Sanding Guide Powder/Spray

Anyone use sanding guides to sand their hot or gloss coats?

I thought I saw a demo (Cleanline’s DVD?) or it mentioned once about applying chalk or marker over a base coat before sanding to a final flat surface to highlight the high and low spots.

Since I switched to these Mirca sanding screens I’ve been watching how they fair these base coats on autobody work and they apply this powdery sanding guide over the surface prior to sanding and after each grit they apply the guide again to highlight the scratches and imperfections.

Anyone doing this with either epoxy or Polyester?

and if so what are you using?

I’m about to buy a can of the 3M or Mirka guide powder but was wondering if this doesn’t apply to Surfboard resin sanding

 

Also what’s the most common sanding schedule start to finish for epoxy versus polyester for machine (7" disk)  sanding?

do you start at 60/80 for epoxy and finish at 320

or do you start at 100 and finish at 220

is it 100-120-150-180-220?

or

80-100-120-150-220?

or

100-150-220-320?

I mean where can you skip grits and where can’t you to offset the lower grit scratches

some wood/composite surface workers sand up to 12000 and beyond before applying a final coat

do those schedules differ depending on the size and types of sanders you use

like what if it’s a 5" RO versus a 7" disk?

sorry I’ve been out of action for years now and trying to get started again

got allot of sanding and reglassing to do to clean up around here

need to take a sanding class again

where’s that ronald patterson guy - my hero :wink:

I have done tons of “Fairing” boat hulls and structures.  We use a “guide coat” or “tracer” to help pick out lows and get the surface flat or a smooth curve.  I have never heard of anyone using it on a board though.  Usually we’d just get a puff can of a flat, quick dry lacquer in black or any dark color.  Then just mist it on the surface.  Not too heavy or it will gum up your paper.

 

Aloha Oneula

Guide coats aren’t necessary and have never been commonly used in making surfboards.  

The primary reason being that it isn’t really that hard to get a flat, fair surface on a surfboard.  This is because surfboards are shaped true and fair to begin with.  While in boats or automobiles, the surfaces aren’t true or fair to begin with.  So the main purpose of Bondo and Fairing Compounds on boats and cars, is to fill in the dips etc allowing enough material buildup for the sanding process to fair out all the dips and bumps to create a final fair surface.  Usually this takes several applications of alternating steps of Fairing Compound and sanding them out fair as possible.  In this process, a guide material can be a huge asset in locating remaining dips and bumps.  Especially considering how large the surface areas are on boats and cars compared to surfboards.

Assuming the surfboard’s foam is shaped out fair and true, then the lamination, when properly done, is pulled tightly to the foam transfering the foam’s fairness accurately into the surface of the lamination.

Then if the lamination is sanded or filed properly, where any layers overlap etc, the sanding coat can be laid down smooth and fair.  Given enough time for the resin to flow out flat, the foam’s accuracy and fairness will be telegraphed all the way out through the glass job and onto the surface of the sanding coat.  Thus leaving a near perfectly true surface for sanding.

If this is all done effectively, the final sanding of the hot coat, will be fast and easy to sand out perfectly smooth.

All that said, a critical reason for not using a colored guide coat, is that surfboard glass jobs very often have tiny pits or bubbles in the sanding coats that are near impossible to see. These tiny pits can often extend through into the lamination layer.  A colored guide coat can fill and stick in these pits.  So that, even after sanding, will leave a normally clean glass job full of tiny colored specks that you won’t be able to get out.

As far as sanding grits used…  I start with a 50 grit grinding disc for sanding the boxes and laps if they aren’t as flat as I would like.  Then I use 60 or 80 grit depending on how much of the hotcoat I want to remove using a Hard Flex Pad.  Then 150 with Medium Flex Pad.  Then 220, 320, 400 with a Soft Flex Pad.  And lastly 600 with the Softie Flex Pad.  For gloss coated boards, I usually just go out to 150 or 22o grit unless it needs pinlines or resin colorwork.  Then I will those areas with 320.

If you can ever catch me sanding when you are out on the North Shore your welcome to watch.

Mahalo Bill hope you are doing well

that’s why I love this place

 

bit the bullet on the big and heavy milwaukee which should improve my sanding (especially the flats) tremendously

just hate the mess it makes to the neighborhood plus I’m now both sensitized to epoxy and allergic to fiberglass dust now.

Gotta wear my PAPR hazmat suit to do it these days

hard to believe we amateurs used to use a 6" pad on a hand drill and hand sand everything else half naked back in the 60’s-70’s

probably still the best method

I guess we’re all just impatient and or lazy these days

I’ve found that I can skip grits at the lower end, but not at the higher end. On epoxy, I’ll go 80 on a hard pad to get it flat, then skip 100 and go to 120, then maybe go to 220, 320, 400. The 120 takes a bit longer, but it will smooth the 80 grit surface if it’s not scratched up too badly. Same with skipping 150 and going to 220. But to be honest, I’ve never tried to go from 80 straight to 150, like Bill suggests.

Iv’e also found that epoxy sands easier when it’s ‘green.’ Anybody else do this?

I learn that let 100 max between 2 grits for dry sanding.

On completly dry (hot box) epoxy filler i used to go quickly with 60 grit RO sander semi hard pad + mirlon pad for finish matt surface then finishcoat PE resin.

It’s pretty harmful to sand not completly cure epoxy. For occupational medicine it’s when sanding “soft” resin that most people develops an allergy to epoxy.

So sand it completly cure with a lower grit higher speed and RO sander with vacuum extraction, finally faster than other way !

Sorry for my franglish

 

Bill’s description of fairing and why it is used on boats but not necessary on surfboards is accurate.  A good shape with a tight glass job and a good hotcoat will sand flat.  The key to skipping grits for me has always been the quality of my hotcoat.  A nice hotcoat over a good lam means a quicker sand.  Lowel

funny

but when i was a 16 year old high schooler, i thought the ultimate job was to be a pinline taper and sander for my classmate Brian Higa who was making some pretty good surfboards back then. We were going to move to the northshore, Brian would shape them, my brother and friend Mark would glass them and I would pin line and sand which I really took a liking too because of both the mental and physical element behind it. Brian went on to live out that dream while the rest of us went on elsewhere.

These days I prefer the aroma, and the sensitivity required of the blending of the grains and texture when sanding exotic woods like koa, milo, kou, mango, sandalwood, cedar, bocote, tulipwood, and others. While the burden of trying to wrangle and manage a 9lb spinning wheel of death and destruction (at least to your glass job) doesn’t seem as much fun as I remember. More like work than art in a way.

Its weird but I do enjoy wet sanding boards by hand for some reason and watching the change in texture that comes about from that effort.

Sanders and Laminators;  The best potential for money making in a Glass shop/factory…  Lowel

Bill, we don’t make perfectly flat shapes, and then we don’t do great laps. So we get “issues”.

Just look at Oneula’s work place it’s a 10 x 10 popup outside.

We don juice no stinking chaping rooms, with da fancy chaping lights, and we don juice no stinking manufactured surfing board blanks, we make our own stinking blanks. Das why our boards stink. 

I think that I would surf soooo much better if I only rode boards from really good shapers. But, I’m having a lot of fun. Too old to be surfing like I’m in a contest, and too young to be a longboarder. Just want to have fun.

This is an 8-0 round pin made in 2012.


hi bernie. if you sand the board slow speed and within a day of hotcoat . it will sand a lot easier before the coat gets to hard. huie told me this way. also rails and bottom edges can be hand sanded with a sanding board and also bottoms can be hand finished with a large block with eva pad. . i have seen a few vids of glass shops using sanders at high speed  and that is one way. you can also use low speed with high torque to get good results. . if your paper is sharp and resin at right cure time,a board can be sanded nicely in half an hour or so. if you leave it too long then it will take a lot longer and be harder to get flat. (mirka paper is very good espeically in higher grits as it doesnt clog. 3m freecut is also excellent). i would recomend home builders to try not to emulate production factorys as a an extra 15 minutes finiishing a board is of no consequence to a home builder. for a home builder to achieve professional looking finishes then they should take the time to finish by hand. and slow down the sander. especially at higher grits. a good finish coat you can go straight to 400 grit freecut low speed high torque . this will save a lot of work as 320 scratches require a lot more effort to remove.

 

bottom laps on the tail of a board i think are the hardest part of a board to sand ( especially by machine). so as recomended by huie i switched my bottom lam to 5 or 6 oz and then let the deck glass hang at the tail so its a zipper lap at the tail tapering to a full lap as you head up the board. this is a taped lap and very easy to sand and finish . with professional results. home builders need to take different approaches to production factorys as we have different requirements. so you see a badly sanded tail lap on the bottom to will hit weave and create weak areas in the tail. and amature sander will fuck this up every time. by huies recomendation i have discoverd to completely avoid the process by hanging the deck glass. the extra glass on the bottom has negilble weight increases for the home builder.

bottom laps on the tail of a board i think are the hardest part of a board to sand ( especially by machine). so as recomended by huie i switched my bottom lam to 5 or 6 oz and then let the deck glass hang at the tail so its a zipper lap at the tail tapering to a full lap as you head up the board. this is a taped lap and very easy to sand and finish . with professional results. home builders need to take different approaches to production factorys as we have different requirements. so you see a badly sanded tail lap on the bottom to will hit weave and create weak areas in the tail. and amature sander will fuck this up every time. by huies recomendation i have discoverd to completely avoid the process by hanging the deck glass. the extra glass on the bottom has negilble weight increases for the home builder.

 

 

**aw’’  thats naughty paul  you have only told them half of what i said  haaa’’   are we talking polyester resin here ?
**

 

 

 cheers huie

Thanks Paul!

and you are right about the hand sanding

you can never go wrong with hand sanding

its just a slower process

 

Huie

its for both

I have more problems with epoxy though

even with norton champagne it get build up and then heating which is bad

just switched to these Mirka sanding screens which has less clogging and better airflow to reduce heating.

the fact that it cuts with little if no pressure is a god send to me especially if the sander isn’t a 7-10lb high torque beast.

anyway i finally got the right tool for the job, a milwaukee 5540

not quite healed up enough yet to use it though

ah yeah sorry huie that was for polyester. epoxy is a little different . but low speeds are good for both

 

yeah bernie high torque with speed control. im on 1 speed often even slower with trigger control. i use a rupes italian sander that is used by boatbuilders and panel industry

Figure out some way to cure your epoxy after you’ve lammed.  A few hours under UV would be a good idea.  If properly done in a warm room and a warm cure afterwards you shouldn’t have anything gumming up.

yup lowell

that’s the ticket 

not having facilities or the time to do a proper job is a big challenge

apartment/condo dwellers have got to have it worse