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1 US gal (3.8 L) of Waterlox will cover 500 sq ft per coat. 1  qt (0.95 L) will cover 125 sq ft per coat. You can use Waterlox’s online “Purchase Assistant” to help you determine how much finish to buy: https://www.waterlox.com/support/purchase-assistant.  Typically, you’ll need 2 basecoats and 1 topcoat. This means that for a 500 sq ft area, you would need 2 US gal (7.6 L) of Waterlox Original Sealer/Finish and 1 US gal (3.8 L) of whatever topcoat you choose. You may need more coats for very porous, untreated, or recently sanded wood surfaces. Waterlox is a potentially harmful chemical solution, so you must always protect yourself against its effects during use. Wear safety goggles and gloves whenever you are handling this product. Nitrile gloves work best for this purpose. Ventilation is crucial when using Waterlox. If you are unable to ventilate the area properly, you should not use this product. Cross-ventilation is best to aerate the room and to help the finish dry. For best results, place a box fan in a window or door with another window or door open on the opposite side of the room. You should ventilate the room while you are applying the finish and while it is drying between coats. Continue ventilating the area for at least 7 days after applying the final coat to ensure the finish is properly dried and to help evacuate the solvent odor. It is imperative that you vacuum the surface you want to finish completely before applying the Waterlox. This will remove any dust or debris left on the surface so that it doesn’t get painted over.  Consider using a shop-vac or a canister-style vacuum for best results on larger surface areas. For smaller surfaces, use a damp microfiber cloth to remove any dust particles. After vacuuming, wipe the surface with a dry rag to get up any remaining flecks or fibers that the vacuum may have missed. Wrap your sand block with 220-grit sandpaper and rub it across the surface of the wood in 2 ft (0.61 m) to 3 ft (0.91 m) sections. Be sure to go with the grain of the wood as you sand it.  Do not sand the wood too roughly or this could remove any existing protective stain. When finished sanding, wipe the surface with a rag to remove any leftover debris from the sanding process.
Buy enough Waterlox to get the job done. Purchase safety goggles and gloves. Ventilate the area properly. Vacuum or dust the surface thoroughly. Lightly sand the wood surface.