How to clean mold/algae off of roof? archived

Also if someone could comment if this is just an aesthetic thing, or if it's actually bad for the roof, I'd appreciate it.

thanks!

I have it on our slate roof and I love it! I can't imagine that it is "bad" for the roof...

Can't believe it would be good for an asphalt shingled roof. It is growing there, can't be good in the long run. Not sure how it could be removed. We removed it from our old 20+ year old roof. We got a new roof. Perhaps a call to a roofer might shed some light on the issue. kmk, your right about it not being an issue on a slate roof. It is not going to grow through slate.

Things You’ll Need:
Push broom
Chlorine bleach or copper sulfate crystals
TSP
Pump sprayer
Ladders or portable scaffolding
Hose and fresh water

Chlorine Bleach Solution
Step1Spray all the plants growing near your house with water, and this will help protect them from any damage caused by the chlorine bleach solution.
Step2Mix 1 part bleach to 3 parts water and apply to the mildew-covered area with a hand pump sprayer. Adding some tri-sodium phosphate (TSP) will help clean the roof at the same time.
Step3Let the solution sit for 15 minutes, then rinse it off with a hose. Check to see if any mildew remains on the roof. If so, it will feel slimy when you run your hand over the surface). If mildew is still present, allow the roof to dry and repeat the process.
Step4Always rinse the roof after applying the chlorine bleach solution. If you leave the bleach solution on the roof, it could damage the shingles.

Copper Sulfate Solution (Alternative)
Step1Spray all the plants growing near your house with water, as this will help protect them from any damage caused by the copper sulfate solution.
Step2Prepare a mixture of copper sulfate and water, using a ratio of 12 ounces (dry measure) of copper sulfate to 1 gallon of warm water.
Step3Apply the solution to the mildew-covered area and wait for the mildew to turn brown.
Step4Sweep the mildew off the roof using a push broom.
Step5Rinse the roof with a hose and clean water.

Preventing Mildew From Forming
Step1Removing overhanging tree branches and allowing sunshine and air movement over your roof. This can eliminate the mildew-friendly environment and stop it from growing.
Step2Installing zinc strips under a row of shingles near the ridge of the roof will prevent mildew from forming. The mild chemical reaction caused by rainwater coming in contact with the zinc inhibits the growth of mold and mildew.
Step3Applying asphalt roofing shingles containing a copper additive in their surface granules is an option. The copper granules in combination with rainwater have a mild chemical reaction that prevents mold and mildew.
Step4Spray-on commercial products that you apply and leave on are also available. Annual application reportedly blocks the growth of mildew.

Holy batman, you talk like a man with experience with this problem.

Posted By: wedjetHoly batman, you talk like a man with experience with this problem.

Or some one who is good with copy / paste!

Seriously, I'd agree with kmk's comment in particular regarding slate and tile and in general with other roofing products except wood shakes. Moss and / or mold will be more prevalent on the northern or extremely shaded roof sections. Removal of same can be quite hazardous to even professionals and can cause damage to the roofing. One passive form of control for moss is to install a "raw" copper ridge cap or strip above the affected area. Rain will create copper sulfate and will wash over the area and keep the problem to a minimum. Moss on shakes is not good. The constant presence of moisture will eventually rot the wood.

Both, actually. I left mine, though it was prevalent under a tree, on the brick and my chimney. Thought it looked better actually, since it wasn't that pervasive. Was told it was too risky a job to attempt myself-- ever slip on wet mildew? on a roof? Me neither... sought to keep it that way.

ummm, hold on here,,,,,, unfortunately, contrary to kmk's hope, the extended presence of mold, moss, or any other moisture-laden/moisture-bearing growth on ANY exterior surface material does not bode well for that area(s) full longevity of service. Remember, slates are NOT absolutely impervious to moisture, it just takes water a helluva longer time to migrate through it compared w/ other roofing materials. Yes, of course.... functionally they 'shed more water' than they absorb, but I'm pretty sure they are still 'porous' by pure definition. They're only sedimentary stone, and I believe water DOES molecularly go through sedimentary & metamorphic (& I think technically it can't go through igneous at a molecular level, BUT,,,,, water can certainly ACT upon all rock formations eventually).

See here -specifically for the comment of 'moss on slates':
http://www.inspect-ny.com/roof/SlateRoofsATJ7.htm

So, while it may "look quaint", and might not discernably -or visually- be causing degradation to the slates...... it really IS affecting them, just over LOOOOOONG periods of time, and it is a condition that should be cleaned if the slate(s) is to last it's "full service life" as a roofing material.

For the other roofing material types - asphaltic, tiles, synthetics, etc. ... they should be cleaned since their degradation -due to moisture- is more immediate and pressing.

Perhaps the heat and relative dryness of mid to late summer will do the job for you.

My mom recently had her entire house and garage professionally cleaned to get rid of moss, mold, etc. The service used a solution that was something like four times as strong as Clorox bleach. Sounded highly effective but also highly toxic. I've got my doubts about it. I'd google on it and try searching sites for do-it-yourselfers, maybe the DIY network. Good luck!

I might actually do some research myself, since our garage has plenty o'moss on the roof. :sad:

I stand corrected....I have lichen on the slate. And while it is on the north side of the house under partial shade, it is quite dry and flaky in appearance. My lichen isn't even seasonal...it is there year round. Long, hairy, growing and invasive moss is another beast all together!

kmk... well, whether you 'lichen' the plant growth or not :wink: ...... it's still not good for the slate to have something growing on/into it, and should be cleaned off.

I'm lovin' my lichen...it's just the right shade of blue-green!
You know - I am all about appearances...:wink:

Turns out that Mr. Jmo isn't so keen on climbing onto the roof to take care of this himself (although ctrzaska's directions were quite detailed...). Any recommendations for someone we might be able to call to do it?