Paint gauge needed for wet sanding?

[anson89]

I'm about to learn how to wet sand soon and will be an available option when I start my website. I've heard somewhere that paint gauge is needed to ensure safe wet sanding? Is this needed, because I don't have to funds right now to buy a paint thickness gauge.

Thanks

[zinc02gt]

I've done it to my own personal vehicle without a PTG. Just don't use anything more aggressive than 1500 and use some common sense. Avoid edges and give at least 1/2" spacing away from the edge.

[anson89]

Gotcha. I'm watching some videos on wet sanding. Not sure about the edges, or 1/2" spacing you're talking about - but once I'm done with these videos, I should be good to go.

Thanks

[Rsurfer]

Originally Posted by anson89

I'm about to learn how to wet sand soon and will be an available option when I start my website. I've heard somewhere that paint gauge is needed to ensure safe wet sanding? Is this needed, because I don't have to funds right now to buy a paint thickness gauge.

Thanks

It appears you are doing this for money. You would be foolish to wet sand a car without a PTG. How would you know that it's safe to wetsand without knowing how much paint you have.

[MI Mike]

I'm not sure if Mike Phillips or someone at AG would do this but, I also was looking into a paint gauge, they are expensive. Would someone like Mike or AG be willing to rent a gauge out to someone for a couple of days. They could ship it out prepaid express, insured. The user then could return it insured and express, or forward it at AG request to the next user, etc. Not sure if its workable, but just a suggestion.

[Mike.Phillips@Autogeek]

On the topic of a PTG or Paint Thickness Gauge for wet-sanding. If you can get one before tackling a wet-sanding project then do so.

A PTG is going to tell you if you're working on factory paint or a repaint, a factory paint job is going to have a uniform paint thickness on each panel, this can range from the 4.0 mils to the 8.0 mils but you should see a trend forming as you measure each panel in that most your readings will be in a close range, like,

7.8 mils
7.6 mils
7.4 mils
7.8 mils


And so on. If you come across a reading that like 28.5 then you can generalize that this panel has been re-sprayed.

If you're working on a car and the readings are all over the board, but also in a much higher range, like,

28.2 mils
26.4 mils
32.5 mils
22.4 mils

And so on, this is a good indicator the car has been repainted.


A paint thickness gauge is going to tell you if you're working on a factory paint, a repair or a complete repaint... (generally speaking).

It's not going to tell you how much clear you have to work with because a paint thickness gauge reads total film build, not just specific layers.


As for

Originally Posted by anson89

Gotcha. I'm watching some videos on wet sanding. Not sure about the edges, or 1/2" spacing you're talking about - but once I'm done with these videos, I should be good to go.

Thanks

The 1/2" spacing thing he's talking about, I'll take a guess at, I think in one of the articles I've written on sanding I mention a rule of thumb guide I use that is actually a "Rule of Thumb" guide. That is when sanding, since I always have my thumb with me, I use it for a guide as to how away to stay away from edges and raised body lines.

Don't have time to type the Rule of Thumb up right now or dig through my posts to find it but if I have typed it up it would be in one of these threads...


Removing Orange Peel & Sanding Marks with the Griot's ROP and the Wolfgang Twins

Fight or Flight Method for Gaging Surface Temperature


How long will a half sheet of wet/dry sandpaper last before it stops cutting and you need to replace it?

Basic Hand Sanding Techniques


Two Schools of Thought when Hand Sanding - Straight-lines or Crosshatch Pattern


Wet-sanding - Fresh Paint vs Factory Paint


RIDS and Feathersanding - A Highly Specialized Technique by Mike Phillips



Maybe if someone can locate the technique I'm referring to and copy and paste it to this thread.

[A4 1.8tqm]

Here it is, from the thread Did some wetsanding

Originally Posted by Lasthope05

This is exactly the reason why we practice on scrap panels first. When your wet sanding you should always leave a 1/8" gap between the edges and body lines. They edges and body lines have the thinnest layers of paint and are most susceptible to sand-through and burns like you experienced.

Originally Posted by Mike.Phillips@Autogeek

This is a very good point. That is, paint will tend to flow a little off of high points or body lines and as such paint can be thinner in these areas and that's why you don't want to sand too close to them.

I use my thumbnail as a measuring tool, which is about a 1/2 inch in length, as a simple guide as to how close to sand to the edge.

A good rule of thumb, (no pun intended), is to never sand where you cannot safely use a rotary buffer. It's easy to sand close to an edge and not actually sand on the edge, it's difficult however to buff close to an edge without accidentally buffing on the edge.

The most common question that comes up on this topic of not sanding or buffing close to edges or body lines is

If I don't sand and buff all the way to the edge, won't there still be orange peel left in the paint in these areas?

The answer is yes, at least a little. How much time you want to invest into sanding and buffing close to edges and body lines is up to you but it's hard to get paid for that kind of meticulous work.

Two ways to remove orange peel close to body lines and edges is to use painter's tape to tape off the edges or body lines and then sand and buff up to the tape line, or sand up to the tape line and use a compound by hand to remove the majority of sanding marks, (because you can exert a lot of pressure using a few fingers to work a compound to a small area), and then do some careful machine polishing to remove any fingermarks from the hand rubbing process. Both of these techniques are time intensive and usually a little nerve wracking.

[richy]

Like the other posters have said, you would be foolish to attempt this without a PTG. Highline makes one for about $200...much cheaper than ONE paint job and would pay for itself again and again. I had a Mercedes I was working on last summer that had very, very thin paint on one door but ample thickness everywhere else. Obviously someone had tried to wheel out a scratch and had removed far too much clear at some other time. Had I not known this, I would have or could have gone through the clear on that door....that alone saved me and there have been several other times as well. Highline is a Detroit company..I went right THERE and picked mine up. Although Mike is technically correct that it does not measure the clear in and of itself, you can ascertain how much clear you're working with by taking a measurement at the inside door pillar or inside trunk area where the paint is thin. The difference of the 2 is going to give you the amount of clear. There are some general guidelines too...over 100 microns is safe; 80-100 is thin...use mild pad and a product with little bite like Menz 106; under 80 is very thin and would only use a glaze type product...you don't want to remove anything. I like using microns as a measurement increment rather than mils...more accurate in my opinion. Hope that helps.

[Shade Tree]

Originally Posted by Rsurfer

It appears you are doing this for money. You would be foolish to wet sand a car without a PTG. How would you know that it's safe to wetsand without knowing how much paint you have.

Agreed.

I had to replace my PTG and found one from Ecometer for $225. No way I'm footing the bill for a repaint.

[Mike.Phillips@Autogeek]

Originally Posted by A4 1.8tqm

Here it is, from the thread Did some wetsanding

Thank you for the Super Sleuthing!