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Campy -> RE: Oil Poly. vs Water Poly. vs Finishing Resin (4/26/2008 6:38:47 PM)
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Campy,
I can't really argue with that logic. You mentioned water base poly. Do folks use this strictly for the ease of clean-up, and lack of noxious fumes? Or do they use it because oil based poly doesn't "play" nicely with foam and primer/paint? I am tempted to use an expensive cross-linking, oil based poly, due to the fact that it seems to warp the wood less. It is also reputed to be "significantly harder, and more durable". However, if there are additional issues with this, I will likely resort to another even MORE expensive yet slightly less durable cross-linking water based poly. (My wife is going to kill me.)
Chris
< Message edited by ardrhi 4/25/2008 5:56:53 PM >
As meyersflyers said, the key is to use a sealer on the wood 1st. Here is a basic "How To" for glassing and painting with latex.
Hope this is of some help.
Glassing with Water Base Polyurethane
1. Sand the model with 220 grit and remove any highs/lows you may find.
Fill as needed with lightweight filler and sand.
2. Give the wood 1 thin - medium coat of wood sealer. I use the
commercial stuff. What this does is twofold - it stops the balsa
from soaking up too much of the poly and at the same time protects
the balsa from the water in the polyurethane.
3. When dry, sand lightly with 220 to remove the "fuzzies".
4. Some people say to apply a light coat of 3M #77 adhesive to the
wood at this point. I have found that this is more trouble than it
is worth since if you have a wrinkle, the complete piece of fiberglass
has to be removed to straighten it out.
I prefer to lay the fiberglass cloth on the part/area to be covered and
smooth it out using a SOFT brush. Brush FROM THE CENTER TOWARDS THE
EDGES. The static electricity usually holds it in place. I normally
use 1/2 oz (.5 oz) or 3/4 oz (.75 oz) fiberglass cloth.
5. Using WATER BASE polyurethane and a FOAM brush, start at the center
and brush towards the edges of the fiberglass. All you want to do is
stick the fiberglass to the balsa, so excessive amounts are not needed.
Any additional pieces of fiberglass should overlap each other about
1/2 - 3/4 inches.
Let this dry. DO NOT SAND !!
Brush on another coat of polyurethane. This coat can be a little heavier.
Let this coat dry. DO NOT SAND !!
6. Mix up some polyurethane and microballoons. I use 1 part
microballoons to about 5 parts polyurethane. This will be on the thick
side.
Brush on a medium coat of this mixture and let dry.
7. Wet sand this with 220 or 320 grit paper. BE CAREFUL, AS YOU CAN
VERY EASILY SAND RIGHT THROUGH THE FIBERGLASS.
8. Check the fiberglass carefully to insure the weave is filled. If
the weave is not completely filled, repeat step 6 and 7.
9. SPRAY a coat of water base polyurethane on the plane and let dry.
DO NOT SAND !!
10. Spray a THIN coat of primer on the plane. When this is COMPLETELY
dry, block wet sand with 220 or 320 grit as much of the plane as
possible to highlight any highs/lows you may have missed during your
sanding/prep. The areas that can not be block sanded, CAREFULLY sand
by hand. (TIP: CA some of the wife's/girlfriends fingernail file boards
together. Wrap the sandpaper around them so you can block sand in tight
areas. The CA helps prevent the boards from disintergrating in the water)
Fill any low areas with a lightweight filler and sand when dry.
Apply a THIN coat of polyurethane to these areas.
When the poly is dry, repeat this step until you are satisfied that all
the highs/lows are removed.
11. SPRAY a thin coat of polyurethane on the plane. When dry, spray
the primer.
12. When the primer is dry, you can apply your rivets, panel lines and
other detailing desired.
13. Now you can spray your paint.
Painting with Latex
First, if you have not done so, I strongly recommend you read the article
by Roy Vallencourt on using latex paint.
http://www.modelairplanenews.com/how_to/latex1.asp
I do disagree with Mr. Vallencourt in a couple of areas. These areas
of disagreement are based on my personal experience using latex.
1. I add 1 1/2 caps of FloTrol per quart of latex paint PRIOR to any
diluting. The Flotrol retards the drying slightly and allows the paint
to level itself.
2. Use ONLY water for thinning the paint. My experience has shown
that using windshield washer fluid gives a slight tint to light colors.
3. My best results with latex have been between 25 psi and 30 psi.
Under 25 psi I don't get the coverage I would like and over 30 psi the
paint starts to have a "dimpled" appearance.
4. I have not had good luck using a heat gun to promote quicker drying.
I know of several people who have had good luck using this technique
though. You can try it and see if it works for you or not.
5. I strongly suggest and highly recommend the blue 3M brand of masking
tape. What you want is the "60 Day Safe Release". This can be
identified by a paper appearance to the tape and on the side of the
wrapping is an adhesive index. You want a 2 dot adhesive rating. The
2 dot adheres reasonably well, yet will not pull up even fresh underlying
paint.
6. Flat latex will take an average of 7 - 10 days to "cure". Semi gloss
and gloss latex take 14 - 21 days to cure. To see if the paint is cured,
press your finger firmly on a hard area of the plane (I use the cowl
area). If a fingerprint remains, the paint is not cured. The
fingerprint will disappear in a day or two.
7. Gasoline powered planes will be fine with the paint as is. Glow
engine powered planes need to be clear coated. I suggest waiting until
the latex is cured before clear coating.
For clear coating I suggest one or 2 sprayed coats of a water base
polyurethane. My personal experience has shown that it is fuel RESISTANT
to 10% nitro and various reports indicate no problems with 15% nitro.
By fuel resistant, I mean if you let the clear coat dry for a minimum
of a week before exposing it to fuel AND you clean your planes at the end
of the day, you should have no problems. If you let the residue sit
overnight on the plane (or more than 4 hours), it will become sticky. If
you want fuel proof, use Ultracote or Lusterkote clear. Oil Base
polyurethane is also fuel proof, but it will start yellowing in about
6 - 8 months. The yellowing is not that noticeable on dark colors, but
very noticeable on light colors.
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