I keep reading about people using primers for exposed parts like the wheel wells.   Primers are by definition very porous.  They are designed to absorb surface coatings and have a high surface energy (which is the opposite of waxing with low surface energies) as a way of promoting bonding.  In addition, the epoxy backbone is sensitive to UV light and has the bonds broken at that frequency and energy, (acrylic polymers are not very sensitive to UV frequency and thus are long lasting in sun).  Why not use a urethane?  It will not stain or discolor as easily as epoxy based primers.  True, the primers tend not to run as easily and are easier to apply than a gloss.  And a gloss will not hide flaws very well but I'm sure all of the work out there is flawless!

 

So why use a primer?  What am I missing?

Dan,

 

Who said they are using a primer?

 

However, if someone is considering the use of an epoxy primer, consider this experience.  I prepped my airplane with WLS 2-part primer and flew it for 1.5 years before finally painting it - you see, there were a few "experiments" that had to be straightened out before it was worth putting on paint.  You are right about it having high surface energy if that means is was also susceptible to easy formation of static electricity.  I never got the LORAN to work as it shut down shortly after takeoff.  Passing my hand over the cowling would cause the hair to stand up on my arm.  I was worried every time I had to drain the wing fuel and refill it from plastic gas cans. The airplane spent maybe 200 hours in the sun during the pre-paint period and there was no degradation of the primer. 

 

Ignorance is bliss! 

 

Make sure your Good Angel is always around....

 

The use of the Lancair grey fuel tank sealer is beneficial because it can be brushed on and still produce a sealed, high gloss surface that also hides many imperfections - really!  Perhaps it can be obtained from the manufacturer in white?

 

Don't use Krylon - it won't seal the porous glass - but, it is light, looks OK and can be removed with a swipe of acetone.

 

Builders should consider sealing glass/carbon beyond the purpose of neat, easy to clean wheel wells.  Hydraulic fluid or oil that leaks into porous glass/carbon skins will eventually seep thru and can/will cause the lifting of the paint on the other side.  It may also weaken the structure.  In light of that, I suggest that the interior areas subject to Hydraulic fluid leaks and the interior of the cowling subject to oil contamination be sealed some how.  Over time, a white sealed cowl interior reveals all kinds of engine compartment ailments. 

 

If weight is a concern, switch to electronic charts.