Canvas outside and 1/4" ply inside?

[dales133]

I used sheets over 3mm ply on my roof but its covered with aluminium.
I used canvas over 3mm ply on the rest and as far as looks,quality and just about every aspect id recomend canvas over sheets.
As they say the qualitys remembered long after the costs forgotten

[KCStudly]

From what I have read; some people have had trouble with cupping due to canvas shrinking (I think big Mike had this on his first attempt to pre-cover the walls on the Big Pink, IIRC, or maybe it was a prior attempt?); some people pre-shrink (hose down and let dry hanging or laying flat); some people have suggested taking the canvas to a commercial laundry mat and using the big machines there to pre-wash (tho I don't think they fully grasp how much yardage that would be... and I don't recall anyone reporting that they actually have done it this way); some people report that they didn't have any problem with shrinkage, that in fact it is a good thing... "the sock effect"... but, again, IIRC these were all people who built the box first and then covered (not 100/ct sure on that, so for what it is worth... I forget what the second thing to go is ); and finally, at least one person said that they bought pre-washed canvas (without sizing).

So, my point is, there does not seem to be any consensus. If in doubt, hose it down and let it dry in the sun to preshrink. IIRC, on his second attempt big Mike laid his canvas flat on his sealed driveway (I assume he swept or hosed it off well first), hosed it down with the garden hose, and then let it dry in the sun. I seem to recall a wall sized piece of canvas shrinking something like 9 or 10 inches over 10 ft. I can't imagine being able to get my driveway clean enough that the canvas wouldn't pick up dirt and debris, so if it were me, I would try hanging it on a line (or the big straddle hoist frame that my friend Karl has out at my build location).

I just had a quick look back thru the 10' Standie Foamie build (the precursor to The Big Pink) and was not able to confirm my recollection, so perhaps some one else can pipe in with a better memory.

[dales133]

I hung mine over my trailer frame and hosed it down.
Weve had some stinking hot days and very cold ones since i aplied the canvas with no adverse effects so far but then again its over thin ply and under cover

[rowerwet]

I canvas only after the walls are in place. Since I'm only applying glue and smoothing it in one three foot vertical stripe at a time, and then waiting to do the next stripe until the last is well stuck, my unwashed and unshrunk canvas doesn't get to shrink as it dries, it really never gets wet until being filled with paint, after the TBII has cured and it is stuck to the walls

[Don L.]

Thank you all.
It sounds like washing the canvas is more effort, but perhaps worthwhile.

Roweret, when you glued the canvas on how wet or sticky is the outside of the canvas? I am assuming you do not put a top coat on at that time. What I'm getting at is this, if I glued canvas to the wall while it is laying flat and it starts cupping as it dries maybe I could lay some boards over it and maybe some weight to keep it flat. That is as long as the boards don't stick to the canvas.
Your advice is much appreciated!

[rowerwet]

It gets lightly tacky in spots, mostly where a section overlaps another. I perforated my foam, then roll on enough glue to see every hole has a dot of glue on it, with bed sheets, this will soak through in most areas, for canvas it won't soak through much at all.
I would expect the fabric to relax when painted. Boards would stick, or cause wrinkles IMO

[dales133]

Yep i recon they would stick to.
Id apply the canvas when its all together,we know this works because its been done countless times.
Your proposed method might work flawlessly but its going to be a massive headache and step backward if it does bow as it dries.

[GPW]

Lotta’ If’s around here lately , I thought we worked all that out previously ...

[rowerwet]

Unlike epoxies, paints, and glues being used as intended, with millions in research, manuals that are fully researched, and tech reps to deal with the failures and odd questions, we are on the lunatic fringe or cutting edge. People tend to want a step by step guide before investing their money.
Those of us who have built, know what works for us, the rest are hoping for a step by step. To the experienced it seems we see the same questions over and over, to the firstop timer it's a big leap.
The real answer is, GO TRY IT OUT! make some test panels to answer any doubts.
Some results will be effected by your local ambient conditions, but it has been proven in almost every area of the US.

[Don L.]

No doubt I will try it out! I don't doubt that the system works, I have seen so many good looking campers and read lots of threads with varying methods and results. I have some small from panels 3' x 4' that I could experiment glueing canvas to but I don't think they will behave the same way as a 7' x 12' piece of foam if cupping were to be an issue. I would like to avoid a mistake that size. I appreciate and value everyones time and input!

[GPW]

Where did this "cupping" issue come from .... First time we've heard that one eh ??? Get the shovels out !!! Again !!!

[KCStudly]

No, not the first time. Just can't seem to recall where. For some reason I think big Mike saw this when he was experimenting with pre-covering prior to the 10 ft Foamie Standy/Big Pink.

[Don L.]

I thought I read a thread with something about warping, maybe cupping is my term for it. I don't need to know where exactly, was more interested in what y'all had to say about it.

[GPW]

I for one would like to see the comments on this supposed effect ... TRUE , you could (possibly) get warping to a degree by covering one side of a sheet of foam that’s unsupported , but I think we’ve worked out all these issues in the past ( the Big Thread , which newcomers are hesitant to read before “commenting” )
While we impose no rules on building , there are successful Procedures that should be followed .. Just as with ANY other material ...

I’m sure you could get a sheet of 3/4” plywood to warp covering it on one side ... so don’t blame the Foam ... Blame the procedure ...

Currently I’m preparing some 1/4” Masonite sheets for painting on ... ( Art) .. The primer (Gesso) states on the tub to paint both sides to avoid warping ... Clearly stated !!!
 
Note: I can visualize that a piece of foam supported between two saw horses , would already have a slight sag in the middle (gravity) and covering would only make that worse .... naturally .... Covering a finished cabin wouldn’t see much of a chance of that , well tested now , even with my 18oz. Heavy canvas Shrinking 6” (L) on the FoamStream ...

Due to the manufacturing process of foam sheets , you can see “WAVES" in the foam on some sheets ... Not to be confused with warping ...

[Don L.]

When you say Big Thread you mean this one 'Thrifty Alternatives ..Building Foam Campers ', right? It is a big thread! I have read lots of it, not all of it though.