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A lighter mix of the love would do it, and it would need rinsed off. Perhaps 2-5gal SH to 35gal water 22+oz dawn and 16oz ISP. If it has oxidation than another method would be needed, such as a solvent to cut the oxidation and a higher pressure rinse. If that is the case you may be preping it for paint??


Is this your own house?? Have you done this before??
I would not suggest walking on your metal roof if it is wet with chemicals. If it is easy for you to reach, and a small area than a bottle sprayer will get you by. If it is a large portion of roof, I would call in a pro with the proper equipment. Using household bleach will work but very slowley especially if its not just a small spot, use it full strength if that is your only option. If you have more than 100-250sq. ft to clean it might take you days with a sprayer and household bleach. Be safe if you go ahead and do it, but I would price the job out if there are any pros in your area. The cost of a fall is much greater than a few hundred bucks.


Also if the metal is very old, very oxidized, or showing bare metal anywhere, the SH may eat the weakend remaining enamal off, or cause rust on bare spots.



-- Edited by Baltimore MD Roof Cleaning 410-482-4367 on Thursday 16th of July 2009 11:29:47 PM

TSP (tri-sodium Phosphate) is a painters cleaner, that enhances gloss and cleanliness, you can add some if you want but it isn't nessecary.  The 16oz is ISP (isopropyl Alchohol) .  I would start with the weak mix and see if it is working after about 5-10 minutes it should be rinseable (Don't let it dry on the roof), then add more SH if it is too weak, but that mix will be close, if not strong enough.  The reason a lighter mix is neccesary, is that it is not as harsh on the paint, and the algae should not be as thick as it is on asphalt, or tile shingles.

The two reasons to rinse it off are that the salt is harsh on the paint after it dries, and it will leave noticable chemical stains f not rinsed.   Don't sweat the rinsing, it dosn't need to be rinsed perfectly and the lighter mix is safer for rinsing down onto the ground.

If your going to prep it for paint instead of just cleaning it, I would recomend a natural solvent that can be downstreamed in a pressure washer, then pressure washing the Metal to remove oxidation and loose paint.


-- Edited by Baltimore MD Roof Cleaning 410-482-4367 on Friday 17th of July 2009 07:01:08 AM

I think The Roof Cleaners of Chester County Pennsylvania 610-842-2104 is right.Go for it.

Also I forgot to mention that Roy's method will remove the oxidation without the use of a pressure washer, keeping us on the no pressure soft washing side of things.

Bill,
The secret is the truck wash and foaming it on with a foamer attachment. If it is bad you will have to brush it. This works much better than just love. Also put some Ammonyx Lo in the solution and downstream on. Try it you will love it.