LionessRacing

Festool abrasive for gelcoat

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Time to strip the crazed 1962 gelcoat on deck and cabin. Festool 125mm Rotex, linear, 4mm RO, and detail Sanders with mini dust collector. 

Recommended type of abrasive and grit sequence ? 

Plan to remove all crazing/cracking and then rebuild,, with Awlgrip 545, ultra build,  545, color. Working in sections. 

 

looks like Saphir is the starting point 

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Would you strip the gelcoat back to the laminate or just sand it back to a surface that your paint system (545...) will bond to?

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Coarse, until it is time not to go coarse any more.

I take a wooden paint stir stick and hold it up to the hull with the wide face against the boat curving around it.  If there are still low spots that are smaller than a paint paddle where there is a crack smiling open between the hull and the stick... I keep the grit coarse in sanding as any priming you are doing is just to fill low spots.  One of those things where you almost want to get to know your high spots, prime around them, and keep on going.  If 40 grit won't reach down and wipe off roller stipple in a low spot, 80 grit is pointless...  80 grit only scratches .022.  120 scratches .012  220 scratches .002

So... If you have roller stipple deeper than .022 over a 5 inch circle, then you need to add 22 mils to the surface to get level to your nearest high spot surrounding that roller stipple.  That takes two coats of ultrabuild to get a few mils on top of the high spot and fill the low spot.  So... Stay coarse until you get an even scratch over the surface with a coarse grit in primer.  Once you've got one material, it is very easy to add even layers of material to evenly build up to go through the grits.  Going through the grits while you have roller stipple and orange peel still on the surface, won't take off material off fiberglass the same rate as it will primer so you get smoother but your high spots remain high while the lows turn into smooth dog dishes. 

Spot roll known low spots, put a wet mil gauge in them.  If it doesn't read 22, you don't get 10 when it dries after the roller stipple is off.  Those are the rules.  Sand everything smooth as you can, and any low spots... hand sand them for tooth and roll on another coat just in the lows first.  Then roll the whole surface.

I am a fan of Mirca Abranet HD, and Norton Blue Mag abrasives for gelcoat removal, just because it lasts.

 3M production green is OK, but buy a box.  Don't sand into the skin coat of veil mat, or you'll have a porosity nightmare.  The 4mm orbit will be fine for top coat, but a 5/16 orbit will make removal go faster.  Change your paper every 2 square feet if you are using aluminum oxide grit.  If you can see what you are doing and you are wearing a half mask and goggles, it's not going fast enough or your paper quit cutting.  A full face respirator and an 8 inch pad sander makes time of gelcoat removal with the occasional wipe of the face mask to see.  Take a t-shirt, put your face through the hole and tie the arms behind your head and it'll be a lot less nasty when you get through sanding at the end of the day.   

Only sand in vertical overlapping passes.  Your elbows don't work well to fill or feel low spots from horizontal standing, and it takes a foot long rubber squeedgee to pull a horizontal low on a wine glass hull.  Vertical is easy to feel and see and straight pulling putty vertically can let you define the flatter of the two shapes.    

3M gold is fine for anything once you get to primer.  Ultrabuild is rather hard if you want to sand it much past 80 grit, so treat it like an epoxy base coat as a fairing medium instead of as part of a priming system and it works well as a marker of a high not to violate.  

3M Vinylester putty is something to think about, while you still have a polyester boat.  Once you start fairing in epoxy your sanding cycle time becomes long and tedious.  If you've got a void in the gelcoat... use 3M and a dremel with a carbide burr to cove out a spot and fill it.  Over fill it, then burn it down with 40 grit.  All you want to do is spend an hour going around the hull in a circle and fixing things that shouldn't be there that you can see.  Shop vac with a brush, acetone in a squeeze bottle and a little plywood plate to mix on saves a lot of sanding cycles later on.  If you can see a hole, fix the hole before you prime it with epoxy.  

If you see a literal open black pin hole and you've primed once... Take a ball burr, dig out the hole and kiss the surrounding surface with a bit of 40 grit on a thumb and fill the hole with 3M vinylester.  If you have a lot of voids or porosity, I'd take a look at interlux 2000 as a base just because the application window is faster than ultrabuild.  Literally squeedgee it in, and roll it with a 1/4 inch fuzzy roller on a 4 inch frame.     

I'd suggest not working in sections, for priming unless you work in half of hulls.  Square paint lines are not fun and feathering out to bare glass from primer is difficult until you get enough mils thickness on to work with.  It does not take very long to prime a whole hull, and the mixing and cleanup time is the same whether or you prime the whole thing or a 10 foot side.  I'd save doing 10 foot sides for catching up areas that you aren't happy with.   

If I'm doing a fairing job that requires bare glass to primer, like repairing damage on one hull side at the peak of the tumble home...  I like to use Awlfair and Sprayable fairing compound.  The sprayable fairing compound can be spot rolled.  Which means on stuff smaller than 90 feet, you can roll the hull.  Then board it down until everything that isn't supposed to stay, is gone.  Sprayable is brown, ultrabuild is white.  That makes a terrain map that says if you hit a hard white spot and haven't fully sanded the brown around it you need more material because you haven't rebuilt the thickess of the gel at it's thickest point around... say a high bulkhead.  

125mm is a shade smaller than 5 inches.  You'd be well off to think about an 8 inch pad sander with 80 grit on it before you prime just to smooth out any spots where the gel coat was shot double, and the 5 inch sander fit down into the run.  Normally one side of the bow and transom ends up heavy handed if the guy spraying gel coat had lead feet and didn't move his feet every time he shot a shot.  So the rebuilding of the surface takes a bit of filler, a 5 inch sander will tell you damn lies about where a stem line ought to go as you can take a flat surface and round it into a soccer ball.  An 1/8th inch low for a foot on one side of the stem is visible as the whole rest of your primer job you'll have a radius that gets cut square at the face, and to round it out you'd have to grind glass to get the two to match.  Don't.  Aluminum yard sticks can be handy to hold and look at and see which side is the double shot side.     

A pad sander with an 8 inch pad will show you where your 40 grit fit into low spots from double passes of gel.  Idea is to 545 with a 4-5 inch weenie roller and get it into the texture with a brush, and damn near squeedgee into pin holes... Then come back with a candy stripe or thin fuzz roller and put enough ultra build on that you can see where you are lacking material because of where the roller isn't kissing the surface.  Visualize a 7 inch West systems resin roller rolling along, and missing 5 inch circles that are low, because the gel coat was shot double.  When you roll with a foam roller, you can roll the low spots and the high spots just the same, and the same 5 inch sander can sand the low spots and the high spots.

A wider roller than what you used to sand, with a thicker nap than your lowest low spot, can add a bit more material to your lows.  The goal is to put on more material than what you took off, without doing a lot of sanding in between. 

I would think about, 6 kits of ultrabuild if you don't want to pull much putty.  That sounds like a lot of material, but in mils 4 gallons per side isn't much.  With a 60's boat, the amount of gel you've got to deal with is expensive to add back a similar amount of material.  The path of least sanding, is to add back enough mils to fill your low spots, bury your high spots, and then sand just til the color changes on the high spots.

  Once you have the material on, you can basically sand by brail if you are sticking with the 5 inch sander.  Wipe away the roller stipple with 40 grit.  Roll on two more coats... Wipe away the roller stipple with 40 grit scratches with 80 grit still going in vertical overlapping passes...  Hit it with a water hose and while it is wet look at your reflections.       

3M dry guide coat is your friend.  I like a 3M short board with 60 grit on it at that stage... as once you are flat, the low spots are filled in and you no longer have any signs of hard fiberglass high spots you can prime your way home with 545.  A 3M short board is 16 inches long and takes auto body inline paper.  Basically just replace the random orbital sander marks in the guide coat with criss crossing X's of 60 grit scratches and anywhere that still has random orbital marks is a low spot.  At that point you can determine a tack of either spot priming (Pencil marks only) using a quart more ultrabuild, or spot puttying with a dab of awlfair.   

If you haven't done some fairing work before, grabbing a line plan for the hull that shows buttock and futtock lines can help you pull a string or straight edge going into the stem and transom counter following the line the designer drew and the guys building the plug pulled a batten around.  Sometimes you can use a 12 inch tape knife held dead level and add a slick going into them, and sometimes you need to work it on a diagonal, diagonally up  the hull to get one to fit as holding dead level will put a putty ramp on.  The cheap way, is to add mils with awlfair.  It just takes a lot of sanding to get a holiday free, pink surface that is ready for primer with no high spots.  After stripping the gel, you shouldn't have any real live high spots... in that the whole surface is low to where it was.  Adding back an 1/8th inch of pinky putty with a 6 inch yellow hard squeedgee, and only making kiss contact with the sander, seeing a ridge line and adding a little more thinking it is low around it... leaves a spot in the side of a hull that Stevie Wonder could point out.

The path of least sanding is following the chemical bond window of ultrabuild, and rocking a wet mil gauge while you use it.  The amount of material you have to put on to make the minimum wet mil thickness is stupid.   

If you haven't done any fairing work before, try to avoid pulling putty you can't see through with knife wider than your sander.  Most folks have a hard time sanding off all the putty that they put on, just because it takes time delicately working things back flat, and at 80% sanded you still have a high spot that'll take 8 layers of 545 to fill around until you might not hit it by 320 grit.  

DA sanders are mean to waterlines, and areas up near cove stripes, 3 inches back from stems and transom corners.  You can't sand what you can see, and you can't see what you have a sander on top of... so you have to move the sander back to see.  There should be no pressure on the sander with the pad just in contact with the hull when you do this.  Or you'll end up with a 10-20 mil low spot like a picture frame the whole way around the boat.  It's worth a day to go around and hand sand/block or vibrating 1/4 sheet pad the waterline and up to the cove stripe to remove the gel down there, and even then it is worth doing a double pass with your ultrabuild on your edges on the first rolling. 

You can spot prime 545 over high spots that are almost close enough to make it through.  Take some painters tape, tape out a square around it 5-6 inches past where you hit... roll on three or four coats.  Come back feather edge the tape line, lightly hand sand the high spot and put on some top coat. 

Other slick things that work for new guys...  Cheap and easy ways to spot pint holes:  Get a quart of gray 545.  Thin it down.  Put it on the boat.  Sand it off.  Pin holes are gray if they are shiny.  If they are sanded smooth, then they just were pin holes and now they aren't.  Spotted.  Dykem works well for that too.  Even cheaper is denatured alcohol with a few drops of green or red food coloring, wet a rag down wipe it on and it tints a white boat pink or green. Sand it off.  Pretty hard to miss where you have sanded, if it is white again... you sanded.  If it is still pink, you haven't.  Pink or green dots will be pin holes at a later date. 

If you have a lot of dots that are not real live holes, take maroon 3M scotchbrite and rough it up enough to take the color off the dots.  Then use a squeedgee and apply some ultrabuild or awlquick... or awlfair let it tack up then roll a coat over the top.   

Once you get into finish primer 545 and awlquick type... Evercoat ultrasmooth applied with a box cutter blade works for thin depressions and slight texture from grinder smiles.  My awlgrip rep told me about it.  I drilled a board full of 1/8th inch holes and bought $150 of polyester putties, and it's the only one that does it all without shrinking.  Gist is that if you've got a tiny depression and you need another coat of primer for other reasons, you can fill the tiny depression (3m Dry guide coat leaves a line of texture...) if it is smaller than a box cutter blade and in the realm of roller stipple.  I don't play with that stuff until 280 or 320 grit, just because by the time you are happy enough with the surface to be tack ragging and wiping down to look at it closely you are into the territory where an extra two days of priming over what will be orange peel is pedantic. 

By some strange luck, what you can reach easiest is what you can't see issues with when it's in the water.  Don't drive your self nuts over getting the bottom third of the hull perfect beyond the waterline its self if you've got a boot top line.  The water reflection hides a multitude of sins.  The middle third and up to the cove stripe, stem, counter, and shadow lines are what you can see when it's in the water.  Getting the clam view perfect and not having a walk board high enough to get up high enough to spend the time on what's overhead at the cove stripe is important to avoid.  If your walk board is too low, you'll end up with a 2x3 inch putty flag somewhere just below the cove stripe somewhere you lightly sanded and primed over.  Having a walkboard belly button high at the sheerline, and sitting height for the middle is preferable. 

When it comes to the actual priming, the site location matters as the sun changes the surface temperature and you can get solvent popping on sun lines and other issues.  So doing a half a hull can come into play if the bow sticks out of a barn or something...  just try to avoid doing small areas unless you've got a long board in one hand.  The issue is that batches harden at different rates, and the rockwell hardness of the primer changes over time.  The goal is to have everything the same consist for sanding rate so that doing the same thing all places makes things sand the same.  Otherwise a soft spot, literally sanding from where she gets sun to where she's in the shade can give you a low spot if you linger.

Don't sand shadows lines!

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Fair disclosure:  40 grit turns to 60 or 80 grit on boats newer than the 60's.  Just that 60's gelcoat it is possible to generate an 1/8th inch low spot after sanding.  Newer stuff, that is harder to do...  Grin.  Using 80 grit to clean up an 1/8th inch of gel coat takes a lifetime... 

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To bad he asked about deck and cabin sides, not topsides. Dope. And Festool products. To OP: hire a professional. 

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13 hours ago, LionessRacing said:

looks like Saphir is the starting point 

I've had very good luck with Granat in terms of longevity, but it only goes to 40 grit. If you need the 36 then saphir.

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4 hours ago, Al Paca said:

To bad he asked about deck and cabin sides, not topsides. Dope. And Festool products. To OP: hire a professional. 

Dang...  Must of finally attained resin head reading ability, was waiting for the dew to break.  I thought I was taking a statesmen approach to describe some methods one might use, not to strip gelcoat with a random orbital sander.  

In that case, grab a makita 8 inch disc sander and some 36 grit 3M zirconium discs and do the grunt work with that.  I call mine master blaster, as it fits where a sander/polisher or 7 inch grinder won't. 

Once you've beaten it down... Lay two layers of veil mat in polyester with a 6 inch wide air roller to fill the texture and average out the surface.  Knock the nibs back, with the disk sander anywhere it'll fit.  Use red catalyst, as most 60's boats are green resin.  Red shows what is new today, green is old.  Sand most of the red off till smooth.  Throw some gel coat down and sand it with 40 grit on your random orbital til smoothish. 

The removal for the whole deck other than the cockpit should take an 8 hour day, and a whole box of disks.  Makita 9227c sander/polisher works better for the nonskid surfaces that it'll fit.   Cockpits take another day by themselves.  Inside corners...  Die grinder with a 3M flap wheel works pretty well.  Drill extensions with hex set screws.  Wooden block about beer can size that has a hole through it to make a guide bearing to hold also work, even though a corded drill will sound like it has a rod knock in the bearings by the time you get done from the side load, almost like mixing bottom paint...  

All the rest of the fairing nonsense still lays true except its easier to fuck up a deck than the topsides, though there is less of it so it's also easier to put it back straight, because there is less of it. Slow speeds and a variable speed trigger with a hard backer disk make it easier to wipe out gelcoat out of the fillets.  Otherwise you'll ruin a stack of velco pads on the random orbital by the time things are done.  Easiest way to put the fillets back is to make them a hair bigger and pull them in awlfair or 407 in west systems. 

Take a straight edge and walk around the cabin top sides before you get started, as some boats have some round in them to cheat your eye between the portlights.  Don't try to make flat what wasn't.  I like to walk around and line down the original surface with a sharpie marker and take some pictures.  Print out what you had, lay them on the dashboard of the truck and don't try to add a 1/4 inch of putty to something you took an 1/8th inch off of.

2 kits of ultrabuild.  Up to you on the amount of fairing to do in the nonskid.  Easiest way to get the cabin sides straight is a hutchins random orbital long board.  Easiest way to get the nonskid and general deck straight is a sander polisher with an 8 inch hard vinyl disk and 40 grit. 

5 inch sanders make 5 inch holes...  Use the tools the guys used to build the plug for the mold, and they fit.  There was not a 5 inch random orbital sander in existence when the bermuda 40 plug was pulled...  Pad sanders, 1/4 sheet, 1/2 sheet sanders fit the surfaces.  Newer hulls you need 3 inch random orbital pads to go places. 

Pro tip is to build a stool 5 or 6 inches tall so you can sit on your ass with your legs crossed and work just below you or work between your feet, by reaching under your knees.  Just shorter than a 1 gallon paint bucket, but not kneeling.  You can last a lot longer and get into tighter places that would otherwise put you over-reaching off a staging board.  You've got wide side decks on a bermuda 40 that are helpful but a few spots that will be challenging due to physical dimensions of anyone not 17 anymore. 

 

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Appreciate the inputs, the 125 mm sanders are what we old guys use as the 150mm and bigger take too much out of the hands and arm joints after 60 yrs old.

The linear and detail sanders will get into the narrow bits, and the B40 deck & cabin are pretty wide open. the 'Rotex" is a combination RO and rotary, in rotary mode it's scary fast at removal. 

(Already did the topsides back in the 2005-06 time frame, with the same tools,  then tip & roll outside next to a gravel road... and "paid the Pro" to peel below the water line with a planer back in 2000)

 

Quote

Pro tip is to build a stool 5 or 6 inches tall so you can sit on your ass with your legs crossed and work just below you or work between your feet, by reaching under your knees.  Just shorter than a 1 gallon paint bucket, but not kneeling.  You can last a lot longer and get into tighter places that would otherwise put you over-reaching off a staging board.  You've got wide side decks on a bermuda 40 that are helpful but a few spots that will be challenging due to physical dimensions of anyone not 17 anymore. 

I don't fold so well at this point in life, and boat yoga is becoming a more strenuous sport, hence the incremental approach. Planned to work sitting on deck, and kneeling next to cabin. Not trying to get it all done in a short time, will be doing it in the slip at the YC, so minimizing the dust is a big deal, hence the Festool rig with dust extraction, relatively low profile. If it's too obnoxious, will have to borrow back my generator and go anchor out for the afternoons. 

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See if you can get hold of Mirka Abranet pads. They go as low as 40, dust is even less of a problem and they last longer than traditional abrasive paper.

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On 5/29/2019 at 6:19 AM, GeorgB said:

See if you can get hold of Mirka Abranet pads. They go as low as 40, dust is even less of a problem and they last longer than traditional abrasive paper.

+100 on mirka abrasives, it's what i use on my metabo 150  ...       check with auto paint supply stores...   there's an  Abranet HD  with lower grits , but not sure why'd you want to use that rough if you're only cleaning up scratches and crazing..     plus I would not take off all the old gel coat..

 

https://www.mirka.com/en-US/us/abrasives/abrasives/

 

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Don't necessarily need to strip gelcoat, but the old awlgrip (ca 1990?) has reticulated over the gelcoat crazing. Need to sand/grind down below the crack/crazing. 

 

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UPDATE: 

Found Abranet at the Sherwin Williams Product Finishes store in San Leandro  in 80 & 120 Grits. 

80 grit on the Festool RO was "clean" but way too slow to take off the Old Awlgrip and remove the Gelcoat to the crazing depth. 

Did a test section and used AwlFair LW as an experiment to see how it fills cracks vs grinding below them.  

Mail ordered some Saphir 50 grit and will try to find the Rotex which wasn't in it's box for the weekend. 

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https://mirka-online.com/hd-611-ap-mirka-abranet-heavy-duty-6-in-15-hole-grip-disc-asst-grits-qty-30.html?gclid=EAIaIQobChMI0au79MHr4gIVB1SGCh0rewFzEAQYBCABEgKTWPD_BwE

6 inch, but the mesh cuts fairly easily if you have a pair of shears you don't care about... 

Have a picture of the crazing/experiment area?

Cheers,


Zach

 

 

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Didn’t think to shoot one, will do tomorrow. 

SAPHIR 50 grit was delivered on time to use today,  36 grit was supposed to be here today, will compare, the 50 works at a practical speed using the ROTEX in either mode, and about 2x2’ per disk. 

Got the first section of cabin top sanded, and first coat of 545 on, will try high build 3002 as alternate to fairing compound over crack divots. 

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Abranet on a Festool sander will eventually melt the Festool velcro... their plastic hook is longer then the Mirka hook, so it is pokes thru the Abranet and melts, eventually ruining the Festool pad...  use an interface pad to avoid this problem. 

 

I've gone away from Abranet, I prefer Granat almost 100% of the time.  I find the Abranet has become more fragile in the last couple years and tears alot more easily then it used to.

 

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On 6/14/2019 at 10:45 AM, LionessRacing said:

UPDATE: 

Found Abranet at the Sherwin Williams Product Finishes store in San Leandro  in 80 & 120 Grits. 

80 grit on the Festool RO was "clean" but way too slow to take off the Old Awlgrip and remove the Gelcoat to the crazing depth. 

Did a test section and used AwlFair LW as an experiment to see how it fills cracks vs grinding below them.  

Mail ordered some Saphir 50 grit and will try to find the Rotex which wasn't in it's box for the weekend. 

if you want coarser grits in mirka products, you need to go to automotive paint supply

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1 hour ago, Grande Mastere Dreade said:

if you want coarser grits in mirka products, you need to go to automotive paint supply

This was the recommendation of the MIRKA regional Sales guy... have not worried too much as I have the 36 grit Saphir to try next then it's a question of that vs 40 grit Abranet. 

 

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On 6/17/2019 at 11:58 AM, LionessRacing said:

This was the recommendation of the MIRKA regional Sales guy... have not worried too much as I have the 36 grit Saphir to try next then it's a question of that vs 40 grit Abranet. 

 

don't press hard, let the sander float and let the paper do the work..  press too hard,  too much heat, you melt the little hooks on the pad.. like said above, get an interface pad..

 

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I took a RO90 with 80 grit Granat to the bilge paint, trying to get down to the glass.  I'm 68 and I ended up reaching for a grinder.  Not sure if that helps address your gelcoat situation but it might address the over 60 situation.

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3 hours ago, Jules said:

I took a RO90 with 80 grit Granat to the bilge paint, trying to get down to the glass.  I'm 68 and I ended up reaching for a grinder.  Not sure if that helps address your gelcoat situation but it might address the over 60 situation.

The 50 grit on  125 mm Rotex did ok, I’ve got the 36 in reserve to go faster. 

Just invested in a half sheet RS2 to do the decks. 

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16 hours ago, LionessRacing said:

The 50 grit on  125 mm Rotex did ok, I’ve got the 36 in reserve to go faster. 

Just invested in a half sheet RS2 to do the decks. 

just remember, every gouge you make you have to deal with filler..   go slow

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3 hours ago, Grande Mastere Dreade said:

just remember, every gouge you make you have to deal with filler..   go slow

Yup, that's why the experimentation stage. 

 

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