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Osmotic Bubbles

Posted: Thursday, September 29, 2011 9:18 AM Quote
I have built and finished a Challenger II and the airplane has been flying since July. I used the SS for all the fabric work and the paint is EKO poly. While I am a great fan of the covering system, I was struggling with the top coat, and spent many hours on the paint job. Although the final result was very nice, it was a bear of a job to get there. However, now my frustration level is going vertical, since I have a bad case of osmotic bubbles that developed. It started very small, on one fibreglass wing tip, but now that the rains have started, it has spread to all fibreglass surfaces (both wing tips and the nose). I have read the recent newsletter, where the osmotic bubbles are mentioned, but I'm not clear as to the solution. Will the bubbles disappear once it dries out? Does the surface need to be repainted? (a prospect that I would want to avoid at all costs). If the bubbles disappear, can there be sealer applied to avoid future recurrence? Any thoughts and ideas are appreciated.
I will be bringing the airplane home this week end, and it will be stored dry for the winter.
Thank you.
Martin Kluftinger
Pemberton, BC
Posted: Thursday, September 29, 2011 11:41 AM Quote
We have experimented with a few different brands of waxes and had mixed results. I like the Meguires "Ultimate" wax and have ordered some of the Lo Presti "knot wax" which I think will work the best. Wait until the surface has returned to normal, Wash with something like Dawn dish soap and rinse. Wipe with Isopropyl Alcohol and then wax. It will take 2 weeks to get the results from the "knot wax" test and I'll keep you informed.

Posted: Thursday, September 29, 2011 1:19 PM Quote
Thanks, Jason. I hope that it will dry and return to normal.
It is interesting that it only occurs on a surface that cannot breathe. The outerwing was painted and prepped exactly the same way, with 2/3 being fabric, and 1/3 being the fibreglass tip. No blisters on the fabric portion, so it appears that the paint can breathe through the fabric.
Posted: Thursday, September 29, 2011 2:56 PM Quote
Testing has shown that the cleaner the surface prior to application of the paint the better the adhesion and less particulate under the paint to act as a sponge to attract water vapor through the top coat. The use of Isopropyl Alcohol prior to painting as a final surface wipe to remove any remaining dust that the tack rag didn't pick up seems to help. I have seen blistering on one customers aircraft over sheet metal where the blisters follow what appears to be the arc's of a sanding pattern in the primer coat. Even though this phenomenon is extremely rare and not just related to our products we are actively working towards a solution and exploring every possible option.

Posted: Friday, September 30, 2011 11:02 AM Quote
Yes, the blisters clearly follow the arcs of the sanding pattern. Even so the grit used was 320; also, the use of Isopropyl Alcohol was not suggested at the time I was painting.
Oh well, live and learn. I'm over the initial frustration, and hopefully the blisters will settle down over the winter and we'll have some solution for a sealer.
Posted: Friday, September 30, 2011 3:02 PM Quote
I have heard that some sand paper can leave behind tiny salt like crystals which would contaminate the surface and act as magnets for water vapor. The use of Isopropyl Alcohol is something we just learned about our selves and have started using. Apparently the automotive industry has been doing it for years.