Last details before drilling into the core

To the editor: The recent articles on core construction (Getting to the core Issue 146, May/June 2005, and Construction at the core Issue 147, July/Aug. 2005) could not have come at a better time. Both articles were very informative.

During the month of July, I will be repairing some balsa core damage and then redoing all of the nonskid deck surfaces on my boat. In this rework, I plan to reef out and epoxy backfill every penetration into a cored surface. Unfortunately, the builder of my boat did not (and still does not) attempt to address the problem of mounting hardware on cored surfaces.

I’d like to confirm the details – as I do not want to go through this again. Drill out the fastener hole oversize: Is half an inch a good size for quarter-inch or No. 10 fastener holes? Do I use the same half-inch reef for a hatch hole?

Reef out the core about a half inch back: Does an Allen wrench really work best?

Fill the hole: Is mayonnaise-consistency West epoxy/404 filler the best? Is a syringe the best way to fill a lot of holes?

Rebedding the hardware: Is silicone the proper bedding compound?

I plan to install the hardware leaving a slight bedding compound “gasket” and do the final tightening after the compound has set up – without spinning the fastener where it goes through the compound. How do I do this for the hardware that is screwed on (three stanchion bases in particular)? Or do I not have to worry about this problem because I replaced the core?

The deck surfaces are currently rolled on gelcoat with nonskid compound. Do you have any recommendations about materials to use/not use for this?

Thank you for taking time to advise me on this. By the way, this issue will be one of the non-negotiable requirements of my next boat!

– Harvey McChesney III is a retired manager of production engineering and a lifelong do-it-yourselfer. He and his wife, Sara, live in Pennsylvania and sail their 35-foot down-east boat regularly out of Oxford, Md.

Contributing Editor Steve C. D’Antonio responds: Yes, half an inch is a good size for quarter-inch or No. 10 fastener holes, and yes, for a hatch, you can go deeper. Some folks do to ensure that the fastener holes penetrate the epoxy and not the core. The preferred reefing out tool is an Allen wrench or a nail bent at 90°. Yes, the filler should be the consistency of mayonnaise. A syringe works well for deeper holes; it helps to exclude air bubbles. For shallow holes, a tongue depressor works fine.

As for rebedding, we use GE SilPruf here at the yard for most above-the-waterline bedding. If you can find it, it works well (it’s not a marine product, so check hardware and home stores). Otherwise, one of the SikaFlex products is fine.

The spinning screw shouldn’t be a problem; the silicone gasket around the screw will remain effective and, as you pointed out, you are screwing into epoxy rather than core.

Two-part paints are the longest lasting. If you are comfortable using one of these, Awlgrip for instance, it’s the most effective way to go. Otherwise, a single-part epoxy paint will last a few years.

By Ocean Navigator