These instructions were found on a website that is no longer available. I have found this to be a great method.
YOU CAN USE WATER BASED POLYACRILIC AND GET THE SAME RESULT
The Brushing Lacquer method.
This gives me one of the hardest and lightest finishes I have ever gotten.
Pros
1: Super hard Finish
2: Super Fast Drying time (tack free usually in 15 minutes can add
second coat within 1 to 2 hrs.
3: Idiot proof no mixing, just dip a brush and go for it as it is
already as thin as water or thinner and spreads evenly.
4: Very Light Weight
Cons:
1: Toxic Fumes needs plenty of ventilation ( I do mine on back porch or
in garage)
2: Leaves a slight gumminess on top ( This gumminess is a styrene that
is added to it which helps it cure rock hard. It comes off quickly and easily
when wet sanding with 220 or 320 grit paper but you initially go through a lot
of paper at the very start after you get that layer off a sheet will go a long
way)
Also here is the reason it comes in as the lightest. Like the older
automotive lacquers, you have a color (pigment) and a carrier (the lacquer
liquid). The liquid "Carries" the pigment and glues it to the part, in the case
of polyurethane finish it is a clear type pigment. (I know this isn’t scientific
or 100% accurate, but for most people they will get the idea) Now with the
Lacquer based product the liquid evaporates in the air. 80% of the product is
normally the carrier which evaporates, and 20% of the product is actual material
which will stay on your plane. That is why even though it may be tack free in 15
minutes you need to let it breath for an hour to allow it time to keep
evaporating. So if you have 10 lbs of a material and 80% of it evaporates off
your left with only 2 lbs. Epoxy, and Polyester resin doesn’t have anything to
evaporate it just hardens chemically thus the weight you put on is the added
weight it will add to your plane.
Finally you have all the technical background and my reasons why I use
certain products we can now get down to business. Sorry to bore you but if I let
you go blindly along and just do it, then if something goes wrong or someone
tells you their way is best and this is wrong, then at least you will have some
idea of why you are doing what you are so you can have an intelligent discussion
with someone or know what something is doing if you are having problems.
Secondly because this technique will work with any of the above products so you
are informed of all their properties.
Okay the way I don’t do it but can be done just as easily is to open
your can of lacquer based polyurethane and to wet out the top of the wing. You
have plenty of working time so if you want you can do 1 side at a time or the
entire wing. For now let’s just do one side. You then want to lay your glass in
place and dry brush it down letting the resins underneath hold it in place. You
then do the same to the other side and let it sit for about a half an hour until
it is cured fairly well. Then flip and do the bottom the same way.
The problem I have with this is that there is no weight to the
polyurethane as it is thin as water and goes on just as thin. Now we all know
they fold the glass cloth and those folds don’t like to lay flat very well as
thin as this stuff is.
This is the way I solve that problem and works out very good.
Instead of using the polyurethane to hold the glass down I stand back a
couple feet and using some Elmer’s Duro or 3-M spray adhesive mist a very light
coat over the top of the wing. I then lay down my glass and use my hands to
smooth out any wrinkles. This super light coat of adhesive helps out
tremendously in holding the cloth down to the surface and around the leading and
trailing edges. I then use a nice soft paint brush and brush on a coat of
polyurethane doing the entire top half of the wing and the LE and TE.
NOTE:
It is best to do this with the wing raised up on
some sandbags or something so that after you put a coat of polyurethane down you
can go around it with your brush underneath to make sure you don’t have any
drips or runs. This is very important since this stuff is so thin it will
sometimes run.
Let this sit for about one hour to set good. Later on you won’t have to
wait so long but this is the most important coat as it is what adheres your
glass to your plane. After an hour flip your wing over and trim any loose glass
and lightly sand any rough areas. You want to be careful here you do not go
pulling on the glass and loosen it. (It only has 1 thin coat of resin on it and
it is just sticking it to the wood it will need more coats to seal it down
good.) Now you want to repeat what you have done to the top layer on the bottom
and that is spray a light layer of 3-M (or your favorite spray glue) and lay the
bottom wing glass down and smooth it out. Add a coat of polyurethane to it,
check for drips and let it set for an hour.
After the bottom dries flip the wing over again and trim the glass and
lightly sand and rough spots. (If you have to do any sanding be very careful.
You only want to sand if you have a run or something because the sandpaper will
mess up your glass if you aren't careful.
Now the glassing process gets easier. You want to put a coat of
Polyurethane on the top of the wing, let set about 1/2 hr or until the surface
feels good and dry, then flip the wing and put a coat on the bottom.
NOTE:
Do not sand between coats. Lacquer based
polyurethane creates a chemical bond. What this means is that when you add
another coat over a previous coat it will "melt" into the previous layer, which
means there isn’t no way you will have layers peeling off over time. Also
because the can says right on it do not sand between coats.
While you are waiting for the coats to dry, Go ahead and cut your cloth
for your fuselage. When doing the fuselage I like to make the fin glass one
piece, but you can do it in two if you like. I usually cut my glass for the fuse
so that it overlaps the stab and fin glass which seems to make a nicer seam.
About this time your wing should be ready for another coat. You now have
another option if you like (or can do it) and that is if you have a way of
hanging your wing on edge you can do both top and bottom at the same time. I
have done this with a twin by using wires through the motor mount brackets and
tying it up to a clothesline. On a wing without nacelles I just drill a small
hole into the dowel used to pin the wing to the fuse and wire it up this way.
There is a downside to this and that is because the polyurethane is so thin you
get more of a chance of having runs or drips. The good side is you can do both
sides at once cutting down on time. The thing you will notice as a big
difference between Polyurethane and epoxy is that you can brush it on and don’t
have to worry about using a credit card or like material to "Skreet" your resin
on like you have to with epoxy. In-between coats on your wing you can use the
same technique on the fuse. I spray glue the top half of the fuse including the
fin and the top of the stab and start glassing here.
Because this lacquer based polyurethane is so thin it may take 4 to 6
coats to fill the weave of .5 oz glass. Then after the weave is filled I usually
put three extra coats on so that I can wet sand the part smooth. Because it
dries fast you can have all your glass cut Friday night and spend about 8 hrs on
a Saturday and have your entire plane glassed fully. I then like to let my plane
sit for 2 or 3 days before I start wet sanding the entire plane with 320 to give
me a perfectly smooth finish. Then I can finish it in my favorite finish
techniques.
One last thing to remember and that is even though I only lightly
touched on the fuse the technique is the same, do the top glass flip over trim,
sand if needed, do the bottom. If it is a single engine plane you can hang it by
the motor mount and if not you can use the wing mounting area to hang it by.