Stewart’s Systems question

[Nev]

The Stewarts Systems instructions for aluminium panels specify to etch, prime, then top coat.

However I’ve already sprayed a few panels during the build process with “Aviation” Zinc Phosphate primer, and I’m concerned that it may not be compatible with the Stewart’s Systems process. Any advice ? Can I simply spray the Stewart’s primer over the top ?

Any help appreciated.

[N942VT]

Nev, I've sprayed Stewarts paint over all kinds of primers (and other paints) and they have adhered well once properly scuffed. I'm sure it's not recommended but once the primer is cured I don't think it matters to the paint. Call Stewarts and talk to Andy, he's always good.

[robcaldwell]

I spoke to Andy about this also. He says you can use other primers, including solvent based primers.

[Glenn Patterson]

WIpe the primer down with 70% isopropyl to remove any finger prints so there are no oils worked into the primer while scuffing the primer. Follow the Stewart's sheets for spraying. That includes wiping it down with 70% isopropyl before you spray the topcoat on. If you have not sprayed Stewarts before then I strongly recommend that you practice with it. There are a lot of good videos on Youtube. I have sprayed vehicles out with the solvent based urethanes and acrylics. The waterborne paint is a different beast and lays down different. So find what air pressures work best, right distance between the gun and the surface so that when it is time it should go good. I emphasize cleaning every step of the way to avoid any problems. My friend who taught me to paint had 3 rules to painting. 1st rule is clean it before any sanding, 2 clean and tack before spraying and if in doubt clean again. Worst thing is sand it smooth then run hands over it to feel it. We bought a dozen cheap cotton gloves that we used for handling the parts. We built a booth and hung white poster board in the booth so we could check the gun to see that it was spraying good and all was good to go. Best thing I can tell you with Stewart's is to have a small kitchen scale and use it to weigh the product so it is exact every time. We found that worked better than just using the measuring cups. Also mix the hardener in and stir it in then let it sit about 10 minutes before adding the water so the paint can properly catalyze. If the water is added right away the result is a hazy finish.

Last but most important. Stewarts and every other waterborne companies urethanes and hardeners is as deadly to humans as the conventional solvent based coatings. The Stewarts use a isocynate or disocynate hardener thats that is common to solvent based coatings. The waterborne products are promoted as environmentally friendly and likely just falls in the legal definition. It cuts a very thin line between fact and fiction. If I could paint in the summer based on my experience of painting our airplane with waterborne that I would now use Endura for aluminum and fabric that is solvent based. It is a proven product that is far less costly than the standard aircraft finishes. It has been a long time but I had a conversation with Endura in I think Edmonton and he recommended the grades of urethane for fabric and aluminum. Besides cost it was available at our local auto parts store so no killer shipping costs and risk of freezing in transportation. I will not disparage the quality of the finish as we were able to get the Stewarts to give a glossy glass smooth finish with zero orange peel.

It took me a while to find the SDS or MSDS sheets on the Stewart's products. A person has to wear proper respiratory protection, work in an environment that has good air exchange and wear the nitrile gloves and tyvek type painters suits. The only advantage to any water borne besides not evaporating solvents in the world is that if your shop is heated with wood like ours is that you do not blow the place up. To call it environmentally friend gives a false sense of security that the products are safe. The only environmental friendly component is the water. The catalyzed waterborne products are every bit as human unfriendly and dangerous the solvent based product. We took all the precations of wearing good respirators, tyvek suits etc, built a spray booth that had a calculated air change every 1.3 minutes and I still had a reaction to the hardener. I guess one too many exposures over a lifetime where I had painted a handful of cars and trucks.

[rodsmith]

90% isopropyl is what is recommended, probably no big deal, just less water so faster evaporation.

[Ed.Meyer]

I agree with the comments about the hardener safety. I tried using a carbon filter respirator and that was not sufficient for me. What leaked around the respirator made me feel like I had pneumonia for a couple days. Using a fresh air respirator with a hood covering my head solved the problem. The other comments right on...

[Nev]

Thanks guys. Glenn, your advice is much appreciated!