Okay, so Friday I stopped by Jo-Ann’s Fabrics and picked up a foot of 60 inch wide cotton duck to use for testing. It didn’t say what weight it was on the bolt tag, and the clerk couldn’t say what weight it was, but it looked to be similar to the big roll of 10 oz I bought from Big Duck. I figure the $3.33 was worth my time not to have to set up an area, pull the big roll out, and make sure that I wasn’t shorting myself by taking too much from one corner (even though I added extra into my rough estimate, I had not allowed for the extra needed for the doors… because you need to be able to wrap the door jambs and the doors, so you can’t just use the wall cut outs for the doors; so I’m hoping that, if I do use the canvas, that the extra I allowed will be enough for the doors; either way I will probably glass the tongue box).
I did manage to open up the roll and snip a small corner piece off for comparison to the Jo-Ann’s. The small triangle is the Big Duck. Weighing the Jo-Ann’s confirmed that it is also about 10 oz/sq yd. You can see that the Big Duck has a finer, tighter weave for the same weight. Cost was about the same.
I wasn’t sure and thought that the Big Duck may have been prewashed, but when I dribbled water on both it beaded up pretty strong, so I decided that I had better wash the sample pieces first. I cut three test pieces slightly over size and brought the whole lot home to wash.
On the epoxy/glass sample I was able to trim it with a razor knife, but it was tough and the sample was so light that it wanted to move around on me a lot, making it a somewhat dangerous affair. Scuffed the edges with the small block and 100 grit to dull them up a bit and take the sharp edges off.
I hadn’t weighed the test sample beforehand, but the other three samples where very close to each other (two at 2.35oz and one at 2.30oz). We figured that 2.35oz was close enough and did some weighing and figuring to see how I had done. This is what the surface looked like close-up.
I used one of the 2.35oz blank samples to zero the scale…
…then weighed the trimmed test piece to find the added weight; 0.80oz added. (You can see a little white along the cedar edge where it lifted from me pulling on it with the razor knife.)
The scrap of cloth we weighed figured out at only 5.5 oz/yd^2 (spec’d as 6oz nominal)
and the sample piece figured to have about triple that rate added, so about 2 to 1 epoxy weight vs. cloth weight. To look at the weave it is all well saturated with no signs of dry spots, no pooling or ridges of epoxy, and all of the weave pockets are visible (not over filled), so I figured that I had done pretty well. We did a conservative estimate and figured one ply would add about 22.5 lbs to the whole camper.
I haven’t looked it up yet, but OP suggested that 1:1 glass epoxy ratio should be expected, so I was a little surprised. Maybe I should recheck my long hand math using a calculator? Some of this may be due to the fact that the cedar edge has two plies that overlap the main panel ply, and I did not account for that, but since that is such a small percentage of the total area covered, I wouldn’t think that it could account for such a difference.
I wrote the details directly on the back of the sample.
We had a cold front come in overnight and I'm not sure if that slowed the cure, but with just one ply I was able to dent it with my finger if I applied moderate pressure. With light pressure it just felt a little springy. This prompted me to consider a second ply.
Anyway, yesterday I brought the washed canvas and did a couple of test samples with TB2. The canvas came out of the dryer horribly wrinkled, and I hadn’t bothered to baste the edges, so there were a lot of stringy threads (more than shown here). Even after ironing you can still see plenty of creases, although I didn’t have any distilled water for the iron, so may have been able to do a better job ironing if I had.
After trimming just one edge crisp for along the edge of the cedar (where I intended to start) the oversized piece weighed 0.70oz.
I put a nice fresh piece of plastic coated freezer paper on my blotter (the cut out from one of my door windows; 5mm ply over 1-1/2 inch foam) to use as a work surface.
And here you go. I used 2 parts TB2 to 1 part water. The wrinkles where greatly diminished just by laying it down in the glue, and as you will see, as they dried the creases diminished further, almost disappearing.
As expected there was no problem handling the 3/4 radius at 90 deg to the weave.
The 1/8 inch radius seemed to go fine as well. On this sample I wrapped about 1/4 inch of canvas all the way under, whereas in the other one I lined the cut edge up with the bottom edge of the cedar (as it will be on the inside corner of my door flanges.
The wrapped piece seemed to be drying fine, but on the unwrapped one that side of the canvas (along the 3/4 inch edge) lifted. I was able to open it up a little to get some full strength glue in there, and I think it will stay stuck down now. Maybe something to do with the thinned glue on the relatively sap/resin rich cedar, dunno.
First impressions. It’s true, the PMF is much easier to deal with than real epoxy and glass. No itching, no special PPE (other than rubber gloves and eye protection), simple water cleanup, reusable cups, brushes, etc. We shall see on the durability/armor. Again, it was cold and wet; low 50’s and 75/ct, so maybe not ideal conditions.
I decided to lay another ply of glass on the epoxy test piece, both to see if it added enough armor to justify doing a full second ply on the camper, and to see if it would go around the 1/8 inch radius on a 90 deg orientation. Yes the 1/8 inch radius is no longer 1/8 inch, but pretty close, so IMO still a valid test.
I prepared the piece by wet scrubbing with a well-used piece of greenie pad (to remove any amine blush) then drying well with a paper shop towel and fanning the piece. Just a little light sanding at the seam between the main and 45 deg strips to knock off the prickly bits. I didn’t bother trying to fair this seam for the test, just to see what the next ply would do.
I tried to be more aggressive with my squeegee work (using an old Ho-De-Po gift card) but when I did I started seeing starved glass as evident by the lighter crystal like sparkle. Dripped a little more epoxy on in those areas and dragged it again with less force. As before, I think I got it pretty good with no puddles, ridges of epoxy, and the pockets in the weave pattern still visible (as opposed to being soaking full). There was a ridge of wetness along the edges just off of the foam, so I expect it to be harder to trim, but I didn’t want to mess things up by trying to fuss with the part that will be trimmed off anyway. Doing this dry on dry it seemed to take more epoxy to fill the dappled surface underneath than it had the smooth surface of the foam, and it seemed more sensitive to extra squeegee force (i.e. easier to take too much away).
The extra ply really seemed to blend the jagged line of the seam, to the point that I wouldn’t bother trying to fair that area first.
Back to the canvas you can see that most of the wrinkles have disappeared.
Took the 1/8 radius fine, except as noted for the lifted flap on the butt edge sample.
If I go with the canvas I may have to rough up the cedar better and use full strength glue in those areas.
Getting a late start today, but am on my way to check things out now that things have had a chance to dry.