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Finishing tips

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rehn(at)rockisland.com
Guest

Posted: Thu Sep 18, 2008 10:08 am Post subject: Finishing tips

I found this to be a very good article. 



 



Jerry



 



 



  _____  



Finishing a composite airplane



 



Foreword 

I wrote this because I see a lot of people struggling with finishing their

airplanes and I don't see anything well written on the subject anywhere. I

have seen a number of articles in magazines and books but they all seem to

be written by people who are writers rather then builders and never actually

did the job, let alone would be good at it. The latest example of such

article is in Sport Aviation 2/2003 named The Joy of Sanding, four pages

filled but nothing helpful about how to do the job. I, on the other hand, am

no writer and English is a second language for me to top it off, so bear

with me. My own experience comes from building composite tools and

production parts for kit airplanes as a business and from doing all the

finish work on an award winning Lancair IV P for Mike Shooner under the

command of Arthur Gallant who himself received Oshkosh Grand Champion for

his Lancair 320. I learned a lot on that project. The following describes in

great details the techniques I use to obtain a perfect straight wave free

airfoil shape on wings and the fuselage, and do it with the minimum effort

and cost without spending years on it (or so I think). 



Ok, lets start filling. 

The process goes basically in two stages, first, we shape/contour the

surface, second, we perfect the surface for the paint application. In other

articles you probably read directions about looking for "The Low Spots" with

all kinds of tricks on how to identify them and fill them, then sand, then

recheck and refill again and again and again. This is the wrong way to do

it. Not only is this technique time consuming, achieving a wave free surface

by a patchwork of fillings is just about impossible. The right way to do it

is to fill all of the surface (meaning like one side of a wing or a

fuselage) at once with a coat of filler sufficiently thick enough to fully

fill all the lows, then sand the whole surface as one uniform plain ONCE,

without the need of refilling again. The amount of filler to sand off may

seem overwhelming at first but the use of proper sanding technique described

later on makes this task rather effortless. Using this technique you never

look for low spots, instead you keep sanding until the highs start coming up

through the filler. Some airplanes, because of their building process will

have deep depressions, like in the place of spars or joints, which would be

difficult to fill sufficiently deep and yet smooth in one fill. The builders

natural tendency would be just to do the first big fill, sand to the shape

and then refill the areas of these low depressions as needed. It needs to be

done the other way around, you need to fill these deep depression first,

however that first fill must still stay below the intended finished surface

height, sanding through the top fill into the first filler coat would create

hard spots and uneven sanding properties. The picture below shows a good

example of this first head start fill where we had a significant depression

in the skin in the spar area and the joggle joint on the leading edge. 



I strongly recommend spraying a light coat of black primer, before you start

filling, Even thou this step is not absolutely necessary it is very helpful

in guiding where to direct more sanding and when to change to finer

sandpaper grade. The filler becomes translucent as it gets thinner and the

black color starts showing through as dark spots indicating you are getting

close to the skin surface. 

The filler is a plain mix of epoxy and glass micro balloons, commonly called

"micro". It's not all that easy to work with but it's the lightest filler

there is with good strength and stability after its cured. I would not say

you can not use one of the ready to apply premixed epoxy fillers like

SuperFil but be aware that despite all the advertising hype this filler is

about twice as heavy as home made micro and it will cost a lot more as a

number of gallons of filler are used. The epoxy resin used to mix micro must

be one of the low viscosity types that will allow high ratio of microbaloons

to be mixed in. I have used Aeropoxy and Jeffco which both work well. I mix

it in a large salad bowl about 2/3 to 3/4 of a gallon at a time which is

about as much as I can handle. Mixing is done with a classic flat paint

mixing stick and in a slow motion, trying to mix it fast will not get the

job done any sooner, you will only blow half of the microbaloons in to the

air. The finished mix must be fairly dry, keep adding microbaloons until it

becomes difficult to mix. As long as the mix is visibly flowing and leveling

by itself its still too wet, another indicator the mix still needs more

microbaloons is that the surface turns glossy when you let it sit a minute

that’s the extra epoxy migrating to the surface. Properly mixed micro

spreads with moderate difficulty and fairly high amount of pressure is

required. If it spreads easily it's too wet. 

Be aware that micro has one distinct characteristic, that is, the two

materials - microbaloons and epoxy tend to separate from one another when

still. This characteristic is good for the fact that the resin migrates onto

the surface being filled creating a real good bond to it. The bad part is if

you have to refill an area, the resin migrates into the surface of the

previously applied micro creating hard spots when sanding it. These hard

spots create raised areas, a real pain to deal with so try to avoid that.

Some people squeegee pure resin on the surface to wet it out just prior

applying the micro. I see no reason or purpose of that, I think they got it

from the way the plaster skim coat is applied on the drywall. 

To apply the micro to the surface, use a 6-inch metal trowel. Blob all the

micro (the mixed batch) to the middle of the surface and then trowel it in

the direction toward yourself first to one edge, then run around and to the

other side edge. Always go in the direction of the curve. The trowel is run

very flat to the surface and good pressure, you hold it by both hands by the

top part of the blade with all fingers on top and thumbs in the bottom the

get a good grip, bend the handle up about 30 degrees to get it out of the

way. The low angle and plenty of pressure are important because that is what

pushes the air bubbles that got mixed in to the micro out of the micro. You

will notice that at first it doesn't seem to want to stick and wants to roll

off, but then when the surface starts to get wetted out, it goes on pretty

smooth. You don't have much time thou, if you fuss with it too long or try

to redo an area you did a few minutes ago, it will start to tear up, lift

off and break up. This is because o lot of resin migrated onto the surface

and the micro starts to slide on it and unstuck from the surface easily,

remember this important tip, if you make a pass and you see the micro

breaking up make a pass in the opposite direction, that will smooth it right

up, but then just stop fussing with it. The thickness if the coat should be

somewhere between 1/8 to ¼ of an inch, you shouldn't have any lows on your

surface deeper then 1/8 of an inch .A little bit too much is better then a

little bit not enough because it's still easier to sand off some extra then

having to refill again. It takes some practice, if you want to see how thick

it is , just dip a Popsicle stick in to it. As a general rule, start the

filling on smaller, single curve surfaces like the tail, then large single

curve surfaces like wings, and last the most difficult compound curved parts

on the fuselage, engine cowl, wing fillet so that the level of difficulty

goes up along with your filling and sanding learning curve. On filling the

compound shapes the flat metal trowel will not work, for those you need to

use a flexible plastic squeegee. With 4 fingers on top and the thumb against

the bottom you can "cap" the squeegee so it follows the curve. Home depot

sells nice ones in a tri pack of 5, 4 and 2.5 inch wide. On a part like a

fuselage where you will not be able to fill the whole surface at once, try

to divide it so bring the edges to a break like a corner where blending of

one fill into another is easiest. If the fuselage is oval, do the break

where the curve is the sharpest, its much easier to blend it there then on

the shallow curve. It should take about 2 hours to fill one wing panel on a

small two-seater, up to about 4 hours on a big four-seater. 



Sanding 

There are three aspects of the sanding technique that will enable you to

arrive to that perfect straight wave free surface. 

First, you must use the right size an shape sanding tool for a given job,

different shapes require different tool, boards, blocks, tubes, long and

short as needed, Many builders don't realize (or disregard) the importance

of the right sanding tools. Trying to sand with a chunk of triple folded

sandpaper pushed along with bear hand is not going to work too well. You

will find it a great paradox if you visit somebody's workshop who claims

spending hundreds of hours on finish sanding his airplane and yet you won't

be able to find a decent sanding board in his shop. Make yourself two basic

sanding boards 2,3/4 inch wide 16 and 32 inches long, for the length of one

and two strips of sandpaper. I think the best is to use that white shelving

material. You need to attach an 1 ¼ x 1 ¼ aluminum square tube or a "C"

channel to the back side of it with some screws, that will keep it straight

and also gives you a good grip so you can hold on to it. The 32 inch one

will be used on the wings, 16 inch on the tail, control surfaces and flat

parts of the fuselage. For compound surfaces you will need to make flexible

sanding boards. Not many people know this as I have never seen it mentioned

anywhere but it will make you work a lot easier when the sanding board bends

under the pressure and follows the curve of the surface. You will need two

boards, one should flex rather easy for highly curved surfaces and one

should be fairly stiff for mild curves. The 16 inches length of these

flexible boards should be enough . Use thin plywood, Plexiglas, or whatever

works for you. Get the real sandpaper from auto paint supply store, the one

that comes in 16 inch long strips, they usually carry the best, the 3M brand

is pretty sure bet. The sandpaper grades needed are 36, 80 and 100. Glue it

on with 3M Super 77 spray adhesive (Home depot), spray on only a light coat

of it, that stuff sticks like hell. To remove the worn out paper, heat it up

with a heat gun, it will peel right off. 

On tube shape sanding tools the strips will not work, for those, get the big

sheets for floor sanding from Home depot. 

The second aspects of the sanding technique is the proper sanding pattern.

For an airfoil shape surface, hold the sanding board parallel (at all times)

to the span and sand at 45 degrees angle, use the longest (reasonable)

stroke, across the whole cord if possible. Start at the root end leading

edge side and move slowly to the tip end with each stroke moved about an

inch or two, creating a sort of a tall tight zigzag pattern. When you get to

the tip, go back to the root and start another pass, this time sanding at 45

degrees the other way - 90 degrees to the first pass. After these two passes

move yourself to the trailing edge side and make two passes from there,

again starting the first pass at 90 degrees to the previous one, and then

keep repeating this cycle. It is this sanding pattern, that will level out

the highs and lows into a nice even flowing plain and create the desired

wave free surface. 

The third aspect is you checking the surface frequently for high areas and

directing more attention to them. The best way to check the trueness of the

surface is to feel it by sliding your hand over the surface in long sweeps

in all different directions. If you have never tried this you will be amazed

to find out how sensitive your hand is to even minute surface waves and

unevenness. Direct more sanding to the identified high areas and pass

quicker over the low ones to speed up the process. If everything goes right,

you will have good straight surface just before you remove all the filler

and the high spots of the skin start showing through the filler. Keep

sanding off the excess filler until the highs start to show up as dark spots

across the whole surface. At this point you need to change the sandpaper

grade to 80 for the final sanding stage so you can remove the deep scratches

left by the 36 grade. Do the final once-over with a 100 grade and that's as

fine as you need to go on this. They say a picture is worth a thousand

words. Luckily I have some good ones to show you what it should look like at

this point. On the picture below the right wing has just been filled and is

curing while I'm sanding the left one 



This is a close up of the filed right wing 



Here the left wing is sanded and the right wing is just getting started.

It’s hard to take a picture of an all white surface, it tends to get

overexposed and the details are lost but looking at the pattern of the dark

spots will give you pretty good idea what it should look like. 



This is the horizontal stabilizer just at the point when the shaping is done

and when I switch to finer grade paper. You can see the cross hatch sanding

pattern there. The dark spots will get quite a bit darker by the time all

deep scratches are gone. 



It should take about 4 hours to sand one wing panel to shape on a small

two-seater, up to about 8 hours on a big four-seater. 

Compound curved surfaces are a little harder to do. Keep basically the same

crisscross 45 degree pattern relative to the direction of the milder curve

with your flexible sanding board, but pay a lot more attention to "feeling"

the surface and sanding off the highs. By the time you do all your flying

surfaces you will be pretty good at it. 

Detailing 

There are three kinds of details we have on the plane to deal with, fillets

where components come together and meet at different angles, fitting of

access and inspection panels and uniform control surfaces gaps. 

Take a note here, if you decide to do the control surfaces gaps, you need to

do them Before the general surface filling of the control surfaces, that way

the filler is brought up to and blended to the level required to close the

gaps at the nose area of that control surface. 

Filets are fairly easy, shape a corner of a plastic squeegee to the desired

radius and use that to shape the applied micro into the fillet radius . Run

the squeegee back and forth in alternating directions very flat at first to

evenly distribute the micro, then start standing it up with each pass to

gradually remove the excess micro and arrive to the final radius. Use the

tube sanding tool that closely matches the radius to sand it smooth. 

Inspection panels . In order to have good looking access and inspection

panels, or any other openings like gear doors and baggage compartments doors

or even an engine cowling if its fitted flush with the fuselage, you need to

create a small even gap around them. Here is the trick how to do that. Fist

make sure the covers are exact size and shape, round off the corners, square

corners don’t look right. Apply clear package sealing tape to the backside

and wherever needed as a release and mount the covers into exact position.

Now squeegee the micro all around the recess, or over the whole cover if the

height of it is not even, and then run a mixing stick all around the cover

tight against the edge to create a nice line around it. Cutting down the

width of the mixing stick will help it to go around the corners without

widening the gap and dipping the mixing stick in lacquer thinner will

prevent micro from sticking to the stick and help to keep the line edges

nice and smooth. 

Control surfaces gaps Ever heard about those incredible even Quarter

thickness gaps that don’t change a bit, even when you move the surface ?

Here is how to make them. Apply several plies of duck tape on the underside

of the trailing edge to build up the desired gap thickness. Put clear

packaging tape over it (its slicker and slides better), you will probably be

able to handle only one side at the time. Apply plenty of micro to the nose

of the control surface to fill the intended gap and then some. Cover the

micro with a plastic sheet, using thicker stiffer kind on this works better,

install the control surface into its hinges and slowly move it up and down

through the whole travel so that the excess micro is pushed out. Viola,

after the duck tape build up is removed, you have a beautiful small and even

gap through the whole control surface travel. Before you start removing the

excess micro that got pushed off mark the ends of the travel with a good

line as reference so you don’t lose it and sand into it later. before

filling the rest of the surface, cover the finished gap part with the duck

tape to preserve it. 

This concludes the first stage, the surface shaping. 



Surface finishing 

is the second stage of the work when we remove all the nicks, pits, tears

and finally the scratches. First, vacuum the surface, you need to get all

the sanding dust out of the nicks so you can see them and fill them. Micro

does not work on small nicks, it has too coarse consistency. You can use the

Superfil which is much smoother or you can mix your own filler by adding

cab-o-sil along with microbaloons. To mix this filler, get a coffee can,

fill it 1/3 with microbaloons first, then 1/3 Cab-o-sil. Leave the last

third empty so you can mix it well and add more of either substance if you

want to adjust the ratio, throw some wood blocks in to help mixing it, put

the lid on and mix it well. Fill the nicks with a small one inch metal

spatula. Squeegee the filler on to fill the nick but scrape all the excess

from the surface, it would be very hard to sand. That way you will do only

light sanding over those spots to remove the leftover fuzz. To get the right

perspective what size of the nicks is big enough to fill and which is too

small to be bothered with, use the rule, if you can see it from two feet

away, fill it. Another way to look at it if the nick is no deeper then a

scratch left by a 36 grid sandpaper. 

Pinholes 

These are tiny voids, bubbles and pits caused by air mixed into the filler.

They are invisible until the minute you start spraying the first coat of

primer. They can give you a big headache if you attack them the wrong way.

You might have heard horror stories of builders spraying coat after coat of

primer trying to get rid of them. The bottom line is, you cannot fill the

pinholes by spraying. Yes, if you keep spraying long enough, eventually they

will disappear, but they will not be filled, they will be bridged. Bridged

pinholes can cause the painted surface to develop little pimple like bumps

on the sun when the paint softens some and the trapped air expands with the

heat. 

Luckily, we have a simple effective way how to deal with pinholes before we

even see any. Vacuum the surface real well to remove any dust and then

squeegee pure epoxy resin over the surface. The coat is very thin and the

amount of resin is mall, you are basically just wetting the surface, give it

some time to soak in and squeegee off all the excess. The resin has very low

surface tension so it flows into all those small voids and because unlike

primers it doesn’t contain any volatiles it doesn’t shrink as it cures so

the fill is complete. The second benefit of this step is that the resins

hardens the top shell of the micro, making it more durable. 

A word of caution, many epoxy resins do not cure well and stay gummy at very

thin coat, especially in humid condition. If yours is one of those or you

are not sure, use the West system epoxy for this. 

When this top coat is cured sand it lightly with 100 just to break the

gloss, and you are ready for the primer. 

The primer used in this step is a "high build up" kind, intended for final

wet sanding. There are many on the market so I can’t say you must use this ,

or cannot use that, except maybe for one. You may have seen reference in

other articles (especially the older ones) to use "Feather fill". I have

used it and I don’t understand how anybody can recommend it . This is one of

the worst products I have seen in my life. 



I have been using two kinds of primers so far. 

One is "PPG K200" this is acrylic urethane (two part 4:1), very fast drying,

easy to spray, dark yellow in color. Available from auto paint supply

stores. It wet sands very easy, however it has rather soft properties even

when cured. Mishandling of parts can dent and scratch the surface rather

easily. 

The other kind is epoxy based "US Paint D9002 base /D3002 converter" (Two

part 1:1). Also dark yellow, available from marine supply stores (

www.uspaint.com ) This primer takes longer to dry and it’s a bit harder to

sand but it is very hard and durable when fully cured. I myself prefer the

better durability, even if it takes more work. 

I have not had a chance to try "Poly-fiber Smooth Prime" but I plan on it. 



Wet sanding is done by still keeping the same 45 degrees crisscross pattern

but the sanding blocks are a lot smaller, 11x3 inches for large parts 5.5x3

for the smaller ones. I use pieces of hard foam as sanding blocks. Use the

same "super 77 spray adhesive" and spray just very light mist on it to

attach it, it will peel off without the need of heating it up. Start with

180 grade for fast progress but be aware 180 leaves pretty deep scratches

that would show in the paint so switch to 220 grade for the second half of

the job. On the contrary to some peoples believe, 1 sheet of wet sandpaper

does not last forever, it just isn’t as obvious its getting dull by looking

at it so change the paper often. 

To check the progression and quality of the surface use the squeegee

technique. Pour some water over the surface and squeegee it off with a

rubber window squeegee (Home depot has those), all the remaining pits will

become instantly visible. Keep sanding and checking until they are all gone.

Don’t go crazy if you have a few deeper nicks left here and there, and don’t

sand flat spots or dips into your surface in order to get rid of them. They

will be filled instead. 

For this last filling use polyester based "glazing putty" (auto paint

supplies) This is very smooth creamy filler designed for minor

imperfections. Before you start filling go over the whole surface carefully

and mark all imperfections to be filled with a pencil so you don’t have too

look for them while your mixed putty is curing. Mix the glazing filler in

small batches, it has very short pot life so you have only a few minutes on

each batch. Squeegee it on with a small metal spatula and scrape off any

excess. Wet sand the spots after they cure and you are done. 



There will be one more coat of primer but that is as a part of painting

jrgowing(at)bigpond.net.a
Guest

Posted: Thu Sep 18, 2008 2:33 pm Post subject: Finishing tips

Jerry 

  

 Still on the filling but I  have thought the article excellent as well, often turning  back to re-read parts. 

 but the hardest part at first was :-

  

  2The right way  to do it is to fill all of the surface (meaning like one side of a wing or a  fuselage) at once with a coat of filler sufficiently thick enough to fully fill  all the lows, then sand the whole surface as one uniform plain ONCE, without the  need of refilling again. 2

  

 Strimmer lines as advocated by Graham Singleton  help. I used them and a 2 2 pipe as a roller with thin plastic sheet between  filler and roller as advocated by Kingsley Hurst.

  

 JR (Bob) Gowing UK Kit 327 in Oz

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jan_de_jong(at)casema.nl
Guest

Posted: Thu Sep 18, 2008 4:53 pm Post subject: Finishing tips

I found that a dry mix of Expancel and SP106 works well for the first 

round. Apply liberally, sand once - with coarse boards (I tried the 

mucking about technique too and it takes forever). Careful towards the 

end, but easy to see.

Less dry mix for surface perfecting. Stlll no point in getting too fine.

SP106 also works for pinhole filling.

Ampreg20 is not very good for surface work - it remains sticky a long 

time. The Aeropoxy laminating epoxy may be better - don't know.

Final layer before paint SP Hibuild312 rolled on (ventilate well). Will 

mostly be sanded off using fine paper. Outcome to be seen, looks good.

By the way, in my experience the XS wings need filler in parts (trailing 

outer wing sections) and hibuild all over or the ribs will be visible.

Jan de Jong



JR Gowing wrote:

[quote] Jerry

 Still on the filling but I have thought the article excellent as well, 

 often turning back to re-read parts.

 but the hardest part at first was :-

 "The right way to do it is to fill all of the surface (meaning like 

 one side of a wing or a fuselage) at once with a coat of filler 

 sufficiently thick enough to fully fill all the lows, then sand the 

 whole surface as one uniform plain ONCE, without the need of refilling 

 again."

 Strimmer lines as advocated by Graham Singleton help. I used them and 

 a 2" pipe as a roller with thin plastic sheet between filler and 

 roller as advocated by Kingsley Hurst.

 JR (Bob) Gowing UK Kit 327 in Oz



     ---

danbish99

Joined: 16 May 2015
Posts: 10

Posted: Sat Mar 25, 2023 6:51 am Post subject: Re: Finishing tips

Any idea who wrote this article? Has some excellent tips but I have a few questions for the author. It's posted on the Europa Club site.



Thanks,



Dan

Hitchflight

Joined: 22 Feb 2018
Posts: 94
Location: Derbyshire, England

Posted: Sun Mar 26, 2023 9:59 am Post subject: Re: Finishing tips

Hi Dan 



After some digging I have refreshed the page you referred to so as to recognise and credit the probable authors.



Attribution: Thanks to George Sychrovsky & the late Nigel Graham

Hope this helps. 



We are most fortunate that many good people have donated their achievements in life to posterity. 



Have a contact reference that I will email to you separately.

Regards



Bob

If anyone spots any errors or omissions on the Europa Club website please advise by email to secretary(at)theeuropaclub.org and we would endeavour to fix. 



 	  danbish99 wrote: 	
		  Any idea who wrote this article? Has some excellent tips but I have a few questions for the author. It's posted on the Europa Club site.



Thanks,



Dan

dmac7

Joined: 05 Apr 2019
Posts: 58
Location: Canada

Posted: Sun Mar 26, 2023 11:59 am Post subject: Re: Finishing tips

Thx Jerry, good write up on finishing. I will try to add a Youtube video on a method used by Cory Bird on his aircraft called " Symmetry " a 2004 Oshkosh Grand champion winner.  He called his finish technique "the epoxy wipe method"

https://www.youtube.com/watch?v=43K1qwoHbnc&t=22s

If the link doesn't work just search Youtube for, epoxy wipe method composite aircraft finishing.

Kelvin Weston

Joined: 14 Apr 2010
Posts: 90
Location: Hampshire, UK

Posted: Sun Mar 26, 2023 12:11 pm Post subject: Re: Finishing tips

Hi Dan



The original web article can be found here:



http://curedcomposites.com/index.html



or the page on finishing here:



http://curedcomposites.com/finish.html



Another good article on finishing is Wayne Hicks Cozy IV project:



http://ez.canardaircraft.com/www.ez.org/canardpages/pages/waynehicks/index.html



See Chapter 25 on Finishing

_________________
Regards

Kelv Weston
Kit 497
kelv@kdweston.co.uk

Kelvin Weston

Joined: 14 Apr 2010
Posts: 90
Location: Hampshire, UK

Posted: Sun Mar 26, 2023 12:29 pm Post subject: Re: Finishing tips

Hi Dan



A pdf attached of the "Epoxy Wipe" or "Skim Coating" method extracted from Wayne Hicks Cozy project.



There is also lots of great finishing advice on this forum from Bud Yearly and the late great Nev Eyre.

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_________________
Regards

Kelv Weston
Kit 497
kelv@kdweston.co.uk

danbish99

Joined: 16 May 2015
Posts: 10

Posted: Mon Mar 27, 2023 7:42 pm Post subject: Re: Finishing tips

Thanks everyone for all the great resources - awesome to be able to reach out for help like this. You've surely saved me a ton of time avoiding sand & fill hell!



Best,



Dan

n7188u

Joined: 15 Nov 2015
Posts: 408

Posted: Tue Mar 28, 2023 8:00 am Post subject: Re: Finishing tips

One personal observation regarding finishing:



I thought this process was going to be painful, but actually found it to be not as bad as I thought it would. I honestly did not read the entire procedure posted here but I will briefly say what I did.



1.- Clean and carefully scuff sand the fiberglass or gelcoat.

2.- Using the the fishing line technique, apply a nice think coat of expancell plus West Systems 105. What helped a lot was to use an epoxy pump and a sensitive weight scale to exactly measure the ratio of epoxy and expancell. Keeping the mixture consistent between mixes is key.

3.-  Apply the mix using a dry wall spreader modified with an angle epoxied at the width of the application end. This is also key to keep the spreader from bending and creating a concave surface.

4.- Wait until the applied coat starts to gel, remove the fishing line, fill the groves left by the line.

5.- Using Dura-Block sanding blocks and very coarse sandpaper sand expancell coat until no depressions are observed. Most of the time a single pass of expancell coat was enough. If a few voids are present fix those.

6.- Now the cool part, I used a modified epoxy 2K filling primer made by 5-Star and rolled it on using a small foam roller. Push hard and fill as many pinholes as you can.

7.- Once cured, apply coat of Dry Guide Coat (I used Mirka brand). 

8.- Sand this coat until all of the guidecoat is gone. Don't worry if this results in a good part of the 5-Start 2K to be gone.

9.- Spray one heavy coat of SPI (Southern Polyurethanes) white Epoxy primer. Welcome to pinhole land since this primer will make them show like craters in the moon (it's actually called "cratering" by the people that make the prime which is very prone to doing this). 

9.- Now, without sanding the epoxy primer but before 7 days after applying it,  use thin 3M polyester glaze to fill every pin hole, one by one. This is tedious but the fantastic quality of the 3M glaze makes the job much easier. The 7 day window is important since the epoxy primer doesn't need to be sanded if the glaze and subsequent 2K is applied within this time frame.

10.- Sand the pinholes. This part is indeed tedious because the polyester putty will stick to the sandpaper. The solution was to use a scrap piece of fiberglass and use it to scrape the glaze of the sandpaper. Use only high quality 3M sanding paper. The cheaper red one seems to work better though and the glaze sticks less.

11.- Spray a heavy coat of SPI grey regular 2K primer. 

12.- If any small pinholes show I used red one part lacquer glaze to fill them. Quicker and easier for just a few of them. 

13.- Guide coat, sand until the white shows and almost all grey 2K is gone. the guide coat will show the low spots. Here you need to gage what fillers to use to reach perfection. A little more 2K will fill shallow areas but it is a little heavier. Still I used it. Some polyester 2K glaze is also good. I don't think I had anything deep enough to go to expancell. If you do you have to do all the stuff stated above on that area.

14.- Finally, a coat of SPI white epoxy and you can spray the paint (no sanding needed if within 7 days). Or I flew it on primer for 2 years. The stuff still looks like the day it was applied and no issues with bugs or deterioration. The SPI primer is semi gloss so it looks pretty good too.



And I used a forced air respiration system and a dust collector from Harbor Freight. I think it is a must. 



I can provide more detail on the sandpaper used, 3M glaze PN, 5 Star modified epoxy primer, SPI stuff but will have to collect the info. I can also put together a few pictures. 



I hope I didn't bore anyone with this long post.

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