Custom Search

Sunday, May 2, 2010

Working and Painting Tips for Fiberglass

Introduction to Fiberglass
When considering the strength compared to the space age canopies that are common on most pod and boom helicopters there is no contest. This plastic material is virtually indestructible at the penalty of being virtually un-paintable without specialized and expensive automotive primers and paints, there is also a very limited range of color available.


A wonderful attribute of fiberglass is in its flexibility. However, fiberglass parts will migrate (change shape) while inside the shipping box. When two mating components are brought together and they do not align or mate, the culprit is a warped part. Many become upset and wish to lay blame but dealing with this is very simple when explained a simple procedure. Using a heat gun set at the high setting at a distance of 1-2 feet away, evenly heat the warped part until the outside surface is hot to the touch and the part has become pliable (flexible). Using adhesive tape, mate the two fiberglass parts together and let both parts sit until both parts have reached room temperature. Remove the tape and now both parts are stable and match one another. In some instances, depending on the location of the warp, the part may need to be held in an overextended position to achieve the proper shape when the part is finished.

Working with Fiberglass

Difficult to work with, we disagree. Fiberglass is easier to repair than you think. Using today’s CA type of adhesives, a severe crack in a fuselage can be simply fixed and the repaired section is much stronger than in its original state. Add touch up paint and no one would ever know it had been damaged. There is a limit to this type of thinking where purchasing the replacement fiberglass part is simply cheaper and less work than performing major reconstructive surgery.

The Paint Job

There is no magic to a good paint job, the true secret is time, patience and common sense. A beginner who thinks that they can throw paint onto a fuselage Friday night before flying on Sunday is dreaming, the helicopter would be flyable but even that is a stretch. The average beginner will spend the better part of a month to apply a good clean paint job.

Preparing the Fuselage for Painting

Examine all the fiberglass components to see where work needs to be done to allow a simple "bring up" of the fuselage. "Bring up" describes the necessary steps to complete all the jobs in order to start priming the fiberglass parts. Typical work that is done at this stage is rough sanding on seams and jointed components, filling of surface imperfections, adding panel lines and rivets, cutting required holes and preparation for priming.

1. Start by thoroughly washing all fiberglass parts in mild detergent and warm water, this will remove any residue remaining from the molding process. Next wipe down all the parts with Acetone (from the hardware store). The Acetone will remove all traces of oil or grease that will affect the adhesion of two fiberglass parts or between the paint and the fiberglass. Now using fine steel wool or an abrasive pad commonly used for scrubbing dishes, scuff all surfaces that will be joined or receiving paint. What is important to note here is that we are breaking through the topmost resin surface and creating the best surface for adhesive or primer to adhere to. The prepared finish will have very fine score marks usually seen when the part is held to the light at a slight angle.

2. This is the time to rough sand any accessories or small parts, using the 320 grit sandpaper, that will be assembled and attached at different positions on the fuselage. These can be marking lights, engine exhausts, scale fuel tanks, horizontal and vertical stabilizers, guns, antenna or any scale details being bonded to the fuselage. These accessories should be test assembled to make sure that all parts are prepared, and you will be able to see any problems that may arise in trying to paint these parts. Some thought should be put into how to hold the part as it is being painted. Go ahead and bond these parts at this time using the slow CA glue. A quick note on adhesives, as the fuselage resin is polyester, do not use any regular 5-30 minute epoxies to bond two fiberglass components together. Stability is specially formulated for this purpose and excellent for fillets. Epoxy and polyester will not bond properly to one another, but epoxy is good to bond unlike substances like wood or metal to themselves or other parts.

3. Once the detail parts have been built into sub assemblies, they are ready to paint, use a filler in sections that have gaps or slight surface imperfections, occasionally there are voids (air bubbles in the resin) that occur near the surface that need to be filled. There are a lot of good fiberglass fillers on the market, it is best to check with your local hobby shop to get a recommended product. Try to stay away from porous fillers designed for wood as they will shrink and are not a good choice for large areas.

4. Most major windows and accessory holes have will have been precut, leaving only those that have a user dependency like the type of exhaust system used on the helicopter or the exact exit position for the cooling fan shroud.

4a. When making cutouts or holes in the surface of the fiberglass the best procedure is to drill a pilot hole using a 1/16" drill bit at corners or along a curve. Start with a permanent marker to draw the opening or window. The pilot holes serve to avoid leaving sharp corners which given the nature of a model will be the focal point for stress cracking originating from corners. Once the holes have been made, use the dremel-tool for all other roughing cuts. The cut off wheel is the best for straight lines and either the sanding drum or the curved stone is used for smoothing edges. If the cut out is a window, do not use the dermel-tool for the final work. Switch to a sanding block, square blocks of various sizes for straight edges and round dowels for rounded corners.

4b. In the case of the exhaust opening, it should end up being 1/8" larger across the outside diameter of the exhaust pipe that extends below the bottom of the fuselage. After drawing the circle, use grinding stone and move in small circles until the hole is at the size wanted.

5. Priming the fuselage accomplishes two tasks: firstly, the primer paint is designed to aggressively adhere to the surface being painted and provide the best surface for the colored paint to adhere to; secondly, all surface imperfections will become visible. Depending on the particular imperfection, light sanding with number 600 or 800 sand paper and the second priming will take care of 90% of the highly visible problems. The remaining 10% need to be filled, let dry, sanded again and then sprayed with the second coat of primer. The primer process will be repeated until the surface is as perfect as your patience and time permit.

6. Select your paint color and follow the directions on the particular brand of paint being used as each manufacturer has different requirements.

No comments: