Question about 545 primer

[mrybas]

I’m painting a 47’ catamaran. Im almost done sanding back two coats of Awlquick primer with 120 grit.
How perfect does the surface need to be before spraying 2-3 coats of 545 primer? Will 545 fill/hide any imperfections?
After the 545 is sanded with 320 grit the boat will get 3 coats of awlgrip (sprayed).

[Suijin]

Awl quick is basically a fairing primer, filling bigger imperfections. It’s easy to sand and is thick, while 545 is not. Basically you’ll sand to take the sheen off the 545 and that’s it.

You’ll invariably find pinholes and small imperfections after the 545 goes on as they will stand out like sore thumbs. If they are small just hit them with premium marine filler and sand flush. If larger you’ll want to follow up with 545 on top.

[GRIT]

The 545 doesn't really "hide" anything. It just seals the Awlquick for a better finish/shine.

I haven't, personally, noticed any difference between the final finish using awlquick, or 545, both look the same to me. They say there's more 'depth" to the finish with 545 underneath.


Your boat looks great!

Cheers, and good luck.
Paul.

[Zach]

Consider sanding the boat out with 220 instead of trying to jump from 120 to 320 with the 545. 120 you can still catch a fingernail in the scratch and you can't sand out defects to a feather edge if you've got a load of deep scratches full of 545 in a sea of awlquick.


You'll be able to see the scratches in the final paint job if you don't let the primer sit up for a week or two. You can come back and guide coat the surface, sand out with 320 and see a haze of your original 120 scratches, still... That wasn't in it the day after you sprayed when you sanded it out. That sucks, as you have to sand the thing out again far enough to waste the material that was put on thin down to a smooth surface.



220 on up you don't have that problem, and the 545 lays out a lot nicer. 320 before top coating. Some spray hands try to talk in that awlgrip is magic and going from 220 is just as good if you don't mind 5 coats. It puts a lot of texture in that awlgrip doesn't wet out enough to flow out to a magazine centerfold finish. But, since it doesn't flow out to be super glossy they can get away with less prep work that nobody will ever see craters or pin holes or even roller stipple. Hand sanded 220 grit scratches are deep enough that top coat doesn't cover it without 4-5 coats... So make sure you are 320 grit everywhere before you squeeze the trigger.



I use 3M dry guide coat, to make sure you have all the sanding scratches out between grits. Works well and doesn't clog paper.



Once you are in 545, one thing to pay attention to is that you can burnish the guide coat off, and leave a lot of texture that you can't necessarily feel but can see. 545 doesn't lay down perfectly, and you can have shiny dots here and there and really study and look for/pay attention to them as the difference in surface tension of places like that make it look like cratered paint in top coat. I go over the whole surface with red scotch bright to try to prevent those, as you can get a little bit lower than something that is flat. The boat can look like it has chicken pox worth of craters if you don't.



That can be the remnants of craters, pin holes, and orange peel in primer that hasn't finished hardening up and offgassing. So sand out 320 grit, guide coat it, air hose the dust off, guide coat it and sand it a second time (Takes a 10th the time as going the first round...) and you'll see the last of your surface defects as they might have got a scratch pattern and not been so slick that the guide coat didn't stick.


If your paper loads up, it knocks off your guide coat without sanding. Wait until the primer hardens up. Sanding 545 that hasn't finished offgassing just means that the thickest applications shrinks back compared to thinner areas anyway and the boat will move as you go through the process... Bad news.



If you are using a 5 inch DA, consider getting a 16 inch 3m hand board and a roll of 3M gold in 220 grit to smooth out any waves the DA put in while you are in awlquick.



If you keep using the 16 inch board after you 545, you can see yellow haze on high spots that you'd never believe were high til the board shows them to you. Normally any cratered spots or pin holes, have a high spot beside them or are actually in a low spot already.



3 coats of sprayed 545 is tough to get a full build thickness on without a wet mil gauge as it is a lot of material. It takes a lot of spraying to get enough material on that it doesn't run, but also gets enough buildup to be able to sand out.


I would spray your edges and stairs first and learn your gun angles to get good coverage. The inside corners are a pain in the butt to get coverage as the air from the fan swirls before you get material deposited. Keep that in mind, and the corners of the steps on the outside edge splits the fan, and you can run both sides of it but not get a good build on the actual edge, trying to deposit just on the edge of the steps. You may find that a touch up gun with a round fan does better than a flat fan.



The hardest/finest finish is getting the shadow line and shape straight around the outer edge of the boat where your radius blends together. A DA lets you sand something that isn't necessarily flat, but make it slick. The vertical faces of your stairs are one worth picking on.


It can look perfect in primer as you haven't burned through and are all one color... Hit it with a water hose and stand back and see that you've got a 1/32 wiggle every other foot that undulates like a wave. Real hard to see that in the side of a boat floating in the water on the sides, or flat color primer... but the top at the deck edge and eyeball to eyeball looking down on a floating dock is the perspective that blocking out by hand really makes crisp, which is different from long board sanding. Long boarding you can be dead nuts fair, but if you power sand from the very first round of priming if you do it all by power it can put some shape back into an otherwise fair boat. Real smooth, but a little wiggle here and there that come around from trying to sand down to get texture out of low spots.



Looking flat on the middle of wide panels you've got a little more play in light colors on parts of the boat that are angled less than vertical and can't cast their own shadow than gloss in darker colors. There are some boats out there that are just a blinding enough white that you'd have to rub your hands over to feel the lumps in.



She looks good

[Delfin]

Originally Posted by mrybas

I’m painting a 47’ catamaran. Im almost done sanding back two coats of Awlquick primer with 120 grit.
How perfect does the surface need to be before spraying 2-3 coats of 545 primer? Will 545 fill/hide any imperfections?
After the 545 is sanded with 320 grit the boat will get 3 coats of awlgrip (sprayed).
Attachment 177031Attachment 177032

You'll be shocked at what imperfections that are invisible after the 545 show up when the top coat goes on. If a really smooth finish is what you are looking for, I suggest, as does Awlgrip, that you use their high build primer before the 545 goes on. Their complete system includes this as part of their recommended build up.

[mrybas]

Originally Posted by Zach

Consider sanding the boat out with 220 instead of trying to jump from 120 to 320 with the 545. 120 you can still catch a fingernail in the scratch and you can't sand out defects to a feather edge if you've got a load of deep scratches full of 545 in a sea of awlquick.


You'll be able to see the scratches in the final paint job if you don't let the primer sit up for a week or two. You can come back and guide coat the surface, sand out with 320 and see a haze of your original 120 scratches, still... That wasn't in it the day after you sprayed when you sanded it out. That sucks, as you have to sand the thing out again far enough to waste the material that was put on thin down to a smooth surface.



220 on up you don't have that problem, and the 545 lays out a lot nicer. 320 before top coating. Some spray hands try to talk in that awlgrip is magic and going from 220 is just as good if you don't mind 5 coats. It puts a lot of texture in that awlgrip doesn't wet out enough to flow out to a magazine centerfold finish. But, since it doesn't flow out to be super glossy they can get away with less prep work that nobody will ever see craters or pin holes or even roller stipple. Hand sanded 220 grit scratches are deep enough that top coat doesn't cover it without 4-5 coats... So make sure you are 320 grit everywhere before you squeeze the trigger.



I use 3M dry guide coat, to make sure you have all the sanding scratches out between grits. Works well and doesn't clog paper.



Once you are in 545, one thing to pay attention to is that you can burnish the guide coat off, and leave a lot of texture that you can't necessarily feel but can see. 545 doesn't lay down perfectly, and you can have shiny dots here and there and really study and look for/pay attention to them as the difference in surface tension of places like that make it look like cratered paint in top coat. I go over the whole surface with red scotch bright to try to prevent those, as you can get a little bit lower than something that is flat. The boat can look like it has chicken pox worth of craters if you don't.



That can be the remnants of craters, pin holes, and orange peel in primer that hasn't finished hardening up and offgassing. So sand out 320 grit, guide coat it, air hose the dust off, guide coat it and sand it a second time (Takes a 10th the time as going the first round...) and you'll see the last of your surface defects as they might have got a scratch pattern and not been so slick that the guide coat didn't stick.


If your paper loads up, it knocks off your guide coat without sanding. Wait until the primer hardens up. Sanding 545 that hasn't finished offgassing just means that the thickest applications shrinks back compared to thinner areas anyway and the boat will move as you go through the process... Bad news.



If you are using a 5 inch DA, consider getting a 16 inch 3m hand board and a roll of 3M gold in 220 grit to smooth out any waves the DA put in while you are in awlquick.



If you keep using the 16 inch board after you 545, you can see yellow haze on high spots that you'd never believe were high til the board shows them to you. Normally any cratered spots or pin holes, have a high spot beside them or are actually in a low spot already.



3 coats of sprayed 545 is tough to get a full build thickness on without a wet mil gauge as it is a lot of material. It takes a lot of spraying to get enough material on that it doesn't run, but also gets enough buildup to be able to sand out.


I would spray your edges and stairs first and learn your gun angles to get good coverage. The inside corners are a pain in the butt to get coverage as the air from the fan swirls before you get material deposited. Keep that in mind, and the corners of the steps on the outside edge splits the fan, and you can run both sides of it but not get a good build on the actual edge, trying to deposit just on the edge of the steps. You may find that a touch up gun with a round fan does better than a flat fan.



The hardest/finest finish is getting the shadow line and shape straight around the outer edge of the boat where your radius blends together. A DA lets you sand something that isn't necessarily flat, but make it slick. The vertical faces of your stairs are one worth picking on.


It can look perfect in primer as you haven't burned through and are all one color... Hit it with a water hose and stand back and see that you've got a 1/32 wiggle every other foot that undulates like a wave. Real hard to see that in the side of a boat floating in the water on the sides, or flat color primer... but the top at the deck edge and eyeball to eyeball looking down on a floating dock is the perspective that blocking out by hand really makes crisp, which is different from long board sanding. Long boarding you can be dead nuts fair, but if you power sand from the very first round of priming if you do it all by power it can put some shape back into an otherwise fair boat. Real smooth, but a little wiggle here and there that come around from trying to sand down to get texture out of low spots.



Looking flat on the middle of wide panels you've got a little more play in light colors on parts of the boat that are angled less than vertical and can't cast their own shadow than gloss in darker colors. There are some boats out there that are just a blinding enough white that you'd have to rub your hands over to feel the lumps in.



She looks good

Thanks to everyone for their comments and advice.
Besides the initial stripping of paint which was done with 6” DA, all other sanding has been done by hand with boards/blocks. I think the boat is pretty flat after initial fairing with awlfair, then two coats of awlquick sanded back. I’m sure it’s not perfect, but pretty good.
Should I also sand the 545 with blocks/boards or is it ok to use 320 on a DA?
I never heard of the 3M Guide Coat, I’ll give that a try. Thanks!
I’ll get some more pictures up once I get some 545 on.

[fkittson]

I run a professional paint shop and we paint everything from 6’ fibreglass boat up to 60’. The way we have always done it and get a perfect finish is. Sand original paint to 180 to remove any shine. Mix up west system epoxy with 407 and fill any damage or low spots. Then 3 coats Awlquik and and longboard the whole thing. Then 3 coats of 545. If you still have any pinholes or blemishes you can slick with Awlquik finish sand to 320

[mrybas]

Originally Posted by fkittson

I run a professional paint shop and we paint everything from 6’ fibreglass boat up to 60’. The way we have always done it and get a perfect finish is. Sand original paint to 180 to remove any shine. Mix up west system epoxy with 407 and fill any damage or low spots. Then 3 coats Awlquik and and longboard the whole thing. Then 3 coats of 545. If you still have any pinholes or blemishes you can slick with Awlquik finish sand to 320

That is more or less what I’m doing except used awlfair instead of West/407.
Do you sand the 545 with boards or DA?

[mrybas]

We’re going to spray the hulls tomorrow with 545. I have a friend that has painted several boats doing the spraying since I don’t have much experience.
I decided to hit the hulls once more with 180 grit on the 22” sanding board.

[Zach]

Is that a current picture of the state of things?


If so, don't 545... Hit her with another round of Awlquick.


Before you do that... Take a straight edge/sheet rock trowel or even the side of your board and hold it up tight to the hull and see if it rocks.



Lay it on top of the awlfair patches, parallel the the waterline, long ways to the boat. Take a flash light and shine it under, and look for light in a crack. Anything that has changed color after sanding primer has shown its self as a high spot, or the edge of a low spot that the board is dropping into and riding into the putty you filled.



With that hard of a straight edge around your putty fills... They are normally a high spots that didn't get feathered in, up top by the deck line. If the straight edge, sheet rock trowel, or squeedgee rocks or shows light under it you'll burn the next layer of primer off the high spots again.



If you don't have guide coat, you can squiggle pencil lines around the high spots and on top of the high spots and sand until the pencil lines disappear. The board ramps up on to the high and a squiggle of pencil line disappear off the top of the high, but right where the color change is hard to sand the pencil lines off out unless you hold the board flat and sand straight into it repeatedly without going over it in long passes.



Boarding if you let the board float over the the surface with more pressure on the trailing edge than the leading edge and coarse paper, it'll work the highs down, but if they are built up with a series of fills in a row and the first one is high you end up with a putty ramp.



I call high spots that are putty with vertical edges putty flags, as a straight edge and a bright light will show a crack. The board can go across them and sand off the primer up to the edge, and all the primer over the top of them because it lifts the board up and over, and they are just hard enough material that you burn the primer off around them before they get level to the surrounding surface.

Most folks prime something because the fairing work is pretty good and want to take a look at it one color. Then once it is primed, forget that they were just trying to take a look because it was one color and try to race to finish primer.



If you've got a few spots that need a little more sanding, drop back to coarse grits in localized areas and beat the trouble spots down to where they need to be. A lot of guys once they pick up a roller brush or spray gun won't go back to a grit that cuts harder materials fast enough to level out the surface and mow them down.



Makes for a never ending priming job of trying to put just one more coat over a high spot of bare fiberglass or putty so you can spray top coat. Make trouble spots ever so slightly low and prime them up... Don't have to think about or ever see them again without the kidd glove sanding and panic attack...



A holiday, or slight groove in the putty that has been primed shows as a thick colored primer line in it. More often than not if you sand down til the primer in the holiday is gone in the putty, the flag feathers out and disappears and you are even with the surrounding surface. Basically, putty fills should taper in from a barely visible thickness in color to something dark in the middle and not be square sqaped.



If you look under the left side of the saddle up on deck straight above you, the putty flag that has a thick white bit of primer to its left hand side is a holiday where the primer is thick. Either it needed another fill of putty where the holiday is... or it is a high spot where the primer sanded off and is showing Awlfair.


Sort of a topographical map type thing...



If the green is bare glass, then you can't get there from here as the board digs a halo around each of those as 120 will shred the primer off before you even think about taking down the glass.



They reappear immediately after you prime unless you burn them down or cover the entire surface in enough primer that you can sand it out. That is gallons of material. High build/ultrabuild can do that but it takes a LOT of material to do that.



For putty flags and holidays you can drop back to 80 grit on a hand block guide coat it, sand til smooth and then work back up the grits to 220 and prime an area at a time if you only have a few trouble spots in a 2x4 foot or 4x4 foot area.


The area will be slightly low after mowing it down and really beating on it... but if you put 3 coats of Awlquick over just the areas you have worked on they end up flush and one color to the surrounding surface once you sand it back slick and feather in from the surrounding area you are calling good.



I like to roll repaired areas, as roller stipple gives you some idea of depth of issues and you lose less material to overspray. Weenie rollers or 1/8th inch nap foam work fine, and ray charles can see where you haven't sanded. Spraying in little areas as you go is harder to not miss something.



Almost always, it is better to end up ever so slightly low after sanding putty fills that are done with squeedgees and putty knives instead of screeds and battens. Otherwise they end up 4-6 inch wide high spots instead of perfect to perfect to the surrounding area but out of a much harder material.



Until you get all those beaten down shooting the whole boat just means sanding the whole boat until you find them again and eventually either raise the primer above them, or sand them off.


If you can get 220 grit smooth, and all one color the 545 will stay on the boat when you go to sand it out with 320. Much less than that, and it is a wipe on, wipe off process that you never quite get out of.



How many gallons are you going to put on? I would try my best to put a mixed gallon before adding thinner on each side to have enough material to get out of thew woods.



Lastly, it looks like you've done a real good job sanding out the putty fills at your current working height. I'd look at what it takes to get your staging set up around the boat to get the top of the hull up by the deck sanded at the same shoulder height. Where it hurts to work, is the hardest part to get down fair... But normally also the most visible. Right above the waterline is hard to see on a boat in the water because of all the light reflections. Walking down the dock, the deck line is what most folks see.



My rule of thumb on DA's and power sanding in general is that you can change the material color, and power sand. Once you start burning through what you've done is moved forward a grit and smoothed things out.



Gist of it is when throwing power at something... Is if you prime and sand off everything except what you can't sand off without removing filler... You've filled your low spots and highlighted your high spots, but at some point you better stop before you lose your point of reference and start making low spots. Boards can make low spots but you've got to work your ass off to do it.



If I were in your shoes, I'd consider guide coating and throwing some 80 grit on the board and do a pass down the hull one way, a pass down the hull the other and go look at your putty flags and see if you've got contact around and up over them. If you have areas that are 180 grit smooth with just a kiss here and there of 80 grit scratches, you jumped to a fine grit before your high spots were worked out.



The catch 22 of board sanding is if you try to slick out and get shiny before it is fair in coarse grits, you never get done priming. Sometimes the fastest way forward is to be a little mean, and pile up some dust on the floor and get things flat enough that they stay one color on the next sanding.

[SVTatia]

Originally Posted by Zach

...

I use 3M dry guide coat, to make sure you have all the sanding scratches out between grits. Works well and doesn't clog paper.
...

She looks good

Great responses and lots of learning here.
I have used 545 extensively but I don't spray... I roll and tip.

What does the 3M dry guide coat do and how do you apply it?

[Zach]

It is a real fine powdered carbon dust, that comes in a plastic tin with a red rubber tit on the top and a wax type applicator pad. You put a smear on the surface enough to work it into the texture of the surface and when you sand it off with fine grit paper it leaves the black carbon dust in the surface.


I use West systems carbon filler to refill the 3M applicator. Without having an applicator pad and container with some mighty fine holes in it, its a bit of a pain to figure a way to sprinkle it so you don't end up with so much on the surface that the the sander doesn't just smear it around.


Alternate if you can't get either of those, is green or red food coloring in denatured alcohol. That requires a blow off and wipe down of the surface, so that you can keep using the same rag with food coloring on it throughout the job. Rag goes in quart cup, and just enough food coloring in the cup with a few ounces of denatured alcohol to tint the surface once it dries.


It stains the primer and leaves a stained patch in the low spots and texture. If you need to fill, or spot prime circle the area in pencil and sand off the color.


The denatured alcohol only works if you have an even layer of primer already, but does show that you have fully sanded the 545, and you can restain as you go through the grits.



Working outdoors, both keep you from going quite as snow blind too. White 545 will put your eyes out, but a little color or carbon black cuts the glare.



In hard core fairing, I use a pencil just because a thick line every inch vertical and horizontal gives you a grid pattern to fill. Don't use a pen to mark low spots as the ink can bleed back through. 40 and 80 grit scratches catch the graphite well too so it goes pretty quickly.


Blue carpenters chalk works too, but the first time you smash a chalk ball by accident it almost rivals the mess of dropping a tin of graphite on top of someones head from the staging...

[Zach]

Feathering in putty, with a before and after... Hope it makes sense.


Basically the pencil line goes under the putty marking the edge of what is good, the closest you can get to the low spot that needs to be filled that the long board scratch is still present, but disappears. That can be the shape of texas if you use a long enough board... but since this is a rough fill, it is a circle marking the depression. This one is a low on the back side of a bulkhead.


Over fill the hole, and leave a raised edge so that ray charles could fee that you need to work on it so it can't be forgotten. If you have to wait till the next day, it is a lot faster to sand for an extra minute or two, instead of having to putty a second time and wait another day.



Epoxy shrinks back just a bit, not a lot, but enough that a perfect fill after sanding is a low spot. So even if you use a batten screed, and perfectly contour the shape it can be worth a second skim just thick enough to change the color, to sand out to a finer grit prior to priming. That gives a feather fill type skim. Awlfair is good, but mix a small amount and don't let it start kicking so you get a good slick finish.



If you are working on a round surface, instead of a flat surface, but using a flat thing to pull putty... Bend the flat thing squeedgee, or sheet rock trowel into a slight arc so that you pull putty into a round that is higher than the round you need.


Cheers,


Zach

[Suijin]

3M guide coat is da sh!t. Makes it much easier to see what is what and where you are in the fairing process. Think of it as temporary paint.

I used it when grinding off the molded non skid on my deck. Made it go super quick and kept me from taking off more material than I needed to.

[Delfin]

Originally Posted by Zach

Is that a current picture of the state of things?


If so, don't 545... Hit her with another round of Awlquick.


Before you do that... Take a straight edge/sheet rock trowel or even the side of your board and hold it up tight to the hull and see if it rocks.



Lay it on top of the awlfair patches, parallel the the waterline, long ways to the boat. Take a flash light and shine it under, and look for light in a crack. Anything that has changed color after sanding primer has shown its self as a high spot, or the edge of a low spot that the board is dropping into and riding into the putty you filled.



With that hard of a straight edge around your putty fills... They are normally a high spots that didn't get feathered in, up top by the deck line. If the straight edge, sheet rock trowel, or squeedgee rocks or shows light under it you'll burn the next layer of primer off the high spots again.



If you don't have guide coat, you can squiggle pencil lines around the high spots and on top of the high spots and sand until the pencil lines disappear. The board ramps up on to the high and a squiggle of pencil line disappear off the top of the high, but right where the color change is hard to sand the pencil lines off out unless you hold the board flat and sand straight into it repeatedly without going over it in long passes.



Boarding if you let the board float over the the surface with more pressure on the trailing edge than the leading edge and coarse paper, it'll work the highs down, but if they are built up with a series of fills in a row and the first one is high you end up with a putty ramp.



I call high spots that are putty with vertical edges putty flags, as a straight edge and a bright light will show a crack. The board can go across them and sand off the primer up to the edge, and all the primer over the top of them because it lifts the board up and over, and they are just hard enough material that you burn the primer off around them before they get level to the surrounding surface.

Most folks prime something because the fairing work is pretty good and want to take a look at it one color. Then once it is primed, forget that they were just trying to take a look because it was one color and try to race to finish primer.



If you've got a few spots that need a little more sanding, drop back to coarse grits in localized areas and beat the trouble spots down to where they need to be. A lot of guys once they pick up a roller brush or spray gun won't go back to a grit that cuts harder materials fast enough to level out the surface and mow them down.



Makes for a never ending priming job of trying to put just one more coat over a high spot of bare fiberglass or putty so you can spray top coat. Make trouble spots ever so slightly low and prime them up... Don't have to think about or ever see them again without the kidd glove sanding and panic attack...



A holiday, or slight groove in the putty that has been primed shows as a thick colored primer line in it. More often than not if you sand down til the primer in the holiday is gone in the putty, the flag feathers out and disappears and you are even with the surrounding surface. Basically, putty fills should taper in from a barely visible thickness in color to something dark in the middle and not be square sqaped.



If you look under the left side of the saddle up on deck straight above you, the putty flag that has a thick white bit of primer to its left hand side is a holiday where the primer is thick. Either it needed another fill of putty where the holiday is... or it is a high spot where the primer sanded off and is showing Awlfair.


Sort of a topographical map type thing...



If the green is bare glass, then you can't get there from here as the board digs a halo around each of those as 120 will shred the primer off before you even think about taking down the glass.



They reappear immediately after you prime unless you burn them down or cover the entire surface in enough primer that you can sand it out. That is gallons of material. High build/ultrabuild can do that but it takes a LOT of material to do that.



For putty flags and holidays you can drop back to 80 grit on a hand block guide coat it, sand til smooth and then work back up the grits to 220 and prime an area at a time if you only have a few trouble spots in a 2x4 foot or 4x4 foot area.


The area will be slightly low after mowing it down and really beating on it... but if you put 3 coats of Awlquick over just the areas you have worked on they end up flush and one color to the surrounding surface once you sand it back slick and feather in from the surrounding area you are calling good.



I like to roll repaired areas, as roller stipple gives you some idea of depth of issues and you lose less material to overspray. Weenie rollers or 1/8th inch nap foam work fine, and ray charles can see where you haven't sanded. Spraying in little areas as you go is harder to not miss something.



Almost always, it is better to end up ever so slightly low after sanding putty fills that are done with squeedgees and putty knives instead of screeds and battens. Otherwise they end up 4-6 inch wide high spots instead of perfect to perfect to the surrounding area but out of a much harder material.



Until you get all those beaten down shooting the whole boat just means sanding the whole boat until you find them again and eventually either raise the primer above them, or sand them off.


If you can get 220 grit smooth, and all one color the 545 will stay on the boat when you go to sand it out with 320. Much less than that, and it is a wipe on, wipe off process that you never quite get out of.



How many gallons are you going to put on? I would try my best to put a mixed gallon before adding thinner on each side to have enough material to get out of thew woods.



Lastly, it looks like you've done a real good job sanding out the putty fills at your current working height. I'd look at what it takes to get your staging set up around the boat to get the top of the hull up by the deck sanded at the same shoulder height. Where it hurts to work, is the hardest part to get down fair... But normally also the most visible. Right above the waterline is hard to see on a boat in the water because of all the light reflections. Walking down the dock, the deck line is what most folks see.



My rule of thumb on DA's and power sanding in general is that you can change the material color, and power sand. Once you start burning through what you've done is moved forward a grit and smoothed things out.



Gist of it is when throwing power at something... Is if you prime and sand off everything except what you can't sand off without removing filler... You've filled your low spots and highlighted your high spots, but at some point you better stop before you lose your point of reference and start making low spots. Boards can make low spots but you've got to work your ass off to do it.



If I were in your shoes, I'd consider guide coating and throwing some 80 grit on the board and do a pass down the hull one way, a pass down the hull the other and go look at your putty flags and see if you've got contact around and up over them. If you have areas that are 180 grit smooth with just a kiss here and there of 80 grit scratches, you jumped to a fine grit before your high spots were worked out.



The catch 22 of board sanding is if you try to slick out and get shiny before it is fair in coarse grits, you never get done priming. Sometimes the fastest way forward is to be a little mean, and pile up some dust on the floor and get things flat enough that they stay one color on the next sanding.

Remarkable expertise Zach, thank you.