Partial Paint Correction

[jakeclk]

Greetings all. This is my first post, so please bear with me. I have a relatively new BMW 535i with Black Sapphire paint. I recently detailed it using Menzerna SF4000, SF4500 and Powerlock. After completing a few sections with SF4000 I noticed a few random hairline scratches. They are very shallow in that I cannot feel them with my fingernail. Although the scratches can be found on most horizontal panels, I believe that they are too few in number and far between to warrant a full rework with FG400 (followed by SF4000, SF4500 and PL). My question is whether it is good practice to touch up my car using FG400 in the places that need and leave the rest alone? I would expect that, at a minimum, I would need to finish the treated area with SF4000 and SF4500 then powerlock, but would I need to cover the entire vehicle? Thanks!

[Dr_Pain]

:welcome: to AG! (since it is your first post)

I LOVE Menzerna products and use them all the time. I strongly believe that your rework would not need to go as aggressive as what you are mentioning (FG400). I would personally try PF2100 and follow that with SF4000 OR SF4500. The last two mentioned are so close to one another in terms of end result and performance that nobody could determine the product used. Your question about spot polishing is a good one which brings about a deeper question regarding UMR (also referred to as Uniform Material Removal). A PTG would give you a better idea if it is Ok or safe to use thin the clear in those area alone. With PF2100 I don't think I would be too worried (unless it took 8-10 passes to remove) but with FG400, it is definitely a heavier cut which would remove enough clear to become measurable.

[jakeclk]

Thanks for the quick response Dr. Pain! What is a PTG?

[Paul A.]

Not to intercept Dr. pain but PTG=Paint Thickness Gauge. It measures paint thickness to see how much is there to begin with and them how much was removed after.

Personally, i don't worry about removing too much material even with FG400. It is so incremental it shouldn't cause any concern. Now if you were compunding away once every 2 weeks or so then, yes, you might remove too much clearcoat. Additionally, i wouldn't be too concerned about spot hitting to remove some imperfections and, yes, you want to apply the sealant to the entire vehicle once you done.

It is a good idea, as Dr suggests, to try something slightly more aggressive for your hairline scratches before going all out with FG400. Something between FG4000 and FG400.

[Dr_Pain]

Not to intercept Dr. pain but PTG=Paint Thickness Gauge. It measures paint thickness to see how much is there to begin with and them how much was removed after.

Personally, i don't worry about removing too much material even with FG400. It is so incremental it shouldn't cause any concern. Now if you were compunding away once every 2 weeks or so then, yes, you might remove too much clearcoat. Additionally, i wouldn't be too concerned about spot hitting to remove some imperfections and, yes, you want to apply the sealant to the entire vehicle once you done.

It is a good idea, as Dr suggests, to try something slightly more aggressive for your hairline scratches before going all out with FG400. Something between FG4000 and FG400.

Thanks for spelling out the PTG. I should have done it in my original post.

Here is where I bring a word of caution. His initial process (which created a lot of results, but left some behind) was done with "finishing" polishes, which lead me to think "soft clear". FG400 is VERY aggressive compared to SF4500, so spot polishing (on assumed thin "soft" factory clear) could lead to potential pitfalls especially later if he were to come back and do another polishing or two. How much clear has he left behind? And without a measurements how does he know how aggressive he can be in subsequent attempt (hence the importance of UMR, as Mike would say). Without rehashing an old thread on the subject, we should also discuss that the UV inhibitors in clears tend to migrate to the surface of the clear as it dries. So then comes the question, do I have a uniform level of UV protection and/or will my paint be subjected to different UV bombardment and degradation.

http://lib.store.yahoo.net/lib/autogeek/menzerna-chart-2013.jpg

[Dr_Pain]

Ok, I just re-read the OP..... "new BMW 535i with Black Sapphire paint". I've done enough black BMW to tell you that you have enough to play with. Last one (in Black Sapphire) had factory readings of more than 130+ microns.

[jakeclk]

Thanks again for your input! I just ordered a bottle of Menz Pf2500 and will give it a try.

[Paul A.]

No disagreements at all with me Dr. P and you offer very good, sound precautionary advice. We both agree with doing the least aggressive to remove the problems and saving precious clearcoat. :xyxthumbs:

I think you'll like the PF2500, Jake, but let us now how it does for you. And i like to pay careful attention to how effective it is. If it reduces those more stubborn scratches by say 40-50%, don't get impatient and reach for something more aggressive...simply hit them again with the same approach to get 90-100%.