tkcutlass

Several sources have stated not to skip grits when sanding.
I thought it was to sell more sandpaper.
After doing some wet sanding on my doors I have uncovered some sanding scratches and decided to do some more research.
I think this video helps explain why.
Agree/disagree comments?
https://www.youtube.com/watch?v=Hzrj...Farticles%2Fgr...

JMJ-RIP

This does make sense, if you are skipping multiple grits, the following grit will take longer to get down to the previously used grit cuts.

Years ago when I did this as a profession we started with a light sanding using 400, then 600 and onto buff with 3M Superduty compound. Then the sandpaper companies came out with 800, this graduated us to start with 600 then to 800 and onto buffing. In the early/mid '80's sandpaper continually got finer and finer. Once the grit start to get finer and finer your buffing/polishing compounds must do the same. It will do no good or would be a wast of time to sand out to say 2000, 2500 or 3000 then buff with a course or super duty compound. I moved out of this profession professionally in '84

ijasond

The general rule of thumb we use in the autobody industry is that you want to step up in increments close to double the previous grit. So if you sand with 80, you come back with 180, after that 320-400, then 600-800.

80-180 can be primed, 400 if you’re going to seal it, 600 to paint without sealer, and 800 if you’re only applying clear.

When doing a cut and buff, I generally go 600, 1000, 2000 then compound. Sometimes I’ll run over the 2000 with some 3000 trizact just to make the polishing easier.

If you jump significantly more than double,
you can still get the job done, but it will be a lot more time and work. I can sand 80 grit scratches out with 2000 if I want to, it just takes FOREVER.

oddball

The video is more or less correct. You can skip grits, but you have to sand more with the finer grit to get all the scratches from the previous cycle. The whole point of sanding is to make scratches - we just want them to end up small enough that we can't see them. You could do *all* the sanding with 2,000 grit but it would take an extremely long time.
It's just easier to end up with a good finish, especially as a hobbyist, by using as many grits as possible. This is where sanding in different patterns as moving through grits also helps - makes it much easier to tell when the previous cycle has been sanded out.

ijasond

Man, these young guys nowadays will tell you that "you can't buff 1500 scratches out'. I'm not that old, but I remember when we sanded stuff out with 800 grit and rubbed it out with compound that felt like it had beach sand in it and was so thick you had to cut it with kerosene. There are a lot of good things about the modern products. Compounds don't dry in the cracks like concrete where you need a chisel to get it out and you can achieve some really beautiful finishes, but it's so much more time consuming that it was back then. We used to get a car cut & buffed after paint for $75 in an afternoon. Now it's at least $750 IF you can find someone that will do it and it will take 3-5 days.