In message , Martin
writes
On Thu, 11 Jul 2013 08:39:53 +0100, Chris Hogg wrote:

On Wed, 10 Jul 2013 17:50:43 +0100 (BST), "Dave Liquorice"
wrote:

Nice house wall painting weather, patching up the few places the
paint has failed. One patch I *know* I wire brushed and repainted
last year. It's failed again, because there must be moss embeded into
the stone/old lime mortar.

So how to kill the blasted stuff, preferably in one hit and
permenantly. Will Roundup do it? The weather looks set fair for a day
or two so I could squirt it tomorrow and leave it for a couple of
days to get down into the roots before removing the top growth and
repainting.

Along with what the others have said, Jeyes Fluid will kill moss, but
the smell lingers for a week or two and I doubt if it's permanent.
Creosote may also work but I have no experience. As Janet was
thinking, ferrous sulphate is traditionally used to treat moss in
lawns, but this will slowly oxidise, will probably give you a brown
stain,

black!

Moss turns black (and hopefully dies), but ferrous sulphate stains
concrete etc brown.

and having oxidised may lose its effectiveness, but I don't
know about that last bit.

If you apply too much moss killer you can kill the grass as well as my
wife proved earlier this year.


Another thought, and I don't know how well it would work, comes from
the idea that if you run a strip or wire of bare copper along the
ridge of your roof, the very slow bleed of copper as it corrodes
prevents moss from growing on the roof. Perhaps you could try painting
the patch on your wall with a dilute copper sulphate solution, or a
copper-based fungicide such as Bordeaux Mixture. The latter is
unlikely to leach away in a hurry, so may remain impregnated in the
lime mortar and be a permanent solution (but not a solution, IYSWIM!).

You used to be able to buy 25kg sacks of ferrous sulphate for less than
£10, but then the EC stepped in, and declared it a hazardous substance.
[Well, it certainly is, if you drop a 25kg sack on your foot, or give
yourself a hernia lifting it in and out of the car boot.] These days,
for the ordinary man-in-the-garden, it's only available in (say) 1kg
bags, and costs around £10.
--
Ian