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Thickening Gel-Coat--Advice Please #253574
10/16/12 10:03 PM
10/16/12 10:03 PM
Joined: Apr 2007
Posts: 291
J
JACKFLASH Offline OP
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JACKFLASH  Offline OP
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I am finishing up a few minor repairs to my daggers and rudders, you know the little nicks we get here and there. There are a couple of shallow (1/16 inch) or so nicks only effecting one side of the foil. Instead of filling with epoxy and finishing with gelcoat I was thinking of thickening the gelcoat for the these small nonstructural repairs. The gelcoat is white. What would you thicken it with?


Collin Casey
Infusion Platform + C2 rig and rags = one fast cookie
-- Have You Seen This? --
Re: Thickening Gel-Coat--Advice Please [Re: JACKFLASH] #253579
10/17/12 05:57 AM
10/17/12 05:57 AM
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South Carolina
Jake Offline
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Originally Posted by JACKFLASH
I am finishing up a few minor repairs to my daggers and rudders, you know the little nicks we get here and there. There are a couple of shallow (1/16 inch) or so nicks only effecting one side of the foil. Instead of filling with epoxy and finishing with gelcoat I was thinking of thickening the gelcoat for the these small nonstructural repairs. The gelcoat is white. What would you thicken it with?


Probably white glass micro-balloons (not the phenolic type - which are redish). They sand pretty easily. You won't be able to get it to shine with the micro-balloons in it but it should make for a decent repair.


Jake Kohl
Re: Thickening Gel-Coat--Advice Please [Re: Jake] #253585
10/17/12 06:50 AM
10/17/12 06:50 AM
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Orlando, FL
tback Offline
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what is the "preferred" method for doing this type of repair to foils?


USA 777
Re: Thickening Gel-Coat--Advice Please [Re: tback] #253586
10/17/12 06:57 AM
10/17/12 06:57 AM
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Detroit, MI
mbounds Offline
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Originally Posted by tback
what is the "preferred" method for doing this type of repair to foils?
Thicken gel with colloidial (fumed) silica - Cab-o-sil or WEST 407.

It will make the repair a bit harder than the surrounding gel, so you need to be careful when finishing it off (don't get "dishes" in the surface).

Try to remove as much extra material as you can while the repair is uncured.

Re: Thickening Gel-Coat--Advice Please [Re: JACKFLASH] #253588
10/17/12 07:42 AM
10/17/12 07:42 AM
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Hillsborough, NC USA
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Isotope235 Offline
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When added to gel-coat,
  • Micro-balloons will make the cured resin lighter (less dense).
  • Milled glass will make the cured resin stronger.
  • Fumed silica will make the uncured resin thicker so it can be spread on.
  • Styrene will make the uncured resin thinner and easier to spray.
  • Talc will make the cured resin easier to sand, but makes it softer too, so it's often painted over.

I hope that helps,
Eric

Re: Thickening Gel-Coat--Advice Please [Re: JACKFLASH] #253597
10/17/12 09:57 AM
10/17/12 09:57 AM
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Solomon's Island, MD
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samc99us Offline
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I have at least 1 foil, and probably 2 more, that are in need of similar TLC. I made the mistake of applying gelcoat by hand to one of my Nacra Gen-3 rudder blades a few years back. It looks like sh$t, no more shininess etc. All in an attempt to make the foil better (dumb, this was a hand tuned blade by Phil's Foils, aka C-Class foil builder extraordinaire) .

My current plan is to at least sand down all the crappy gelcoat. From there I am looking for tips. One area of concern that is difficult to clean up is the tip of the blade, which is showing the fiberclass. Should I try and spray new gelcoat in this area? Any tips for blending it back into the original paint? Is gelcoat the actual material used here, or is it a 2 part polyurethane (Interlux Perfection). How about fairing the nicks in the TE back into the original board?

I have more experience with composites and paints this time around but still would like hot tips from the experts. I also have access to proper painting gear and expertise from my shop team that shoots 2-part epoxy based paints on a regular basis, but normally on freshly prepared metals. Should I sand all the way back to the base primer/glass and shoot fresh coats of paint?

Thanks for the help,
Sam


Scorpion F18
Re: Thickening Gel-Coat--Advice Please [Re: samc99us] #253604
10/17/12 01:34 PM
10/17/12 01:34 PM
Joined: Apr 2007
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JACKFLASH Offline OP
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I'm not an expert by any stretch of the imagination but I am dealing with three typs of repairs. The first type are nicks in the trailing edge. Both rudders have this issue when the tiller crossbar flipped backwars during a wipe out and landed on the back of the rudders. The indentions into the trailing edge were less than a quarter of an inch deep. To repair I used a dremel with a carbid tip and removed the loose or chipping off material. I then light worked the perimeter to create a slope from the damage portion to the undamaged portion. I removed very little material during this stage. Given the small amount to be rebuilt, and the fact that these areas are not stressed, I fill the craters with epoxy resin thickened with cobosil and high density filler. I will describe the gelcoat portion in a moment as it applies to all the repair types I am addressing. I also had one of these types of repairs to make to the daggerboards trailing edge which I was nervous about because it is clear carbon fiber on the trailing edge with that pretty patern, and it is black. For this I used the same method except I was more stringent on how much material I removed in the prep, and I added graphite powder to the mix to make the final product black. There will be no gelcoat at this repair but the finish techniques are the same, this repair looks awesome and you can hardly tell it has been done unless you are inches from the board.

The second type of repair is a nick, typically very shallow and only affecting one side of the board. For these I want to simply fill the "divot" with gelcoat and move one.

The third repair type I am fortunate not to have on this go around but I did on my old Hobie 18 where the trailing edge was quite eroded away, 1/4 to 1/2 inch I would say. In this type of repair I would clean the loose stuff away as before. Than using the dremel and fiber board I would cut a slit in the center of the trailing edge where the damage is located. I would than take a cured peice of fiberglass mat and epoxy it into the slit. This than become the backer for filling as described earlier.

As for the finishing of gelcoat I personally like to spray my applications. Sand the repair and immediate area with 180-220 grit, clean well and spray the gelcoat. For small repair like this the cheap prevail sprayers available at the box store for 5 bucks are great. I thin my gelcoat with duragloss made by duratec. Once cured fair in the repair with the surrounding area using the 220, than drysand with 300, 400, and 500. Then wetsand with 600, 800, 1000, 1500, 2000, and finally buff with ultra fine rubing compound such as 3M Perfection. Each sanding step is very breif, used only to remove the scratches made by the previous paper. Assuming your gelcoat is the correct tint (there are many many shades of white), your repair should be pretty unnoticeable.


Collin Casey
Infusion Platform + C2 rig and rags = one fast cookie
Re: Thickening Gel-Coat--Advice Please [Re: samc99us] #253607
10/17/12 02:11 PM
10/17/12 02:11 PM
Joined: Jun 2001
Posts: 12,310
South Carolina
Jake Offline
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Jake  Offline
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South Carolina
Originally Posted by samc99us
I have at least 1 foil, and probably 2 more, that are in need of similar TLC. I made the mistake of applying gelcoat by hand to one of my Nacra Gen-3 rudder blades a few years back. It looks like sh$t, no more shininess etc. All in an attempt to make the foil better (dumb, this was a hand tuned blade by Phil's Foils, aka C-Class foil builder extraordinaire) .

My current plan is to at least sand down all the crappy gelcoat. From there I am looking for tips. One area of concern that is difficult to clean up is the tip of the blade, which is showing the fiberclass. Should I try and spray new gelcoat in this area? Any tips for blending it back into the original paint? Is gelcoat the actual material used here, or is it a 2 part polyurethane (Interlux Perfection). How about fairing the nicks in the TE back into the original board?

I have more experience with composites and paints this time around but still would like hot tips from the experts. I also have access to proper painting gear and expertise from my shop team that shoots 2-part epoxy based paints on a regular basis, but normally on freshly prepared metals. Should I sand all the way back to the base primer/glass and shoot fresh coats of paint?

Thanks for the help,
Sam


I recently refinished my infusion boards and one of the tips was completely broken (4" up from the tip) and had a nasty repair on it. I sprayed all of the under-water surface of the board with a sandable rattle-can automotive primer. I then sanded the foil with a palm sander working carefully back and forth to remove material evenly while also working to remove the small negative hollow (that's always there) behind the main camber in the foil. I sanded until any primer left in the negative and any scratches was practically gone. I then filled pin-holes and chips/dings and did some minor reshaping of the tip with epoxy thickened with milled glass fibers. I used bondo to fill any other minor imperfections and then gel-coated the lower 2/3rds of the boards.

[Linked Image]
[Linked Image]


Jake Kohl
Re: Thickening Gel-Coat--Advice Please [Re: Jake] #253608
10/17/12 02:17 PM
10/17/12 02:17 PM
Joined: Aug 2005
Posts: 2,921
Michigan
PTP Offline
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Originally Posted by Jake
I used bondo to fill any other minor imperfections


I have heard people state not to use bondo because it can absorb water. I friggin love the stuff. You can do a lot of coats of bondo in one sitting since it cures so fast. Obviously the theory is water won't get to it if a proper overcoat is put on, but was wondering your thoughts. I did some relatively serious filling and repair to my F31 dagger and rudder using some thickened epoxy as well as some bondo. I covered it with Perfection after a couple layers of primer. All good until you get a nick you can't really see (taking the board out of the 31 isn't difficult, but it isn't easy either)

Last edited by PTP; 10/17/12 02:19 PM.
Re: Thickening Gel-Coat--Advice Please [Re: PTP] #253609
10/17/12 03:01 PM
10/17/12 03:01 PM
Joined: Sep 2002
Posts: 3,223
Roanoke Island ,N.C.
Team_Cat_Fever Offline
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Originally Posted by PTP
Originally Posted by Jake
I used bondo to fill any other minor imperfections


I have heard people state not to use bondo because it can absorb water. I friggin love the stuff. You can do a lot of coats of bondo in one sitting since it cures so fast. Obviously the theory is water won't get to it if a proper overcoat is put on, but was wondering your thoughts. I did some relatively serious filling and repair to my F31 dagger and rudder using some thickened epoxy as well as some bondo. I covered it with Perfection after a couple layers of primer. All good until you get a nick you can't really see (taking the board out of the 31 isn't difficult, but it isn't easy either)


I've said it a thousand times Evercoat glazing putty. All the attributes of bondo except it's for boats(which of course makes it more expensive).

Jake,
Palm Sander? Really? You're getting slack, but I understand.You're the only guy I know that has 28 hour days, and must not sleep.


"I said, now, I said ,pay attention boy!"

The cure for anything is salt water - sweat, tears, or the sea
Isak Dinesen
If a man is to be obsessed by something.... I suppose a boat is as good as anything... perhaps a bit better than most.
E. B. White
Re: Thickening Gel-Coat--Advice Please [Re: Team_Cat_Fever] #253610
10/17/12 03:11 PM
10/17/12 03:11 PM
Joined: Aug 2005
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Michigan
PTP Offline
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But the cheapness of bondo is awesome! you don't have to care how much is "too much" when you mix it. The evercoat is 4 times as expensive.
of course I spend a ton of money on stupid sh** but can't be bothered to spend 40 when I could spend 10!

Re: Thickening Gel-Coat--Advice Please [Re: JACKFLASH] #253612
10/17/12 03:37 PM
10/17/12 03:37 PM
Joined: May 2004
Posts: 1,403
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Ventucky Red Offline
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I have had good luck using the colloidial silica (West Systems #404) with the the 3M High Gloss Gelcoat. Make sure you have a mask on when working with the silica, as you don't want to breath that stuff in.

I have also used Dynatron - Dyna Glass from 3M... Great stuff, less hassle, but it is green in color..

Re: Thickening Gel-Coat--Advice Please [Re: JACKFLASH] #253626
10/18/12 07:28 AM
10/18/12 07:28 AM

M
MN3
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MN3
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why use bondo at all instead of thickened epoxy?

Re: Thickening Gel-Coat--Advice Please [Re: ] #253628
10/18/12 07:49 AM
10/18/12 07:49 AM
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waynemarlow Offline
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Originally Posted by MN3
why use bondo at all instead of thickened epoxy?

Because you don't have to wait hours for the epoxy to set.

Never really found a good thinner for Topcoat ( there is a difference to that of Gelcoat ) any body recommend anything ?

Re: Thickening Gel-Coat--Advice Please [Re: JACKFLASH] #253633
10/18/12 10:33 AM
10/18/12 10:33 AM
Joined: Jun 2002
Posts: 1,658
Florida Suncoast, Dunedin Caus...
catman Offline
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I think you'll find that for something like your talking about, (1/16" nicks, scratches) get a small artist brush and carefully touch up the spots with no filler. Gelcoat is fairly thick. Let it cure for a few days before sanding. The stuff shrinks alot. So if you sand right away you'll find yourself filling and sanding on and on.

Bondo and such has a more pourous surface and is normaly used to fill larger areas. Glazing putty has a finer filler and is used to go over "Bondo" before priming. Glazing putty is the right stuff for smaller scratches.


Have Fun
Re: Thickening Gel-Coat--Advice Please [Re: Team_Cat_Fever] #253635
10/18/12 12:44 PM
10/18/12 12:44 PM
Joined: Jun 2001
Posts: 12,310
South Carolina
Jake Offline
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Jake  Offline
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South Carolina
Originally Posted by Team_Cat_Fever
Originally Posted by PTP
Originally Posted by Jake
I used bondo to fill any other minor imperfections


I have heard people state not to use bondo because it can absorb water. I friggin love the stuff. You can do a lot of coats of bondo in one sitting since it cures so fast. Obviously the theory is water won't get to it if a proper overcoat is put on, but was wondering your thoughts. I did some relatively serious filling and repair to my F31 dagger and rudder using some thickened epoxy as well as some bondo. I covered it with Perfection after a couple layers of primer. All good until you get a nick you can't really see (taking the board out of the 31 isn't difficult, but it isn't easy either)


I've said it a thousand times Evercoat glazing putty. All the attributes of bondo except it's for boats(which of course makes it more expensive).

Jake,
Palm Sander? Really? You're getting slack, but I understand.You're the only guy I know that has 28 hour days, and must not sleep.


Random orbital palm sander...what else?


Jake Kohl
Re: Thickening Gel-Coat--Advice Please [Re: PTP] #253636
10/18/12 12:47 PM
10/18/12 12:47 PM
Joined: Jun 2001
Posts: 12,310
South Carolina
Jake Offline
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Jake  Offline
Carpal Tunnel

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Posts: 12,310
South Carolina
Originally Posted by PTP
Originally Posted by Jake
I used bondo to fill any other minor imperfections


I have heard people state not to use bondo because it can absorb water. I friggin love the stuff. You can do a lot of coats of bondo in one sitting since it cures so fast. Obviously the theory is water won't get to it if a proper overcoat is put on, but was wondering your thoughts. I did some relatively serious filling and repair to my F31 dagger and rudder using some thickened epoxy as well as some bondo. I covered it with Perfection after a couple layers of primer. All good until you get a nick you can't really see (taking the board out of the 31 isn't difficult, but it isn't easy either)


yeah, me too...I catch flack for it all the time...blah blah blah. If my boat sat in the water all of it's life, maybe it's not worthy...but every single boat I've owned has had some sort of repair done with bondo at some point in it's life. Some fairly significant. I use it to fair the bottoms of boats, I use it to fair boards. Never had a problem. I did, once, use it to fair some minor imperfections on the bottom of a hull and left it explosed. It did eventually disappear/wear away from the water...so I guess it is wise to always top-coat it (like normal).

It is notable, however, to use the "Premium" bondo. It doesn't develop that tacky top layer which saves a lot of time and sandpaper.


Jake Kohl

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