Ed's Cozy Mark IV Project: First layup and first big learning experience

That's how I'm going look at these activities, rather than calling them "disasters". A lot of the homebuilding experience outcome will depend on my attitude and perspective, and learning to deal with issues is one of the benefits of building my own airplane.

I had a lot of trepidation about starting my first layup on the actual aircraft rather than a practice piece. After doing a layup on the old practice kit airfoil, I realized I had forgotten a few things from the last time I had performed a layup, and had a lot more questions. I decided to back off for a few days and spent some more time updating the detailed directions that I was writing, re-watching the Ruran video, and checking some of the forums, archives, and FAQs. I was still a little nervous about going ahead with the layup, but in the end realized that I had an extra piece of seatback foam anyway (for some reason, they recommend you order two of them, even though one piece is enough), so if I screwed this one up, I could just build another one.

There was some question on just how stiff to make the micro that was first going to be applied to the seatback. The general directions and the video talk about using micro slurry, but Chapter 4 says to mix this batch thick enough so it just runs, which sounds more like wet micro than micro slurry. Chapter 3 also mentioned that wet micro should be used instead of slurry for urethane foam, but doesn't mention using it for PVC. Both PVC and urethane have large open pores, which might be the reason for wet micro instead of slurry. I decided on wet micro.

I was using a coffee creamer container to pour the micro ballons into the epoxy. I thought that pouring micro from a bottle would be much less messy that scooping it from an open bag. I used up most of the bottle just covering seatback front, though, so I'll need to find some bigger bottles for the next layup.

I had cut the UNI and laid it on the seatback to make sure it would fit before doing the actual layup. Trying to figure out which way to lay the weave got confusing for some reason. I had cut one piece pretty short, and it just barely covered the seatback, but I figured it would be okay when I did the layup.

The epoxy pump setup did not work as well as I'd hoped. I had to tilt the mixing cup to get it to fit under the resin pump, and the nozzle for the slow hardener pump squirted the hardener straight out to the side, rather than down, missing the cup entirely and leaving a mess all over the scale. I used more of the slow hardener than the fast - the fast comes out like syrup, the slow stuff like water. Once I figured out how to press down gently enough on the punp to get most of the hardener in the cup, it went a lot smoother, and it was fairly easy to tweak the amount of hardener to get the correct ratio. I found another set of pumps at a marine supply store here, and will be replacing that pump nozzle soon. I also forgot to weigh the resin before squirting in the hardener once, and had to set that cup aside for it to harden on its own.

I wasn't worried about my scale only being accurate to within 1 gram rather than 0.1 grams, but it started getting flaky on me after a few mixes, jumping from one value to another. I suspect it may have had something to do with all the resin and hardener I had spilled on it running down the sides, but I'll have to double check it later.

Spreading the micro went fairly easy, although some ended up dripping over the edge of the seatback. After spreading the first batch, I wasn't sure if I could use the same cup to mix the next batch of epoxy or not. I went ahead and did it anyway.

Laying the glass was a nightmare. I had folded the glass and set it aside earlier, but when I tried to lay it over the wet micro, I couldn't figure out how I had laid it out the first time. It always seemed to end up a couple of inches short no matter which way I laid it. I finally ended up cutting it up and using smaller pieces. When I went to the cutting board to cut another piece, I ended up pullng the last foot of UNI off the roll and had to dig under the workbench for another bolt. I had taken the gloves off to keep the new bolt free from epoxy while I hung in the cabinet, and when I tried to put them back on they ended up tearing in several places.

Getting the edges of the two pieces of the UNI to line up took forever, and pulling on the fibers didn't seem to help. I had to keep pulling the piece up and trying to lay it down again to get the edges to match. The second roll of UNI didn't have as clean an edge as the first roll, so I let it overlap a bit. I was glad that I had precut the peel ply before the layup and was able to just pick them from the bench and lay them in place without having to cut pieces off a roll while wearing epoxy covered gloves. (I did have to cut an extra piece for the join between the two pieces on the second layer of the layup.)

I had bought some 4mil plastic and butcher paper to protect the workbench. I used the butcher paper for this layup, and hung the tapered end of the seatback over the edge of the workbench as shown in the plans. The epoxy from the overhanging edge dripped all over the garage floor, and I ended up spreading the mess by tramping in it as well. (I'll be covering the floor with butcher paper for the next layup.)

The directions were adamant about not getting micro between the layers of cloth, but I noticed that the epoxy I was squeegeeing off the layup was turning white, and realized that it was somehow pulling up the micro from the layer below. I didn't know what to do except squeegee off as much as I could. I could see patches of white mixed with clear areas through the glass, and I couldn't tell if the clear areas were dry spots or epoxy, since MGS is so clear. Using my LED trouble light was problematic - I had to hold it at just the right angle to inspect the layup - it was either too dim or too bright at other angles.

I got epoxy all over the squeegee when I laid it down on top of the layup, all over the scissors I was using to cut the glass, and all over the hair dryer and trouble light as well. I had put on the shop apron before the layup, and was glad I did when I leaned over the workpiece and got epoxy all over the front of the apron. The seatback kept shifting around as I was pulling the glass on it, making even more of a mess. I was lucky that I didn't try to adjust my glasses, and I'll just be wearing safety glasses the next time around. I was very careful when wiping the sweat out of my eyes, and will wear a sweatband the next time as well. I cleaned up the tools as best I could when I was finished.

I laid a sheet of wax paper over the layup and set some boards over the wax paper with weights on top of that to keep it from warping while curing.

I had planned on this job taking about half an hour, but I think I spent more like two hours with all the SNAFUs. I went back after a couple of hours to see if I could knife trim the edges, but I hadn't laid the edges of the peel ply straight along the edge of the workpiece, and didn't want to risk disturbing the fibers by trying to cut through both the glass and the peel ply.

I went out the next morning to look at the job. The wax paper had left some smooth areas where the eopxy had oozed up, and the boards had been close enough to the edges of the wax papaer to pick up some epoxy and adhere themselves to the workpiece. When I tried to lift the seatback from the table, I pulled up several pieces of butcher block paper with it - since I hadn't masked off the sides of the workpieces, the epoxy had dripped down the edges and under the workpiece. I think a lot of this will get trimmed off anyway on the next step, and I guess I'll just patch the rest with dry micro. I pulled off the peel ply and found a spot where the peel ply had curled up a bit. When I pulled the peel ply off, the curled epoxy stayed behind. I'll have to sand that off later.