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SANDING SEALER

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Old 09-21-2010, 06:39 AM
  #1
AAN2705
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Default SANDING SEALER

Hi All

Just wanted to know if i could make my own sanding sealer. I read somewhere on the net that it's just dope with some talcum powder added to it.
Is this true? And how much of powder to dope must be used?

Thanks
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Old 09-21-2010, 06:53 AM
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Default RE: SANDING SEALER

I made it that way. I used about half a container of power, then filled the container with 50/50 thinner dope. I don't think the mix is critical.
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Old 09-21-2010, 07:20 AM
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Default RE: SANDING SEALER

You can make it that way. It won't be a sealer though, it will be a filler. (Same with Pactra's "sanding sealer.") The way to seal wood is with thinned clear nitrate dope. Then fill. (I put on a layer of silkspan before filling, too.)
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Old 09-21-2010, 08:57 AM
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Default RE: SANDING SEALER

Hello AAN2705,

I can only tell you what I do and from there on you are on your own.

In effect we are beginning the process of finishing and covering the structure of the model.

Some balsa has fine grain and some has coarse grain.

Fine grain surfaces

Use genuine aircraft dope as used by full size airplane refinishers.
Apply by brush a first HEAVY coat of nitrate diluted about 15% by volume with nitrate dope thinner. Just enough dilution to make it easy to brush on.
Let cure for 12 hours or any length of time more than 12 hours.
Dry sand smooth LIGHTLY with 320 grit paper.

Apply a second heavy coat of nitrate dope (diluted as above) and let cure for 12 hours minimum.
Wet sand with 400 grit wet abrasive paper.
Do not let any water go on and penetrate the wood areas not being finished. (Avoid warping).

You now have a smooth surface ready for the covering.

Coarse grain surfaces

First coat of nitrate as above for fine grain.
Dry sand smooth LIGHTLY with 320 grit.
In a separate small container poor the quantitiy of nitrate dope you expect to need.
Add talc powder to nearly double the volume in the small container and mix thouroughly for one minute (NO MORE THAN ONE MINUTE0 .
Add the solvent (thinner) just enough to make it spreadable with a brush.

MAKE SURE YOU ARE USING HIGH QUALITY BRUSHES THAT DO NOT LOOSE THEIR HAIR.

Apply this second coat always brushing cross grain and pushing a bit hard on the brush to help the mixture to go into any pores, tiny cracks, etc . . . Do not overcoat with this mixture. You can always apply an extra coat where it becomes obviously needed.

If, inadvertently, you have an ovrcoated area that started to cure, use clear thinner to dilute it on the surface and spead it out.

Let that second "filler coat" to cure 18 hours or more.
Wet sand as above for fine grain.

NOTE: I seem to be telling you what to do. I really mean to explain what I do.

Hoping this is valuable informaton for you and any reader.

Zor
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Old 09-21-2010, 09:44 AM
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Default RE: SANDING SEALER

Hi Zor. Good to see ya.

I like to use thinned epoxy. Mix slow epoxy one part A, one part B and 1 part 90 percent isopropyl or denatured alcohol. Brush on in glops and squeegee out thin with a card. When dry, sand or I like to lightly scrape all over with a single edge razor blade held near 90 degrees. Go until all the high shiny areas are gone and you have a smooth sort of burnished finish.

Fills pores and adds strength.

Tom
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Old 09-21-2010, 10:04 AM
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Default RE: SANDING SEALER

I've mixed PolyCrylic and talc with a bit of distilled water for a good cheap filler that didn't stink up the house. Sands real nice with 400grit. I've applied before and after covering with glass. Fills in the weave nicely.

As a kid, I and my flying buddy , made our own filler with Aerogloss clear and his baby brothers bath talc. Slight blue tint and smelled nice after the buytrate vapored off.

Ray W.
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Old 09-21-2010, 02:00 PM
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Default RE: SANDING SEALER


Quote:
ORIGINAL: noveldoc

Hi Zor. Good to see ya.

I like to use thinned epoxy. Mix slow epoxy one part A, one part B and 1 part 90 percent isopropyl or denatured alcohol. Brush on in glops and squeegee out thin with a card. When dry, sand or I like to lightly scrape all over with a single edge razor blade held near 90 degrees. Go until all the high shiny areas are gone and you have a smooth sort of burnished finish.

Fills pores and adds strength.

Tom
Hello Tom,

Good to see you also.

Just a word of explanation for my choice of aircaft dope versus epoxy.

Epoxy in thin layers is hard and brittle. When the airplane structure flexes under flying stresses that epoxy thin layer cracks (develops thin fissures) and there is no forces transmitted across a crack even if it is nearly at the molecular level.

Some people like to finish their model with epoxy and fiberglass cloth. The fiberglass cloth is the reinforcing material. The epoxy just hold the cloth in place. If the epoxy cracks the threads of the glasscloth keeps doing its function. It is appreciably heavier than fabric and dope.

A thin layer of aircraft dope always remain elastic and always have a srinking tendency. It is like a thin layer of rubber stretched over a surface (just to help the explanation). The dope has adherance to the substrate (balsa or others) while of course the rubber would not adhere.

I prefer using aircraft dope for the reason mentioned in the above paragraph. Then there is no need for heavy glasscloth. With dope it is preferable to use a light nylon or polyester fabric or the lightest Ceconite material.

We all have our preferred choice but we rarely see the reasons for that choice like I am posting above.

Send me a PM about "how you are doing".

Best regards de Zor.

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Old 09-21-2010, 02:26 PM
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Default RE: SANDING SEALER


Quote:
ORIGINAL: E-Gap

I've mixed PolyCrylic and talc with a bit of distilled water for a good cheap filler that didn't stink up the house. Sands real nice with 400grit. I've applied before and after covering with glass. Fills in the weave nicely.

As a kid, I and my flying buddy , made our own filler with Aerogloss clear and his baby brothers bath talc. Slight blue tint and smelled nice after the buytrate vapored off.

Ray W.
Hi Ray W,

Concerning talc ___I do not know how long my model(s) would smell like a baby's bum ___Hee Hee !
I do not know either who makes talc baby powder else than Johnson's baby powder. Most available at drug stores (pharmacies) is scented. However Johnson also make some unscented talc which is what I use. I did not find it easy to source. After nearly a dozen stores I found it andbought a large container 425 grams.

It works as well as microballoons and is a lot cheaper in price. It also makes a smoother finish than microballoons. Ifthemodel is so light and filling is really needed than use microballoons. It may save 0.01 gram of weight ___ Ha! Ha!

Zor

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Old 09-21-2010, 03:12 PM
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Default RE: SANDING SEALER

Thanks guys for the help.
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Old 09-21-2010, 03:43 PM
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Default RE: SANDING SEALER

Zor,

No more bums smell for me either.

At 14 years old or so, we had to beg borrow and steal what we could. Money was tight for us so we couldn't fly a new plane until we crashed the current one. Gave us the parts as bellcranks and fuel tanks to complete the new one.

Steve's sister was living with him and his mom when we nicked the talc from his sister's little boys room.

We flew most of one summer on just one burned out glow plug between us but thats for another thread.

Ray W.
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