cowl primer adhesion - what is good enough?

[KayS]

Hi All,

talking about to prime the cowling... i made some tests with grey primer on scrap cowling pieces. after one day of curing it was easy to scratch/remove the primer with my finger nails. now (a week later) i looked at the pieces again and it was much harder to remove the primer but i'm just not sure how well the primer should stick to the fiberglass.

so what is sufficient adhesion for you guys? is there any kind of measure or test to say when it's good enough?

thank you
Kay

[lostpilot28]

What kind of primer are you using? I've noted a huge difference between the rattle can stuff and the primer you would buy from an automotive supplier. I used the water-bourne Stewart Systems to paint my airplane and found that their primer is very tough.

About a year before that I used rattle can primer on certain parts of the interior and it would flake or scratch off very easily. The self-etching primer was a little better, and the longer it stayed on, the more scratch resistant it was. But, Stewart Systems was tough as nails after day 1.