Tech Questions - Sealing the Fabric 1st coat of Poly-Brush


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What is the purpose of Poly-Brush?

You must seal the weave of the fabric before flight. Otherwise, lift will not be created. Poly-Brush accomplishes this along with providing a base chemical coat attached to the fabric. Poly-Brush actually encapsulates the fabric providing a bond to the fabric. Subsequent chemical coats will then adhere to this first coat. Poly-Brush serves a secondary function of securing fabric to the underlying structure. This is particularly important on a plywood surface.

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Should I always brush on the first coat of Poly-Brush?

Yes, brushing does a much better job of filling the weave. If you don't fill the weave sufficiently, you get pinholes later. We don't recommend spraying the first coat.

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What type brush should I use?

We recommend at least a 2 inch wide brush that is a high quality polyester or natural bristle.

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Why is Poly-Brush a tinted color?

So that you can see it as it is applied.

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Do you make Poly-Brush without the tinted color?

Yes, Poly-Brush is available untinted. This is for use on a fuselage of an open cockpit airplane where you do not want a color on the backside of the fabric.

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How do I know how much Poly-Brush to order?

The Poly-Fiber manual has estimates for most aircraft. 1 gallon will cover about 150 square feet for one coat.

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Should I be careful where I store Poly-Brush?

It is flammable so be sure to store it in a safe place. Also, do not store it where the temperature will exceed 100 degrees F for a long period of time. It is not affected by freezing.

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I have some Poly-Brush that I purchased 4 years ago. Is it still good?

The shelf life of Poly-Brush is at least 4 years.

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Should I thin Poly-Brush before applying it? If so, what kind of thinner should I use?

Yes, Poly-Brush should be thinned 1 part of thinner to 3 parts of Poly-Brush. If the temperature is less than 85 degrees F use R 65-75 Reducer. If the temperature is 85 degrees F or above use R8500 reducer.

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What should the temperature be before I brush on the Poly-Brush?

Do not apply Poly-Brush in temperatures below 60 degrees F.

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Is it really necessary to clean the fabric before I apply the first coat of Poly-Brush?

Absolutely! You must clean the fabric using a clean, lint-free cotton rag and MEK. Wipe it down thoroughly. This will remove all oil, dirt, and other contaminants that will prevent Poly-Brush from adhering to the fabric.

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While brushing on Poly-Brush, I notice runs appearing on the underneath side of the fabric. Is that a problem?

It is normal for Poly-Brush to run under the fabric. As a matter of fact, it should if you are getting good penetration. However, you do not want it to drip through to the fabric beneath unless that fabric has already had a coat of Poly-Brush applied. In other words, if you are applying Poly-Brush to the topside of a wing and the bottom side has not been coated, do not allow the Poly-Brush to drip through to the bottom side.

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What if I accidentally allow Poly-Brush to drip through onto the unsealed surface?

Immediately take MEK on a clean rag and remove the Poly-Brush from that area.

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How long does it take for Poly-Brush to dry?

This depends upon the temperature. Usually it will dry in about 15 minutes.

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What about brush marks?

Brush marks are usually not a problem on the first coat. Don't continue to go back over areas with more Poly-Brush. That can cause a problem. Simply brush on a wet coat using one pass with the brush. Go back over the area one time only to smooth bubbles that might have formed.

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