PMF Walk Through

Finishes, paints and coatings

PMF Walk Through

Postby Lee's Stroller » Tue Sep 27, 2016 6:04 pm

I'm sure this topic has been thoroughly discussed but in my searches I've found mixed methods so how does one get the best results with PMF? I've read about people mixing TiteBond II in a bucket 50/50 with water to apply, and other people using paint rollers to apply straight TiteBond II and then laying the canvas over top. Also does one need to epoxy the wood before applying TiteBond II and Canvas? Or is the skinning and exterior paint enough to protect the wood? Like the title states a walkthrough or step by step would be great and feel free to link me to a thread I missed if it's been made already.
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Re: PMF Walk Through

Postby OP827 » Tue Sep 27, 2016 11:29 pm

Did you see this build http://tnttt.com/viewtopic.php?f=55&t=54099#p984564 and how canvas were applied? This build has one of the best application of PMF I have seen on this forum.
My foldable foam trailer build: http://www.tnttt.com/viewtopic.php?f=50&t=61344
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Re: PMF Walk Through

Postby Lee's Stroller » Wed Sep 28, 2016 8:11 pm

Thanks for the link. The canvas job looks really clean. So in this tread the "Mix" was 50% water and 50% TiteBond 2?
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Re: PMF Walk Through

Postby OP827 » Wed Sep 28, 2016 9:19 pm

Lee's Stroller wrote:Thanks for the link. The canvas job looks really clean. So in this tread the "Mix" was 50% water and 50% TiteBond 2?


ghcoe wrote:I used a 50/50 mix when I did my canvasing. I think you will find the bond will not be real strong even with full strength glue. Some people perforate the foam to encourage a better bond. The problem is the foam is just not a great surface for glue to bond to, it usually still pulls off easily because the foam will fail at the glue line. A lot of the bond comes from the shrinking of the canvas or fabric over the surface creating a tight drum like pull to the edges. That is why you want to overlap the edges so it can pull tight across the surface rather than shrinking away from the edges. If that makes sense. :thinking: With the combination of a light bond to the surface from the glue and the tight drum like effect across the surface it really makes for a tight durable surface. For it to pull away from the surface I would suspect you would have to push from the inside of the wall out and something bad has happened at that time. :thumbdown:


Hope it helps. There is also a Big thread http://tnttt.com/viewtopic.php?f=55&t=39373#p719512 in foamie section within stickies that contains many people experience working with PMF. There is also a summary thread for that big thread - http://tnttt.com/viewtopic.php?f=55&t=56186#p1018823
Good luck :thumbsup:
My foldable foam trailer build: http://www.tnttt.com/viewtopic.php?f=50&t=61344
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Re: PMF Walk Through

Postby KCStudly » Fri Dec 23, 2016 1:09 pm

When people refer to "The Mix" it is in reference to using oil based polyurethane and mineral spirits as a penetrating wood sealer; kind of a poor man's CPES... clear penetrating epoxy sealer (but not really the same thing). PMF is different and any dilutions should not be confused with "the mix".

I think the most recent consensus on PMF is to use full strength TB2 (or just slightly thinned with water if your climate requires it for working time). You want a good glue bond so IMO the thicker the glue the better it is able to fill pores and get a good grab. Lay dry canvas over it; press, roll or squeegee down; allow to dry thoroughly, policing for any bubbles or lifting during the drying process; and then top coat once fully dried. Some like to do a diluted wash of glue/water prior to paint to seize the threads, but others don't feel it is necessary (might depend on your canvas selection, whether you pre-washed or not, etc.).

There have been a few cases where people got lifting or bubbling, which is believed to be due to top coating before the adhesion coat was fully dried. Once the top coat skins over there is no place for the moisture from the adhesion coat to escape, so you want it good and dry first. Plus, if you have any suspicious areas it is easier to deal with prior to paint.

The bottom line, as it seems with most things small camper, there are a lot of ways to do something well and have it come out perfectly serviceable, and only a few ways that don't work at all. Do a few small scale tests, start on something a little larger like your tongue box or a bulkhead wall first, and see which techniques work best for you. By the time you get to the side walls you will be an expert!
Last edited by KCStudly on Wed Feb 15, 2017 7:37 pm, edited 1 time in total.
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Re: PMF Walk Through

Postby lthomas987 » Wed Feb 15, 2017 5:12 pm

The specs for TBII say it is allowable to thin with up to 5% water to maintain full strength. Also that adding 5% water cuts viscosity in half. I'd be really leary cutting it 50% with water and expecting good adhesion. My own construction experiments with foam and TBII showed that roughing the surface with sandpaper just a bit helped at LOT with adhesion. As did using a wallpaper pricker.

http://www.titebond.com/frequently_asked_questions.aspx
Can Titebond Wood Glues be thinned?

Most of our water-based wood glues can be thinned with water up to 5% by weight or by volume. Adding more than 5% water to our glues will decrease the bond strength. Titebond Liquid Hide Glue is thinned by gently heating the bottle in a pan of warm water. Titebond Polyurethane Glue may only be thinned by placing the bottle into a pan of warm water.


When I sanded the foam and glued down fabric and tried to peel it later (12 inch square samples.) it peeled up foam and the bond broke in the foam layer. When I didn't sand sometimes the foam failed and sometimes the glue failed.
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Re: PMF Walk Through

Postby IndyTom » Thu Feb 23, 2017 10:14 pm

Sometimes I feel incompetent when it comes to searching. Most of the threads aboutPMF that I find, it is being applied to a foamie. I want to apply it to a plywood skinned ttt, and would love to find someone else who had done it.

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Re: PMF Walk Through

Postby desertmoose » Thu Feb 23, 2017 11:01 pm

IndyTom wrote:Sometimes I feel incompetent when it comes to searching. Most of the threads aboutPMF that I find, it is being applied to a foamie. I want to apply it to a plywood skinned ttt, and would love to find someone else who had done it.

Tom



Take a look at my build. I didn't use PMF, but I did cover my plywood tear with canvas and paint.

1) use Titebond glue only to stick the canvas to the wood.
2) DO NOT put thinned glue on the outside.
3) apply exterior house paint to the BARE canvas.
4) leave it outside for years with absolutely no problems.

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Re: PMF Walk Through

Postby Socal Tom » Mon Feb 27, 2017 4:31 pm

IndyTom wrote:Sometimes I feel incompetent when it comes to searching. Most of the threads aboutPMF that I find, it is being applied to a foamie. I want to apply it to a plywood skinned ttt, and would love to find someone else who had done it.

Tom


I put PMF over my wooden roof. The cloth I used was polyester cloth intended for roofing. Like this https://www.walmart.com/ip/Kst-Coating-Llc-KSTCMPE2-40-inch-X-81-White-Contouring-Polyester-Mesh-Roof-Fabric/26968068?wmlspartner=wlpa&selectedSellerId=1609&adid=22222222227039578086&wl0=&wl1=g&wl2=c&wl3=85504658090&wl4=aud-261800281660:pla-193590562130&wl5=9061192&wl6=&wl7=&wl8=&wl9=pla&wl10=113487702&wl11=online&wl12=26968068&wl13=&veh=sem

I tried the 50/50 TBII, it was a mess, didn't absorb well into my fabric. It worked best to just lay on a thick coat of paint, apply the cloth with a squeege used for autobody work, then add more paint on top. It was lots faster and seemed to stick better. IMO, canvas is great for us over foam, but for use over wood the poly fabic is designed for the job, so why not use it. The TBII gives the canvas structure that it needs over foam, but over wood you already have structure, you just need something to help support the paint.
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