Georgia Jets Home Page

Tips & Techniques
Helpful Articles From Georgia Jets Members

Glassing Wood Structures - Alternate Glassing Technique
By
Tim Fielden

How many of us have wished for a way to minimize the glassing, priming and sanding process when finishing sheeted surfaces? What are the options when the weave is exaggerated after glassing, the second coat of resin does not suffice, and the first primer coat reveals more pinholes in the glassed surface than you can count? The following will outline a solution that I used on my last glassed wing that provided excellent results.

The concept for this glassing technique is derived from an automotive refinishing technique. When a painter paints a car, does he sand between each coat of paint or apply multiple coats of paint forming a uniform consistent finish that is chemically bonded? The answer: He applies multiple coats of paint in one spray session. Let us consider the following; Sanding between coats provides mechanical adhesion, with little true chemical adhesion. This is true for any material, fillers, primers, color coats and topcoats. A wet on wet application forms a chemical bond or melting that creates a single layer of film that is chemically bonded and therefore constitutes a singular coat of material. The advantage of this is less time applying paint and a single layer or sheet of paint.

Let me first address some common concerns regarding absorption and weight. Which is heavier; primer or finishing resin?  A little resin goes a long way and can be applied very thin minimizing film build and weight. Primer on the other hand is often misused by over applying and usually requires sanding between applications. Because one application will not achieve the desired result, it takes much more primer to cover the object and hours of sanding after each application. Yes, the surface needs to be sealed before any additional material is applied, resin, filler, or primer. Therefore, how do we minimize sanding, weight, over absorption and get the structure into the air faster?

My solution to these questions is relatively simple and begins with the standard process of glassing.

Step 1. Prep the surface as usual; properly sand the wood sheeting, thoroughly clean the surface, then apply cloth and resin using a squeegee.

Step 2. Before the surface becomes dry, defined as tacky and not sticky to the touch, usually occurring after about 30 minutes (sheeted surface is sealed although not cured) mix a small amount of finishing resin and reapply with the squeegee. You can see the material filling voids in the cloth weave as you go. Don't try to flood the surface, as this will create additional work when sanding! Let this application dry for 15 to 30 minutes until tacky and check the surface for coverage and voids. If the surface requires additional coverage, apply a third coat using the squeegee technique. It is important to note that both top and bottom should be glassed in this manner within 24 hours or less if possible to minimize any warping from absorption or shrinkage.

Step 3. Let the glassed item cure for a couple days and then sand lightly with 120 grit dry paper and then resand with 220 grit paper. (hint: Spray with a guide coat of flat black before sanding.) The additional coats of resin will permit more aggressive sanding with minimal risk of over sanding into the cloth resulting in fewer defects to be corrected with primer.

Step 4. Double-check the structure for imperfections that may require filling and fill before priming. If you have performed the above steps correctly, the surface is ready for primer. Two light coats sprayed wet on wet will probably get the job done and after sanding, you are ready for final paint.

Cautions

Always use proper safety equipment with adequate ventilation!

Allow enough time for the process, thirty minutes before dinner is not enough!

Apply it thin and you will win! Excess material creates unnecessary work.

There is no substitute for proper surface prep!


Summary

When using this technique, the first coat of resin will seal the wood surface although it is not completely cured. Minimal additional absorption will occur thereby avoiding the airplane killer; weight. The glassed structure will cure in about the same length of time, and when you sand the glassed surface, there is less chance of sanding into the weave. Yes, you will spend a little longer applying resin, but you will eliminate the sanding between resin coats, find fewer major surface imperfections and most likely eliminate a second primer application. Additionally you won't have to set the garage up multiple times for different operations.

The result is at least a saving of one day in prepping the structure for paint and a substantial weight savings if performed properly. The models that we glass and paint have inherently high wing loading and a few ounces saved will have a huge impact on wing loading. Best of all for me, there is less sanding.

I hope you will find the above information useful and try it a least once. What have you got to loose, extra layers of skin?

Tim

Back To Top