Things You'll Need
Small foam brush
Stearated, self-lubricating sandpaper
Linseed, Danish, teak or mineral oil
Wooden cups are attractive additions to a rustic set of drinking and eating utensils. However, wooden cups for drinking should be protected against water, which can cause the wood to crack or warp. Waterproofing protectants for wood are readily available from hardware supply stores, but many protectants are inappropriate for items that will be used for drinking. Nontoxic products are best. However, you may have to coat the cup repeatedly with such a product to make it watertight. Wooden cups protected in this way are nevertheless safe to drink from, and often beautiful to boot.
Coat the cup with the nontoxic sealant, using the small foam brush. Protect your hands with impermeable gloves as you do this. Polyurethane finishes are waterproof and safe for use around children. Oil- or wax-based sealants are better for antique wood products, but are less water-repellent than urethane options.
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Let the cup dry for a few hours, then sand its surface with the stearated, self-lubricating sandpaper. Apply another coat of sealant. Repeat this until four coats have been completed. Do not sand the final coat.
Protect your wooden cup with oil, as an alternative to sealant. Redo the the oiling process frequently, because it is not a permanent waterproofing solution. However, oil does endow wood with an appealing aesthetic quality. Linseed, Danish, teak and mineral oils are all ideal for wood products. Rub the oil into the wood until absorbed, then repeat until the wood can absorb no more oil. Allow to dry for 24 hours.