Can anyone help with a remedy for patches of algae and what looks like in places a black pinhead rash on my outside walls. Have tried a strong bleach which doesn't help much, someone has suggested using a pool algicide mixed with water but others have dismissed this idea. What I am looking for is an efficient and hopefully cheap remedy. Useful ideas will be appreciated.

Hi there, I am reliabily informed that bleach wont work. You need fungicida para fachadas.Make sure you are well covered when cleaning including mask.

You can use copper sulphate (sulfato de cobre) which you can buy at any agricultural store. Mix the crystals with water as for Bordeaux mixture.

Algae and black mould are 2 different things although they both grow in damp conditions. There are chemical treatments but take care as they are potent stuff.
I do know that with black mould the surface cleansing will not cure the underlying problem as it grows from within the wall and will eventually return if not sorted.

I am reliabily informed that bleach wont work but after you that do go olny spray of Chlorine 50/50 mix (water) and dont ware you sunday best , jean are 50/50 colour now adays , will also kill grass and plants ... becareful not get in to eyes and dont used sprayer again for plants ...

symbol Cl. Chlorine is a toxic , that irritates the respiratory system . the volume that mixed for pools would be less and is safe for the body if done right ....

First oof, if it's algae then you have a damp problem that needs addressing tooty sweety.

If the green is a form of lichen (an alga/fungus hybrid/symbiont) then that may simply be a feature of age if like me your house is way overdue for painting.

Personally if it is that, then rather than start splashing chems around, I'd scrape the wall well and paint with a tough exterior paint with an anti fungicide.

Bleach kills about everything if left on it long enough.

HI ALL,
Many thanks for the replies, the problem I have is actually on my boundary wall which is approx 400sq mtrs and I seem to have to paint it every year, have to admit I dont buy the dearest paint-looks like I will have to be less of a scrooge

Know what you mean. It's all very well saying 'Cheap is twice dear', which it is, but the problems start when you HAVE to do the job, but there isn't the money for the best materials.

I tried many things before I discovered that the domestic oven degreaser / cleaner sold by Mercadona works very well. It is in a pink spray bottle. Spray on a little and it foams up, after a few hours wash down with a hose and the black mould is gone.

It works wonders or at least it does for me.

If it is degreaser then chances are that it contains caustic soda ( sodium Hydroxide) . Never heard of this for getting rid of mould . Always wear gloves and avoid skin contact. It will wash away with plenty of water, and if it gets on your skin it will feel slimey. Just wash off with water and then rub on a little lemon juice.
Pete

Bit radical.....

I have not even checked the ingredients but I would suggest it can't be that deadly when it is sold as a domestic cleaner, but obviously care is required when using any chemical. Use at your own risk All I can tell you is that it works for me and my hair has not fallen out and I don't suffer from radiation sickness .... yet .

I never said that it was deadly.
It is quite safe ..... used properly!
It is also used for drain cleaners, oven cleaner, Oh and for making soap!
Pete

Basically it turns the algae into soap.

Yes if you mix it with olive oil!
Use palm oil and olive oil and you ger Palmolive soap!!!!!!!!!!