raised chainplate

[galleywench]

I'm casting chainplate risers (some call them islands) to keep the interface where the chainplate enters the deck out of any standing water that may be on the deck from rain or incoming seas, but I ran into a bit of a problem regarding epoxy brittleness. I cast them last night before bed and they seemed to have hardened up nicely overnight, but when I attempted to open up the mold one of the risers cracked.
I believe it's one of the following problems (but there may be more and it may be a combination of them).
1. I didn't let it set long enough, I've done this before (I get too anxious and want to see results). The epoxy seems to harden better when you let it fully cure over several days (not sure how of if this effects ultimate brittleness, but it seems to).
2. Heat issues, although it was 60 degrees in my basement shop and I only filled the casting with ~3/16" of epoxy. I haven't previously had heat issues with that little mass, but who knows.
3. Thickening agent. I used aerosill (fumed silica) to thicken up the raw epoxy but maybe I should have been using something more appropriate for structural mixes like milled fibers or something along those ideas.

Anyway, I'd appreciate any thoughts you all might have that might help make my second cast a bit more successful.

[Carl-A259]

My thought is the silica should have been fine, mill fiber might have been better. I think of Epoxy as glue, so I might have used a couple of layers light fabric to hold it all together, kind of like rebar in concrete. I've also seen where the chainplate is wrapped in wet out cloth left to setup then used in the mold. Couple of days cure would be better, I know on deck repairs the first 24 hrs, kind of springy, the next 24 rock solid. Curious to others point of view. Carl

[galleywench]

I know on deck repairs the first 24 hrs, kind of springy, the next 24 rock solid.

That's what I would tend to think as well, but I had this happen to me a few months back when I was trying to remove a chainplate from a newly cored deck the day after I glued it up and the epoxy surrounding the chainplate cracked like peanut brittle, and this section had 7 layers of biax glass surrounding the chainplate (although it didn't directly abut the chainplate). I held off pulling the rest of them for another day or so and had no problems.

Whatever the case, I am going to hold off pulling the rest of them out of the mold for another day. I will have to do this over anyway. The vast majority of time spent on this particular project was spent building the mold, doing another pour is inconsequential from a time perspective.

I'm mostly curious if there is some sort of phased cure where the epoxy will have some sort of 'brittle' phase before the molecular cross linking has completed.

[LazyGuy]

My guess would be that you may have added too much hardener. That will cause it to heat up and the head would result in the brittleness. That is just a guess. If the right amount of hardener was used, it may be that it was not fully cured. If you had some left over, take a look at it, see if it shows any sign of heating.

[Triton106]

You may have already thought of it but I will mentioned it just in case... Why don't you just cut G10 to size and bed it in epoxy instead? My friend Rob did exactly that and seems to be pretty happy with how they come out.

[Carl-A259]

kudos on the mold, I was admiring the work that went into that.!! Molecular properties of curing Epoxy??? I'll leave that to the scientist here!! I just mix, smear it on, sand it off and then hit it with a hammer, if it doesn't fall off, I'm good!!

[mitiempo]

I made my chainplate risers by epoxying 2 layers of fiberglass together and then shaping to size and cutting the slot. I never throw away any fiberglass cutouts when I install something - on my boat or anybody else's.

I remember a reference from the Gougeons about being better to use less hardener than normal for something or other but I can't remember what exactly. It is in either their Fiberglass manual or their Wooden boat manual.

[Rachel]

I remember a reference from the Gougeons about being better to use less hardener than normal for something or other but I can't remember what exactly. It is in either their Fiberglass manual or their Wooden boat manual.

Was that for water tanks? (Which they were sort of, as I remember it "We can't recommend this, but when you do it we suggest.....")

Okay, I looked, and they do recommend resin-rich, hardener-lean mixtures IF one decides to make a tank using epoxy.

http://www.westsystem.com/ss/wood-epoxy ... uidelines/

[mitiempo]

That could be it - but I do know it should never be hardener rich for any project.

[galleywench]

You may have already thought of it but I will mentioned it just in case... Why don't you just cut G10 to size and bed it in epoxy instead? My friend Rob did exactly that and seems to be pretty happy with how they come out.

In hindsight I think that would have been a good way to go, but I had plenty of raw epoxy on hand and I have been wanting to try my hand at casting.

kudos on the mold, I was admiring the work that went into that.!!

Thanks, I spent entirely too much time on the mold itself and I am too stubborn to accept failure now and go with another method. I also just picked up a new to me bandsaw on Craigslist and I was itching to try it out on something useful. Originally I was going to go with a modeling clay mold on the deck (Don Casey did an article in 3/09 for GoodOldBoat), but Magic is out of the water and not very level and I don't like monkeying around with the jackstands.

My guess would be that you may have added too much hardener. That will cause it to heat up and the head would result in the brittleness. That is just a guess. If the right amount of hardener was used, it may be that it was not fully cured. If you had some left over, take a look at it, see if it shows any sign of heating.

I hadn't thought of that and sure enough, I pulled the leftover pot out of the trash and it looked like it boiled. It melted through the plastic on the bottom. So I think I might have been a bit hardener rich. Normally I'm pretty careful about measuring, but I did this in my basement shop where I didn't have my normal measurement containers that are stored in the boatshed. I eyeballed the mix - DOH! I'm hoping that's the root cause.

So last night I cleaned off the mold and did a few things differently. First, I coated all the chainplates with wax because they didn't want to let go of the epoxy when I pulled them yesterday even though I had wrapped them in clear packing tape (I've had success with this before). The second thing I changed was to add some 'milled' glass fibers (I shredded up some 1708 into 1/8" pieces) to add some additional strength. Finally, I actually measured the epoxy ratios this time. Shame on me for eyeballing in the first place, I should know better, but I'm thankful that I didn't do this while doing my recore. Cleaning a bit of epoxy out of a mold is a far cry easier than grinding off part of my deck.

Everything seemed to set up nicely when I checked this morning; no overheating visible, and I am not going to touch the mold until tomorrow to make sure everything is cured. I hope I'll be able to report back with success, otherwise I'll be relegating the mold for kindling and going with some G10 or laminating up a flat sheet to cut up into smaller plates.

[Figment]

Yes, milled fibers or chopped strand would have worked.

[galleywench]

I'm happy to report that my second attempt was more successful. I'll chalk it up to a number of things that I changed:
1. Milled fibers
2. Waxing the mold and not relying on just packing tape
3. Waiting longer to pull from the mold
4. Here's the biggie: ALWAYS MEASURE YOUR EPOXY RATIOS. I've been really lucky up until now because I have not mixed a single bad batch over the course of my recore and I'll attribute it to being very careful, so it serves me right when I get arrogant and just eyeball the stuff. Lesson learned.

I'll wait till they fully cure over the next day or so and then sand the ragged edges off and make them all uniform, but I think they will work nicely once they're cleaned up.

http://1.bp.blogspot.com/-IvrCo9y5ntQ/T ... AG0716.jpg

[bigd14]

I noticed about halfway through my rebuild project that some of my thickened epoxy was very brittle. I got some ominous cracking noises on my foredeck as the thickened epoxy that I shoved under the edges of the recore splintered! Luckily it has subsided to only an occasional crackle with no noticeable change in deck stiffness or structure. I guess its "settling in". Anyway, when I realized that, i started adding a shot of milled glass fiber in all my subsequent thickened epoxy batches. On the next boat milled glass fiber in thickened epoxy will be SOP.

Galleywench, I like your raised CP block idea. The absence of such a system on my boat was a major cause of the moisture problems that necessitated my recore.