A friend of mine owned a business in Vero Beach FL for years. He would
treat roofs for mold and moss and mildew. The treatment consisted of a
regular spraying with a diluted bleach solution. No scrubbing. The normal
rainfall would wash everything off. I would think that once it was treated
a few times, the moss would lose its grip and be able to be washed off.
Wash from the top down, and don't blow the water into the joint overlap.
And be careful when walking on that old of stuff. I'd try just a pump up
sprayer, and a good strong sprayer, and try it from a ladder or scaffolding
before actually going up on the roof. The moss could be slick, particularly
after you hit it with bleach. Use proper safety gear, and be sure someone
is videoing for America's Funniest Home Videos.
Once you get it under control, I'd still spray it every couple of months to
keep it from getting started again.
Bleach kills moss just fine.
I've used a pressure washer with the chemical feed from a bucket of
bleach solution on a stone patio in an area that grows moss and algae.
I've also used this on an asphalt shingle roof in the same area with
good results. Pressure washing with bleach solution kept the moss and
algae away a lot longer then pressure washing with plain water. I
suspect that walking on a slate roof with a pressure washer gun might be
a bit dangerous, so you may need to do this strictly from a ladder.
Unless you have a tall bucket truck, easier said than done. Almost all
slate-roof houses I have seen are 2-story with a steep pitch, and the
last thing you want to do is to walk on old slate, unless you are an
expert. There is a reason that even historical restoration people are
starting to embrace the faux slate made out of old tires and stuff. In
cold wet climates, real slate beats wood shakes and thatch, but it is
still an expensive PITA.
Yes, I wouldn't recommend walking on wet mossy slate, working from a
ladder or scaffolding would be better. Rental aerial lifts are a lot
more readily available these days and I'd recommend that for the initial
washing to get the moss off. Once the moss is off, a regular wash from a
ladder with the bleach solution should keep it from coming back to the
point of needing extensive cleaning again.
I recently rented a nice self propelled 45' reach aerial lift that is
light enough to be trailerable with a normal truck (requires outriggers
to be lowered before you go up, but all hydraulic controlled from the
basket). One nice feature with this boom is that it had built in hoses
for air tools and for pressure washers, so you just connected to the
quick connects at the bas and in the basket and didn't have dangling
hoses in the way.
I don't think that slate by itself would support moss growth. While it is
possible that the slate is deteriorating to the extent that it is
generating a growth medium, it seems more likely that debris is collecting
on the roof and shade is protecting the moss from drying out. SO the
question is whether there are increasingly large trees leaning over the
roof where there were none before.
Get moss killer from HomeDepot. It concists of ground zinc, copper and
other acidic metals. Sprinkle it all over the moss. Moss don't like
acidic environment. You may have leaf/mulch build up on your roof making
soil for moss to grow. Clean the roof.
A zinc strip at the top of roof is common where I live, Laundry bleach
will kill it now but moss grows in debris , is roof covered by a tree
and not steep pitch so it collects dirt. Mold or green coloring is
common and no harm but moss to me means roof doesnt clean itself by
rain, by moss you mean it is maybe 1/2" thick and it pulls up intact?
My slate roof has green mold, but no buildup in thickness. Moss would
be a problem. The only true moss I have or have seen grows on the
ground. Roundup will kill it but take longer and cost more than
I like the inexpensive bleach solution, but won't my roof and back yard
smell like bleach?
I don't know if it's moss, but it's a moss like substance that grows on
the spaces between the slates on the north side.
Slates have two big nails holding them. 5ft of snow or a person wont
budge them. Moss in between shouldnt cause harm, they lift a bit, look
underneath to see if it grows under slates, minimal green growth wont
hurt anything , you made it sound like the roof is covered with moss
which to me means debris and dirt, then the roof wont breath and wood
will rot, a photo is always a good idea. Bleach smells only a few
days, a garden sprayer pumped up with a straight spray might reach
I used to be able to buy Copper Sulfate for the garden, I cant now
because its poisonous. Sprinkling copper, Zinc, and" metals" might
require serious caution, I would not want wind blowing in my
direction, and on a roof you can get crazy winds since they deflect of
the house. Maybe in a liqued solution, but I used Copper Sulfate to
Kill Trees, a dust mask is not good enough protection with CS.
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