Fiberglass finishing and painting

[Michael]

I'm starting this thread in the quest to learn more about the process, as I want to finish my Top Flite DC3 with fiberglass and then paint.

At the 'Pilot's Meeting' last night, a few people made suggestions and offered sources of information and product.

I'm hoping this thread becomes a resource that we can all share.

I'll start with some questions.

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1. I was told that it would protect the shape of the balsa wood if I sealed it first. What product should I use, and how must I apply it?

2. What kind of fiberglass material should I use? Where can I get it? How do I apply it? Is water-based polyurethane OK?

3. Once applied, should I sand it, and should I apply more polyurethane coats?

4. Do I need to use a primer if I intend to paint with light colours?

5. Is there anything I didn't ask about, but should have?

[Ededge2002]

I would speak to Ben. He used water based poly and glass on his Nooner wing and it turned out fabulous.

[Papa]

Hi Michael, have a look at this video. It looks simple and if you take your time it will be a great looking finish.

Deluxe Materials Eze-Kote

Jack.

[wollins]

I use WBPU (Water Based Polyurethane) by Varathane. Anytime you are going to use WBPU on balsa (esp sheeting) you need to first seal it with an oil based sealer. Oil based polyurethane, varnish, lacquer, etc all will work. Give it a coat and then sand smooth before usng the WBPU. It seals and protects the wood from absorbing the poly.

On balsa sheeted wings I like to glass and then cut out the ailerons. I normally glass the whole plane. It prevents a lot of hangar rash besides adding a lot of strength. Don't forget to do top and bottom at the same time to get equal drying action and to avoid warping the wing. You can get away with doing left or right first but always top and bottom together.

To support the wing so you can do both sides at the same time, you can hang it with a dowel thru the wing mount bolt hole. Just an idea.  Also keep in mind that fiberglassing will generally add between 40 to 50% of the "before structure weight" to the finished product.  In other words if a plane uncovered weighs 2lbs then after glassing it will weigh up to 3lbs.

STEP DETAILS.
1.  APPLY ONE COAT OF OIL BASED POLY to seal the balsa from absorbing the water based WBPU. Let dry overnight and then sand!

2. APPLY FIBER GLASS CLOTH APPLICATION WITH FIRST CLEAR COAT OF WBPU brushed on, left for two to three hours or overnight for harder finsh. Two oz cloth for the forward fuse, 0.75 oz for the rear and tail.

Apply the FG with overlapping pieces on the fuse. Brush it down with a DRY hairbrush. This makes it cling to the surface based on static electricity. On the wing, try to do the bottom as a close fit and then overlap the top piece. Or you can do the bottom and then let the top hang over about 2 inches to be trimmed later.

3. WBPU APPLICATION. (SECOND COAT WITH BAKING SODA MIX - (40% starch to 60% WBPU)
Filling with just WBPU (first coat) will not completely fill the weave and not filling the weave creates a great look if you ARE NOT looking for a smooth shiny finish. If you are, I have found that you can fill the weave with a mixture of the WBPU and baby powder or cornstarch  to achieve a consistency similar to Mayonaise.

However, any additive that makes the Poly opaque, should be avoided in the initial "wetting out" coat. The PU, needs to be clear at least in that first coat, so you'll be able to easily *see* and remove any air bubbles under the glass cloth, or any "dry spots."

After that first coat has been done, then adding a pigment or thickener such as baby power or cornstarch should not be a problem, at all. So the first coat should be kept clear, to avoid any dry spots or air bubbles. How much filler? Probably 50/50 or so.

Pour enough WBPU to work with into a small container, and then mix in baby powder or cornstarch  until you get the consistency similar to Mayonaise. The consistency is NOT vitally important ... thin or thick, it doesn't seem to make much difference. Also, the filler is a pain to mix in...it tends to clump up, so it takes a few minutes to get it really mixed well.

Apply using a coarse brush. Make sure to get out all the air bubbles, wrinkles and excess by using a credit card as a squeegee. Use paper towels to soak up any excess liquid or roll a toilet paper roll over the entire surface. This blots up the excess and nicely sticks the cloth to the surface.

Again, make sure the top and bottom of wings are covered at the same time otherwise the shrinkage as the water dries out of the poly can warp the surfaces.
 
4. SAND AND REPEAT IF NECESSARY. (This third coat or application – also mixed with baby powder or Corn Starch if you want that smooth finish)

You can stop at two coats if you desire. The glass should be totally adhered. The reason for multiple coats is what type finish you want. The more coats, the smoother the finish. I usually average about 3 coats and that leaves just a hint of weave (cause I don't use the baby powder or cornstarch – matte is more scale!) to make it like a matte finish. 

5. PAINT.

Sand the FG/poly with 220 grit lightly and then with 400 grit to finish up. Need a good base for the paint to grab. After that, wipe entire plane down with rubbing alcohol to remove all the finger oils.

You don't have to use low adhesion tape to mask with as you would on bare foam painting because the paint adheres to the Poly/glass much better, so the tape won't pull away your paint upon removal.  Just use regular painter's masking tape.

A lot of people swear by Eze-Kote as shown in Jack's video but it costs 7.5 times the cost of WBPU and the advantages don't merit the cost IMHO.  Based on my research (I wanted to try it myself) the advantages are:

- You can seal the wood with it.
- It dries faster.
- It's slighter harder.

So ... is that worth it being seven times the price? I guess it depends on how important those three things are to the individual user. Me ... I think I'm gonna stick with WBPU. 

Colin

[Linden]

That's going to look really cool Michael!

Linden

[Michael]

Hi, Linden. 

[Papa]

Hey Linden welcome to the forum.

Enjoy.

Jack.

[Polecat]

Michael

Over the years  [a good 25] I have used Pacer Z-Epoxy finishing resin, 3/4 oz. cloth over everything, centre section of the wing is 2 oz. in layers. The epoxy dry's in 4-5 hours and is easy to sand.
Brush one coat of resin on the part [top of wing], now lay the 3/4 cloth on and smooth out, this is a bit of work, after your done, take a roll of toilet paper to roll off the excess resin, let dry over night. Next day take a sanding block and sand off the over cloth around the edges and sand the surface of the wing. Now you can do the bottom.
Put another lite coat of resin on the top and bottom of the wing, you my want to do the toilet paper thing again.
Now sand the wing with 220 and finish off with 320, vacuum and use a tack cloth to get all the dust off, now you are ready for your white primer. I use Rust-Oleum Painters touch primer now on glass cowls of my electric F 1's. You can sand either wet or dry.
This process is done all the parts. A lot of work but you get a very good finish.
This process is used by the guys who are building scale stuff.
I did a Dave Platt Spitfire many years ago and all my nitro racing F 1's planes where done this way and where spray painted with 2 part epoxy paint and the clear coated.

Hope this is some help.
Ken

[Linden]

Thanks everyone!

[michaely]

Interesting thread.

I'm easing myself back into r/c plane construction after a pause of close to a couple of decades and have been reading online and doing a few experiments on substitutes for dope in open framework fabric finishes and for finishing resin in balsa sheeted structures -  because of the cost and limited or non- availability of the Sig dopes and Hobbypoxy/K&B finishing resins and their direct clones.

Colin, I understand the use of a first coat of oil base polyurethane on wood to prevent thin balsa sheeting from otherwise warping from the water in water based poly being applied to only one side of a balsa sheet and I experienced this warping at first with wbp.  But I took the suggestion of someone on the "basement rc" forum to brush a couple of very light coats of wbp on one side of a balsa sheet to make the surface impervious to the water in wbp in subsequent much heavier coats of wbp.   I did this with 1/16" balsa sheeting and the sheeting warped  very little and reflattened when the wbp cured.

I haven't tried oil based poly yet..... has anyone tried continuing to use oil based poly on second and subsequent coats to fill the weave of fiberglass or polyester fabric; I suspect it would fill with fewer coats than wbp.

Starch and baby powder as weave fillers; yes.
And I vaguely remember another household product I used decades ago for this purpose: powdered gelatine, used in food preparation to make glazes, etc.  I still had a few tablespoon sized packets in my finishing supplies so I tried in out on a 1/16" thick balsa sheet to which I had already attached strips of .75 oz. fiberglass cloth and different grades of silkspan.   The gelatin powder dissolves in hot tap water and is applied with a brush.  This was the practice of modelers a long time ago who wanted to fill the weave of a silk covered wing before applying dope  that would otherwise tend to bleed through the porous surface of the silk and accumulate on the underside where it did no good and created an uneven finish. 
Anyways I tried liquid gelatin and it filled the weave of the fiberglass and silkspan much faster than wbp .   I didn't try a mix of starch or baby powder and wbp for comparison.   The gelatin dries fast with a harder and more glossy surface than the wbp.  Subsequent coats of wbp did bind with the gelatine filler coats,  although I routinely pass a 400 or 600 grit paper over  previous coats of  gelatin or any urethane to enhance the mechanical bond between coats.
Gelatin powder, btw, is made from animal bones and bone marrow - it is protein - and is still sold as Knox Unfavoured Gelatine, sometimes I gather with a Kraft Foods label.  I checked online and it is cheap, something like a box of four packets for less than a dollar.
If you want to try this as filler, hold out for unfavoured gelatine - Jello, despite coming in attractive colors - apparently doesn't work as well (smiley)

good luck

michael

[bfeist]

Welcome to the forum michaely.

When I used water-based poly to glass my nooner wing, I first sealed the balsa with sanding sealer. I found this tip elsewhere on the net and it worked like a charm. One spray, dry, sand, another spray, dry, sand and you're ready for fiberglass and water-based poly. Here's a pic of the can. I bought it a home depot.