Stewart System and Mogas

[stede52]

For those of use using Stewarts system, I have found some issues using Mogas. The Stewart paint has no issue with the Mogas, however, the primer and glue does. I want to be very clear about the fact I really like their system and will use it again but I will be changing their process around any areas were Mogas could get under the paint. Currently, I don't know if Stewart System has a solution for the problem but at the time when I talked to them they didn't so here is what I would suggest doing:

If you're using auto gas in your engine you may want to follow this process because auto gas will migrates under any exposed paint edge and soften both the Stewart primer and glue holding down fabric. To eliminate this problem you need to use a catalyzed automotive epoxy primer (epoxy primers adhere best to fiberglass) rather than Stewarts glue and primer around the fuel caps and fuel header relief valve. Here is the process I used to fix my problem:

1. Cover the wings per the instructions using the Stewarts glue, however, when you come to the tank filler openings glue down the fabric to within ½” – 1” of the filler edge leaving exposed fiberglass around the opening and clean of any Stewart glue.

2. Prior to brushing and spraying Stewarts primer, tape off an area about 3 inches from the edge around the filler opening onto the fabric you. Do the same around the header relief valve. This is the area where you will be spraying two or three coats of automotive epoxy primer rather than the Stewart primer. Apply the auto primer to the fabric and onto the exposed fiberglass and to some point on the aluminum part of the filler opening, making sure the fabric edge and fiberglass is sealed. Since the automotive primers are impervious to auto gas it will eliminate any possibility of auto gas getting under the fabric edge and lifting the paint. Pull the tape from these area as soon as you’ve completed applying the primer and allow it to cure. Once cured lightly sand the tape edges (don’t sand thru the primer onto the fabric) so they won’t be visible after priming and painting with the Stewart system.

3. Now tape off the auto primer area leaving about ½” of the outside edge of the auto primed area exposed. Do this on the area were the header relief valve will protrute thru the fabric on the fuselage also. Continue the Stewarts primer process up to these new tape lines.

4. Prior to painting remove the tape covering the auto primer areas, sand the area with 320 sandpaper and continue with the Stewarts painting process. Stewarts paint adheres very well to the auto primers.

Keep in mind there may be other ways to fix the problem but this worked for me

[gkremers]

Steve,
Thanks for the post. I finished covering the wings before you posted on this subject. I have the fabric right to the edge of the metal ring, if you put the cap on the fabric comes right to that point. Sounds like I may have to cut it back? I am using Stewarts Eco Fill but will have a professional shop paint the plane. My guess is they will apply a primer over the Eco Fill before final paint. I spoke with Jason about having a paint shop shoot over the Eco fill and he said no problem. They can paint over the fabric edge maybe 1/8 inch down into the filler ring. Do you think I should cut the fabric back anyway.

Thanks for your input..

Gary

[stede52]

I tried exactly that and it didn't work because I found out that the stewart paint doesn't stick well to non primed aluminum. The auto gas simply migrated under the paint to the fabric and glue and started bubbling. The bare aluminum needs that primer for the stewart paint to attach. However, what they could do is is shoot automotive epoxy primer on the area an inch or two around the cap and onto the exposed aluminum, that will seal the edge of the glued fabric and primer from the auto gas and provide the base for the stewart paint to attach to.