On Friday, March 25, 2016 at 10:43:03 PM UTC-4, Charlie M. (UH & 002 owner/pilot) wrote:
On Friday, March 25, 2016 at 3:18:18 PM UTC-4, wrote:
On Thursday, March 24, 2016 at 4:20:54 PM UTC-4, vontresc wrote:
So after attending Uncle Hank's presentation at the convention I have been
inspired to sand out the crazing in my gel coat. I am planning on the
600-1000-1200-1500 wet sanding process and then buffing out the finish.

I understand the basics, but does anyone have a good primer on the process?

Thanks

Peter

Start with one grit finer than you think you need. Finer grit leaves less scratching to remove later.
If you guessed wrong it will take a lot of time to flatten the crazing. If so go down one step. I never go below 600 as it takes forever to get out scratches.
Except for edges and ends, we do it all with the orbital.
My sanding pattern is(remember my example where I dropped the mike?) is left to right as far as I can hold a consistent pattern- about 24 inches or so. 2 traverses at the start, then shift about 1/2 inch on each pass. When all the way across, do the same in reverse. Finish off with one set of passes at 90 degrees with the same offset. Keep the surface wet.
Note where the end of your pattern is and set up again with enough offset to get uniform coverage.
A 1000 grit disc will go about 4 feet on a Std class wing and then not much is happening.
I block and finger sand leading edges and tips.
When crazing is flatted, do the same with 1500 on orbital.
Then 3000.
Buff.
Wear wet weather shoes.
UH

I will a little bit to here......

"It all depends on the sludge". So, what do I mean?

Depends on the grit you're using and how do you clean the surface.

I like a "fairly cheap ~12" red rubber squeegee", (the black ones tend to degrade and leave dark schmutch [sp] on the surface....) to remove water and "stuff" from the surface.
When using coarse grades of paper, a "good paper" will make a lot of "semi-solid" stuff come off with the water when new, not so much when worn.
When you get to fine paper/pads, even new will produce less "semi-solid" stuff with the water than coarse grit worn.
When either produces a lot less "semi-solid" stuff compared to new paper/pads (of a certain grade/grit), it may be time to change the paper/pad.

So, starting at 600grit wet, fresh paper yields a "sludge" of near "wet yogurt" when new, going to "2% milk" when worn.
Starting at 3000 grit wet, fresh paper/pad yields "whole milk" when new going to "diluted skim milk" when worn.

This sorta takes into consideration of different area volumes you may cover, how wet or dry the surface is, how hard you press, etc.
It's all in the sludge.

The better the sanding, the better the polish can be. It's always faster to do a bit more sanding than to try & polish up a poor sanding job.

[Coarse in this post is 600 grit wet, fine/final is 3000 grit wet with several steps in between]

I've seen several different grits of compound take out sanding marks, But yes, fine sanding marks makes a better finish with less polishing. But polishing takes off less material.