A MOUSE IN THE HOUSE!
Q: I store my small sailboat in an open space under a roof. Mice have chewed up the existing foam flotation as evidenced by the pile of chewed up foam on the floor. I need to replace the foam, but don’t want a recurrence. It does not seem possible to keep the mice out, so I have to find something they cannot destroy. I could spray, pour or put blocks cut to size in the space, but what to use? I understand that spray foam is available, but I have heard it’s not too effective. I was thinking of covering any foam with 1/4in hardware cloth or epoxy resin. I hear about closed-cell and epoxy foams, but don’t know much about them.
Lou Kosko, firstname.lastname@example.org
DON CASEY REPLIES
The easiest repair will depend on the location and accessibility of the damaged foam. In all cases, the best choice for flotation foam is closed cell polyurethane in a 2lb density. Where the foam-filled space is irregular or access is via an opening smaller than the configured foam (often an owner-cut access hole) a two-part pourable foam is almost always the best choice. Here, the trick is to reorient the boat with each small pour to force the liquid to flow into the area you are foaming.
If access is easy—under a seat or side deck, for example—I would use block foam. The problem here is you are probably not going to find 2lb polyurethane in block form. It is more likely to be polyisocyanurate, which is chemically similar and has all but replaced polyurethane for rigid foam. Polyisocyanurate, which is cream-colored, can work fine, but if you are not going to protect the foam, extruded polystyrene (XPS) is a better choice. This will be either blue (Dow Styrofoam) or pink (Owens Corning Formular). Avoid white rigid foam (expanded polystyrene, or EPS) which is not a good choice for floatation use.
Whatever foam you use, keep the mice away from it with a couple of coats of epoxy resin. Do not use polyester as that will attack the foam. For a more durable coating, consider sheathing the foam with a layer of 4oz. or 6oz. fiberglass cloth wetted out with epoxy resin. Epoxy is quickly damaged with UV exposure, so if any of your coating or sheathing will see much sunlight, you will need to scrub (with water) the cured epoxy to remove the surface wax, sand lightly and paint to protect the resin.
I might also adopt a cat...
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