Skins with identical physical properties greatly reduce the forces of shear along the skin to core glueline. Of coarse the foam has a much lower density then the wood or fiberglass skin and the panel will be stiffer for any given weight with a thicker core. A thinner or lower density core could be used with thicker skins to produce a panel of adequate strength, no thermal bridging, better fastener holding, etc.

There would obviously be a weight penalty, but based upon design and vehicle it might not be significant.

Even 6mm aquatek is only 45-50 bucks a sheet. So with a less expensive foam of say half inch you get a 1 inch panel that weighs around 50 lbs. A 1 inch composite panel with 18 oz wet laminated glass is close to 29 lbs.

More to follow......

 

[Gunner207]

That would take my little slide in up to about 500 lbs total structure.

Switching to okoume 4mm skins saves 18 pounds a panel and costs 20 bucks more. Probably money well spent. The 13mm PE foam core costs an additional 60 a sheet.

Another option would be coosa board or carbon core structural fiber reinforced foam without skins, build the structure then have it rhino lined by a roofing applicator.

 

[The Artisan]

Have you seen it? Obviously not marine ply. I've seen cheap 2.7mm Meranti listed elsewhere too, but I suspect it's the same as the luan sold at HD. Thick core and very thin faces.

Sorry no just did a quick search for it for ya..
Kevin

 

[rruff]

I was planning to get marine ply from Noah's. 6mm Meranti for the floor (2" sandwich), and 3mm Okoume for the walls and roof (1" sandwich). I don't know if B/BB grade Aquatek is adequate, but the 6mm is only $38 plus 10% off at 10 sheets, and 20% off at 30 http://www.noahsmarine.com/ItemMatr...d&selelement4=undefined&selelement5=undefined. 3mm Okoume (Lloyd's) is $46 with the same discounts. http://www.noahsmarine.com/itemdesc.asp?ic=EURO3 Shipping is reasonable compared to other places I've looked, ~$1/lb.

You'd like to have panels that aren't easily penetrated or broken by impacts. This implies reasonably thick and sturdy skins. Bending stiffness (core thickness) can work against you here, since a large object impacting a rigid wall will break it, while a more flexible wall will bend. Insulation value is another consideration, which you can get with a thicker core.

My floor bolts directly to the bed mounts on the frame so there will be quite a bit of cantilever to the edges which support the walls and roof. I'm not sure if 2" thick is overkill. One consideration there is that I can't get 1.5" XPS locally (only 2" or 1"). I want enough flex to deal with frame twist since I'm not using a pivoting mount. On the walls and roof 1" core with 3mm skins will be adequate, and I don't want to go thinner core for insulation reasons.

On my build I estimate ~90 lb of plywood in the floor, and ~198 lb in the rest of the camper, with a total shell weight of ~630 lb. Using 4mm Meranti vs 3mm Okoume would save basically nothing (higher shipping would cancel the lower price), and add ~250 lb to the weight. It would definitely be stronger, but I'd rather have the lighter weight.

 

[The Artisan]

rruff how large is your camper?
Kevin