Ronseal Diamond hard Dark oak Satin Floors Wood varnish, 2.5L. Want a floor varnish that lasts? Look no further. With Diamond Hard protection, this floor varnish from Ronseal will keep your wooden floors protected and looking great for longer. It’ll protect your floors from knocks, scuffs, spills and heels, so it’s ready for whatever daily life throws at it.. This dark oak floor varnish from the Ronseal Diamond range can be applied to interior using a brush. The varnish dries in just 30 minutes and will cover up to 18 m² per litre on average. Floor varnish by Ronseal.