A poultice is a moist, soft mass used to treat inflammation of a body part. It is often applied with heat. It can also be used to draw out stains and other contaminants from a porous material.
In our case, it is a way to draw out oil from oil-soaked wood. The stringers in this boat have, over time, absorbed engine oil that has been spilled in the bilge. They’re not damaged enough to warrant replacement, but I want to get the oil out of them to facilitate sealing of them, and paint adhesion. A good way to do that is by making a poultice of ground up non-scented kitty litter (dried clay) and lacquer thinner. The lacquer thinner is a solvent that soaks into the wood, dissolves the oil, and keeps it in solution long enough to leach out through osmosis to the kitty litter where the oil concentration is less. This may sound like snake-oil. But it really works. Try it.