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OT: Q. about pressure washing comp. roof

Toolbert

Stainless
Joined
Nov 29, 2003
Location
Vashon Island, WA
I've long been aware that you aren't supposed to pressure-wash composition roofs. But I have a moss problem and for other reasons, the usual moss-killing chemicals are not an option.

An acquaintence is recommending that I go with a "new" pressure washing company, dedicated to cleaning comp roofs using a 1000 psi 10 gpm pump and a special roof-cleaning wand, that his company says is faster and far less damaging to comp roofs than "traditional" pressure washing at 2500 to 4000 psi, 3 gpm. Says while it's still damaging, it's ... less damaging.

I've spent a couple hours googling and reading and have found absolutely nothing that gives an objective opinion of this "new" method. Most of the shingles in question are "50 year" architectural grade, 5 to 10 yrs old. I gotta do something, but the last thing I want to do is destroy all that roofing 40 years before it's time.

Anyone have specific knowledge of this high-flow, relatively low pressure cleaning? I need to decide whether the damage is an acceptable tradeoff.

thx

Bob
 

dp

Banned
Joined
Aug 17, 2005
Location
Puget Sound, Washington
I use 1% bleach to kill it, a push broom a week later to get rid of it, and zinc sulphate to keep it gone a long time. Not a good job in the rain, though. I don't see how a composition roof can survive a pressure washer, but be sure the moss is dead or you'll just end up forcing it under the tiles and into the cracks.
 

Timw

Stainless
Joined
Nov 8, 2005
Location
N E Florida
If you take a 2000 psi pressure washer (typical size) and run it 1/4 - 1/3 throttle you will lower the pressure it puts out. I used to P W my boat and trailer after a day on the ocean in saltwater. I just turned the throttle down so I didn't damage anything or blow off decals. It's like having a high pressure garden hose.
You can also backoff the distance with a fan tip to lesson the pressure. When P W ing wood decks or fence you need to back off or you damage the wood.
 

tomwalz

Stainless
Joined
May 4, 2006
Location
Tacoma, WA
I do mine with a garden hose and a stndrd adjuztable nozzle. Works fine. Takes a while but I pick a warm day. It is quiet up there. No one bothers me and I can watch the negihbohood kids playing.
 

David/toledo

Hot Rolled
Joined
Mar 4, 2003
Location
Toledo Oh
Here is a pdf link for you cam from a painting contractor form
http://www.asphaltroofing.org/pdf/tb_217.pdf
David/toledo
__________________
David Enterprises Inc.
Toledo,Oh
user_online.gif
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Toolbert

Stainless
Joined
Nov 29, 2003
Location
Vashon Island, WA
Thanks for the replies. The water runs off into organic garden beds, ponds and wetlands supporting frogs, turtles, birds, bees and other sensitive critters in addition to humans. I choose not to apply poisons or toxics. Do what you want in your own yard and I'll do unto mine ... I'm not making a political statement.

Bleach is not so bad, it can be applied in a mild enough dose to be neutralized before it does any damage on the ground. That will be used in the sunnier areas where the moss buildup is mild, and a mild treatment would be OK if I hadn't let some of the structures get out of hand, but I don't think a dilute bleach is going to help the worst ones.

Algae isn't an issue - I don't care if the roof is the wrong color since little of it is visible anyway. Issue is the rapid moss buildup characteristic of roofs in the PNW esp. facing north or always shaded by trees.

To do again, the roofs should be metal, but it's too late now.

Bob
 

jameskevin

Plastic
Joined
Aug 10, 2022
Any chance of confining a stronger bleach & TSP wash to the gutters and a barrel?
Try making a gutter solution by mixing some Dawn liquid detergent with two gallons of water and half a cup of bleach. This solution uses a scrub brush to scrub the outside of your gutters. Let it sit on the gutters for ten minutes or less, scrub once more, then rinse away with a hose and a sprayer.
 

bikemutt

Aluminum
Joined
Mar 5, 2022
Living in the PNW, where moss was invented, it's an annual battle. My understanding is any chemical means to control moss really needs to be applied when the moss is growing, i.e. not now. I choose to use non-staining Moss-Out designed for composition roofs and decks, it comes in a powder-granular form, as well as a liquid concentrate. I use a hose-end sprayer to apply the liquid concentrate from ground level since falling off the roof is no longer on my bucket list. I don't know if Moss-Out is poison or not, I believe it's designed to expose moss to an unsuitable pH. Since most PNW houses have gutters, it may be possible to temporarily route the downspouts outside the bio-sensitive zones long enough for the moss control to work and then biodegrade to ambient.

As far as removing the existing moss, when I got bids to remove the moss, filtered by only low pressure merchants, all of them quoted more than it would cost to replace my roof. I judiciously started applying moss control, after three years, I won. A 1500 ft2 roof on a single level home is doable that way, 2-story or more homes, or larger ones may be beyond what a homeowner wants to attempt.
 

Superbowl

Cast Iron
Joined
Feb 12, 2020
I would not even low pressure wash. It does not take much to wash the sand off the shingles. Once the sand is gone the uv light starts to break down the shingles. Bleach might work. Iron fertilizeris used to kill moss in a lawn so you might try it on the roof. Perhaps clear plastic would hold enough heat in the summer sun to kill it. I put the zinc panels they sell to control moss near my roof peak which keeps it from getting established.
 

akajun

Hot Rolled
Joined
Jul 1, 2011
Location
Brusly, LA
Pressure wash, even 1000psi will damage your shingles
My brother has a “ Softwash” business
His roof chemicals are mostly just bleach and a strong soap
He has applied a mold killer like mold armor but it takes longer to work
He also has a roof rejuvenator which is some kind of oil that softens the shingle

His background is in evironmemtal science and cleanup and he knows how not to kill landscaping and plants
 

APD

Stainless
Joined
Nov 5, 2005
Location
Hudson Valley, NY
I've long been aware that you aren't supposed to pressure-wash composition roofs. But I have a moss problem and for other reasons, the usual moss-killing chemicals are not an option.

An acquaintence is recommending that I go with a "new" pressure washing company, dedicated to cleaning comp roofs using a 1000 psi 10 gpm pump and a special roof-cleaning wand, that his company says is faster and far less damaging to comp roofs than "traditional" pressure washing at 2500 to 4000 psi, 3 gpm. Says while it's still damaging, it's ... less damaging.

I've spent a couple hours googling and reading and have found absolutely nothing that gives an objective opinion of this "new" method. Most of the shingles in question are "50 year" architectural grade, 5 to 10 yrs old. I gotta do something, but the last thing I want to do is destroy all that roofing 40 years before it's time.

Anyone have specific knowledge of this high-flow, relatively low pressure cleaning? I need to decide whether the damage is an acceptable tradeoff.

thx

Bob
May not be possible in your situation, but its another suggestion no one has mentioned: Can you cut some tree limbs to provide more sunlight to that area of the roof?
If not, I would remove with a stiff bristled broom/brush first. Then a mild bleach solution could be applied with a garden pump sprayer (no runoff).
Then some simple copper flashing in a few place will inhibit moss and lichens from returning.
 
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