You're getting good advice on how to handle the holes. I agree that you want to get all the wet or damp core out. I like to use a Dremel #115 bit (when I have a large enough hole to fit it in). I use a dental pick on smaller holes - it's amazing how well it will "grab" core and pull it out.
After vacuuming out the hole, I clean with acetone or denatured alcohol, then tape everything off (to avoid sloppy mess) and wet out the inside of the hole with neat (i.e. plain/liquid) epoxy. I either paint it in with a pipe cleaner or a bent acid brush or I sometimes inject it in with a syringe, let it sit and soak in, and then suck it back out (which leaves the soaked in stuff there). Next I fill the hole with thickened epoxy (colloidal silica usually, or structural filler).
As was mentioned, filling a "blind" (no outlet) hole can be tricky because it's easy to get air pockets (which is not good). I have used a number of ways to get around the problem.
1) Use a syringe (if you don't thicken the epoxy too much you can still run it through a syringe) and start with the tip at the back/bottom of the hole. Start filling and as you do slowly withdraw the syringe, filling as you go. A variation is to tape a piece of tubing onto the end of the syringe (such as heat shrink tubing).
2) On really deep holes or ones that have a lot of "upper cave" where you have back cut, method #1 might still leave air in that upper cave part. I have put a second piece of tubing in the hole alongside the syringe, with the inside end up in the "upper cave." Then I use the syringe (in the back of the hole) and a lot of pressure to flood the hole with thickened epoxy. Air will come out the secondary tube. A fair bit of epoxy will also flood out the hole, but if you plan for that you can re-use it for the next hole(s).
3) Sometimes I drill a small second hole at a high point (depends on situation/cosmetics), sort of like Ray shows, only I then fill from the bottom hole and let the air come out the small upper hole. Sort of like filling the lower unit on an outboard. When epoxy starts to come out the upper hole you can tape it off and nothing will leak out the bottom hole, so you can tape that off at your leisure (after withdrawing the syringe).
If you don't want to buy all the various epoxy/fillers/etc., I have recently been trying out WEST System's "610." This comes "pre-made" in a caulking tube and either mixes itself as you press it out through a special mixing tip, or you can dispense it and then mix it sort of like one of those 5-minute-epoxy tubes (then put it in a syringe). It is thickened with colloidal silica. WEST say that it can also be used to wet out holes (even though it is thickened). I'm not sure how they do this, but they have it formulated so that when you push or move it it thins out, and when you stop it thickens up and just sits where you put it. Pretty slick! Although it's around $22 a tube (no way you would build a boat with it!), for small jobs I think it may actually save money because you can mix a very small amount, go through fewer gloves, it's very tidy, etc. I'm going to keep a tube "in stock" from now on. My only wish is that they made it in a smaller tube so I didn't have to carry a full-sized caulking gun around to dispense it.
There might be some places I would want to wet out with neat epoxy before using 610, but then I would be comfortable wetting out with it in many situations. They also say it will wet out up to 12 oz. cloth, but I've still always used traditional epoxy for that (so far).
WEST sells small syringes, or you can get them on Amazon, etc. (the ones with the longer plastic cone shaped tip are called "catheter tips").
Note that epoxy has insufficient UV resistance, so it needs to be painted or gelcoated over to protect it.
Couple of "random" tips:
1) Along with all the other protective gear, I wear disposable nitrile gloves. I don three or more on each hand, then I can just pull off a contaminated one mid-job and keep on going with the fresh one that's behind it.
2) On smaller holes I tape right over them with blue tape and then cut out the hole with an Exacto knife. Sounds putzy but I find it works out well when all is said and done (with epoxy, I find that prep/protection is always worth it over just hoping not to make a mess).
Good thing you caught the silicone (don't get me started! :amgry and are taking care of this now :thup
After vacuuming out the hole, I clean with acetone or denatured alcohol, then tape everything off (to avoid sloppy mess) and wet out the inside of the hole with neat (i.e. plain/liquid) epoxy. I either paint it in with a pipe cleaner or a bent acid brush or I sometimes inject it in with a syringe, let it sit and soak in, and then suck it back out (which leaves the soaked in stuff there). Next I fill the hole with thickened epoxy (colloidal silica usually, or structural filler).
As was mentioned, filling a "blind" (no outlet) hole can be tricky because it's easy to get air pockets (which is not good). I have used a number of ways to get around the problem.
1) Use a syringe (if you don't thicken the epoxy too much you can still run it through a syringe) and start with the tip at the back/bottom of the hole. Start filling and as you do slowly withdraw the syringe, filling as you go. A variation is to tape a piece of tubing onto the end of the syringe (such as heat shrink tubing).
2) On really deep holes or ones that have a lot of "upper cave" where you have back cut, method #1 might still leave air in that upper cave part. I have put a second piece of tubing in the hole alongside the syringe, with the inside end up in the "upper cave." Then I use the syringe (in the back of the hole) and a lot of pressure to flood the hole with thickened epoxy. Air will come out the secondary tube. A fair bit of epoxy will also flood out the hole, but if you plan for that you can re-use it for the next hole(s).
3) Sometimes I drill a small second hole at a high point (depends on situation/cosmetics), sort of like Ray shows, only I then fill from the bottom hole and let the air come out the small upper hole. Sort of like filling the lower unit on an outboard. When epoxy starts to come out the upper hole you can tape it off and nothing will leak out the bottom hole, so you can tape that off at your leisure (after withdrawing the syringe).
If you don't want to buy all the various epoxy/fillers/etc., I have recently been trying out WEST System's "610." This comes "pre-made" in a caulking tube and either mixes itself as you press it out through a special mixing tip, or you can dispense it and then mix it sort of like one of those 5-minute-epoxy tubes (then put it in a syringe). It is thickened with colloidal silica. WEST say that it can also be used to wet out holes (even though it is thickened). I'm not sure how they do this, but they have it formulated so that when you push or move it it thins out, and when you stop it thickens up and just sits where you put it. Pretty slick! Although it's around $22 a tube (no way you would build a boat with it!), for small jobs I think it may actually save money because you can mix a very small amount, go through fewer gloves, it's very tidy, etc. I'm going to keep a tube "in stock" from now on. My only wish is that they made it in a smaller tube so I didn't have to carry a full-sized caulking gun around to dispense it.
There might be some places I would want to wet out with neat epoxy before using 610, but then I would be comfortable wetting out with it in many situations. They also say it will wet out up to 12 oz. cloth, but I've still always used traditional epoxy for that (so far).
WEST sells small syringes, or you can get them on Amazon, etc. (the ones with the longer plastic cone shaped tip are called "catheter tips").
Note that epoxy has insufficient UV resistance, so it needs to be painted or gelcoated over to protect it.
Couple of "random" tips:
1) Along with all the other protective gear, I wear disposable nitrile gloves. I don three or more on each hand, then I can just pull off a contaminated one mid-job and keep on going with the fresh one that's behind it.
2) On smaller holes I tape right over them with blue tape and then cut out the hole with an Exacto knife. Sounds putzy but I find it works out well when all is said and done (with epoxy, I find that prep/protection is always worth it over just hoping not to make a mess).
Good thing you caught the silicone (don't get me started! :amgry and are taking care of this now :thup