Bedding screws in epoxy?

[goyousalukis]

Quick question. I have my gunwales temporarily fastened to the breast hook and knees with drywall screws. I now want to install the permanent #10 screws. I've read that all fasteners should be bedded in epoxy. Do I drill a constant size hole and then fill it with thickened epoxy and then drive the screw home after it cures, or should I drill a smaller diameter hole into the knee and then a bigger diameter hole in the gunwales? I also read about countersinking the hole a bit before epoxy.

Any help on this process would be appreciated!

Justin

[Peter HK]

Don't drill and fill with thickened epoxy...it doesn't hold as well as a screw into wood with unthickened epoxy...so drill an oversized hole in the gunwales, seal with epoxy and bed the screw into the boat with epoxy. With regard to countersinking this depends on the intended finish- do you want to show the fastener or not. I generally don't like visible screw heads so I do a deep countersink and bury the head under thickened epoxy or a wooden plug depending on finish. I often remove screws after gluing and plug with wooden trunnels as I generally don't like metal fasteners left in but you have do something at the ends to prevent the epoxy failing in a peel stress situation (with glass or screws or timber).

Cheers Peter HK

[PAR]

I disagree Peter, bonded fasteners hold far better then those that aren't. In fact, tests have shown that bonded machine screws or bolts, fine threads particularly, hold better than bonded wood screws (thread count).

I don't think rub rails should be epoxied in place, but bedded in polyurethane or polysulphide. The fasteners can be bonded, but care should be taken so the rail isn't. Rub rails as their name suggests, take a beating and will need to be repaired or replaced at some point. If glued in place, this becomes much more difficult.

Justin, log onto westsystem.com and download their "user's guide" which will explain fastener bonding and other techniques.

[Hirilonde]

As far as fasteners go I agree with PAR. Fine thread fasteners into wood reinforced with neat epoxy is the strongest fastener. If they are to be removed some day then I like to spray the fasteners with WD 40 or similar, install into epoxy saturated wood, remove while epoxy is set, but still green, then reinstal after the epoxy is well cured.

I covered my gunwales/rubrails on my Spindrift with a continuous bumper guard. They are not exposed visibly at all any more and receive no abrasion. So I epoxied mine and removed all fasteners like Peter suggests. If they were bright and exposed I would do as PAR is suggesting as sooner or later they will need replacing. I am a huge fan of making stuff that will likely need replacing easily replacable. It is why I hate 5200 for all but securing ballast keels.

I am not trying to be diplomatic here, and anyone who has read my posts over the years knows this

[PeterP]

The way I read it Peter HK is essentially saying the same thing: re-read his post. Don't run your screws into thickened epoxy plugs as it is too brittle and will chip and flake. Better to run the screw in, back it out, soak the hole in neat epoxy to waterproof/strengthen the fibre then re-set the screw. United in purpose, divided by common language? PeterP

[goyousalukis]

Thanks guys!

My rub rails are already epoxied on my spindrift, so that is a done deal. I suppose if they ever become ugly, I could plane off the first lamination and epoxy on a new one. My boat won't get as much use as I'd like though, so it may not be an issue.

I want to plug my holes, so I will counter bore a little bit, drill the hole, drive the screw, remove the screw, soak the hole with neat epoxy, drive the screw and then plug the hole.

Thanks again,

Justin

[Peter HK]

I disagree Peter, bonded fasteners hold far better then those that aren't.

The way I read it Peter HK is essentially saying the same thing: re-read his post

Peter P has it right here...I was advising bonding with thin epoxy rather than screwing into a cured, thickened-epoxy plug.

Cheers

Peter HK

[PAR]

Agreed, screwing into cured epoxy isn't the way to go, though you can drill the cured epoxy and bed the fastener in the hole, with similar results. Lastly, you can also heat the screw to about 160 - 180 degrees and thread it into cured epoxy. The epoxy will deform, mold around the threads and when cooled, will hold tight. Of course it would be best to back it out (once cooled) and coat the threads with straight epoxy, then reinsert, for a really good grip.

[Charlie Jones]

And a third bulder concurs- epoxy the hole withn neat. and set the screw.

[Alan Stewart]

I think i would have just glued the gunwale on with the #10 screws. If you dry-fitted the screws before gluing the holes would have been soaked in epoxy and when you screwed them in you'd be done! I've had so so many drywall screws snap off on me that I would be afraid to do it this way and if you remove the drywall screws too soon you risk breaking the glue joint too late, the screw.

I think an example of fasteners that should be "bedded in epoxy" are any of those that are used to install hardware (drill, install, remove, drill bigger, fill, drill, install). But certainly if can't hurt to encapsulate your encapsulated screw.

My 2¢

-Alan

[Oyster]

In reply to the issue of removing sheetrock screws from parts in the building stage, heat a tip of a hand held screw driver with a hand held propane torch and then use that to loosen up the fasteners first before you attempt to use a power tool to fully remove them.

[Charlie Jones]

Or heat the screw with a soldering gun. I too broke a bunch before I learned.

[Hirilonde]

Or heat the screw with a soldering gun. I too broke a bunch before I learned.

Hmm, did you lose your "jump-it"?  

[hokeyhydro]

By jump-it you mean jump box? Can't use my jump box for screw removal til it gets off charge . . . ran that puppy dead welding with coat hangers . . .

[Charlie Jones]

Yes-a battery jump starter. And no- this was while building the Princess 22 and I hadn't discovered the Jump-it yet