What is the best skin to put under canvas?

[mikeschn]

So I think we've ruled out coroplast under canvas. So I'm starting a new thread with the question, what is the best skin to put under canvas?

It's not for structural reasons... we determine a long time ago that structurally, canvas over foam is plenty strong.

It's for aesthetics.

On my mad dash it's very clear to see where the plywood edges end, and the foam begins. It'd be nice to get rid of that, and let the side be one smooth continuous surface.

Is the answer a real thin sheet of plywood? Or is there something better? I certainly don't want to sabotage all the benefits of using foam!

Your thoughts?

Mike...

[ghcoe]

I think that canvasing is like paint. The better the application surface is prepared the better the covering application outcome.

At this point I think you are going to have to use a filler of some sort to fair it out. The canvas canoe guys use a lapping or mastic compound https://www.youtube.com/watch?v=JoEUPHG9BfM. I did a lot of fairing on my build before the application of canvas with Fast and Final drywall filler layered with Gipper primer between coats. I have not used any wood in my construction outside of the floor and some internal floor supports. Foam and wood have different expansion/contraction properties so what ever is used needs to be flexible to a point.

DSCF3727.JPG (154.22 KiB) Viewed 1606 times

[KCStudly]

Despite all of the fairing work I did using light weight vinyl spackle prior to starting to glass TPCE, I am still seeing very slight variations between my roof foam and the embedded roof spars. Depending on temperature the foam expands at a different rate from the wood.

I'm not sure how that will be once the roof is fully glassed and the bodywork is done, but I can live with the result either way, whether it stays fair or projects thru with temperature changes later.

I would be tempted to experiment with GPW's suggestion to use chip board as a more stable and fairable base. The only draw back I see is the stock sizes that are readily available might result in more seams to deal with. Also, you would want to compare pricing and see if it really ends up being cheaper than plywood.

[Alan_H]

So I think we've ruled out coroplast under canvas. So I'm starting a new thread with the question, what is the best skin to put under canvas?

It's not for structural reasons... we determine a long time ago that structurally, canvas over foam is plenty strong.

It's for aesthetics.

On my mad dash it's very clear to see where the plywood edges end, and the foam begins. It'd be nice to get rid of that, and let the side be one smooth continuous surface.

Is the answer a real thin sheet of plywood? Or is there something better? I certainly don't want to sabotage all the benefits of using foam!

Your thoughts?

Mike...

Mike,

Good question. Are you looking for future reference purposes, or how to fix yours?

I'm not building a foamie, but I plan to skin my TTT with 1/8" Luann and then apply the canvas over that. I would imagine that if you will be skinning over anything, the substrate, whether it be wood or foam becomes irrelevant. The 1/8" Luann is light enough, IMO, that it will still retain the weight savings of the foam, but still give you a nice flat and stable surface for the canvas to adhere to, and not show imperfections and joints.

However, I don't have any experience with the chip-board, nor do I know a source that I can get it in 4' x 8' pieces to avoid seams in a normal build.

[mikeschn]

Hi Alan,

Future reference.

I'll probably build another foamie in a year or two... and I'd like to keep it light, smooth, and seamless...

Mike...

[Alan_H]

So.... I started looking into this Chipboard stuff again. Uline carries it, however, they come in .022, .030 and .050 thickness. .022 is available in 48"x48", the other two, the biggest is 40"x48".

Just doing a little keyboard thinking here.. (I guess that's like thinking out loud on a forum )

Would .022 be thick enough to not curl up when applying "the mix" to weatherproof it? This stuff is made from recycled paper.

Alternatively, with the 40x48 sheets moving up to .050 there would be a lot more seams to contend with. Would this be an issue when covering with PMF? For one thing, the PMF would probably telegraph the seams through, unless some extra filler work is done to seal them prior to application.

I guess this would be a lot lighter than .125 Luann, but the next question... would it be too light to do any good? and does the extra work of seam-sealing justify the weight savings.

Another downside... ordering from Uline... 250 sheets to a case fir the .050 or 425 sheets for the .022. Even if I need 30 sheets, then I've got a whole lot extra on hand for other stuff....

[KCStudly]

Okay, so I went ahead and committed to fiberglass for the outer skin on my build, but I did experiment with PMF. What I found was that they actually weigh virtually the same.

The other thing I have learned is that foam is one of those "pay me now or pay me later" things. If you want it smooth, no matter what you do you are going to have to work for it.

My tactic has been to get the foam as close to smooth and fair as I could using the lightest weight materials that I could (foam, GS, and spackle) before going to something heavier (epoxy/epoxy fillers, glass and primer fillers to come). Where the glass layers overlap I can either sand the extra layers to fair, or add fillers where there aren't any extra layers (depending on how I staggered my seams... I want at least two layers of 6oz cloth).

While it has been said that you can sand the canvas and glue, I have doubts that it can be made as smooth as sanding the much harder epoxy (I haven't tested this myself). So to fair canvas seams, plywood seams, and chipboard seams, it means you are probably going to have to add fillers.

I know FG isn't for everyone, but at some point, if you want a finer finish over foam, it starts to make more sense. If I had started working with it sooner I would have probably skipped all of the troublesome work trying to get the foam and spackle smooth... it was so delicate that I often found myself doing as much damage sanding, and got into a do-redo loop... and just started with a hard coat of fairing filler and epoxy. That would have given a stable hard base right from the git go and made the cloth and fairing operations to come go that much quicker.

Just saying. Smooth ads weight, no matter how you slice it.

[ghcoe]

When I faired out the foam on my build I used Gripper to create a sanding barrier. Gripper does not sand well with the lighter grit sand paper. I add filler over Gripper and then sanded the filler smooth. Once I got the filler sanded to where I wanted it I would apply another coat of Gripper before adding more filler and sanding. That way the work I just did would not be sanded away with the next sanding.

[GPW]

Just a couple ideas ....
1. Heavy weight brown Kraft paper which comes in wide rolls , and is fairly common ... it does wrinkle when applied damp , but shrinks tight as a drum while drying. ( same material as chipboard and plywood--- cellulose) We used it on model plane wings for years , over beaded foam .
2. Using smaller , thin chipboard pieces with staggered joints for strength , and the seams filled and taped ... like drywall ... which can be finished very smooth ...

And there is always the Third option which is adopting the Foamie “Code of the road” and accepting certain common traits of foam construction, like seams , and overlaps ... What would be considered imperfections on a “wooden teardrop” or extremely smooth on a tent .... A Foamie is NOT your usual trailer , but is a Light , easy to tow, easy to make and inexpensive alternative to the status quo... I do believe the secret is coming up with a snappy paint scheme to “disguise” anything annoying to those cursed with the critical eye.

[mikeschn]

Glen,

That Kraft paper sounds interesting. will it hide the joints that I am trying to hide?

It's certainly weight effective.

Have you ever played with that on a teardrop? Got pics?

Mike...

[GPW]

Not on a TD , but on many hot-wired RC plane wings ... It hides a lot , thicker paper the better .... Years ago a dept. store here went out of business and i bought a large roll of Heavy kraft paper ... It was at least 4 times as thick as the regular Kraft brown paper. Great stuff !!! Wish I had several more rolls ... It was too heavy for planes , but great for other projects ...
Curious , just like the thinner Kraft paper , if applied damp , shrunk tight as a drum when dry ...

I know it must seem silly using paper , but as we’ve said many times before , it’s the same material wood is ..... Cellulose !!! And it’s lots easier to waterproof too ...

[mikeschn]

So is this 75# paper enough to hide all the imperfections underneath?

It does come in 60" wide rolls, so there are no seams!

http://www.papermart.com/extra-heavywei ... =4604#4604

Mike...

[GPW]

That looks like some Serious Kraft paper ... But as you know Mike , it really needs to be tested before being confirmed “foam-worthy” .. Can you get a sample , surely they’ll send you some to see/feel/ try out ... ?
Actually , I’d like a roll of that around here in the studio ... all kinds of uses ...

[KCStudly]

I was unclear about how the paper weight standards worked, so I did a little search. This link helped clarify it some for me.

I'm not sure that the 75 lb. index or cover weights will smooth things out nearly as well as the chip board. Perhaps a few layers glued up and sanded with fine paper to prevent tearing?

Though having it on a roll and 60 inches wide is a big plus.

[GPW]

I’ve just got back from looking all over and we’ve seen a strange market ..... Either you can buy chipboard in small sizes for reasonable prices , or you can buy it on giant rolls that weigh over a ton ... But nothing in between ... (that we’ve found as yet) I do clearly remember when I worked at a frame shop as a kid we’d frame oversize pictures and maps and we’d use chipboard as a backing , and it came in 4X8 sheets ... But that was some time ago ...