Copper develops a protective light green patina over time when it is left outside. This is why the Statue of Liberty, for example, is green rather than bright copper in color. The patina is extremely important for outdoor copper items like statuary and roofs, but it does not necessarily protect from the general dirt and grime that builds up on any roof over time. When you clean your copper roof, use natural ingredients that will not destroy the patina as they remove the buildup and gunk.
Things You'll Need
Push bristle broom
Scrub brush with stiff, nylon bristles
Mix your cleaning solution. Use three parts lemon juice to one part coarse salt. This means if you use six cups of lemon juice, you will need two cups of coarse salt. As you may imagine, if your entire roof is copper, then you will need more than one batch.
Sweep off your roof. Get rid of as many leaves and as much loose debris as possible before you start scrubbing. Otherwise you will just create a muddy, lemony mess.
Scrub your roof with the lemon cleaning solution. The salt will remove grime but will leave the patina intact. The lemon juice will brighten up the surface of your roof. You can scrub in an upright position using the push broom and dipping it in the mixture periodically, or you can tackle tough dirt and buildup with the scrub brush.
Rinse off the roof. As you clean, rinse off the roof periodically so that you can see how you are progressing. Use the garden hose to rinse the salt and loosened dirt away. Work your way from one end of the roof to the other (right to left) so that you are not standing on the wet part of your roof at any time.
Let the roof dry. The copper should dry quickly on a clear day. Allow about 30 minutes for water to evaporate.
Treat your newly clean roof with a polyurethane spray. This will keep your roof from getting dull and dirty again quite so quickly and it will protect the patina from weathering.
Baking soda can be used to take on really serious buildup if the lemon juice and salt alone do not work.
Wear non-skid shoes and do not work alone when you are cleaning a roof.