Thickened epoxy fill coats?

[Alan Gage]

I've been thinking of using epoxy thickened with cabosil for fill coats on my current build. The thinking was to possibly fill the weave with one coat and that the cabosil might give better abrasion resistance than just epoxy alone. But the closer I get to applying that thickened epoxy fill coat the more I'm having reservations; the biggest one being the stiffness the cabosil adds to the epoxy. The hull should be quite stiff but I'm worried in case of an impact it might be more flexible than the fill coat and that I could end up with spider cracking or, worse, chunks flaking off.

Any thoughts?

Alan

 

[Jim Dodd]

Maybe try a sample piece ?
​ Mix up 1 1/2 oz. You probably don't want to wait long enough for it cure, to give it a proper test. But that's my best advice.

I used to fill my weaves with graphite and mixed epoxy, below about the 3" waterline. Never had any spider cracking, don't think the cabosil would behave any different. But can't say I've done that.

​Jim

 

[BWCA66]

You're planning on painting the boat I believe. Cabosil tends to cause the resin to dry white rather than clear depending on how thick you mix it.

 

[Alan Gage]

Maybe try a sample piece ?
​ Mix up 1 1/2 oz. You probably don't want to wait long enough for it cure, to give it a proper test.

That is correct.

I used to fill my weaves with graphite and mixed epoxy, below about the 3" waterline. Never had any spider cracking, don't think the cabosil would behave any different. But can't say I've done that.

Were all your fill cots mixed with graphite or just the last one? How thick (consistency) was the epoxy? Did you roll/brush it on or was it too thick for that?

If I do it I'll me mixing the epoxy very thick (consistency) so that I have to spread it on with a squeegee. I always notice that the heavily thickened (consistency) epoxy left in the cup is considerably stiffer/more brittle than un-thickened. Unsure how much of that is to do with the filler and how much of it is because it's so much thicker (cross section). Since it doesn't all run to the bottom of the cup like unthickened epoxy it's obviously going to have a thicker cross section and be more stiff on the sides of the cup. But if one coat of thickened epoxy gives you the same cross section as 3 coats of unthickened how much stiffness difference will there be?

These are mostly rhetorical questions I've been asking myself but if someone had an answer, or more thoughts, I'd be glad to hear them.

You're planning on painting the boat I believe. Cabosil tends to cause the resin to dry white rather than clear depending on how thick you mix it.

That is correct. Thinking of adding some liquid pigment to the thickened epoxy as well. Both to get it closer to the final color and to possibly take advantage of any plasticizing affect the pigment has.

Alan

 

[southcove]

Sure is easier to get a really smooth surface for painting if you are using Cabosil or one of the other bulk fillers...lighter, cheaper all around, than just filling the weave w expoxy. I wonder if that Q. couldn't be asked directly to one of the vendors, like West (recognizing that you are looking for the practical field answer not the company answer).

 

[Guest]

Thinking of adding some liquid pigment to the thickened epoxy as well. Both to get it closer to the final color and to possibly take advantage of any plasticizing affect the pigment has.

I’m not sure I am following, but my experience has been that adding pigment does a wonderful job coloring the glass if used with the initial epoxy coat(s) to wet out the cloth, so the pigment is actually in the fabric, and does less or near nothing if used as a fill coat or top coat.

 

[latremorej]

I'm kinda with Mr mcrea, I don't think that the dye wI'll add anything to the mix other than color. I only have a limited experience but I dI'd make some kayak hatch covers, first with only glass and epoxy then again with the liquid pygment. I didn't notice any difference between the two in regards to stiffness or strength.

Jason

 

[Jim Dodd]

It's been awhile. But I know I rolled them on, and on at least one occasion, I applied two coats. No trouble with bonding the second coat. I remember being more concerned if the colors would match, from two different batches.
It was a pain to sand, to level waves, or runs.

I taped the hull. and there was a slight ridge, that could be scraped.

I remember recoating a stem, as it had worn down some.

​ I used a mix ratio of about 4 resin by volume - 1 graphite powder, again by volume.

Could it be done with one fill coat ? If you are going the peel ply route, I'd say definitely.

​ No peel ply, maybe.

Are you going with Dynel ?

I still have two canoes with it on. My original Pearl. and a 38 spl.

Jim

 

[Muskrat]

I tried a while back to harden epoxy. There's a thread about it somewhere. Honestly it didn't seem to work that well. The epoxy was not as abrasion resistant as the s glass/epoxy, I think because I couldn't get enough hardener in before it got way too thick to roll on. But, if you want to mess with it I've got a lb. each of white aluminum oxide and silicon carbide powder. Not much softer than diamond. I can send it your way if you like. I have some kevlar pulp filler that might work better, it would make your fill coats a fiber matrix like the rest of the laminate, add some flex and abrasion resistance, but it would have micro fuzzies when you sand it.

 

[Alan Gage]

Right or wrong I decided to give it a shot tonight (fiberglassed last night). Meh. Had to squeegee it on but it was a thinner coat than I expected. Certainly didn't fill the weave with one coat and not the time saver I was hoping for. After the resin started to gel just a little it seemed to work better (thicker coat). I'll see it through to completion but I doubt I'll be doing this again.

my experience has been that adding pigment does a wonderful job coloring the glass if used with the initial epoxy coat(s) to wet out the cloth, so the pigment is actually in the fabric, and does less or near nothing if used as a fill coat or top coat.

That was absolutely true. It went on thinner than I thought it would and the color is virtually non-existent.

I don't think that the dye wI'll add anything to the mix other than color.

I was thinking about my previous experience with pigmented resin on the original Bloodvein. The tinted resin was a little different to work with and after it had set up seemed to be a little more flexible. A few months ago I read a paper from West Systems and they said when they intentionally added too much liquid pigment to resin (20% instead of 10%) that it actually tested stronger. They assumed the reason was extra flexibility. Now whether or not it actually makes a real life difference or not I don't know.

I tried a while back to harden epoxy. Honestly it didn't seem to work that well. The epoxy was not as abrasion resistant as the s glass/epoxy,

Yeah, seems like a stretch for it to be as tough as the fiberglass. I was just hoping for something better than plain epoxy and hoped it would be faster/easier to apply too.

I'll post another updated tomorrow after the first coat has cured.

Alan

 

[Jim Dodd]

Any Peel Ply this time ?

Jim

 

[Glenn MacGrady]

I'm not understanding some of this, and perhaps it's too late, but there can't be anyone in the world who has built more skin coat boat with pigmented resin than John Kazimierczyk of Millbrook Boats, who has been making the best whitewater slalom open canoes in the world for 30 years. From his construction page:

"All boats are laminated from a combination of S type fiberglass, which is stronger than E type, and Kevlar fabrics, using a high quality Vinylester resin for superior strength and durability. I use a pigmented skin layer (first fiberglass layer) for color, rather than a gel coat, to keep weight down. Usually the pigment color bleeds through into the Kevlar layers which are vacuum bagged. When this happens I know that there is a good mechanical and chemical bond throughout the lay-up. If you don't like the look of this, you can paint the interior of your boat with an exterior latex paint. The color gray looks nice on the inside."

He does solid colors and all sorts of graphics, patterns and psychedelic swirls.

Kaz is very approachable. I'd just email or call him with any questions. Then you'll be getting the advantage of world class experience.

Video of fancy lava pattern Shacho : https://www.facebook.com/363016740342/videos/10155558393835343/

 

[Jim Dodd]

Great links Glenn !

Thanks !

 

[Canotrouge]

Kaz is the bomb, his boats are the best and the price, I don't know how he makes living, are great!! I would like to have an AC/DC, a Prowler, and maybe a Coho and... I sold my Shacho this summer to get a Prowler, but our dollar is so crapty that it will have to wait!

 

[Alan Gage]

I may have condemned the process too soon. Second coat tonight and it might have filled the weave. We'll see how it looks tomorrow. Squeegeeing it on takes longer than a roller but seems to be using less resin. About 10 ounces for the 2nd fill coat tonight. Will be interesting to see how it sands.

Any Peel Ply this time ?

Only over the dynel skid plates.

Alan said: "I was thinking about my previous experience with pigmented resin on the original Bloodvein. The tinted resin was a little different to work with and after it had set up seemed to be a little more flexible. A few months ago I read a paper from West Systems and they said when they intentionally added too much liquid pigment to resin (20% instead of 10%) that it actually tested stronger. They assumed the reason was extra flexibility. Now whether or not it actually makes a real life difference or not I don't know."

The stuff I put on last night, which I added liquid pigment to, is still quite pliable tonight. I pulled a glob out of the mixing cup and can bend it back and forth but it's not sticky at all like uncured epoxy. We'll see how it does over the next few days.

Alan

 

[Alan Gage]

I'm not understanding some of this, and perhaps it's too late, but there can't be anyone in the world who has built more skin coat boat with pigmented resin than John Kazimierczyk of Millbrook Boats, who has been making the best whitewater slalom open canoes in the world for 30 years. From his construction page:

"All boats are laminated from a combination of S type fiberglass, which is stronger than E type, and Kevlar fabrics, using a high quality Vinylester resin for superior strength and durability. I use a pigmented skin layer (first fiberglass layer) for color, rather than a gel coat, to keep weight down. Usually the pigment color bleeds through into the Kevlar layers which are vacuum bagged. When this happens I know that there is a good mechanical and chemical bond throughout the lay-up. If you don't like the look of this, you can paint the interior of your boat with an exterior latex paint. The color gray looks nice on the inside."

I'd guess the phrase "first fiberglass layer" is the key. I assume at least the outer layer of fiberglass is being saturated with color which makes for a much more opaque color than I'm getting with a squeegee. When I did my first Bloodvein I tinted the resin for the wetout coat. It was nearly opaque but it took half a dozen (or more) thin coats of tinted epoxy rolled on the top before I finally gave up and called it good. Those thin coats didn't do much at all.

Alan

 

[Guest]

I've been thinking of using epoxy thickened with cabosil for fill coats on my current build. The thinking was to possibly fill the weave with one coat and that the cabosil might give better abrasion resistance than just epoxy alone. But the closer I get to applying that thickened epoxy fill coat the more I'm having reservations; the biggest one being the stiffness the cabosil adds to the epoxy. The hull should be quite stiff but I'm worried in case of an impact it might be more flexible than the fill coat and that I could end up with spider cracking or, worse, chunks flaking off.

Any thoughts?

I have only used cabosil (or various of the West adhesive fillers. . . . .or, back in the day, fiberglass dust collected from the RO sander bag) when I need a serious thick paste of epoxy for something, usually for something hidden from view.

West has a handy chart comparing their various filler agents:

http://www.westsystem.com/ss/filler-selection-guide

Unless I am making a pasty fillet or gap filler I go pretty light with any additive, or at least lighter than the recommended max.

I use pigmented resin when I am trying for a (near*) color match on exterior patches or when tinting a Dynel skid plate to match (or black pigment with graphite powder if going with a black skid plate). I spray paint the same color over patches and kid plates for UV protection, and the underlying color match helps hide the inevitable paint scratches.

*This stuff:

http://www.explosivepowersports.com...-1oz-100508/?gclid=CMPuvr3TlNACFVEkgQodAZ0NpA

The little 1oz tubes have a long shelf life (it helps to knead the tubes a bit when they get older). It isn’t a full ROYGBIV of spectrum, but I can mix a dab and dab to get close to purple, teal or etc. Any marine supply store will carry those little tubes of color agent. I seem to use more black pigment (skid plates) than anything else, followed by red (lots of red boats).

I am amazed at how little pigment it takes to deeply color the cloth. A dab half the size of the eraser on a pencil will amply color the fabric when added to 2 or 3 ounces of epoxy. I use the little 1oz tubes of “Color agent for polyester and epoxy resins” which are 50% pigment and 50% plasticizer. In that little dab will do me I doubt that the amount of plasticizer provides much additional anything.

Somewhere (West System or Chesapeake Light Craft shop notes) I remember reading a max recommended pigment volume, and it wasn’t much. I really appreciate West’s abundance of on-line information and comparative charts. Likewise CLC’s archived-since-1995 Shop Notes; there is a wealth of epoxy, glass and fit-out information on the CLC site. The fit-out stuff, bungee knots and webbing tricks, is especially valuable. Worth bookmarking.

http://www.clcboats.com/shoptips/

Same limited quantities for adding graphite powder. West 423 graphite powder recommends “up to 10% by volume or one tablespoon per 5oz of epoxy” and I usually use half that. Graphite powder is so fly away weightless that it is easier to mix in smaller amounts.

 

[Alan Gage]

After squeegeeing on a few layers of this cabosil thickened epoxy I was ready to give up on it. It takes quite a while to apply and it's hard to get an even coat without some lines and ridges. I hoped that with such a thick resin I could get by with only one or two fill coats but that wasn't the case, each coat was actually very thin. I suppose I could have put it on thicker by not wiping it back off so hard but it would have been tough to keep an even thickness.

Fast forward to today I finally flipped the boat back upside down to go over it with the sander and smooth the surface. I could believe how hard it sanded. I usually do this step with 100 grit because I find 80 takes off material too fast and I cut into the glass. It didn't take long until I gave up on the 100 grit and then the 80 grit too. I ended up sanding the surface down with 60 grit and it still took way longer than it normally does with 100. I'd say that cabosil thickened epoxy was definitely harder than plain epoxy.

Whether this will actually make a difference in the real world or if it's enough benefit to go through this whole process again on the next canoe is yet to be seen.

Alan

 

[Jim Dodd]

Maybe the application tool was at fault ? Thinking a foam brush, or small foam roller, might have left a smoother, thicker coat???

Jim

 

[Alan Gage]

Maybe the application tool was at fault ? Thinking a foam brush, or small foam roller, might have left a smoother, thicker coat???

Jim

The way I mixed it was way too thick for a brush or roller. It was peanut butter consistency.

Alan