The cedar used in Alton's products has an inherent resistance to rot. If the cedar is not regularly retreated the colour will fade to a natural silvery-grey. Alton currently uses an exclusive Golden Honey Wood Preservative on all greenhouses. The warm, natural colour looks superb in any garden setting and the additional wax content helps disperse rainwater. How much is required? Coverage depends on many different factors including moisture content and cleanliness of the timber, but a rough guide to help you (based upon 2 coats) is given below. All models up to 20' long = 2.5 litres Octagonal's models = 5 litres..