PMF, it just doesn't seem right to me

Finishes, paints and coatings

PMF, it just doesn't seem right to me

Postby Dutchoven61 » Wed Nov 16, 2016 1:55 am

Im building a small standee and am considering all options for skinning the thing. Thinking about using fiberglass on the top. Would consider FRP or maybe truck bed liner. Might consider roofing it with that rubber based Paint (i forget what they call it)

PMF just doesn't seem right to me. Glue over cotton canvas? How do you seem that? Can you sand it? Is it water proof enough for roof? I assume I can apply it over 1/8" Luan. Would the cloth rip on seams areas? How come nobody made a really good youtube video about doing PMF? Start to finish with lots of tips and tricks.

You end up painting the stuff with what kind of paint? I would like to use a high quality oil based paint. Can you paint over dried glue?

Come on, There are tons of you builders out there, give me the goods here!

P.S. Aluminum scares the bejesus out of me for some reason.
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Re: PMF, it just doesn't seem right to me

Postby cubbyboy57 » Wed Nov 16, 2016 6:46 am

I just finished my build and am no expert, but am very pleased with the way my trailer came out. I too couldn't find much how to on the subject and almost overthought the technique, but bought a bottle of titebond glue, some canvas, and a quart of "gripper" primer and used some scrap wood to experiment -- I was concerned about how hard it was to get the wrinkles out and my experiment showed that wasn't an issue ( saw posts where people were washing the canvas and ironing it) I didn't do either. I think the "gripper" primer is preferred because it is a thicker primer -- you can really put it on thick before it wants to run. I did my priming over days so it always had 16 hours or so to dry between coats. My 4x8 trailer I think I used 4 gallons of gripper (6 or 7 coats) and 1.5 gallons of paint (3 coats).
I used water based paint, but I think you can use oil based if you wish. It is exterior paint -- so it is made for the elements.
To get the seams watertight you over lap the fabric. You want your fabric seams to fall away from your wood seams so the ends of the plywood are protected. Basically I have 2 layers of canvas where the edge of the plywood is. I did my edges first, and trimmed the top canvas to the edge so my seam "bump" (about 2in wide) runs down both sides of the front and over the top. I only used one layer of canvas on my hatch and on the inside you see the edge of the canvas (I haven't finished out the galley yet). I used 1/4 in Masonite for my front radius and I can tell from the inside that there is no moisture getting through the PMF.
Some people route out the wood before so the overlap is smooth, but I didn't - you can barely see the overlap after the 9 coats of material.
Use just enough glue to hold the canvas down and to work the wrinkles out -- the smoother your canvas the less you have to sand later. You want the fabric to soak up the gripper/paint as that is the waterproofing -- not the glue.
If I remember right it took about 4 generous coats of the primer for the weave of the fabric to go away and then the finish is as smooth as you want it -- I used a roller so I have a slight texture to my finish.
I sanded any runs and after a couple of coats the few wrinkles I missed. I also would sand the seam bump back down to the canvas so the paint would build up and make it less noticeable. I think if I kept priming/painting it would completely disappear, but I got tired of painting and can live with the "shadow" of the seam.

I chose PMF because I knew I could work with it -- I too was concerned about working with aluminum (and the cost of a mistake). And I worked alone -- I didn't have the extra hands to help me. I thought fiberglass would be too messy and the idea of the fumes/respirator wasn't appealing as I knew I would be working in the 90+ heat of the late Texas springtime.

I saw a post the other day where a man is building cabinets for his van and he has a pretty good youtube video of how he used fabric screening over foam board to build them.
http://www.tnttt.com/viewtopic.php?f=55&t=67373 Pretty much the same technique -- he shows it on the inside seam instead of the outside.
I don't post youtube videos, but have several pictures in my gallery and my build journal that shows the steps I took.
Hope this helps - good luck on your build - I have begun to enjoy my effort in the great outdoors!
james
http://www.tnttt.com/viewtopic.php?f=50&t=66132
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Re: PMF, it just doesn't seem right to me

Postby Pmullen503 » Wed Nov 16, 2016 7:02 am

Easy enough to do a small test piece to check it out.
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Re: PMF, it just doesn't seem right to me

Postby daveesl77 » Wed Nov 16, 2016 7:39 am

Well, for hundreds of years, going back to the time of the Greeks and Phoneticians, boats used cloth coverings over wood decks to protect against the marine environment. The cloth would be impregnated with various sealing methods, but in the last couple of hundred years paint was mostly used. It was attached to the deck with various glues. Airplanes were originally covered with cloth. Zeppelins the same. Canoes were made from it. The list goes on and on. It really does work, our campers front and rear sections are protected by it. It is cheap, easy to use and looks very good if finished with a bit of care.

dave
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Re: PMF, it just doesn't seem right to me

Postby desertmoose » Wed Nov 16, 2016 8:24 am

My tear DOES NOT have PMF ON IT.

It is canvas covered.

I do not agree with putting titebond or any other glue on the top of the canvas. Glue is used to stick the canvas to the substrate,
Then step away from the glue bottle.

Apply a coat of good exterior paint to the BARE canvas.

Glue is meant to stick stuff together. it's not a resin to encapsulate the canvas fibers.

Other people have used glue on the outside with good results, but IMO, it doesn't belong there.

Take a look at my build journal to see how the canvas looked before applying the paint. I used exterior latex house paint, and the canvas really soaked it up.

It's been 4-1/2 years now with no required repair. I have touched up a few spots that were stained by birds. Touch up works great.

If I ever build another camper, I will use a canvas covering. I also made fishing pontoons and a storage cabinet for the deck and covered them with bed sheets instead of canvas. Same thing though, keep the glue from saturating the cloth and let the paint do it's job instead.

Sam
See our build journal at: viewtopic.php?f=50&t=45718

See the shakedown trip at: viewtopic.php?f=2&t=50112

More photos at: http://photobucket.com/horny_towd_teardrop
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Re: PMF, it just doesn't seem right to me

Postby Andrew Herrick » Wed Nov 16, 2016 12:48 pm

Just remember that expedition wall tents, which are used in some of the harshest conditions on the planet, are made from canvas. Don't judge all canvas by the cheap dropcloth stuff. Sunforger or marine canvas will weather just about anything.
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Re: PMF, it just doesn't seem right to me

Postby Dutchoven61 » Thu Nov 17, 2016 2:05 am

OMG you guys all rock! Thank you. I feel so much better and will do PMF. I looked at the build log for desertmoose and it was very helpful. cubbyboy57 saw the posting, thank you too. Pmullen503 gonna make a sample tomorrow. will try the TBII and the TBII as glue only and follow up with paint.

Wow I feel like I didnt make a mistake taking on this project now, thank you all.

:D :) :lol:
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Re: PMF, it just doesn't seem right to me

Postby QueticoBill » Thu Nov 17, 2016 7:57 am

I believe from having built a lot of scenery with canvas a water based first coat is advised to size it or shrink it tight. The TB3 may do that. And you can buy it in widths and lengths that would not require seaming.

Regrettably, classically it did work best with lead based paint, but I'm sure some less toxic coatings perform well. Was used as a porch floor covering at times.
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Re: PMF, it just doesn't seem right to me

Postby Dutchoven61 » Mon Nov 21, 2016 1:47 am

I did a sample and found that I think I will use bed sheet on the side and 10OZ canvas on the roof. I will use the TBII soak method. I tried the glue down and paint the raw canvas and I not too impressed. the heavy weight canvas is a bit hard to work with. Should be good for the top. :D
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Re: PMF, it just doesn't seem right to me

Postby rowerwet » Mon Nov 21, 2016 12:50 pm

I wrote the PMF instructable to help people who wanted to try it, as there wasn't and still really isn't a perfect step by step way to do it. I actually didn't have the time to take pictures or videos of my build, and on all of the projects since my hands get way to sticky and messy to take pictures.
Unlike stich and glue fiberglass, there is more than one idea about how to do PMF, which is why you read of people putting TBII on top of the canvas (don't know where that started) and all the different ideas about covering seams, buying canvas with no seams, washing and ironing the canvas, etc.
The teardrop I show in the instructable was built in 2011, the PMF on it has never been repainted, and the teardrop still lives outside in my yard, currently serving as my kids "fort". The fabric has not rotted, the paint has not cracked or come loose, and even though the kids like to climb on the roof, the roof fabrci still doesn't even show any wear.
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