clear over enamel

The tech sheet for OMNI MC161 clear indicates that as long as you used the hardener in the MAE, you can. So there doesn't appear to be any chemical incompatibility, at least for that particular clear. However, the clear is supposed to be applied within one week of the color. That's to get a chemical bonding between the clear and the color. If you are past a week when you clear, then you will not have the benefit of a chemical bond. To obtain a mechanical bond, you need to have some sandscratches present. My guess would be that they should be 400-600 grit and that 1500 grit would be too fine for a decent bond. However, I've never done it and don't know about the appearance of a clear over 400 grit scratches. The possibility of a clear over existing, cured finishes is not covered in the tech sheet. I suggest you do a test panel on something to see the effect, just to make sure. Of course you could always sand with 400, shoot another coat or two of color and then clear within the one week period. As I see it, the risk with the 1500 grit scratches (or none at all) is delamination of the clear due to poor bonding. That fine a prep is usually more for a subsequent compounding operation than a recoating one. Perhaps someone who is experienced in spot (not panel) repairs of existing BC/CC finishes will provide some better guidance here.

Rod

Don

I'll give you my opinion: Probably not much overall advantage, generally. Could be worthwhile for show ponies. It was used years ago before BC/CC finishes to provide a more "glamorous" appearance. At least that's the way it was promoted.

It can give a little better "depth appearance" to a single stage finish but it obviously adds to the time and expense of any project. I have used a clear over the MTK acrylic urethane SS on my own AC-B because I think it makes vinyl cut decals look a little better. It tends to smooth out the sharp edges and give them more of a real painted-on appearance. It also gives a little physical protection to the decal. The same would go for the MAE I would presume.

The following are the disadvantages as I see it:
1. Costs more
2. Takes more time - at least two and probably three additional coats of material - all within an application time window.
3. Any slight scratches that might occur in the finish will show up as white. They show up more than they otherwise would.
4. The clear contains isocyanates in the required hardener (they are urethanes) in addition to the required hardener in the color coat, which also contains isos. So going with clears requires fresh air breathing equipment unless one wants to play fast and loose with their own health.

Some products are formulated such that a certain percentage of clear can be added to the final color coat instead of a separate application. The OMNI MAE does not indicate that possibility, although the OMNI MTK does permit up to 50% catalyzed clear to be added. Of course that doesn't apply to the decal situation :o).