Moss almost everywhere

[Mike Halmarack]

I live in a block of flats with a concrete tiled, pitched roof. There's moss on the roof, moss blocking the gutters and moss stuffed downpipes. Consequently, the pricey range of water butts being theoretically fed from the downpipes remain empty after the recent rainy period.

Several remedial options are being considered. What I'm wondering is how soon the moss problem would return to this current level if the roof was pressure washed or steam cleaned? In terms of recurring cost would this be an economical option?

[Andrew]

How old is the building ?. Even concrete (?MArley) tiles have a lifespan of only about 60 years. Pressure washing is generally a bad idea.

The best way to deter moss is encourage the world to revert to using coal for heating, cooking and electrical generation :-) This will deal with moss and also treat black spot on roses !.

A possible localised solution might be to fit a length of copper wire along the ridge of the building, both sides of the ridge and wrap bits of lead around the cable at intervals. This will leach gradually down the roof and might deter the moss.

[Chris Hogg]

A strip of copper wire or tape fastened along the ridge will stop moss forming. I suggest you get the roof and gutters professionally cleared first, then have the copper fitted. Crawling around on the roof of a block of flats covered in moss is not for the amateur DIY guy.

[alan_m]

Another option may be to scrape the roof followed by a spray of Benzalkonium Chloride or bleach to help re-occurrence for a number of years.

There are various Youtube videos where it seems to have been done properly with steam cleaning (pressure washing) but a near neighbour did a DIY job with a pressure washer on concrete tiles and the results were rather poor, both cosmetically with surface damage to the tiles and not actually removing all the moss.

[Tim Streater]

We just had our roofs cleaned professionally. The work involved pressure cleaning and removal of all detritus from the gutters, as well as applying two coats of anti-moss spray. Also redoing ridge tile pointing, any tile replacement needed, and verifying that all the roof timbers are sound. Well worth it.

[Mike Halmarack]

The buildings are early 70s. Sorry to hear that pressure washing may not be the answer.

Might that be the most expensive option? Great for a vigorous and divisive argument though.

This might be the best solution, though as the theoretical contents of the water butts are intended for watering vegetables, I don't know to what extent copper and lead run off will affect the flavour.

[Mike Halmarack]

Certainly not for this amateur DIY guy.

[Mike Halmarack]

That's a pretty comprehensive approach. I wonder if the kitty would cover it. If not, maybe finding the best way to keep the gutters and downpipe clear will be the most popular option with residents.

[Mike Halmarack]

Thanks for the advice and vid links. A communal film show might swing it.

[Brian Gaff]

That chemical that people referred me to on here did a very good job on concrete. Still no sign of it returning after a couple of years, but I have plenty left at the recommended dilution. The issue for you would be how to get it to penetrate on a sloping roof, unless you have a cherry picker or something like that. Brian

[alan_m]

Don't rule it out. The guy in the video links I posted about scraping the moss also pressure cleans some very delicate roofs using reduced pressure and hot water/steam. He varies the pressure and uses different types of nozzles etc. dependant on the job. The kind of control that you wouldn't have with a domestic pressure washer, and possibly not the solutions provided by a cowboy gutter cleaner.

A biocide treatment of the roof may result in you not being able to use the roof run-off for a few weeks/months for watering crops. However if the moss is bad it will quick reappear without a biocide treatment.

[Andrew]

Your roof is 50 years old. You and your neighbours need to be aware of the lifespan of concrete roof tiles and start saving for replacement at some point.

[Andrew]

Just get your neighbours to squirt any unused Timolol eye drops on the roof every 28 days :-)

[Mike Halmarack]

Maybe get some of the fitter pensioners busy with concrete tile moulds and a cement mixer.