Canvas PMF

[Shirestone]

There are lots and lots of posts online about PMF on foam.
I have done the inside completely and will be shortly working on the outside.
I'm wondering if you have particulars about materials and methods. Everyone seems to have their own take on what works best.
I have read lots on the TNTT site regarding multiple tests that everyone has tried.

I am using 2" XPS and 8-10 oz canvas. I don't have access to glidden gripper in Canada.
I guess my biggest question is....What is the pre treatment on the foam to make the canvas adhere best.
On the inside of my trailer pockmarked the foam, then sanded the foam then used Bullseye 123 primer and then did a 50-50 TB II glue to water split to adhere the canvas. I then painted it multiple times, thoroughly soaking the weave. I find that although it works I would hope that there might be something that might stick better to the foam.
I have read that the canvas acts like a sock and doesn't stick the best but surely there must be some method that sticks relatively well.
I'm hoping I can get a definite answer on this in order to decide a direction to go next.

I know this has been asked many times but would like some more input.

Thanks in advance.

[John61CT]

This was always a "work it out yourself" experimental process anyway, now that Glidden Gripper has been discontinued

there really is no definitive recipe anymore, basically we are back almost to square one.

I would not use TB outside myself,

my path would be to look for a primer that is truly waterproof and shows powerful adhesion in testing

and use that directly on foam that has been rough sanded, spiked then cleaned

soaked through embedding the canvas / mesh material and then coated on the outside.

The outermost paint then only for UV resistance and aesthetics.

[Juneaudave]

The science of polystyrenology has come a long way, yet we have much to learn....

[Pmullen503]

Do a sample on some scrap foam and scrap canvas. If when you pull it off, some foam comes off then that's as good as it will get. The foam itself is the weakest link. The "sock" concept is the correct way to think about the PMF system.

That said, you should sand the foam to get past the glaze from the hotwire process to get better adhesion.

[RJ Howell]

I agree with doing a sample and you see what works best for you with the primer and diluted TBII. I found a good primer that worked better than my attempts with TBII. Others have better success with TBII. I sanded for prep, hand hand sand that is.. way too easy to make a dent with a power sander.

The days of Glidden Gripper is gone now. A used a bonding primer and it worked very well.

With all that said, I would price fiberglassing against PMF. I found for better material and higher quality bonding primer it was very close to the same costs and for me was easier (and quicker) to do.

[TimC]

My son and I used an old scraggly wire brush on the foam prior to glue and canvas on his build. This opened up tiny, "deep" little kerfs in the foam surface which the glue penetrated. It was fast, virtually dust free and is still holding on very well. I'm not afraid of using TBII on exterior surfaces as long as they don't have standing water on them. Of course, there is very little reason not to use TBIII. It just cost a few bucks more per gallon.





My almost six year old woodie TD has PMF on the roof and sits in the yard all summer. TBII on lauan plywood, canvas and six or seven coats of exterior house paint. Have had no problems with delamination. I've been in some incredible all day storms on the road and multi-day rains while sitting in the yard and have no problems.

[QueticoBill]

I'm not sure but Mad Dog primers may have a product that is like Gripper. Thick and adhesive like. Their site is down at the moment but some product info here: https://www.uspaintsupply.com/paint/mad ... -original/

They had or have primers for various substrates, including fiberglass and vinyl. Worked great on old house.

[Postal_Dave]

I've documented bunches of experiments on PMF on the forum. As they said, you have to do some experimenting for yourself to get this right. Also, it familiarizes you with the process before you start work on the actual camper.

This is what I've found to work the best.
I sand the foam to make rows and get the hot wire melt off. Then wipe it down so any loose material is gone. Then make the pot marks in it. (I don't want the sanded material inside the pot marks.)
Then I pour full strength TBII on the surface and smooth it out, making sure I fill all the pot marks and rows with glue. This creates anchor holds for the glue and canvas. Then let that dry for 24 + hours.

(Quick experiment here. Pour a big drop of TBII on a piece of wax paper and let it dry for 24+ hours. Pour the same size big drop next to and over lapping the first drop. So it looks like a Venn Diagram. Let that dry for 24+ hours. Now peel the glue drops off the wax paper and try to pull the two drops apart. It will not break at the seam.)

Then I pour a lot of full strength TBII on the canvas and work it in on one side of the canvas, then flip the canvas over and place the glue covered side of the canvas on the foam. Then scrape and press the top of the canvas to get out the wrinkles and make sure the glue is in good contact with the foam. Wait another 24+ hours for that to dry.

(If you try this method yourself on a scrap piece of foam and canvas, you can pull the canvas off and see how much foam it brings with it.)

The rest of the instructions here are just for finishing it off.
I start to layer diluted TBII to soak the weave of the canvas. It can take days for diluted TBII to dry. After all that, I prime and paint the canvas and it is well protected from the weather.

BTW: Don't use diluted TBII to adhere your canvas to the foam. I've done many experiments with it and it is much weaker than full strength TBII for adhesion.

Always try several different methods and experiments before working on your camper. It will save you a lot of time and money in the end.
Good Luck

[Noc3]

what dave said. full strength tb2 adheres best.

[gregkn73]

What kind of canvas do you all use?

[TimC]

On the foamie we diluted TBII 75% glue to 25% water. Have had no problems. 75/25 was sufficient strength for our purpose. In my experiments on scrap, on samples left to completely dry, there was little difference in tear away strength for different degrees of dilution. There was a big difference when we scratched the foam first as I described above.

We had time for the TBII to set and spreading the diluted TBII with a paint roller is a breeze. On my canvas over plywood I diluted 50/50. Going on five seasons and no problems. Our goal wasn't to save drying time or use less glue. Dilution is to make spreading on large surfaces quick and simple with two sets of hands on a warm day in the shade.

I pre-shrunk the canvas on my Woodie TD. For the foamie we just used it as is with the wrinkles and all. It is amazing how the canvas shrinks and pulls the wrinkles out as it dries. Make sure you cut the pieces big though. If you don't pre-shrink and you cut to fit the space it won't reach the edges after it dries.

What Pmullen said, "If when you pull it off, some foam comes off then that's as good as it will get. The foam itself is the weakest link." Experiment and BYOB! (build your own build) YMMV

Bought our 10 oz canvas at Big Duck Canvas. Prices aren't bad and it doesn't have the "pills" that the harbor freight stuff has. And no seams. The canvas on my Woodie was drop cloth from Menards. Pills and seams, but decent quality. Big Duck is worth the extra few bucks IMO.

[John61CT]

AFAIK no one has actually used PPG Gripper yet.

Yes not the same, likely not "as good" but maybe good enough?

[ghcoe]

I dilute TBII 50/50 and have had no problems yet after 3 builds.

I thin it for a variety of reasons. The main one is that canvas can rot if the weave is not fully filled. This is a condition that canvas canoes can have if the canvas is not applied properly. Canoe makers use a dope that is closer to TBII before thinning, but they apply it with a short stiff bristle brush and they work the dope into/through the canvas once the canvas is stretched over the hull. Working the dope through the canvas also bonds the canvas to the hull since they do not apply a glue before stretching the canvas. Lots of work.

I do not preshrink my canvas. The 50/50 mix loosens the weave and lets the canvas lay down better. Also, since the diluted TBII takes longer to dry and the canvas is more saturated. It allows the canvas to shrink and pull tight across the surface like a drum.

Diluted TBII gives me a longer work time in different weather conditions. If it is colder out I may drop the dilution to 25/75, but when explaining to people my technique it is easier not to complicate things.

Dilution makes the glue go farther. I can usually do a build with 1 1/2 gallons of TBII.

I sand the foam, but do not perforate the foam. I feel if there is a delamination it is easier to correct with no perforations. If for some reason a delamination happens to pull out foam or glue dimples from perforations, getting the canvas to lay flat again might be a challenge.

just my thoughts, George.

[GPW]

We’ve used thinned TB2 for years and years with no problems , We’ve even used oops paint to secure the canvas , that works too …

Gotta’ remember , it’s the SOCK effect that holds everything together … Eight years and still going strong !!!

[gregkn73]

Canvas or Windows screen material? Pros and cons?