Deck repairs: waterproofing stachion mounting holes

[Paysay]

My question regards waterproofing through-deck bolt holes that penetrate a balsa core. I've read and followed instructions found at numerous sources including old postings here in Sailnet that explain how to waterproof a balsa deck core around the bolt holes by reeming out the core around the bolt hole then filling the hole with thickened epoxy and reboring the hole through the cured epoxy. My question is "Why thicken the epoxy"? The deck at these locations is under compression load and I doubt that coloidal silica (sp?) helps improve the compression strength of epoxy. What am I missing? In fact, I did use unthickened epoxy on a couple of bolt holes on my own deck this past fall with good results (so long as I adaquately sealed the bottom of the hole). I did have to top off the epoxy as it soaked into the core, but that seems like a good thing.

I have a good number of holes that have not yet been waterproofed. how should I proceed next fall?

[sailingdog]

Actually, the thickening agents in epoxy, whether it is colloidial silica or some other high-density filler, serve two purposes when doing this type of repair. First, they thicken the epoxy to help it stay where you put it, instead of dribbling out—now this isn't so important when the hole is on a deck, but if the hole were on the side of the boat, it would make a big difference. Second, they do add quite a lot of compressive strength to the epoxy resin.

For instance... imagine a bowl of jello. That's epoxy.. push your palm down into it... not too hard to do is it. Now imagine the same bowl filled with jello that is filled with peanuts. Now try and push your hand through the jello... Now, do you think it is easier or harder to do than when it was just plain Jello???

You really should be using thickened epoxy for potting the holes. Almost all of the books and most of the people who write about it, including the people here on Sailnet, say use thickened epoxy for a reason.

[Freesail99]

To re set the deck fittings themselves I would use sikaflex 291 which flexs much more then 4200 with the same holding power.

[shantijwk]

How does Sikaflex 291 compare with boat life caulk as a hardware bedding material?
I agree with the additive to thicken the epoxy. In a bind I have used the contents of my beltsander dust bag.

[sailingdog]

Sikaflex 291 and 3M 4200 are both polyureathane-based sealants. BoatLife LifeCalk is a polysulfide based sealant. Polysulfides tend to be a bit more reactive and while good for bedding hardware, will tend to attack plastics, like ABS, Lexan and Acrylic/Plexiglass.

I would say that BoatLife LifeCalk is slightly better for bedding deck hardware, than either 3M 4200 or SikaFlex 291, especially if they're bonding to teak, as the polysulfide tends to grip oily woods much better.

[shantijwk]

Thanks Sailingdog

[sailingdog]

De nada Shantijwk. What kind of boat do you have?

[sailingfool]

The straight epoxy is more subject to chipping or cracking when you drill it with a large bit, the paste drills cleanly and wont chip.

[sailingdog]

Originally Posted by sailingfool

The straight epoxy is more subject to chipping or cracking when you drill it with a large bit, the paste drills cleanly and wont chip.

That's true... thickened epoxy does drill more cleanly... Hmm.. forgot about that.

[geedunk]

I am replacing the "wench pads" on my '80 Hunter 30' -naturally the 1" teak does not conform to the fiberglass hull where the bimini and wenches mount-question: do i need 2 use a special sealant or will silicone augmented latex sealant suffice for this application? Also, the wench bolts r waay too long and interfere with headroom in the qt. berth--is there a reason they r so long--as i plan to cut them to fit the nylok nuts closer? Thanx.