Always sand your repairs with a sanding block.
Examples shown are an aluminum block from
Great Planes, great for rough cutting, and a
simple block made from a 1 x 2-inch hardwood
your skin from the chemicals. I cut my
aluminum foil, then mix the epoxy and
wet out the fiberglass cloth when it is
positioned on the carrier. Using an acid
brush with a stick taped to it for the long
reach required in the forward section, I
brush on some epoxy in the repair area.
Using sticks, I position the repair patch
in place, pushing it down to get good
contact, and remove the aluminum foil
if I can. With my stick, I press down the
fiberglass cloth to get uniform contact.
Don’t worry if you can’t remove the
aluminum foil carrier. It can stay there
forever. Allow the epoxy to cure for at
least 24 hours.
With the structure sound, I can begin
the cosmetic repairs. I like this part;
finishing is fun. Coarsely sand the outer
skin to aid in filler adhesion. I plan to use
an automotive lightweight, easy-to-sand,
two-part filler. Lightweight filler sands
and shapes easier than regular filler. Put
a layer of filler over the depressions and
let it cure.
Always use a sanding block from this
point on to get a flat, smooth surface
with no waves. Holding sandpaper in
bare hands will create waves. I have two
sanding blocks for most of my work: an
11-inch aluminum T-bar from Great
Planes, and a hardwood 1 x 2 x 11-inch
sanding block. My heavy work is done
with the aluminum T-bar using 60-grit
sandpaper, and finishing work is done
with the hardwood block with 120-grit
sandpaper on one side and 220-grit
sandpaper on the other side.
Start with the 60-grit sandpaper to
smooth the filler. The goal is to get a flat
surface. It will take a couple of coats of
filler to get all of the relief areas filled
and back to shape, so take your time.
The next step is to sand the rough
scratches caused by the course
sandpaper, first with the 120-grit sanding
block, then with the 220-grit paper. Use
contact cement to attach the sandpaper
to the sanding blocks.
To remove worn sandpaper, warm the
old glue with your MonoKote heat gun,
peel the sandpaper off of your sanding
block, then use contact cement to
adhere your new piece.
In my next column, I’ll discuss priming
and painting. Until then, let’s burn some
kerosene. See you at the field.
Jet Pilots’ Organization (JPO)
120 Model Aviation M AY 2014