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Applying Fiberglass Cloth — Finishing model parts

Applying Fiberglass Cloth — Finishing model parts

When you need a durable and tough surface on your model airplane parts, nothing comes close to fiberglass cloth and resin. They provide a smooth sub surface for primer and painted finishes and, once you’ve done it couple of times, it becomes very easy to do. Here’s some Tips how I do it for the sub-wing of my 1/3-scale Fokker Triplane.

Supplies and Material

Workshop Secrets -- Working with Fiberglass and Resin

You’ll need Pacer’s 2-part Z-Poxy Finishing Resin (www.franktiano.com), denatured alcohol, mixing cups and stir sticks, paper towels, and fiberglass cloth. For all my “glassing” jobs, I use 3/4-oz. (per sq. yard) standard weave cloth. I get it from a company called Thayarcraft. I use their Type 106 cloth (.73oz) and it is very reasonably priced. The cloth is very fine and forms readily around curved shapes. Extremely easy to apply.

Workshop Secrets -- Working with Fiberglass and Resin

You’ll also need 220, 320 and 150 grit sand paper, and when it comes time for priming, some quick-drying automotive Spot and Glazing putty will make quick work of the little pin holes that will show up.

Workshop Secrets -- Working with Fiberglass and Resin

For current pricing, check with Thayercraft Inc., 710 W. Green Dr., High Point, NC, 27260; (800) 218-1375; www.thayercraft@cs.com

Start by cutting the cloth to size. It comes on a roll core and you simply lay it on a clean cutting surface and use  a new, sharp hobby knife to make a clean cut with minimal snags.

Workshop Secrets -- Working with Fiberglass and Resin

Workshop Secrets -- Working with Fiberglass and Resin

Above are the two halves of the Sub-Wing Structure. I have sanded it smooth and added filler to any dings and large seams. A quick wipe with a tack cloth makes it ready for the Fiberglass cloth.

Workshop Secrets -- Working with Fiberglass and Resin

I use throw-away mixing cups. A scrap of balsa makes a handy stirring stick. Just use a clean cup and plenty of paper towels.

Workshop Secrets -- Working with Fiberglass and Resin

Mix equal parts of PartA, PartB, and denatured Alcohol.

Workshop Secrets -- Working with Fiberglass and Resin

Drape the cloth over the part and apply a thin strip of resin down the center. This helps hold it in place while adding more resin.

Workshop Secrets -- Working with Fiberglass and Resin

Apply a second strip of resin 90 degrees to the first. This starts spreading the cloth out for a smooth finish.

Workshop Secrets -- Working with Fiberglass and Resin

Now add two diagonal strips of resin so you have a Union Jack pattern shown above. This smooths out wrinkles and loose patches.

Workshop Secrets -- Working with Fiberglass and Resin

When you get to the edges add more resin to form a bead along the sharp corner radii. This seals the wood. Now set the part aside on top of some blocks to lift it off the workbench and let the resin cure overnight. When cured, you can trim away the cloth and resin from the edges by rubbing it with 220 grit sandpaper. You can then cover the other side of the Sub-Wing with another piece of fiberglass cloth. Set aside and let dry overnight.

Workshop Secrets -- Working with Fiberglass and Resin

After the second large side is trimmed, apply smaller separate pieces to the left and right ends in the same way. Allow to cure and trim away the waste cloth with 220 grit sandpaper.

Workshop Secrets -- Working with Fiberglass and Resin

The front part of the Sub-Wing is covered with a single piece of cloth draped over both the top and bottom surfaces. Apply resin along the leading edge and then onto them top and bottom surfaces.

Workshop Secrets -- Working with Fiberglass and Resin

Allow the extra cloth to drape off the part until the resin has cured. Then use some 220 grit sandpaper to trim away the waste material.

Workshop Secrets -- Working with Fiberglass and Resin

Sand through the cloth and resin along the sharp edges and it will cut through the cloth so the waste part drops free. Don’t use a sharp knife as you will always cut into the wood.

Workshop Secrets -- Working with Fiberglass and Resin

Sand at a sharp angle to the edge and the resin filled fiberglass cloth will fall away without much wood being exposed. Sandpaper is the tool to use.

Workshop Secrets -- Working with Fiberglass and Resin

As with the main part of the Sub-Wing, the front piece ends are covered with separate pieces of cloth. Use the same techniques as shown above.

Workshop Secrets -- Working with Fiberglass and Resin

Mix small batches and if you have any left over, go on and use it to cover other parts. You can also use the resin to fuel proof engine and fuel tank compartments. No sense in throwing away perfectly good mixed resin. Maximize your usage buy thinking ahead and preparing the parts of your model needing finishing.

Workshop Secrets -- Working with Fiberglass and Resin

When sanding the resin beads along the sharp edges, use a metal sanding bar for a smooth straight, edge. Apply some more resin if there are any exposed wood areas along the sharp edges.

Workshop Secrets -- Working with Fiberglass and Resin

Once all the parts are covered and the resin has cured and the cloth has been trimmed, scuff the surfaces with 220 grit sandpaper and apply a second layer of thinned Finishing Resin and allow to cure overnight. Another sanding with 320 grit sandpaper, and you’re done.

That’s it! Stay tuned as we will soon be priming and painting parts of the Fokker Triplane!

Shop Tip: As I mentioned before with my covering tips, use a chemical blocking hand cream like “Invisible Gloves” while using any solvent and finishing resins. Afterwards you can clean up with mild soap and water.

Workshop Secrets -- Working with Fiberglass and Resin

Updated: April 3, 2017 — 2:08 PM
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9 Comments

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  1. Thank you for the detail of your instructions. I am weeks away from my first attempt at applying fiberglass to a model. I am building a dummy wing section to practice on first and will apply your tips.
    Thanks again.

  2. thanks for the tips. My first efforts with glass have looked pretty bad. I knew to use epoxy but didn’t know about the alcohol;.

  3. What exactly does the alcohol do? Also at what percentage is it mixed wit the epoxy?

  4. Great stuff ! One question, when mixing parts A and B, they are 50/50 like any epoxy but what percentage of alcohol is added?

  5. You can do this using Minwax water based Polyurethane too. No need to wait overnight for it to cure. The one thing to keep in mind is that the WB poly can warp the wood, so you need to seal it first by dry brushing the poly into the wood, let it dry, lightly sand it, and apply a second seal coat. Then you can apply the glass and poly and have it done in a few hours. Then you can apply a few coats of sanding primer, wet sand it smooth and apply the finish. I used latex paint on my Top Flight Corsair, let it dry a few weeks, then top coated with automotive clear coat. The plane looks great, and is very light. Techniques are the same, but saves a lot of time.

  6. I used glass resin and the edge if junk mail credit cards to smooth on the wing “no cross patterns just front to back”. it only leaves what is needed to adhere the glass to the wood. This article is very informing. The pic of the cup looks like it is divided into 3rd’s but with a tapered cup how are the portions equal as they look?

    1. The graduation markings are closer together as the cup taper becomes wider making the portions equal in volume. One portion epoxy part A, one portion epoxy part B and one portion denatured alcohol.

  7. I need to make a Fokker D-VIII cowling with glass. Hope I can get some in/to Bangkok! Thanks, Paul

  8. Thanks for a well written tutorial. Would this method also work the same way for EPP/EPO Foam models or is this for balsa/ply only?

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