Create a perfect fiberglass finish, part 2

Jul 03, 2012 14 Comments by

Last week, Rick Michelena shared the steps to prep your aircraft for a perfect fiberglass finish. In the second part of his three-part series, he begins the fiberglass work and gets the model ready for paint.

Here are the simple items needed to produce a fiber-glass finish that will last for many years. You will need the following: 3/4-ounce fiber-glass cloth, 90% isopropyl alcohol, Z-Poxy finishing resin, mixing cups, stir stick, scissors, and sponges cut in small squares.

After laying the fiberglass cloth onto the surface to be glassed, place 10cc of resin and 10cc of catalyst in a mixing cup. Mix well. Add 10cc of 90% alcohol and mix until the resin becomes clear again. Upon the first introduction of alcohol, the resin will become cloudy. However, keep mixing until it is clear again. This step helps the resin to flow.


Cut the fiberglass cloth slightly bigger than the surface to be covered. Apply only enough resin to wet the cloth. Use the small sponge pieces to spread the resin all over the cloth. Strength only comes from wetting the cloth. Extra resin only makes your model heavy and adds no additional strength. When the sponges become hard, use new ones.

After the resin has cured, about three hours, use a piece of #100 grit sandpaper to cut the fiberglass cloth that hangs over the edges. Simply sand on the cloth, and the extra cloth will fall off, leaving a clean edge in prepararion for glassing the other side. Once everything is fiberglassed,  add one additional coat to help fill the weave. When the final resin coat dries, sand the entire fiberglassed surface with #150 sandpaper in preparation for the next step.

Fiberglass cloth and balsa are not sheet metal. Therefore, fill the weave of the cloth to achieve an excellent finish. Here is a technique I developed many years ago, and it saves me both time and material. Buy acrylic lacquer auto primer and simply use a roller to fill the weave of the glass cloth. Trying to do this by spraying primer is a waste of time.

The parts look like this after rolling on the automotive primer.

The entire wing has now received the first coat of primer. It is now time for bodywork lesson #1. The primer is used to detect flaws and fill imperfections. After the primer dries, about 30 minutes, block sand with the B&D Mouse sander in a block-sanding motion.


As you can tell, nearly 90% of the primer has been removed. At this stage, sand with #220 paper in an “X” pattern. The remaining primer areas are actually low spots but have now been leveled by the primer. After everything has been block sanded, apply a second coat of primer. This coat and all subsequent ones will be sprayed.

Here is an example of “pin-holes” that were in the epoxy glass fuselage. These are easily filled using light-weight spackling. Use your fingers to push the spackle into the pinholes and rub off the excess with the palm of your hand. Allow this to dry. Then lightly sand the area and spray a second coat The pinholes will be gone!

Purchase a non-shrinking glazing putty from a local auto body paint store. Apply a small amount to your finger and dip it in lacquer thinner. It will smooth out the putty and require minimal sanding. Address all imperfections with glazing putty. Then spray primer on that area only. Once everything is perfect, wet sand all the primer before painting.

Wet sand the entire model with #400 auto body sandpaper. I like to use water and a little ammonia to help remove any impurities. Wear latex gloves so that your fingers never touch the paintable surfaces. This is because the oil from your fingers is enough to cause problems later.

Here is a photo of items now ready for paint. Tune in next week, when we paint the aircraft, add graphics, panel lines and rivets, navigation lights and clearcoat to complete this project.

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14 Responses to “Create a perfect fiberglass finish, part 2”

  1. Kim Jeppesen says:

    Nice work!

    I’m not that experienced with fiber glass covering, but I need to learn as it’s soon time to cover my TF DC-3

    Thanks for sharing Guys … and Girls ;o)

  2. Gerry Yarrish says:

    Excellent post. Covering models with fiberglass and resin at one time was like a black art, and few would share their techniques. This type of resin is so much more rugged than Film covering and it makes the plane almost hangar rash proof! Great article. thanks

  3. Phil Hultin says:

    I’ve fibreglassed balsa floats using this kind of technique – but I definitely picked up some good pointers here. Using small sponges is way better than the acid flux brushes I’ve been using. Thanks for the detailed descriptions.

  4. MadDog says:

    Thx for sharing!

  5. Thor Fjellstedt says:

    This is a very helpful post. I am new to building models with this technique. It will be a great guide. Thanks a lot.

  6. Gordon says:

    Good article. I would have liked a little more detail on the application of the resin. I have not seen sponges used from this before. I would have thought they would soak up too much of the resin.

  7. Barry says:

    I’m a bit surprised that the author used 91% isopropyl to thin out the resin. I thought the standard practice was to use denatured alcohol containing essentially no water. Has anyone else successfully used 91% isopropyl for this?

    • Tony says:

      Hi Barry, Isopropyl is denatured alcohol. Using 91% alcohol will do the job, but costs much much more than denatured alcohol ( in South Africa anyway !) As a matter of interest methylated spirits , I am told , is also denatured alcohol.

  8. Gerry Yarrish says:

    I use rubbing alcohol all the time with no issues

  9. Rick Michelena says:

    Hey Barry,

    I have always sought out the least expensive method of building. As noted in another post, I used to use denatured alcohol. However, a few years ago, I tried 91% alcohol from Walmart with no negative effec ts. I noticed that the introduction of either denatured or 91% alcohol still causes the epoxy to cloud up…simply mix with a stir stick until it is clear again. You will have no issues, I promise. Good luck!

  10. c.s.ang says:

    How many % weight added compare to film?

  11. Mark Williams says:

    Is there any way to fibreglass an EPO plane?

  12. Model Finishing Services says:

    Here are the simple items needed to produce a fiber-glass finish that will last for many years.

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