How to avoiding sanding burn

Just want some tips on avoiding sand burn. Sanding a hotcoat to a sanded finish from 150 to 320 and although it looks good in the right light, it also shows some good burn in another light, when closely inspected. The problem areas are on the rails for sure.

How much should be hand sanded and at what grit?

How to effectively sand rails without burn? (Softer sanding pad)

Thanks…

Seems if your power sander is burning, you should keep it moving quicker over the area. Slower speed helps some, but don’t let it sit there and cut, creating heat.

Can’t burn hand sanding unless you are built like the Incredible Hulk.

Don’t think hotcoats need 320.

hey guys- (unless we in new zealand are calling them something else) a hotcoat only needs to be cut back to around 180gt (finishing with the orbital) then spray finished- with a healthy amount of flatting additive, finally hand wet/dry sanded with some 1200.

we used to sand a board in 20 min and have it upstairs in the show room in about another 10. flawless pro finish

speed is the key-

keep your machine moving- dont hang in the one spot!

i hate to keep saying ‘we used to’- but we were churning out some big numbers so we had our techniques pretty wired.

-big grinder with 16gt hard pad, to cut down your laps flush

-switch to big sander with hard pad 80 gt, cut all the ‘shiney’ away to matt (rails n all)

-then soft pad 120 gt

-then random orbital 180 gt to finish.

no hand sanding with a block involved (other than tweaking hard edge up to fin toe)

in the case of a request for a gloss + polish send them to the factory down the road!!!

Heist,

Appreciate the professional input.

All we are looking for perhaps is a start to finish professional quality sanded finish.

Just a question, what is the spray finish and flattening additive?

Here’s what were doing (for an average shortboard) and maybe you could tell us what we’re doing wriong:

  1. approx 1/2 L resin with 15cc Surface agent and 13cc MEKP for the hot coat (we’re in a pretty cold climate around 8 to 15 degrees C at the moment)

  2. Sand off large irregularities (laps, futures, nose) with 100 grit

  3. Then progessively finer and finer… 150…220…320…420…

The result we end up is close to show room, but not 100%. Still most of our problems around the rails; high lap irregularities; nose and tail etc.

Also, the sanding disk marks show up as marks as well (when fine detail is examined)

Are orbitals better at giving a final finish? Or is hand sanding with 1200 hundred adequate?

Thanks a lot for the input

Unless you can really handle a disk sander and have the right pad (3" thick soft foam), I would not recommend that you use it on the rails. To get the finish that I assume your trying for, you’ll need to glosscoat after sanding the hotcoat. There’s really not enough hotcoat over the average lam to go from 80 to 600 and do a thorough sanding without cutting into the cloth someplace. I recommend that you use the slowest speed on your sander and an 8" medium disk with 80 or 100 on your hotcoat and do the rails by hand. This will get everything flat. Wipe it down between grits throughly. Use a soft pad next at 120 and glosscoat. Cut the tapelines carefully with 180 or a file, and start at 320. Switch to 400, 600, 800. The swirl marks are from incomplete sanding on one of the previous grits. Burn marks result from staying in one place too long or trying to get out defects with too high a grit for the job. Blow off the paper on the disks regularly since paper clogs will make scratches and cause heating. Check the ChipFish thread on glosscoats for input on this.

Howzit canuk, Try applying a baste coat of lam resin on the rails before hotcoating. The baste should cover the rail and past where the lap is on the deck and also the nose area on the deck and underneath the nose. The little extra resin will help from hitting the weave, started doing this a few years ago and it really makes a difference in the finished product, only takes a couple of ozs of resin. Aloha,Kokua

yo canuk’ here is a reply i sent to someone else who was asking of my clearcoat process.

im sincerely sorry for just copy and pasting it onto you. so just disregard the irrelevant coments for louis…

hi louis, firstly may i say what a beautiful web site you have for addiction surfboards!! i was very impressed, i really liked your fish concept (model af-70)… i have a passion for non-conventional shapes, i would love to see more of your fish ideas ( 5’5"-5’8")

i thought because my mother, and half my family is canadian, that i more than owed you a reply!!

my old factory was at a time the biggest producer of surf boards in nz. it was a well oiled, if filthy!, machine!

chiefly i was the sprayer, but we were a small crew and i became very proficient in glassing, sanding, dings, and eventually shaping.

i will try to help you with the clearcoat process- im sure you can save hours of sanding.

as i mentioned in my post,orbital finish your board to 180 gt.

the main body of the clear is called “acrylic lacquer premium clear” ( thats what we call it here in nz anyway)

-thin the acrylic clear to 50 % with 2-way auto thinner ( more thinners depending on humidity)

i saw in your web site that you, or your sprayer looks very competant, so you guys already know about the finer details of thinning for temp etc… to avoid bloom…

-to your thinned mix of clear add “flatting additive” or “flatting base” ( 2 names we know it as). this is a substance used in auto and furniture applications mainly, to remove the gloss from a finish- it works wonders filling bad sanding marks too! i swear i could spray a board sanded with 40 gt and make it look showroom great!!! it looks and feels kinda like ‘vaseline’ petrolium jelly- same milky colour too.

add around 2 'golf ball size dollups for every litre or so of thinned mix ( increase this ratio when you get real good, to fill even rougher sanding) stir it in really well.

  • now filter this all into your airbrush ( very important. flatting base loves to clot!)

  • now spray! first coat to the top and bottom should go on wet and generously, because you have thinned it so much it should be dry within a minute( maybe with the help of a hair dryer)

-2nd coat top and bottom is a HEAVY ‘dust coat’. open up the brush to very high volume, large fan and low pressure ( just enough to expel the paint without stipple) hold the brush high above the board and let it rip!

almost try to fill the spray booth letting the paint settle onto the board on its own gravity. when this dries you should be left with a semi gritty finish- but with no scrathes visible

-a very quick lick with an old piece of 1200 wet/dry with loads of water onto the board and you have a great ‘pro finish’

NB. for a glossy finish do a super heavy dust coat, then 400, 800, then aggresive 1200 gt (all wet sanding still)- you’ll get the gig pretty quickly.

hopefully i was some assistance, i have tried to describe it all in fairly non professional lingo- i apologise if i have insulted your ability!!

let me know how you get on mate.

Brad.

oh- and listen to petec and kokua, they know what they’re on about

I hand sand with 100 grit and a flat block of wood to begin with. I hand sand at the same grit with a medium pad for the rails. I try and get most of the shinies out with this. Then move to a power sander for the finer grits, 120 and 240. Keep the speed as low as it will go if your learning to sand. Then spray with Klear floor polish otherwise known as Future. This stuff works well as a thinner too. Remember, hand sanding is safer, so if in doubt, hand sand it. Tends to be a lot quicker than fixing sand throughs. Don’t get too hung up on it though, I’ve seen boards with great finishes sitting round for months before being sold but at least your trying. Also are you using a good quality sander? This makes a very big difference in my experience.