Join Date: Apr 2006
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Sounds like someone used cheap oil on an asphalt parking lot.
If you are sure the problem isn't from the non-skid, i.e. maybe a sticky layer of old wax on it? Well...you could tell your guests you follow the old custom of washing their feet when you greet them, please sit down before you board. Or, warn them outright, just tell them there's a problem with the parking lot to please carry their boat shoes and change at the dock.
One of the yellow cleaners commonly sold these days like "Goo-be-gone" should clean off whatever is on their shoes real quickly, I'd use that with a plastic "Scrunge" or other kitchen scrub pad, and then some rag or paper towel, to do a fast cleanup on shoes. Or any automotive "bug-n-tar" remover.
I'd say to get those surgical over-booties that hospitals use but I don't think they'd give good traction on a boat for long.
If your guests can't appreciate "we've got this crazy problem and we have to spend hours scrubbing unless..." then you need to rethink the guest list. Or, hide their car keys until after THEY'VE cleaned the decks.