My house has a hot mop tar roof with pea gravel, and we’ve been here 10 years. I never worried too much about the moss but it was getting pretty bad, and I finally decided to do something about it.
I had a 1/2″ wire mesh screen frame I’ve used for other projects and it’s the perfect size for sifting the pea gravel from the moss.
I set it up on a clear area, and then used my plastic scoop shovel to scrape the moss/gravel off the roof as far down as I could go, dump it on the top of the screen, let the gravel fall through and most of the moss tumbles down the screen to the bottom onto a piece of plwood, where I scoop it up with the scoop shovel and into plastic bags.
And now that it’s all clean I used up my Lily Miller Roof Moss killer on about 400sq ft. Then I used a 50/50 bleach/water mix on another 400 sq ft. And left the rest untreated. Based on what I see in a month or 3, I’ll treat (or not) the rest of the roof.
It sure looks purty, all cleaned up.
Here’s my setup with half-clean half-mossy roof:
Here’s a detail of the moss with shovel for scale. Quite a varitey of different mosses up there.
And finally a completed section, nothing but clean gravel.
Edited 9/28/2008 1:15 am ET by geoffhazel
Replies
Bless you my son, for cleanliness is close to Godliness and all that...
but what have you gained?
I doubt that you helped and the mechanical agitation and traffic may have hurt things here and there. Be very carefull around those curbs and cants with that shovel.
But assuming that all is fine and undamaged, if you want clean roof, do prevention here on in instead of the work you just did. Wash it down with a percolate or sprinkle zinc powder.
My guess is that this has an interior drain because I see a tall gravel guard and because moss normally will not grow without regular supply of moisture. So I bet there is puddling where the moss was prolific. That would suggest a poorly executed construction originally which leads to shortened lifespan for a BUR roof. No flat or low slope roof should ever allow puddling of water.
Which comes back to the Q of interior drains - or maybe clogged scuppers at edge. Be sure to keep them clean so water can drain.
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The roof is built up about an inch higher over most of the area, and the outer foot is and inch lower so theoretically the water can migrate from the flat areas to the outer edge, and then route to the drains. If there's moss, however, the moss and roots trap the water, so I think I'm better off without the moss than with it.
There was a blue spruce tree overhanging one corner of the "clean area" that dropped needles for years and that area was very heavy with moss. Tree is now gone.
So it was a failure to keep the tree debris cleaned up that resulted in the growth. That junk trapped the water that allowed the moss to grow. I remember a tree scum puddled roof once that had made enough soil that there were 3-4 foot tall trees growing there.I'm betting that now the source of trouble is gone, so is the problem.Good time to start watching it closely. A lot of those BUR roofs were only designed as 15 year jobs, and if it had moderate to poor workmanship, it starts leaking at 10-12 years. So keep an eye on the edges, cants, etc for cracks and shrinkage, separation, blisters...
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