How to check the quality of your sand job prior to spraying clear coat/glossing?

General Discussion
1

So I’ve done it again. I thought the sand job was pretty good doing 80-120-150-220, handsanding on the rails and using the machine on the deck and bottom. I tried to check that I don’t have any scratches and did some extra hand sanding where I could find scratches which I could see when I rubbed sanding dust into them. Thought I had it this time. Still, after spraying H2O clear the scratch marks really stands out. So once again I will use a scotchbrite satin finish to hide them instead of a the nice gloss I was aming for. Hopefully this will be the last time, so how can I check the board to see if I have any scratches I need to sand out before spraying clear or glossing? 

2

…hello man, first you have a confusion there.

Or you sand to put a REAL gloss coat OR you sand to put a spray finish OR you sand to have a hot coated finish. If you do what you did, you ALWAYS have sanding scratches if you apply those clears intended for gloss…

3

Reverb is right. Generally a sand for gloss is around an 80 grit finish and a hard pad depending on who you ask. If you’re just spraying a clear acrylic on a sand finish shortboard then you’ll want to finish around 320. A lot of the bigger brands are finishing with 320 grit block with the “scratches” going nose to tail. You could also save some time by cutting with 150 instead of 80 grit if it’s a sand only finish.

4

I sand down to 100grit then apply one thick coat of clear spray paint which fills all the scratches. The key to getting the spray to fill the scratches is to apply it from a reasonable height, say at least 12 inches. This way the paint partially drys on the way down and fills the scratches nicely. I end up using one whole can for a board. I always use a satin finish. If U wanted a gloss I reckon I’d use a resin gloss coat, but I can’t see the point.

5

Haarvard - Polyester is the only thing which fills scratches in one hit.

 

If you are attempting to get a gloss finish with anything sprayed, you will invariably need more than one coat, with a rub between coats. Whether Acrylic or 2pac, the solvent content evaporates, the surface you walked away from shrinks, pulling into the sanding scratches. Wet-rub with 400 and go again.

 

JD

 

 

6

Sand to 220, wipe down with this and ride.

 

 

7

Sorry I wasn’t clear. I’m not doing a traditional gloss, but trying to get a glossy finish spraying c3d industries H2O clear coat over epoxy. I’m spraying it as outlined in this thread http://www.swaylocks.com/forums/uv-clear-used-gloss-coat with the exception that I run tape along the rails to avoid runs. Need to sand at the tape edge, but I prefer that over sanding runs on the flats. The clear coat fills the scratches no problem, but they are visible at certain angles. I’m guessing the refractive index of the clear spray is a little different than that of the epoxy. To me this looks like scratches from the coarsest paper which I havn’t been able to sand out. My problem is that I don’t really know when I’ve sanded enough with the next grit, it’s hard to see the scratches until I get the spray on it. Are there any tricks to make the scratches show up better prior to spraying?

8

Haavard

Do you do any hand sanding??

I would say skip the 80, go to machine sanding with 100 straight away, then 180, then 320, don’t chase all the shinies with the 80, but use all grits to obtain shine free,scratch free surface

Of course, dont do the rails with 100, but by hand, or machine with fine grits

This is how i try to do it, still failing occasionally

cheers

9

I try to keep hand sanding to a minimum, but handsand the rails and sometimes to get the boxes flat if I hit the weave when grinding down the boxes and if there are some fisheyes I can’t get with the machine. Might be the culprit. I feel like it takes forever and worry about overheating if I go to 120 directly, the shop I buy sandpaper at don’t have 100. 

10

Todays Hot Coats are very clean.

No bumps. No lumps.

The industry standard is 180, 220, 320.

If glossing, maybe 80 grit with a hard pad to get flat. Maybe some blocking too.

All machine. Just a little hand sanding rails.

11

…yep, possibly due to that is that I see lot of crappy boards…included many big brands that I saw almost all in Japan…

12

I think a fair share of crappy boards end up here too. Whenever I wanna feel better about my (lack of) board building skills I go to the local surfshop. I can find cosmetic flaws on just about every board there with the possible exception of some of the GSI boards.

13

In the end it didn’t come out too bad. Josh is right, the spray didn’t fill the scratches completely, I could feel some of the scratches with my nails. I sanded the board with 320 dry then 400, 600, 800, 1000, 1200 wet which took out most of the scratches. I can still see some dull halfmoon scraches in some places, but not too bad. The guy who picked up the board was pretty stoked so I can’t complain. Will try starting sanding with higher grit next time, thanks for the advice.

14

The way I was taught. was

  1. Knock down plugs with 60.

  2. 150 power sand both deck and bottom

  3. 180 oscilate to get ride of scratches.

  4. Sand Rails with soft pad 240.

  5. Hand Sand Rails with 180 then 240.

  6. Power Sand with a soft pad on 240 both bottom and deck

  7. Oscilate with 240

  8. Wet rub with a 500 sia disc on an air compressed oscilator to finish

Then you can do your clear spray, and either wet rub the shine off or polish it out.