PMF vs Epoxy/Glass - TPCE Wants Your Vote

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TPCE Wants Your Vote - Which method should I use, PMF or Epoxy and Glass?

PMF
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50%
Epoxy and Glass
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50%
 
Total votes : 16

PMF vs Epoxy/Glass - TPCE Wants Your Vote

Postby KCStudly » Sun Oct 04, 2015 10:48 pm

I’m having a terrible time trying to make the final decision whether to use PMF (poor man’s fiberglass = TB2 glue, canvas and latex paint), or to step up and use epoxy and fiberglass, to cover The Poet Creek Express.

For those of you who may be unfamiliar with my build, TPCE is a hybrid foamie build, similar in shape to a Benroy, with 5 mm plywood inner skins and 1-1/2 inch blue foam cores. It has mostly cedar framing, though very minimal, especially in the walls and roof to wall join. Most of the hard points are small 1x pine plates (or blocks) let into router pockets in the walls. The plan had always been to use PMF for the outer skin, and I have already bought a big roll of 10oz x 72 inch wide cotton duck from Big Duck canvas.

The thing is, my project has kind of snowballed into a labor of love taking many more man hours (man years, really) than expected, and I have managed, I think, to achieve a certain quality of build that probably deserves reconsidering the added expense and durability of an epoxy and glass outer shell.

I have spent a lot of time doing foam “bodywork” to get the surface reasonably smooth and true to my intended profile, including rounding over the roof to wall edges with a 3/4 inch radius, so don’t bother suggesting a switch to hard panel covering options. Plywood, Filon, FRP, or aluminum skins won’t work for me, so please don’t suggest anything like that.

Let’s compare,
Pros for epoxy/glass:
1. It is very durable. My tests show that two layers of 6oz cloth would provide very good dent and abrasion resistance. An important distinction for my moderate off road style build.
2. It is very permanent and when painted for UV protection promises a long and maintenance free service life. I would also feel much better about storing the camper outside until I can find room in my overcrowded garage.
3. It is light weight. I haven’t nailed down an exact figure, but my test pieces only show about 3oz per square foot prior to surface finish, so maybe 37.5 lbs for the whole camper is a conservative estimate.
4. The glass cloth does not need to be pre-washed, shrunk, dried or ironed.
5. Seams and laps tend to blend fairly well.

Cons for epoxy/glass:
1. The epoxy is much more expensive than TB2 glue, and since the glass cloth (at 60 inches wide) is about the same cost as the canvas (at 72 inches wide) it will also cost more to do two layers.
2. The glass is itchy to work with and not nearly as easy to handle as the canvas. It wants to pull out of shape and strands of glass pull out of the cut edges much more readily than the cotton.
3. The epoxy is kind of noxious and requires much more diligence in handling (careful mixing, and acetone cleanup). I would be more concerned about making a mess on the floor of my loaner work shop, though that can be worked around by laying drop cloths or cardboard. I tend to “run hot” and covering up with long sleeves and PPE does not help.
4. Since I have already assembled my major panels, I won’t be able to conveniently position for horizontal application on the walls and front, although I will be able tip the cabin over partially to do the walls. The hatch has a “bustle shape” with a largely vertical reverse tuck under at the rear and I want to get the majority of the hatch skin applied with it in place to avoid locking in unwanted twist. Wetting glass on a vertical surface is said to be very difficult, and I can only imagine how hard it will be to do my door headers and the lower portion of the hatch.
5. I have very little experience with composites, but have been doing okay with the smaller jobs and tests that I have attempted.

Pros for PMF:
1. Less expensive and I already have about a gallon and a half of TB2, and big roll of quality cotton duck canvas.
2. Handles easily with no itching, warping, or stretching grossly out of shape. Seems to be more forgiving with loose threads when handling.
3. Easy water cleanup.
4. May be easier to apply for someone with little composite experience.
5. Dents from incidental contact and hail have been reported to self-heal after spending time in the sun, or if a hot iron is applied using a damp rag as a buffer.

Cons for PMF:
1. Less durable; does not form as hard a shell. Allows dents.
2. Requires prewashing, shrinking and ironing.
3. There have been several reports of issues with blisters (although it is also reported that these can be re-adhered using the iron trick).
4. Seams and laps need to be very neatly trimmed and planned out as they tend to sit proud.
5. There have been a couple of reports of questionable performance: a bad case of delamination due to a dry application (that was able to be corrected), seams starting to pull apart, and a tear in the canvas (the later two suspected to be due to not preshrinking the fabric, but also possibly due to fabric shrinking over time... IMO, not enough data or history to be sure at this point).

So, I ask that you vote in consideration of my situation, not based on what you would do in your situation. Feel free to comment on what you would choose for yourself and why, but please vote with your recommendation for me and my situation.

No guarantee that I will opt with the majority vote, but I am waffling on the fence and your input may help me decide which way to go.

Thanks.
Last edited by KCStudly on Tue Oct 06, 2015 6:50 pm, edited 2 times in total.
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Re: PMF vs Epoxy/Glass - TPCE Wants Your Vote

Postby dales133 » Sun Oct 04, 2015 11:54 pm

Pmf!
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Re: PMF vs Epoxy/Glass - TPCE Wants Your Vote

Postby KCStudly » Mon Oct 05, 2015 7:23 am

Thanks Dale!

Please select the button at top to register your vote. Currently 2 FG vs. 0 PMF.
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Re: PMF vs Epoxy/Glass - TPCE Wants Your Vote

Postby dales133 » Mon Oct 05, 2015 11:39 am

KCStudly wrote:Thanks Dale!

Please select the button at top to register your vote. Currently 2 FG vs. 0 PMF.

Ill have to do it on a computer later,no buttons on tapatalk
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Re: PMF vs Epoxy/Glass - TPCE Wants Your Vote

Postby S. Heisley » Mon Oct 05, 2015 6:54 pm

Just to throw another thought into the mix, I bought some inexpensive boat plans to make a small, one man boat. (It's now on the back boiler and maybe never built since I got an inflatable kayak.) For the boat, the fellow recommends using fiberglass sheeting with TBII. He says you can use epoxy resin if you want to; but that TBII works just as well.

Frankly, with all the work you've put into your build, I would go with the fiberglass. ....Probably the epoxy, too, because of the denting problem you mentioned with TBII...but then, again, I remember the experiment that I did with epoxy covered boards. (pg 11 of my build thread) Those dented, too!

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In the end, you pick your poison and hope it works the way you want it to.
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Re: PMF vs Epoxy/Glass - TPCE Wants Your Vote

Postby Pmullen503 » Tue Oct 06, 2015 10:44 am

I would add two more criteria to your list: fiberglass/epoxy can be sanded very smooth and is virtually invisible over wood. If you want a smooth glossy painted surface or a bright wood finish (think cedar strip canoe) then fiberglass/epoxy is the way to go.

Covering the inside roof will be tough with either but vertical surfaces really are not that bad. Just watch out for runs with epoxy. Covering curved corners like the hatch will be easier with glass than with canvas. Use bias tape or bias cut cloth (no darts or overlaps to cut.)

You could cover the outside with PMF and save the fiberglass for a stunning bright finished interior; a stealth land yacht!

That said, I went with PMF with flat paint for a workman-like finish on my toy hauler/camper. I've build 11 wood boats covered in glass and epoxy so I'm comfortable working with it.

The additional cost is small when you think of the time and money spent building the rest of the camper.
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Re: PMF vs Epoxy/Glass - TPCE Wants Your Vote

Postby KCStudly » Tue Oct 06, 2015 11:45 am

Inside is already finished, Red Chestnut stain and poly over Okoume.

I'm definitely leaning way over hard toward epoxy/glass at the moment. :thumbsup:
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Re: PMF vs Epoxy/Glass - TPCE Wants Your Vote

Postby angib » Tue Oct 06, 2015 12:39 pm

I would add a third option - glass in polyester resin. Much cheaper than epoxy and very forgiving to use. Not as long lasting as epoxy, but there are 40-year old boats with polyester/glass sheathing over wood, so that's not exactly a short life. Most of the same finishing work as epoxy/glass if you want a smooth finish.
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Re: PMF vs Epoxy/Glass - TPCE Wants Your Vote

Postby KCStudly » Tue Oct 06, 2015 6:38 pm

Sorry Angib, I'm going over blue foam, so polyester resin, or rather the MEK hardener is a 'no go' for me.
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Re: PMF vs Epoxy/Glass - TPCE Wants Your Vote

Postby kayakdlk » Tue Oct 06, 2015 6:54 pm

KC, In reading your pros and cons one thing stood out to me.
Dents from incidental contact and hail have been reported to self-heal after spending time in the sun


Since you are putting this over foam and not wood I was wondering if the fiberglass and epoxy would hold up to a hard rock or hail or would it just shatter/crack as the foam gave underneath from a hit. I know it would work fine over wood but maybe the PMF is a better option over foam since it seems that it self heals and maybe more forgiving in long term usage of your teardrop.

I think I would lean toward PMF. Especially after I saw the video Lucy from Mesa Arizona did on her teardrop. She indicated she sanded to get the PMF smoother and her stripes looked really good.

Good luck in your decision

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Re: PMF vs Epoxy/Glass - TPCE Wants Your Vote

Postby KCStudly » Tue Oct 06, 2015 7:55 pm

I hear you Dan.

I took the 2 ply glass sample and whacked it on the corner of the bench a couple of times pretty hard, and it didn't leave a mark or dent. A day or two later I did it again to show Karl and it made a tiny little white spot.

I guess I can do a hammer test comparison next time, but neither sample is backed up by the 5mm ply, as in the full scale build, so maybe not a valid test.

I think the breaking or tear strength of the glass fibers must be significantly higher than the cotton, though I have not found empirical data.

My thought is that in a scrape or tree branch poke scenario the glass will brush off more, whereas the canvas will dent and be more likely to let the offending intruder grab hold and take a bite, and thus more readily pierce through.

I'm also wondering about solar heat rejection. I wanted to tie the color scheme into the black Jeep, but with concerns about temperature and melting foam around 212 deg F, I am limited to light colors. I had thought that a light gray might be a good compromise, but have since read of at least one case where a converted CT owner switched to white from gray and noted a significant reduction in surface temps.

I haven't found any info specific to epoxy layups, and I doubt that there is much, if any info on PVA glue and fabric, but if I look at the thermal conductivity listings for the constituent materials, or similar, it looks like the glass and epoxy may not do as well as the cotton. This may not be a fair interpretation, so take it for what it is, not much.
Last edited by KCStudly on Fri Nov 27, 2015 9:51 am, edited 1 time in total.
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Re: PMF vs Epoxy/Glass - TPCE Wants Your Vote

Postby S. Heisley » Tue Oct 06, 2015 8:50 pm

:thinking: You could paint it white with black accents. ...Maybe black and grey or black and red accents?
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Re: PMF vs Epoxy/Glass - TPCE Wants Your Vote

Postby KCStudly » Tue Oct 06, 2015 9:08 pm

I know. White is so boring (no offense intended to all of those white camper builders out there, it is the most practical color for heat rejection).

We're getting a little OT here, but that never stopped me before, so...

I was thinking gray with darker gray scallops, long thin ones trailing from the front corners back, kind of like Charlie B's orange and white Lilgizmo that shows up in the hall of fame header pic every now and again. Now I'm thinking mostly white, or very slightly tinted gray in white with lighter gray scallops, perhaps a royal purple pinstripe.

If I haven't already done so, I'll explain the purple over on the build thread.
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Re: PMF vs Epoxy/Glass - TPCE Wants Your Vote

Postby Alan_H » Wed Oct 07, 2015 9:39 pm

I think one thing you're missing for your durability test is the fact that the paint on the outside of the PMF is going to add strength and durability to your build.

I get that you are probably leaving it off for now based on an apples to apples comparison of coating methods, but the paint seems to be an integral part of PMF not only for waterproofing, but also durability of the canvas. OTOH, paint on the fiberglass is just a UV protectant and exterior visual enhancement, not a necessary part of the process.

Just something to consider.
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Re: PMF vs Epoxy/Glass - TPCE Wants Your Vote

Postby KCStudly » Wed Oct 07, 2015 10:40 pm

Yeah, the thick Zinsser primer I put on last night did seem to make the canvas that little bit better, but on one of the samples the edge of the canvas pulled away from the foam, as if the primer drying pulled it up.

The PMF is very impressive, I must admit. (waffle)

Tonight I cleaned off the work bench and recycled the plastic sheeting out of my vacuum bag set-up. Used it to line the bench for covering duties. (tilt)

With the primer I can still dent the foam with my finger more easily than the 2-ply glass (which takes some effort to depress just slightly and springs back), but it seems to also spring right back better than it did before; even on the radius edge that I thought might be more susceptible. (nice volley, boy is my head swimming).

Maybe I really should do that test with the TB2 and glass weave. :thinking:

Damn, just when I thought I had made my final decision... and the weather isn't getting any warmer, either.

Okay, I scuffed the little raised bits of canvas "hair" with the small block and I think I should hit it with another round of primer and some paint.
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