Priming aluminum skin: a procedural question

[Bcone1381]

I have no experience priming or painting. I read on another popular aircraft builders forum that many builders prime aluminum skins before dimpling a to save time, energy, and the abrasive pads last longer. My situation: I have fabricated my boot cowl skins, and I would like to dimple and install nut plates next. So, it appears like its time to prime these surfaces. My wish is to prime the interior of the boot cowl skins, install the nut plates, and then move on the next task in the building process. Final paint application would be WAYYY down the road....after the fuselage is covered with fabric, the engine hung, and the engine cowl is fabricated. I don t even know what color I want the boot cowl to be yet!

But the local Paint Supplier says all epoxy primers need to get painted with in 3 days of application. If they don't get covered, then the primed surface needs to be scuffed, cleaned, and a coat of primer reapplied before painting.

Reality is I wont paint the interior skins, I guess I will go ahead and prime them....but my question is....

Is my paint suppliers information that "all Epoxy Primers needs paint within 3 days of application" accurate?

No Primer/Paint wars please. Primer and Paint topics can get personal. Share with me your methods in a friendly, and agreeable manner.

[Bdflies]

No expert here, but I can relate my experiences. It's so humid here, in S. Louisiana, we epoxy coat our kids, to prevent rust!

Seriously, primer as soon as possible is a must where I am. Past a couple of days, a topcoat will definitely require a good scuff. I've waited much longer than a few days, scuffed and sprayed top coats many times. Never heard of respraying primer. Never saw anyone spray a second coat of primer.

Just my experience.

Bill

[rodsmith]

That is typical, in fact products I have used in the past have said 24 hours. But the few I have used just said to scuff and clean if waiting longer, didn't mention another coat of prime. I only use epoxy primer on steel parts, something cheaper on aluminum, just has to be compatable with the top coat you are using.

[Mark Goldberg]

I see no reason not to prime the interior of the boot cowl parts. IIf you want to. And I would never top coat aluminum interiors - only primer. Steel parts require both primer and top coat. I would leave the outside of the skins bare until you are doing your final painting.

It is common to scuff up primer (with Scotch Brite) that was applied long time before. Otherwise the top coat will not stick. MG

[Archer39J]

Good stuff, I would have had a similar question when I got there. Figured I'd just prime the interior of those panels and leave be, whole exterior will get stuffed, primed, and painted later.

[Bcone1381]

I am thankful for everyones response. It helps a great deal and gives me a much better understanding of the big picture of what the process should look like.

Brooks

[Bdflies]

Reading my message, I failed to mention that, when prepping aluminum for primer I acid etch and alodine before priming. It's really not difficult and I think the etch promotes great adhesion. Some folks do a nice scotchbrite scuff and prime, without etching. That too seems to work.

Bill

[Bcone1381]

Request for more schooling.....

My questions concern safety, and prudence....for example, what is a normal and acceptable practice...for painting.

Its still winter in Michigan, but I have a heated shop. If I want to paint inside, do I need to build a Paint booth to prime the inside of the Boot Cowl Skins and a few small fuselage areas that received heat from the torch ? I see people build paint booths inside of there shops, but want to believe that I don't need one...that drop clothes are good enough.

Then if I fabricate my own small paint booth out a collapsable - folding canopy (Like one that might be uses in the summer at the beach) and drap the sides with Visqueen, I want to believe that I will be safe "Priming and painting" inside of it with my charcoal respirator....but think maybe I should have some fresh air pumped in with a fan. Which requires the air to exit...seems like its getting complicated.

[Ray Strickland]

Brooks,
My experience (painting two homebuilts) is that for very small jobs done with a spray can you can get by with a drop cloth. When you move up to HVLP or higher pressure you will be dealing with fine atomized paint that will go everywhere and settle on everything. I painted ny first airplane in my garage w/o paint booth and wish I had taken the time to build one. With my Bearhawk, I built a in my hangar a 14’x 24’ paint booth using 2x4’s, 2x3’s, and furring sticks covered with 4 mil plastic. Filtered air going in; filtered air going out; moved by three 20” box fans protected by the exit filters (would have been better to use four fans). Kept my hangar nice and clean and kept dust out of my paint job. Cost for all materials was about $300, I think. For single part paint and Stewarts (what I used) you can get by with a charcoal mask (you’ll need fresh cartridges about half-way through). It is my understanding that any solvent based two-part paint includes cyanide as an ingredient which the charcoal mask will not protect you from...you need a fresh air breather system for that. The water in Stewarts two-part paint is supposed to eliminate the cyanide danger. Maybe some real paint experts will chime in and share their knowledge and experience.

[Mark Goldberg]

My understanding is that urethane and poly urethane paints with catalyst for sure require a fresh air supply. But epoxy paints (also two part) can be shot with using a mask with charcoal filters.

And for whatever it is worth - I have never had a paint booth. But you can get a cleaner paint job having a well cleaned paint booth. Mark

[Bcone1381]

Thanks for the feedback Ray and Mark. In the near future my projects fall into the category of small jobs with a spray can. The paint store sent me home with a rattle can epoxy primer.....its rattle can like I have never seen before. There is a procedure to follow that punctures an inner sealed reservoir of "part B" then after the can is shook up, its sprayed on like spray paint. It was kind of expensive, but I think a pretty good product for my near future needs and simplifies thing for this rookie doing a small job.

I have looked over the Material data safety sheet and will be calling around monday to double check that my mask is compatible with it.

[Bdflies]

Brooks, allow me to make a suggestion. Paint a sample of something, with your rattle can epoxy. Let it cure as long as they recommend. Then, rub it good with a rag soaked in MEK. If the primer stays on, you're good to go! If the MEK takes the primer off, don't use it. It's not a good thing to spray an expensive top coat, to realize that it's lifting the primer...

Bill

[Bcone1381]

That sounds like a good idea Bill.