Rustins Quick Dry Polyurethane Varnish Extra Tough Satin Oak 250ml. This water-based, coloured polyurethane varnish is tough and durable and will resist cracking, peeling and blistering. Can be used on bare wood, hardboard, MDF, and unsealed cork. This product is suitable for outdoor and indoor joinery in both hard and softwood, doors, windows, garden furniture and conservatories, and can also be used as a sealer for concrete.