PMF Failures

[Mark Gunter]

Hello All,

I’ve read (just a little) and watched videos (just a little) about so-called Poor Man’s Fiberglass. I’m just today doing the finishing touches to the canvas on my own build. When I’m done, I’m going to share my own experiences with it.

In the meantime, I’m very, very curious to hear about PMF fails. I’ve seen a lot of advice and warnings about how to do it, but not so much about the failures that have informed current accepted methods. So I’m hoping to get some response in this thread about PMF failures. In what way did it fail? What led to the failure? What would you do different if you were to do it again?

Did you saturate the canvas or other fabric with glue both under and over? Did you just glue the fabric down then saturate with paint? Were there problems with shrinkage over time?

I hope to get some horror stories here that may help myself and others.

Or, perhaps, there are no horror stories to be told. In that case, PMF really has a damn good track record. Note: I’m not really interested in hearing the virtues of Fiberglass vs. PMF, I’m very familiar with fiberglass work, what’s new to me is PMF and so far I haven’t heard the horror stories.

[Pmullen503]

I rolled TB2 (thinned 10% with water) on the foam and back side of canvas. Then applied the canvas and smoothed out the bubbles and pressed the cloth into the glued foam. I worked in about 2 ft sections at a time, unrolling the canvas as I went. Then I rolled on another coat of the thinned glue. After it dried for a few days I painted with latex paint, 3 coats.

It's been 10 years and the only failures have been a few bubbles. Those were reattached by putting a wet cloth over the bubble and applying an iron that was hot enough make stream when it hit the wet cloth. Leave it on for about 5-10 secs and then press down with a dry towel for another 20-30 secs while it cools. The heat reactivates the glue. This is also a way to steam out small dents in the foam.

It's important to either sand the surface of the foam or use a wallpaper perforator to remove the glazed surface of the foam as it comes from the factory. You'll get much better adhesion that way.

[Socal Tom]

The biggest problem with PMF, is that no 2 installations are the same. The fabric is often different, the glue is different, the paint is different. How the glue and paint are applied is different, the substrate might be different ( foam, or wood or both). At the end of the day, if you have covered the canvas thoroughly with paint it should be fine. If you didn't then you might see problems. If someone did have problems, you probably can't blame PMF without a host of potential installation errors.

[TimC]

Similar to Pat's experience on my two PMF builds. One is from 2016, the other from 2020.

2016 version was PMF over ply. I liberally applied 50/50 TBII to the plywood. Had help applying the canvas and then brushed the canvas all over with a wallpaper smoothing brush. Then immediately applied another liberal coat of 50/50 TBII. Did a light brush of the wallpaper brush again. When that layer coat was tacky I applied another coat of 50/50. Of course inspect throughout and brush where needed. After that I applied more coats at 75/25 TBII until I thought the texture would show with several coats of paint. There are now about seven light coats of exterior latex house paint. First coats were "opps" paint at about five or ten bucks a gallon. Random finish (matte, semi-gloss mixed). Last three coats are semi-gloss exterior. I repainted last summer because I wasn't in love with the color. Other than a good cleaning and a quick light sanding with a hand sander and finish cleaning I just added the new color. No lifting, no bubbles, looks good as new. Full disclosure, there were few vertical surfaces. Just the roof front and hatch back. Hatch was PMF'd on a bench.

2020 version (my son's) was PMF over rigid foam. Before PMF I took an old ratty wire brush and scratched the entire surface of the foam. Wiped it down to eliminate dust and applied TBII. The first three applications of TBII happened before the previous coat was dry, thoroughly saturating the canvas. Then "opps" paint and finish coats of semi-gloss. A small number of bubbles showed up prior to painting on vertical surfaces and I attribute that working too quickly on a hot, 85 degree day. With a syringe we applied more TBII and clamped the surface. That was easy to do since we had not painted yet and a little spackle filled the screw holes necessary for the clamping technique.

I'm a PMF fan and though I have built a couple boats using epoxy/fiberglass I prefer PMF. I might even build a PMF boat if it didn't live in the water. Oh wait, that's just crazy talk!

Used 10oz canvas from bigduckcanvas.com on version 2020. Reasonably priced, no defects, no seams and available in 64" widths at that time. I used Menards 8oz paint drop cloth canvas on version 2016. Seam was in a good location and was able to cut the width in half to eliminate it.

Tim

[Mark Gunter]

Thanks, those testimonials are helpful. I’m no stranger to fiberglass work either, but I chose the canvas/glue/paint method because of the ease of doing it. So far, I’m very happy with how the canvas has gone on. I’ve seen multiple videos that stress the importance of washing the canvas to shrink it; however, I found it to be too costly and ineffective to try to wash canvas large enough for my lil standy. The two sections I did wash were a bit too large to completely unfold and the result was not very good. When applying the canvas, I found that the washed pieces needed way more ironing and although the end result looks good, it’s not nearly as good as the unwashed canvas I applied, which went on like silk.

[TimC]

I didn't wash the canvas. On the first TD I merely rinsed it in cool water and let air dry then applied. On the second TD we applied right out of the package. I found that any wrinkles or folds shrunk right out and made a drum tight covering. The fabric was left wide and long and trimmed after the PMF dried thoroughly. I've seen the suggestions to pre-wash and iron. I found it unnecessary if you leave enough fabric to allow for shrinkage.

Tim