Doing the Epoxy Wipe

This is a great technique. I first became aware of it when reading an article about Cory Bird and his most perfect Symmetry.

In "the old days" we would apply filler, then use progressive grits of sand paper until we had a very smooth finish. Then we would apply primer, or maybe more micro, to fill all the pinholes. Then we would sand it off, only to find that the pinholes where still there. Over and over and over.

Using the epoxy wipe method I sanded with 36 Grit, then a quick once-over with 80 grit. The epoxy wipe fills pinholes, pot holes, scratches, gouges and all sorts of other sins. It also does a great job of hardening the soon-to-be-painted surface.

Today, we filled the forward fuselage, the tail cone, upper cowling, lower cowl and the upper surface of the canopy. I used West 105/206 epoxy and applied four skim coats.

The idea is to apply it, then squeegee off as much epoxy as you possibly can. When it gets tacky, repeat. With all the components I was working on, I just kept rotating through. It took us about 4 1/2 hours. It really helped having Sandy mix while I was working. It was warm in the hangar - 88 F degrees.

I also wanted to keep track of the weight I was adding. We kept track of every cup mixed and I figure we added 2.2 lbs.


Now, I'll sand it all with 180 Grit and it's ready for paint.

Sanding

Over the years, we have learned better sanding techniques than were called out in the original plans. I'd thought I'd cover some of the main sanding tools that I now use. (As always, click on the photo the the full size image).

Again, the main idea is to lay your filler material on THICK, then sand down the high spots until you just reach the fiberglass. There are two excellent on-line descriptions that describe best practices.

Chapter 25: The Contouring Process

and

Finishing a Composite Airplane

1. Sand Paper The first strong recommendation is to buy only automotive body shop quality paper. I think that the 3M paper is the best and longest lasting and is my preference, by far. I get my paper at a local automotive paint shop supply store.

Almost all of the work will be done with 36 grit paper and I keep a good supply on hand. I really like the stuff that comes with the adhesive backing. It's 2" wide by 16" long.

2. Small Sanding Blocks Try and avoid doing any sanding, at all, with just your fingers - always use a sanding block. If you use solely your hands, the paper will follow the contour of the thing you are trying to sand down and you will not get a smooth surface.

I make extensive use of the rubber sanding blocks - there are both 6" and 8" available. I stick the paper to both the curved and straight sides.

For fillets and the like, I simple stick some 36G on a piece of cardboard tube.

I have also used this single stick board for many years.

3. Long block I used some shelf board I had laying around and cut it to 32" and mounted a section of aluminum angle for a better grip. This length allows me to use two 16" sticky back strips. With fresh paper, this is a great tool and really cuts into the micro.

I strictly use 36 grit on the whole plane until I get the contours that I want. When I have that desired shape I switch over to 80 grit. All the 80 grit does is to knock off the highest cuts left by the 36G.

All sanding should be done at 45 degree angles.

Don't worry about deep scratches, pin holes, deep holes or black holes. The next step will take care of it all,

Next, comes the epoxy wipe!