Epoxy and Hardware Bedding

[Stu Fyfe]

I know this has been covered in the past, but the search for this section is still down. I want to inject some unthickened epoxy into the drilled holes before I screw the cleats into the plywood. Should I coat the bronze fasteners in something to make them easier to remove when the time comes, or should I just screw them in without a coating? I was planning on bedding the cleat to the surface area with Dolphinite. Will Dolphinite and epoxy cure properly next to each other?

[ 05-29-2005, 11:40 PM: Message edited by: Stu Fyfe ]

[Ray Frechette Jr]

Well if you don't add anything to make it easay to remove in the future,,, and it gives you a hard time to remove in the future,,,,

YTou could just build a new Boat!

Or you could use a soldering iron on the stubborn screw to heat up and loosen the epoxy's grip on it rather quick.

[RodB]

Read the Gougeon Book for lots of info on this... You can hardly go wrong sealing up any and all wood with epoxy, then use bedding compound like 4200 or 5200 (both which are hard to remove later on) or compounds that are not so permanent.

RB

[Ian McColgin]

Dolphonite is one of the smears I've happily used for bedding. As you know but some forget, a good bedding compound is quite different from a bonding glue. The obvious difference is that it allows removal. Less obviously, bolted or screwed fastenings should be bolted or screwed, not also glued. If you use a hard glue like epoxy, any movement will cause cracks allowing water and may preceed surprising catastrophic failure if the fastenings or wood deteriorate over some years. If you use a soft glue like 5200 and the fastenings are not really doing their job, the wiggle damages the wood and again, in the extreem, can lead to catastrophic failure.

In case one thinks these thoughts the product of an over-fervid imagination (and it is true my mind runs to things that break just now) - All the tracks on Goblin's booms and masts were, unknown to me, epoxied and screwed. Over the years the epoxy crazed a bit admitting water under the track and causing specky rot all over. But my first clue that I might want to look came when the clew of the mainstaysail pulled up the track and outhaul while we were trying to leave Edgartown in a sunny but blustery 35+ knot southwester. We were not even hard on the wind. Now, this all had been through bolted with nice SS. What happened was the deterioration that can happen with SS in a moist but anoxic environment. Plus a little punky wood.

Sealing the wood with some thin epoxy is always good practice. I used to soap the threads but haven't bothered in years as the epoxy releases from bronze or ss with just a little enthusiastic torque.

I see no reason why any conventional bedding compound would have a problem curing on the surface of wood where the screw hole is epoxied. What little contact there could be is at the top of the hole.

I personally prefer to have the wood hardened and the threads the screw cuts in the wood sealed with epoxy. If you are even a little lucky, future restorall after removing to paint or varnish goes easy with some bedding on the screw as well and the same screw finding the existing threads in the wood.

Bolted fittings I personally like the hole just a hair big and very solidly epoxied. I then have bedding compound along the bolt inside the hole.

G'luck

[ssor]

In addition to the advise that Ian gives, I like to countersink the fastener holes so the the bedding compound squeeses around the fastener shank like a small o-ring.

[RodB]

We shouldn't fail to mention the tremendous additional strength of fasteners installed with a surrounding layer of epoxy...see Gougeion Brothers Book.

RB

[Stu Fyfe]

Thanks everybody for your suggestions. Looks like it'll be epoxy in the holes and Dolphinite as the bedding compound. Redwing goes in Thursday. Enjoy the season folks!

[WoodenBNut]

I'm not quite sure of the "epoxy in screw hole" method you are refering to here? (1) One way is to inject epoxy into the hole and then screw in the screw before the epoxy has set. This is strong but you will have much difficulty ever removing the fastener. (2) The method I prefer and use is to drill the screw hole larger than the screw. I inject an epoxy/silicon mixture (not too thick). Wait for the epoxy to cure. Drill the correct(smaller) tapered screw hole in the hardened epoxy. And then insert the screw. Now you have an expoxy encased fastener that should not let water into the surounding wood and that you can remove in the future.

[WoodenBNut]

Sorry!!! I had a typo. That is an epoxy/silica filler mixture - NOT epoxy/silicon. You definitely do not want any silicon here!!

[Nicholas Carey]

Originally posted by WoodenBNut:
(2) The method I prefer and use is to drill the screw hole larger than the screw. I inject an epoxy/silicon mixture (not too thick). Wait for the epoxy to cure. Drill the correct(smaller) tapered screw hole in the hardened epoxy. And then insert the screw. Now you have an expoxy encased fastener that should not let water into the surounding wood and that you can remove in the future.Of the two methods you outline, this provides the stronger grip, as the load on the fastener is distributed across a larger surface area.

You can make it even stronger by using machine screws (more threads) instead of wood screws.

The Gougeon boyz suggest drilling the oversize hole, filling it with epoxy/silica and setting the screw, coated in mold release, in the epoxy until it's cured.

But you could get the same effect by simply letting the epoxy cure, then drilling an appropriate sized hole and tapping it for the machine screw.

[Ian McColgin]

Side note on screws v. bolts set in the wood. Through bolts are easy and covered above.

Some way back the GoogeBros recommended over-boring, filling, drilling and tapping with bolts. However, folk like myself were too lazy and we'd just plnad the bolt in the epoxyfilled overbored hole with some release agent on the bolt and fitting edges. Some epoxy is displaced as you put the bolt in and needs to be dabbed up. Being too cheap to buy mold release goo, I used Ivory bar soap - easy to run the bolt threads across that.

We put the bolt in through the fastening so it would be held correctly. For the drying I left the washer out, so the mold-threaded hole would be enough deeper that the fitting could be properly secured when it was installed with the washer.

I was not happy self-threading pilot holes in an epoxy filled over-bored hole. That always seemed to me, given the smaller number of threads and their large size and the taper of the screw (that last solvable with a proper tapered bit) to make for shattering problems. Epoxy soaked wood in a hole drilled the proper size for the screw and the screw put in to normal tension which the epoxy is wet works very well, leaves strong threads in the wood-epoxy matrix, and one can readily install and reinstall through many cycles.

[Stu Fyfe]

Once again, Thanks! Ian, how's Grana look?