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Aircraft
Maintenance TroubleShoot > Aircraft
Paint Stits Poly Fiber and Randolph
Pinholes in fabric surfaces
1. Close examination of pinholes in fabric surfaces with a powerful magnifying
glass will reveal the pinholes are merely voids between the threads in
the fabric weave which were not filled with the preliminary coating being
used. Most commonly found where fabric is applied over solid structures.
Voids in the weave below the surface trap escaping solvent vapors which
build up pressure and balloon through the soft, partly dry outer film causing
small bubbles which eventually break or are sanded off, leaving a hole
down through the fabric weave.
2. Too much atomization of air pressure on spray gun.
3. When using the Poly Fiber "Stits" process the following suggestions
have been found to be effective in eliminating pinholes. After the finishing
tapes are in place, apply two brush coats of Poly- Brush over the tapes
and over the leading edges and other structures where pinholes may be suspected.
The Poly-Brush for this application is reduced only 25% with Poly-Fiber
Reducer, then add one ounce of BR-8600 Blush Retarder per quart of Poly-Brush
to delay the drying and allow the brush marks to flow out before the coatings
flash off and lock in the brush marks. Continuing to brush the surface
after flash off begins will imprint brush marks in any coating. Information
is from Stits Technical Bulletin #91-2 August, 1991.
Loose Dacron fabric
1. Especially in cold weather. Fabric was not heat tauted when installed.
Improperly heat tauted fabric may appear to be satisfactory on the ground
in 60 degree weather but will develop wrinkles and flutter in the prop
wash area when flying at altitude in cold air causing fatigue cracks in
the surface.
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