With epoxy being pretty much waterproof as well as tougher than any kinda plywood I've ever known or used (goes for solids too) I think in watercraft the DFD procedure for fasteners is always a better protocol than just putting 'em into a hole.

There likely are some circumstances where it's not recommended, thus I'll be waiting to hear about 'em from other forumites having more experience than I lay claim to.

Here are my thoughts on the topic.

The key thing is to ensure you don't construct in a way the provides an opening for water to get to the wood.   so when it comes to drill/fill/drill, i have some variations on the theme that i use.

classic drill/fill/drill is where you make a hole bigger than you need, fill it with epoxy and then drill out a smaller hole that can handle the actual size of the fastener.  this works great for machine screws and any other type of fastener that you expect to through-hull with a bolt on the back side.

drill/fill/drill does not work well if you are trying to thread something into a hole (e.g., a wood screw) as the act of trying to cut threads into epoxy can easily crack the epoxy layer exposing the wood unless you are going to go to the trouble of actually using a thread cutter to properly cut grooves into the epoxy.

so my variation on drill/fill/drill when there is no through-bolting (like a wood screw) is to place the wood screw into the wood (you should drill a tap hole to start) and put-it-in/back-it-out several times and then remove the screw.  then i will take raw epoxy and drip it into the hole so the hole is filled with epoxy and let it sit for a couple minutes, and then before it cures, perform the same operation, (screw in and screw out)....and then let the epoxy set (in this step, you want to see excess epoxy getting pushed out of the hole)...  this then seals the inside of the hole with epoxy and prevents water intrusion. 

when i do the final set of the screw, i will put silicone sealer (can get it from a hardware store) on the screw and dirve it in a final time...but i will not try to go deeper or over tighten it relative to the in/out activity in the preceding steps as this could crack/open the wood.

this has worked well and i have not had a failed hole (e.g, water intrusion or a screw that has pulled out unexpectedly) with this approach.  and to highlight, this approach does not permanently glue to screw into the hole....it just waterproofs and strengthens the hole the screw is in.

hope this helps.

h

 Hspira, you replied to the unwritten question in my OP -- how to deal with a fastener like a wood screw that is not in a through hole. I was thinking that cutting threads into epoxy with a wood screw would be kinda sketchy. Your method sounds reasonable, and without anyone else suggesting another method, the one I'm going to go with.  Thanks!

The last part for me to figure out around this is how to set the square part of a carriage bolt head into the epoxy so I can remove it. A variation on the fixed carriage bolts in the ENP center bulkhead. Here's what I'm thinking:

1. DFD the hole and then counterbore for the square part of the head.

2. Wrap the carriage bolt threads with teflon tape to fit snuggly in the drilled hole. 

3. Cover the head with some type of release. This is the part I'm uncertain about.

    * Ideally it will be certain to allow the carriage bolt to release, but be thin enough to ensure that the carriage bolt's square head fits snug in the finished hole.

    * I'd like to use a release that I have around the house or is easy and cheap to get. I'd rather not have to buy something like Pam or hairspray that I'll use 3 squirts of, and then will just sit around unused forever.

4. Fill the counterbore with thickened epoxy and set the carriage bolt in it.

5. Remove the carriage bolt from the hole and enjoy.  

Does this sound reasonable? What can I easily use for a release though? One thought is after wrapping the bolt with the Teflon tape is to punch it through a piece of Saran Wrap. Can't get much thinner than that. The other more common way to go about it is to put some wax on it. I have down in the basement an ancient can of butcher's wax I use to wax the tables on my saws. The problem with wax is it seems it would be difficult to get even thin coverage.   Any thought on that?

digger

Hi Digger,

for release material in the past, i have used saran wrap and duct tape.

so i see you already thought of the saran wrap.  in this particular scenario, i think either might work.  it's something you could probably do a test with on a piece of scrap wood.  i am a big fan of doing a little test to sort out stuff like this.

i don't have a lot of experience with release agents that would be painted or sprayed on....and like you, not interested in having chemicals or sprays around the house that i don't want.  the only other thought i had, if a test with saran wrap or duct tape did not work, is could i use something like a waxy lip balm applied to the screw to get the job done.

h

Johnson's Paste Wax is my go-to release agent.I use it for a lot of other stuff, anyway, so I always have some around.

Or raid the kitchen for some olive oil. I've had the best success with the expensive extra virgin stuff, probably because it contains the most complex molecules.

Butter works, too, but it goes rancid and attracts animal pests.

Tallow, either by itself or mixed with beeswax, has a long nautical history and does not bind with epoxy.

As far as waterproofing screw holes, my #1 Faering Cruiser was built by CLC in their shop. Every screw that I've removed during maintenance had epoxy and silicone sealer in the hole. That sounds like a ringing endorsement of Howard's process to me.

Laszlo