OP827 wrote:... KC is building with glass and epoxy too. I am interested in objective cost comparison of two methods. I am not convinced that PMF is actually substantially cheaper for time and material than epoxy and glass. Both methods have pro and cons. Epoxy glass gives more rigid and better finish surface than canvas. Canvas are more user friendly and safer to glue, self healing under sun as some reported here. Both surfaces are equally easy to repair. If you decide to build, I would encourage you to do your own testing on scraps and decide what you like more...
Well, TPCE isn't complete yet, but I wouldn't say I didn't finish it... just not yet.
I did a bunch of experiments and found that epoxy does not work as well with cotton cloth as it does with fiber glass (FG) cloth. The cotton does not absorb the epoxy the same way that it would water or water based products; and you can't see through it when it is wet to see if it is fully saturated and stuck down; whereas with FG cloth the epoxy soaks in readily, causing the glass to go clear so that you can readily see that it is saturated.
Two plies of 6 oz cloth provides a very solid surface over foam board. I did a test panel of each (2x6oz vs. 10oz... or was it 12oz? IIRC 10oz... duck/TB2, both with mesh unfilled, no sealer or top coat). Surprisingly, they weighed exactly the same. When struck relatively hard onto the corner edge of my work table the canvas tore in a triangle and made a dent in the foam; the FG cloth bounced off and I had a hard time deciding if I could discern where the impact had occurred. I wanted better impact resistance so I leaned toward FG.
Contrary to popular belief, the FG... at least in this schedule (i.e. just two plies of 6 oz) is not brittle. My 12 x 10 inch test panel over 3/4 thk foam, now several years cured, can still be bent back on itself in a 'U'-shape and it comes right back when flattened, no discernible delamination and no cracking. I think this cracking myth comes from comparing catastrophic impacts of FG cars and boats to those of metal cars; yes, thicker schedules of glass are more rigid and will "break" when they fail, compared to metal cars that crumple and dent. Both would be considered wrecks, but the metal can be hammered out (before applying body filler!!!), whereas the FG needs to be repaired in a similar manner to how it was constructed in the first place.
In my area, at my local marine supply outlet I have been paying about $8 or $9 per yard of 60 inch wide 6 oz cloth (about 2x the cost of a single ply of 10oz cotton at the time I bought... and the prices on cotton are about half that now
Big Duck 10oz cotton duck cloth, and the last gallon of West System with hardener was quite a bit more than my first, something like $130, pick up, no shipping. I must be on at least my 3rd gallon, but there have been a few quart containers here and there, too... and I'm not done filling the weave or fairing. TPCE is 64 wide x about 50 tall x 9'-8" long with 6 inches wrapped under the floor on all sides, not including the tongue box (TB). Add more $$ for fairing fillers, ratio pumps, a cheap digital scale (highly recommended) and alternate hardeners (you bought 'slow' but the weather turned cold, so now you need to go buy some 'fast'
Don't worry, tho, your project will take longer than you think and the weather will change again
).
Remember, you can't use cheaper polyester or vinyl ester resins with polystyrene foam; and you can't use stranded mat cloth as a cheap buildup with epoxy, either (it has binders in it that are not compatible with epoxy).
The health hazards and inconvenience of wearing PPE are real with FG/epoxy. If you are gonna do it, do it right; no excuses and no cheating. If you don't already have and know how to use a proper vapor/particle respirator, plan on another $35 or so.
I use scrap sticks to stir with and save used Tyvek sleeve from work to protect my arms. Disposable nitrile gloves are not cheap and that cost can add up fast. My preferred mixing cups are cut down DD ice coffee cups; they do have a bump up in the bottom, so you have to take care when mixing to squeegee all around, but the are "free" (unless you count how much money you spend on their coffee!!!
).
On getting a nice finish: there is no "easy" way. If you want to do PMF and have it come out looking very nice and presentable you can do it. There are plenty of examples here. It will take attention to detail, special care and effort, and more material and time (surface prep, work place prep, plan your folds first and fill "jambs" before main plies, some people use jigs and fixtures to hang the canvas while applying, plan and execute your trims, folds and overlaps carefully, fill the weave, block it, fill some more, block it... do it again). Same can be said with FG. The nice ones don't just happen, they are created through hard work.
Rather than sanding through the structural fibers, the idea is to add enough filled epoxy ("thick") over the weave (or high build primer) so that when you sand it back you are not cutting into the strength by interrupting any of the long fibers. The smoother you lay down the glass (i.e. surface prep and care in layup) the stronger the cloth will be for a given thickness, and the less filler will be needed. Again, time and attention to detail make a nice job. Haste and slap dab make something fast and campable... and most people won't care or even notice, but the ones that do will. Some won't know why one person's creation doesn't look as nice as another, but the ones that do will shake your hand and tell you what a great job you did... or will assume you bought it from a factory.
I waffled in my planning and had already started using light weight vinyl ceiling spackle as a fairing compound to prep my foam for PMF. Then I changed my mind and decided to go with FG. If I had it to do over I would more closely follow the Rutan method, which IIRC sands the foam smooth and fair (remember, they use special grade foam... we need to at least take the "glaze" off), then apply a loosely filled epoxy coat before the weave. This gets a good bite on the foam and lets the cloth embed into the "thick". I prefer using the dry on dry layup method for larger surfaces, so I would do the loose thick over the foam, wash amine and sand to fair before the cloth layup. That way you start right off with a moderate hard shell. I spent too much time and material chasing soft filler and foam; it moves under your sanding pressure and expands/contracts with temperature changes. In the evening after my day job I'd fair a section of foam up to blocking or spars, etc. and come back on the weekend in the AM to find it no longer fair... move on to somewhere else and look at it again in the evening and it would be fair again. Get the foam "close", get the hard shell on, do the cloth layup... I found that working by myself on such a large project at a shop away from my home, it was not practical for me to do layups and weave filling all in one "wet/tacky" session, so I ended up washing amine and doing surface scuffs a lot... then fill the weave with thick thick... then find that thick thick wasn't thick enough and it slumped down a wall. That's where I laid the cabin on its side to do the side walls "in the flat", things got tedious and my project sort of stalled for a couple of winters. You can't use epoxy below 45 deg F, and probably shouldn't even go below 50.
Mind you I'm not even going for an automotive quality finish. I just want it to be relatively wart free. I thought about just leaving the weave, but once you have a couple of overlaps to fair or more heavily wetted areas, you end up with a mixture of unfilled weave and fair areas... too hard to maintain a uniform weave appearance.
What I'm trying to say to the OP, and others is, don't assume that you have to do FG to make it nice. You have to do a lot of good work to make it nice, whichever material you choose. And it will cost more than you think, regardless. By my estimation the typical budget overrun described by posters here is about 1/2 again to double what you thought. Don't believe me? Keep track of every receipt. Believe those who say they did it on the cheap (and they have a "nice" TD to show for it)? IMNSHO, they didn't keep track. Sure, there are people that can scrounge the right materials at the right time, or just plain have access to materials through their business or jobs, but overall, be realistic.
When in doubt, test. Do a small sample. Then scale up your test to something of moderate scope that can actually be used in the finished project, like a tongue box or a chuck box. Then decide.
I will finish TPCE. It will be the way I envision it. There will be things that I am not totally happy with, but it will be "nice" to my standard. Everyone should use the methods that they are best suited for and build to there own standard. There's plenty of room in the pool. Come on in!!!
I’ll see if I can find him … ( be back )
