Wet Sanding

[Shootist]

Is it necessary to go beyond 2000 grit when wet sanding fully cured clear coat?

[Michael Stoops]

Re: Wet Sanding

It's not really necessary, but it might be helpful. The more you can refine the scratch the easier it can be to buff out. We generally go from 1500 to 3000 grit with finishing discs on both grits. But so much depends on what you're looking for as a final result, where you're starting, etc.

Can you give us some more specifics on the project?

[Shootist]

Re: Wet Sanding

Thanks for the quick response, Michael! If it weren't for the awesome results I got from your Ultimate Compound, I probably wouldn't have noticed the pinholes in my clearcoat It's a '97 Infiniti J30 with a dark maroon finish which I've decided to sell. It's been garaged for about 2 years but apparently the clear was etched by acid rain while it lived outside for 2 previous years. After applying the UC, I couldn't stand the imperfections, so I wet sanded 1000, 1500 and 2000 (3M Imperial) respectively. I tried to remove the 2000 scratches with multiple rotary applications of UC, but they are still slightly visible. It's now become an obsession because the finish is just about flawless. Pretty sure the M105/205 combo would remove them based on what I've read at MOL, but I can't find it locally. I read somewhere that sanding beyond 2000 was really unnecessary.
BTW, I did try to remove the pits with more aggresive compounds before sanding, but it only seemed to burnish them in.

[stanclub]

Re: Wet Sanding

Thanks for the quick response, Michael! If it weren't for the awesome results I got from your Ultimate Compound, I probably wouldn't have noticed the pinholes in my clearcoat It's a '97 Infiniti J30 with a dark maroon finish which I've decided to sell. It's been garaged for about 2 years but apparently the clear was etched by acid rain while it lived outside for 2 previous years. After applying the UC, I couldn't stand the imperfections, so I wet sanded 1000, 1500 and 2000 (3M Imperial) respectively. I tried to remove the 2000 scratches with multiple rotary applications of UC, but they are still slightly visible. It's now become an obsession because the finish is just about flawless. Pretty sure the M105/205 combo would remove them based on what I've read at MOL, but I can't find it locally. I read somewhere that sanding beyond 2000 was really unnecessary.
BTW, I did try to remove the pits with more aggresive compounds before sanding, but it only seemed to burnish them in.

One thing about wet sanding is to be sure clean your sanded out material often enough. If not, you might sand it back in, and create deeper scratch. I normally will run a waterline through my DA, and I can sand with continuous water that keeps washing off the material, or I could get pigtails ( due to DA sand ) even with P3000 3M Trizact disc.

Normally if the clearcoat is sanded clean, you should be able to remove all P1500 sand marks without any leftover. I will go up to at least P2000 just to be sure ........ in some case, I will go up to 3000 or even 4000, to gain better shine after buffing.

[TH0001]

Re: Wet Sanding

I remember reading somewhere that "sanding is the easy part" and while it is easy to sand (you just rub abrasive paper over the part) it is difficult to do correctly. It really is a learned skill as too much pressure or any contamination on the paint's surface can cause the abrasives to dig into the paint and cause very very deep marring that requires a long time to polish out. This deep marring is often referred to as tracer scratches and it is often better to sand these out then polish them out.

Is it necessary to go beyond 2000 grit when wet sanding fully cured clear coat?

Mr. Stoops gave a perfect answer (no surprise there!). Factory cured paint is often far harder than the the fresh paint that body shops work on, and thus using a finer grade of sand paper can make polishing much easier. If you use too aggressive of a grade of sand paper you can get texture lines in the paint even after you buff the heck out of it. For me personally I always finish with a high grade of paper.

What might help you also is to use a cross hatching technique when sanding. Start with your most aggressive paper going in one direction (let's say left-to-right; right-to-left) until you are happy with the surface. Stop and inspect often (and make sure the surface is clean!). Once you are happy with the resulting finish the cutting is done. The subsequent steps are going to focus on refining the sanding marks to an acceptable level.

For the second step (finer grit) sand in a direction perpendicular to the first grade, so in this case up-to-down and down-to-up, inspecting often. This will allow you to gauge when you have fully removed the more aggressive sanding marks (all of the left-to-right sanding marks will have been completely removed and replaced by up-to-down marks).

Continue in this cross hatch manner until you get to the highest grit. By using the cross hatch technique you can almost guarantee that when you go to polish the paint and restore gloss you won't be left with any surprise tracers.

I tried to remove the 2000 scratches with multiple rotary applications of UC, but they are still slightly visible.

At this point it might just be easier to sand out the visible marks with 3000 grit Meguiar's Unigrit sandpaper. Again, work in the opposite direction of the marks. It is normal (particularly on hard paint) to require several applications of an aggressive compound/wool pad/rotary to fully remove any remnants of sanding marks. Also keep in mind that you are removing paint (and a relatively considerable amount compared to other techniques) so going for absolutely perfection may not be advisable, particularly if you have already sanded so aggressively and have really deep tracers.

Best of luck!

Todd

[BlackScreaminMachine]

Re: Wet Sanding

^ Great tip on alternating hand motion while changing grit. Makes complete sense.

[BobbyG]

Re: Wet Sanding

It's not really necessary, but it might be helpful. The more you can refine the scratch the easier it can be to buff out. We generally go from 1500 to 3000 grit with finishing discs on both grits. But so much depends on what you're looking for as a final result, where you're starting, etc.

Can you give us some more specifics on the project?

It's really hard to argue with sound logic!

[Shootist]

Re: Wet Sanding

Thanks, Todd and all for suggestions and observations! So far, I have only worked on the hood since it and the front fenders were painted some years back after the hood was damaged by my sister-in-law's Ford Club Wagon!
The body shop applied copius amounts of clear, so I've had a good margin for error. I'm gonna get some 2500 and 3000 and try the cross hatching method
I gotta say though, you have no idea how much depth and clarity you get in your paint when you get it baby smooth. I was literally blown away! Most factory paint jobs these days are mediocre at best. Even BMWs and Benzes have slight orange peel issues. I will post pictures when it's corrected.
What I found is that no amount of cutting and finishing will give you the depth and clarity of a careful light sanding unless you own a Ferrari or such which I'm sure is sanded at the factory.
Having said that, I can understand people not wanting to try this on a newer car. I was fortunate that I had an older Infiniti which did have a fine factory finish on it, but at best is now worth maybe $3,000.

[Michael Stoops]

Re: Wet Sanding

I tried to remove the 2000 scratches with multiple rotary applications of UC, but they are still slightly visible.

While UC isn't technically recommended for use via rotary, we know of several people who've had great success with it. Still, it wouldn't be our first choice for removal of sanding marks. Even so, depending on the paint and how it was used, UC may well be able to remove fine, uniform sanding marks. Which leads us to ask - what pad were you using it with, and what speed on the rotary? That can make all the difference in the world, regardless of what liquid you're using.

[Shootist]

Re: Wet Sanding

Which leads us to ask - what pad were you using it with, and what speed on the rotary? That can make all the difference in the world, regardless of what liquid you're using.

I used (3) different 9" pads made by S.M. Arnold in St. Louis. They seem to be of excellent quality. First was a yellow Speedy Foam Buffing Pad (50 ppi), then tried their Black Polishing pad (90 ppi) and finally went with their Twisted Wool Tuffer Buffer.

Speeds were anywhere from 600 up to maybe 1800...trust me, I tried everything. I also tried it by hand using Megs foam applicators. The clear just seems super hard.

I think I just need to do the 2500/3000 grit and then follow up with some 105. Would have done that from the get go if they had been readily available. Oh, BTW, I also tried some MG medium cut.

I also just noticed there is a thread for wet-sanding...sorry I didn't post there.

[Michael Stoops]

Re: Wet Sanding

OK. The softer foam pads at slower speeds, especially with UC, are not going to be up to the task of removing those sanding marks. It's just not a potent enough combo unless the paint is really soft.

For removal of the type of marks you've put in, we'd go straight to M105, a wool pad, and 1400 to 1800 rpm on the rotary. Exactly which wool pad and what speed we use will depend on the paint.

[Mike Phillips]

Re: Wet Sanding

I remember reading somewhere that "sanding is the easy part" and while it is easy to sand (you just rub abrasive paper over the part) it is difficult to do correctly.

Might have been something I wrote... I often write or say in a class...

"Sanding is the easy part, that's putting scratches into the paint, the tricky part is getting them out"


Technically we instill sanding marks, but in the context of the idea I try to get across on the topic of sanding, the word scratches fits better. Then back it up with sound information and education and everyone gets the idea.

Something I've noticed in all the years I've been teaching classes is that most the people that sign-up for the advanced class to learn how to wetsand, after they learn how to do it and what's involved, they find they don't really want to do it.

[Shootist]

Re: Wet Sanding

Nothing ventured...nothing gained. I've learned a lot and done no irreparable damage. The sections I've done are 95% flawless. Keep in mind, this is a '97 Infiniti we're talking here.
Makes you realize how crappy modern paint (orange peel) is laid down at the factory...even on some very expensive makes. Photos coming!