Sandpaper grades

[sauce1001]

Hi all, I'm at the beginning of a college course doing vehicle body repair and I'm looking for a bit of help with sanding body filler.

I've read that P600 wet sanding would be comparable to using P400 dry

Does anybody have a link which details how a grade of paper will perform when used wet or dry?

 

[richie00boy]

I've only seen the comparison on paint data sheets.
When dry the paper clogs and the dust not being washed away tones down the cutting effect. if you say it roughly makes it 50% less effective you can work out the equivalent wet grade - i.e. add half the rating on.
If you are using a decent extraction system though the dry rating won't be increased much at all.

 

[postie jon]

painters at my old garage used to DA sand with p400 discs dry,then a quick scuff over with wet p800, thats before water based paints became law.
is there nothing on u tube from 3M?

 

[mart]

As a young person I would just add, always wear some type of mask when dry sanding.

 

[steveo3002]

id say its roughly half....so 800 wet = 400 dry

 

[ajlelectronics]

Can anyone explain why that is? Is it the water that enhances the cutting edges or what?

 

[Barlidge]

Surely grit size is grit size whether wet or dry so you cant change the spacing between the grit? But maybe when dry the fact thats is more likely to be clogged between the grit with waste material means they cant cut as deeply so less effective?

 

[steveo3002]

Can anyone explain why that is? Is it the water that enhances the cutting edges or what?

never sussed why...assume dry is rated differently ? 400 wet n dry is way more coarse to feel /look at than a da disc