Chuck, During High School I bought a used boat I think it was a Herters Duck Boat. It was plywood covered with canvas. A previous owner had put hot roofing tar on the bottom. I ran traps out of it one season, seemed to be an ok boat. I couldn't get it to stay put on the top of my Model A coupe!
I remember those Herters Duck Boats liked the looks of it but never saw one in person. Bought a ton of archery gear from them and a good amount of other stuff. One highlight of the year was when the inch thick catalog from them would show up , what a wish book.
Hey Chuck, I remember my dad getting that catalog every summer and I'd spend days as a kid looking at all the hunting stuff and decoys. Also. there were some old time decoy makers from the Chesapeake Bay in Maryland that made goose and swan decoys shaped with wood lathes and covered with painted canvas. Dave.
JD, since you are a fellow who is good at unbiased experimentation, I suspect that you may already have some data.
1. How much money could a builder expect to save by using this material instead od fiberglass and epoxy?
2. How much weight penalty would a builder expect?
3. How much strength penalty should be expected?
If I'm going to change materials or technique to make a gain in one area, I get cautious about having to pay penalties in other areas. Just seems to be a law of Life.
I do have some data but not near enough to draw many conclusions. You are correct about changes having consequences. Sometimes disastrous, sometimes for the better, and sometimes just not worth the work. A big factor in doing something "different" is figuring out what is good enough and/or is it worth the cost/savings.
1. I would estimate the cost of PMF (poor man's fiberglass) to be 50% or more less than epoxy/fiberglass.
2. Don't see a practical difference in weight. Only enough glue or epoxy is used to fill the weave. Which weighs more 6oz. fiberglass cloth, or cotton bed sheet? That difference couldn't be enough to matter.
3. One would think PMF would be weaker (and it probably is). One of the questions, is it strong enough? How and where we apply it can make a difference. More suitable as a waterproofing, protective and strengthening skin than used as a part of the structure. Think in terms of canvased covered strip canoe, not a Uncle John's pirogue that the fiberglass holds the floor to the sides.
Anybody have any experience with canvas covered canoes?
"Spererimation" still on going, but a couple things stand out.
Wood glue and/or paint primer will stick to foam insulation but not very well. It may be strong enough and has worked for some folks but I'm leery.
Glued cloth to wood is much better, but takes a couple days to cure to max strength.
Unlike fiberglass cloth, overlapped cotton cloth can not be feathered with the sander.
May be a project that works but one wonders if it is worth the effort.
JD, in my experience, many kinds of "cloth" can be bonded to many materials for imptovement of strength. I even repaired broken, plastic, table fan blades with epoxied strips of a cotton hanky. Worked for another 30 years.
"Unlike fiberglass cloth, overlapped cotton cloth can not be feathered with the sander."
A little more "spearimanting" has shown this can be overcome. Adding more glue over the seam/splice, letting it dry completely and then feathering it together with the sander makes for a smooth transition.
I tried to repair/reinforce a scarf joint in a plywood panel using PMF. It did not work well.
My assessment of the experiment at this time is, it will provide a water proof and scuff resistant finish. i.e. canvas covered canoe.
Fiberglass and epoxy will work better for providing structural strength i.e. striped built boats.
I may one day revisit this idea but right now I don't want to put forth the work needed to make it work.
Test are ongoing. These samples were glue up in Oct. 2018 and were left outside on the ground. Picture was taken 8/8/19 but little change since. No delamination or rot in the coated cloth or wood. Pretty impressive to me for unpainted bed sheets and pine plywood.
Yeah, it's kinda embarrassingly exciting to realize that I just learned a lesson - the SECOND time. Or, third. sigh But, it IS easier yo correct an error when building with wood. Especially before we've epoxied on fiberglass. Maybe even adding in a "new design feature"?
After sitting the boat in the sunshine many bubbles appeared under the cloth. This is not an issue with the paint. The glue has released from the wood and fabric. I do not know why.
I did have issues with drying because of the weather. Perhaps it failed to bond because of the long drying time, or because the glue was not under pressure while drying.
At this point I plan to use the boat as is. Even if the cloth fails the boat will still function.
Looking close up at those blisters, I can tell you that paint is not the problem. The paint held; the surface is not broken, it is still integral. The problem is something causing pressure UNDER the paint. A likely culprit is moisture. Moisture could contribute to both poor surface adhesion and gas pressure.
Jack that is my assumption and most likely the cause. Worst weather possible for building damp and cold. I foraged ahead and now I'm paying the price.
Despite the problems I think PMF may be a workable choice. It will not replace epoxy and fiberglass but could be an alternative with limitations. More will be learned with usage.
The coat looked robust; it was withstanding the pressure from underneath. I think that, under the right conditions of application, it could be a viable system.
You are an inveterate experimenter, and you report your findings unequivocally. You and Joey both do a good job that way.
Guys don't be too hasty to decide based on my results. You have to factor in my ineptness and lack of experience working with it. I am 99% sure the problem was caused by the extremely damp weather. The inside of the floor was done some time before the outside with no issues.
I will say fiberglass/epoxy is no harder to do if you are familiar with that process. I actually used 3 coats of glue (almost 2 gal.) to completely fill the weave, so this decreased the cost difference some. Probably could have gotten by with 2 coats and then finished the filling with paint.
My efforts were not successful but others have reported it to work. I would not use it for a design that needs the cloth as a structural component. It may offer a choice as a surface coating/fairing, but little need for that. Canvas canoe builders pretty much have that process down pat. The concept probably falls in the "It works, but why would you?".