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Builder's Tip: Prime First
From Bits & Pieces Newsletter, December Issue
Many aircraft builders have discovered that priming gets more and more difficult as you go through building parts. As we start on the building process, we tend to think of “painting” as the thing we do right at the end, after we’ve made the aircraft.
If priming is considered as a first step rather than a final one, it can save loads of time in the construction process. Alclad aluminum is pretty good without priming, but it’s worth considering priming all parts as a first step. The day you start unpacking parts, if it’s a kit plane, or the occasions when you’ve started accumulating aluminum parts that you’ve made, are good times to start priming.
You need to have a plan for how and where to spray, and each part needs to be set aside to prevent damage as the primer hardens.
The editor’s favourite primer
Your editor’s personal favourite is Sherwin-Williams self-etching epoxy primer 988 - G.B.P. It forms a hard protective layer and will prevent your parts from scratches while you continue the build. The inner surfaces will need no more rust protection than this.
988 - G.B.P.comes in cans or in quarts and a little goes a long way. It’s olive drab, but who cares? It takes paint very well. It’s not a bad idea to buy both a couple of cans and a quart. The cans can be used on smaller parts and the spray gun used to prime bigger areas. Although a self-etching primer will attach well to untreated alclad since it contains an acid-etching component, Alodine or Alumiprep acid etching beforehand is a good discipline since it makes double sure that the surfaces are thoroughly etched and clean. The author used Alumiprep and used less than a pint for the whole aircraft (RV-9).
Alumiprep acid etch