Plant growth onthe external walls of buildings has often been encouraged especially on older building frequently wetwalls on more Northern aspects will be more prone to growth of moss.
Wile lichens will often grow really well in more southern aspects.
in a few cases the growth may have been encouraged for its ascetics Plant growth can be quite luxuriant especially were the owners of the property have applied fertilize.
When such growth become a problem they should be removed with a the blade of a old knife,spatula,or a stiff fiber brush never steel Wire .
the walling now being clear of all live growth may be spayed with a dilute fungicide.
a green house sprayer will suffice for this and will Not generate much pressure and will not damage the brickwork or excessive over-spay.
A flood coat should be applied to the surface to be Treated commencing at the top of a vertical surface and moving slowlyacross horizontally allowing the run down about six inch.
The next coat to be applied to the previous run down .
the treated area to be left for several days then given a second brushing to remove The dead vegetation this is far more affective now the organism is dead Some types of toxic washes such as copper,carbonate,ammonia solutions are relay good but may stain some brick or stonetry a small Sample piece first and allow it to dry ,always take care when using chemicals follow the instructions to the letter and take extra care not to Breath in any over-spay You may have been advised to use a week solution of hydrochloric acid or muratic acid to remove relay obstinate stains,but The indiscriminate use of such powerful chemicals is ill advised and far better to rely on the tryed and tested methods described .
The same process applies to patios and concrete driveways making sure not to let the over-spay affect gardens and boarders .
last but Not least wash out all spraying equipment and store your poisons in a securely locked cabinet.