Epoxy resin gloss coat - what grit to start

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TheWhale's picture
Joined: 04/12/2017

Ive found lots of threads on what grit to finish on, but wanted to see what grit people start with?

I would like to start with 320 (400 on rails) to reduce chances of burn through, but doesnt seem to knock the shine off very easily.  Starting with 220 (320 on rails) seems to remove shine the easiest. I do keep my sander on lowest setting (600 rpm). Maybe increasing speed would make the 320 remove shine easier?

tried metal brush every couple seconds to clean the 320 and didnt seem to help much either.

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Huck's picture
Joined: 12/07/2009

Yeah I don't know I'm just a hobbyist but my initial thought is - If the finish is pretty smooth try 220 wet & work your way up. If your sandpaper is used not new its a little less likely to hit weave. Take your time don't rush it, and modulate the pressure. Wipe it down periodically as you work.

I usually hand sand so its a little different, but by the final coat its pretty much all wet sand for me.

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TheWhale's picture
Joined: 04/12/2017

Thanks Huck. My only real trouble spots for weave are the nose and tail right on the rails. Flats are fine. Maybe I should be sanding these areas (rails on nose and tail) by hand as well. I have been using The blue super soft pad on power sander for rails (medium pad on flats).

i usually start wet sanding after 320, but thats just an arbitrary point I picked. Could certainly try wet at 220 as well.

i always make a list of things to try on my next board to improve, ill add these. Simple enough to give a try.

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lemat's picture
Joined: 04/17/2010

If it clog to sanding disk, your resin is not fully cured and or your mix was off. Cured it in an oven is best thing to do. Final barcol hardness must be high so with a real sander, vacuumed orbital, good sanding grit made for plastic sanding, like abranet, you can start with a lower grit around 180 then move to 240, etc fast with perfect finish. The key for sanding is to use modern products designed for sanding. Many board builder move to them now, specially with epoxy. 

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TheWhale's picture
Joined: 04/12/2017

Thanks MS and good idea on the sandpaper.

no issues on curing and waited about 4-5 days before sanding. I was just experimenting with using 320 so I was using brush very frequently to make sure there was nothing between sandpaper and board.

As far as the sandpaper, I always just buy the generic 3m sandpaper at home depot. Never even knew they made specific plastics sandpaper. Will definitely check that out too.

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McDing's picture
Joined: 05/22/2004

If you can find it or order online;  Indasa Whiteline or Redline for fill coats and their Wet n Dry for gloss.  Less clogging and lasts longer.  Less expensive too.  Remember the grit depends on how good your coat of resin is.  Nice and even with no brush strokes means you can start with a finer grit.  Some guys sand without water.

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That which can be assorted without evidence was read in an illegal magazine.

deanbonkovich's picture
Joined: 10/18/2008

TheWhale wrote:

Ive found lots of threads on what grit to finish on, but wanted to see what grit people start with?

I would like to start with 320 (400 on rails) to reduce chances of burn through, but doesnt seem to knock the shine off very easily.  Starting with 220 (320 on rails) seems to remove shine the easiest. I do keep my sander on lowest setting (600 rpm). Maybe increasing speed would make the 320 remove shine easier?

tried metal brush every couple seconds to clean the 320 and didnt seem to help much either.



It's funny, I was thinking about this very subject recently and now a post to the same effect pops up. For me if it is a nice hot coat 320 grit can remove the shine without a huge amount of difficulty. 400 grit for the rails is not a silly idea to try either IMO. RPM wise I like to go for 900 (second lowest). Above that and I seem to lose tooth. Hand sand the rails for me. Any coarser for starting off and burn throughs become a real risk I find.

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TheWhale's picture
Joined: 04/12/2017

Hi Dean,

Thanks for the input. I was thinking the same thing. The first hot coat come out very smooth after sanding. I think I just wasnt putting enough time on it.  After 1 or 2 quick passes on 320 (lowest speed) the shine was scrathing up but not fully removed so I dropped down to 220. Think I need to bump the speed up on sander with 320 grit and give it a couple passes on next board.

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TheWhale's picture
Joined: 04/12/2017

I forgot to add, I dont use additive F in my fill coats. When I use that I get tons of zits/ pin pricks on the surface. With no F, comes out almost perfect. Maybe thats making it a little harder to remove shine?

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tenderloin tom's picture
Joined: 12/12/2012

120,220,320 worked for me for epoxy.hand sand rails 220 .then 3 coats of behr tile sealer  

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Scrub it kook

lemat's picture
Joined: 04/17/2010

Additive f with epoxy works like parrafined styrène with polyester, evaporation of solvent allow dispersion of light paraffine all over surface so resin can't react with air around while curing. For epoxy it's amine in hardener that can react with air moisture to produce a grease film all over surface, called blush, that reduce hardness and clog sand paper. Start by cleaning with water and scourer. Fully cure at higher temp cook blush. AddF work but as it's xylen base highly volatil can't be keep long time or add xylen...

Blush free, cured epoxy, have an high hardness but epoxy thougness don't help sanding. Specifically made for sanding tools are here really efficient. I used to make both epoxy or poly finish. Vaccumed Random orbital sanders seems efficiently less with poly than old school rotative polishers but far far better with epoxy. Can use lower grit with faster and better finish. I see that most builders that works with epoxy used them know. Plus reducing sanding powder is a very good idea to protect from contact epoxy allergic  reaction that's more often come from sanding not fully cure epoxy without cares. 

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