PMF vs Epoxy/Glass - TPCE Wants Your Vote
Posted: Sun Oct 04, 2015 10:48 pmI’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.
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.
You could paint it white with black accents. ...Maybe black and grey or black and red accents?