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Wetsanding 101
#1
This will be a comprehensive rundown because doing it wrong can easily cost you hundreds to thousands of dollars, so...let's get it right. This is written for people attempting to wetsand oem paint for scratches, etching, blemishes etc. and also body shop paint for excessive orange peel or surface debris. Wet sanding can give a car a "show quality" paint finish, and remove many surface issues, but it does take some knowledge and experience to get there.

First things first; whether you have clearcoat or single stage paint on your car (90 % of todays oem paints are clearcoat) the amount of paint is generally about the same at 1.7 to 2 MILS. 1 MIL is a THOUSANTH OF AN INCH. To understand how thin this is, think about a clear cigarette wrapper, then fold the wrapper over itself (doubled ) THIS IS YOUR PAINT THICKNESS if you have oem paint. another way to view it is that it's as thin as a baby's hair (50 microns, which equals 2 MILS) This DOES NOT include E coat/primer etc, only the TOP LAYER of paint. Total film build with E-Coat and primer, base color and clearcoat is between 4.5 MILS and 6 MILS generally speaking. Differences depend on make and paint type.
Body shops GENERALLY lay it on a bit thicker because of atomizing reasons at the gun etc. even if they only apply 2 coats (standard) , but you can expect about 2 MILS from them unless you have asked for more coats or been told otherwise.

Why know this? Well...wet sanding removes a LOT of paint even at 2000 grit, so you have to have a bit of an idea just what you have to work with.

The basic premise in wet sanding a body shop job is to remove ONLY the top paint that has dirt/debris and orange peel and overspray from the paint shop, and get a glassy smooth surface. Ok, here's how you do it;

You'll need;

1).A VERY CLEAN bucket.

2). 2000 grit wet sandpaper (3M recommended) 1500 grit is good also , but for a novice I feel 2000 is more user-friendly since it removes paint slower.

3) A foam sanding block and a rubber sanding block. Just get foam if you only get one, but buy both if possible.

4).3M Fine-Cut rubbing compound if by hand (or 3M Perfect-It III Rubbing Compound if you use a rotary+ cutting pad) This is what I use, however-there are MANY product recipes that will get you to the same result.

5).3M Finesse-It II Finishing Material (or equivalent polish) if by hand (or 3M Machine Glaze if using a rotary+ finishing pad)

6). 3M Imperial Hand Glaze... If you're applying a WAX afterwards that is. This is optional as it just gets washed away in rain or a carwash, but it will temporarily add depth and gloss. If using a paint sealant/ polymer, skip this step due to bonding issues.

7). PATIENCE!

Take your CLEAN bucket, add a DROP of dishwashing soap and fill the bucket with water. Drop a few pieces of UN-CUT wet sandpaper into the bucket. LET THEM SOAK AT LEAST HALF AN HOUR. This is IMPERATIVE , to soften the paper, or else you will get gouging and cutting from sharp edges or wrinkling.

After the paper has soaked , remove it and place it face down on a flat clean surface, and place the sanding block in the middle of it. Now, you want to FOLD the EDGES of the sandpaper over itself (overlapp the paper) so that there are NO FACTORY EDGES LEFT on the sandpaper. AGAIN-THIS IS AN IMPERATIVE . You WILL get DEEP side cuts from a factory edge that will be IMPOSSIBLE TO REMOVE without repainting. Skip this step and you've wasted your time.

After you've wrapped the paper around the sanding block so there are no factory edges on it, you're ready. Use the foam block with wet paper for areas that have curves and are rounded, use the rubber block for the flat areas. The foam will suffice for all if necessary.The rubber blocks are more rigid so they actually will cut faster too, so be aware of that.


Next, find the ridges and edges and creases and do this; use masking tape to cover them. Sprayed paint is affected by gravity and the film build is always thinner on these areas, so you can't sand them down to the same extent as other areas, and the tape will prevent you from going through.You can always remove it after you're finished sanding the panel and make a light pass over it to blend it with the rest, but if you buff it out properly you'll never notice a line.


Throw some water from the bucket on the panel and work the paper WITH LIGHT PRESSURE in an X pattern, criscrossing over at each pass. This is to ensure a flat and even result in paint removal. DO NOT SAND IN CIRCLES, as you risk getting a wrinkle in the paper that can cause a deep scratch. Every couple passes you want to dunk the paper back in the bucket to rinse and re-wet it (keep the water slightly sudsy to prevent "sticking" or binding of the block ). Some people like to let a garden hose run slowly over the panel, and I've done this too, but you will have to tape the metal hose end or it will scratch up the paint. Make sure the hose has no dirt/sand on it either .
Every few directional passes, STOP, wipe the panel with a cotton towel or clean rubber squeegee, allow it to flash dry so you can see what you've got. It will look dull and hazy, but you will be able to see where you've taken off the surface orange peel because orange peel will appear as darker spots in the hazy paint... WHEN YOU HAVE SUCCESSFULLY REMOVED THE ORANGE PEEL-STOP! Some may want to stop JUST BEFORE the orange peel is flattened out, because it provides more "headroom " for removing future scratches, and also gives an oem look, which you may or may not want.

Do a panel in this manner SLOWLY and dry it to make certain you have sanded EVENLY. You don't want to have some areas where the orange peel is all flattened and gone , and others where it's greatly visible. Err on the side of caution. You can actually COUNT your passes in the X pattern as you move along , and that might help give you uniform paint removal. KEEP THE PAPER/BLOCK WET!
The paper loses it's bite after a panel or so, which then requires more pressure or passes to take the same amount off as initially, so change the paper for each panel at least. Make sure the rest of the paper is SOAKING before you use it. Dump the bucket at each panel too, so any grit/ dirt dosen't get back on the paint. 1 small grit of sand under the block can ruin an otherwise perfect finish.

There will be areas where the X pattern will be difficult to impossible, but just try a perpindicular approach of overlapping. NEVER wet sand with only your hand as a backer in 1 spot. You WILL actually see indents from the pressure points caused by your fingers, especially on dark colors. You CAN use your hand in curvy areas that the blocks can't get well, but ALWAYS move it around and overlap, and don't stay in 1 spot for more than a couple passes.

FOR SCRATCHES ONLY: If you're only attempting to sand out a scratch, there are a few things to know. A general rule of thumb is; If you can feel the scratch with your fingernail, it's probably too deep. Also- on clearcoated cars (this won't work with a white car) the scratch MAY be removable if the scratch appears WHITE. This is because urethane clearcoat turns white when it's abraded. If you see the car color INSIDE the scratch, AND/OR as stated you can feel the scratch with your fingernail as you rake across it (your fingernail "catches" on it ) then the scratch is either too deep with little to no paint underneath it, or through the clear completely, and the color you're seeing in the scratch is either basecoat or primer. Touch up or repaint is the only alternative. Now, if you attempt to sand out a do-able scratch, follow all the above wet sanding instructions, BUT, sand primarily in the DIRECTION ( not perpindicular) of the scratch. You will have to sand the surrounding area a bit too, or you will find you have a very flat, glassy area with no orange peel where the scratch WAS,and the rest will have orange peel and the sanded area may look conspicuous. The rule here is; once the orange peel is gone, and the scratch is still visible...you're on dangerous ground. The more inclined you are to keep sanding to remove the scratch fully can either make you a hero or bite you bad if you go too far. You'll know when you sand through-there'll be a different colored area start to appear because the basecoat tone appears a bit different in contrast to a basecoat with clearcoat over it. (On single stage paint you'll see primer when you've sanded through ).You have to decide ahead of time if the scratch bothers you enough to risk it. If you can't live with a touch-up mark on a scratch, then go for it, but you have to accept repainting the panel if you fail, because the sand-through mark will be worse than the scratch touch up in most cases. At least as obvious. A good wet sander can save themselves or others hundreds of dollars for a repaint in removing some scratches , including many on panels that have been "keyed'. Usually, in bad cases , you have nothing to lose in trying.


After you've done a panel to your satisfaction, you need to buff it out with the listed compounds. By hand, you may need to work the rubbing compound 2 maybe 3 times on the panel before you go to the polishing (Finesse-It II ) compound. Same for the polishing compound. Use only COTTON rags or towels if doing by hand.

By rotary, use the other compounds and the appropriate pads. Mirror- like results await you if you have been careful and patient.

This is something that just takes experience. It is TIME CONSUMING, so be patient. I do recommend you practice on a junkyard panel or a lawn mower etc. first. Better safe and it will give you some confidence. I had to make mistakes before I learned what not to do, and got to the point I have with my SC and a few show quality trucks that looked like mirrors, with no mistakes.

A word to anyone wanting to try to completely level all the orange peel on oem paint and make it show quality; Don't even try it unless you've done it before, and know what you're doing. oem's are REAL thin, and you can cost yourself a repaint fast. You get sometimes only 8-10 passes of the paper ( 1500-2000 grit) and that's all you really get to remove before you're on shaky ground. There is also a rule that states you should never remove more than 3/10ths of a MIL (varies per manufacturer) when wet sanding or buffing, due to the fact that most of the UV inhibitors migrate to the upper .5 mil of paint on the surface. Taking most of that UV out of the paint leads to premature paint resin failure, at least on cars that regularly sit in the sun. This is one reason show cars can get away with it easier, they're typically garage queens. If you want to know what "premature paint failure" looks like, well, if you've ever seen a car that had white spotting (blotches) in the clear, you've witnessed it. Once the paint gets too thin the UV is gone and the sun and elements break down the resins.

In closing, this is a very valuable skill that can work wonders on automotive paint, and solve a LOT of problems. But it takes a few tries to get the hang of it, and you should be ready to make mistakes, so realize beforehand what you want to risk and what you don't. Remember;The best rule of thumb in wetsanding = once the orange peel is leveled, you must stop.

Good luck, email me at ; [email protected] for any further questions.
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#2
This is an old thread but exactly what I was looking for...got it printed out...I have done alot of body work but never the fine wet sanding and polishing like described here...thanks because I have some issues with my MVIII paint...willie
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#3
Thanks Willie, if you have any trouble or questions not covered, just give a yell here, take your time and good luck!
[Image: xstorquesig.jpg]
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#4
I like to start off with a cinder block, working my way to a red brick, preferably acme, and eventually on to 000 steel wool. If further finishing is required, a brillo pad should get you where you want to be.
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#5
Quote:I like to start off with a cinder block, working my way to a red brick, preferably acme, and eventually on to 000 steel wool. If further finishing is required, a brillo pad should get you where you want to be.

:rofl: Confusedpit:
2008 Mustang GT

Acquired 3-11-08 with 4 Miles


Best ET, 13.4 @ 105.04 Mph Almost stock!

2.1 sec 60 FT



New mods:

JLT tune/CAI

Steeda Tri-ax STS




1991 Lincoln town car

143k

Acquired 1-22-09



1992 Lincoln town car (given to dad)

104k Acquired 8-24-08
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#6
Quote:I like to start off with a cinder block, working my way to a red brick, preferably acme, and eventually on to 000 steel wool. If further finishing is required, a brillo pad should get you where you want to be.
You know, the brillo works good to remove shoe polish.........

But dont use it on paint!!!!Confusedoapbox:
ASE Master Tech with 15 years experience


Daily Driver: 1994 GMC Sonoma, Extended Cab, 2WD, with the 4.3 V6 Vortec.
Future plans/projects: Finishing that darn 64 Malibu SS
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