Build Primer - Triumph Spitfire Restoration Passenger's Door

Again with the lack of pictures...when I think it'll help, I put in some screen captures from the video. Not the best option, but better than nothing, I guess. To the video:

The video comprises two "full" visits to the garage. I put some extra hours in at work during the week and was able to take Friday off, so I took advantage of it and got over to the garage nice and early for some work.

After enjoying my tasty breakfast sandwich (yes, from Old Mystic General Store again), I got to it.

So good.

The first visit, Friday, was focused on getting the door in 2K build primer that I picked up from Southern Polyurethanes. Based on their recommendation, I went with a gallon of the regular build stuff (as opposed to the high build) and it was about $110 for the kit, consisting of a gallon of the primer and a quart of the activator (it's mixed 4:1). The purpose of the build primer it to take out the last little bit of imperfections you have by filling the low spots with a thick paint (it's about the consistency of household latex). Being so thick, it requires a larger spray gun tip, SPI recommending between a 1.8mm and 2.5mm.  I got a 1.8mm tip with my gun, so I was going with that.

I did find some perfect spots for the build primer to fill where the high and low spots had paint or filler (or not) as well as some sanding marks. I was hopeful that it would do so, and it did.

A bit hard to see, but the crater is there, along with some sanding marks

Long shot of the highs and lows prior to build primer application.

If your panel is pretty straight to begin with, you ultimately will sand the majority of the build primer off. Sound like a waste of money and time? Yeah, I guess it is, but the panel is that much straighter when it's done. Again for my situation SPI recommended the regular build vice the high build. The high build stuff (because it has more solids) runs about $160 for a gallon kit (same mixing ratio). Since most of its sanded away and I'd probably not need a whole gallon of any build, the gallon of regular build made more financial sense.

The pot life of the build primer is much shorter than the epoxy, with only about 30-45 minutes available to spray it. There is no induction time and it sprays pretty quickly, only requiring about 3-5 minutes between coats. I mixed way, way too much to begin with since I wasn't sure how far it would go, but I got about four coats on for the first round, leaving about half of what I mixed to cure and go to waste. Lesson learned.

After four coats.

The build primer went on pretty easily. It dries with a flat finish, unlike the glossy epoxy primer. Once it was dry (book calls for 30-60 minutes; I waited the full hour), I started with my sanding plan, starting at 120-grit (I didn't have any 100-grit) and working up through 220-grit (I didn't have any 320 that day). Most of the primer came off, as expected, and I found some additional spots that stayed rough to the touch, telling me that sandpaper was not touching those areas, indicating a low spot.

White-ish spot showing a low. The wrench is there to give the camera a focus point.

I think that the 1.8mm tip is a bit too small for me, so I ordered a 2.2mm tip from Amazon. I'll be able to try that out the next time I'm spraying the build primer and hopefully it'll work a bit better for me. The 1.8mm tip wasn't bad, it just felt like I could use a bit more flow.

Following that door work, I shifted over to the boot lid, which didn't go well on Friday, but I mainly fixed on Saturday. I had to take a lot of the "old" paint and filler off to get at some pretty bad wavy spots (some of which I made worse).

On Saturday, I finished up the door, filling in those last few remaining spots with about three more coats of build primer.

Final door condition with some minor bare metal spots.

All in all, I was happy with how the door came out and, after getting it sealed with epoxy right prior to shooting color, I think it will paint out fine.

As for the boot lid, I got some new filler on it and spent a bit more time working on the highs and lows with the shrink disk and hammer and dolly. There are still a few spots on the back of the boot lid (in between the hinge points) and along the curve, but otherwise it is coming along fine. Another hour or two of filler work on it and it'll be ready for another coat of epoxy.

Filler work needs just a bit more, but coming along.

And that was about it. Again, this stuff is slow and tedious, but I'm happy with how it's coming along, however slow it is.