Over the winter some green mildew has settled on the upper face of my footing blocks and I would prefer to clean this off before laying further courses up to dpc.

 

During my boating days I used a teak cleaning fluid that caused the winter green that settles on a wooden deck to lift and wash off. Can someone suggest a non marine equivalent cleaner?

Common household bleach would be my choice.  Unless someone comes and says it will rot the blocks.

Probably not worth bothering about, just run a brush over it and carry on.  If you really want to get rid of it then washing with a mild bleach solution as @ProDave suggests would be as good as anything.  I clean our sandstone patio with mild bleach once a year, works a treat and if hosed off with loads of water doesn't seem to cause any harm to the garden.  I don't actually use liquid bleach, but just a spoonful of calcium hypochlorite ("pool shock") in a  bucket of water

Wet & Forget, Patio Magic etc?

I would go for either a stiff brush or pressure washer. I don't know enough about chemicals to risk an adverse effect

1 minute ago, Onoff said:

Wet & Forget, Patio Magic etc?

 

Are they cheaper than hypochlorite though? 

 

I bought a 5kg drum of hypochlorite about 4 years ago.  I still have about 4.9kg of the stuff left.  I reckon there will still be some left when I shuffle off this mortal coil, at the rate it gets used for cleaning the patio and paths.  5kg of calcium hypochlorite granules will make approximately 166 litres of normal household concentration bleach.  Last time I bought some I paid around £20 for a 5kg drum from a  local swimming pool supply company.  That works out at about £0.12/litre of concentrated bleach solution, so it's a pretty cheap way to clean stuff.

13 minutes ago, JSHarris said:

Last time I bought some I paid around £20 for a 5kg drum from a  local swimming pool supply company.  That works out at about £0.12/litre of concentrated bleach solution, so it's a pretty cheap way to clean stuff.

 

 

I have a vague recollection from O level chemistry that if the compounds are mixed in the wrong order the whole concoction will explode due to some exothermic race condition?

39 minutes ago, JSHarris said:

Probably not worth bothering about, just run a brush over it and carry on.

 

 

Just another irrational neurosis of the first time self builder. If I do not remove the mildew I will spend the next 20 years imagining there is a natural fissure point in my walls because the mildew reduced the mortar adhesion at that course.  

I read somewhere that the residue from soda blasting is sold to the railway companies in the US and spread to keep track side weeds down. Over here in the UK nobody wants to buy the "waste" it seems.

 

I tried back in the Summer the washing soda residue from my electrolysis rust removal tank on our patio, not sure if it did anything tbh. 

14 minutes ago, epsilonGreedy said:

 

I have a vague recollection from O level chemistry that if the compounds are mixed in the wrong order the whole concoction will explode due to some exothermic race condition?

 

 

No, it's fine, the only slight risk is the same as that from handling bleach.  Just chuck a couple of table spoons of calcium hypochlorite into a bucket of water, stir well, then brush it over the blocks.  If you want to mix up a litre of concentrated bleach, then chuck about 4 or 5 tablespoonfuls of the stuff into a litre bottle and shake it very well to get it too dissolve and you will end up with a solution that's pretty much the same as unthickened household bleach.

"jeyes fluid" is what i used for cleaning paths before i got  power washer .

but if you have a power washer that's easiest way 

just been doing that today on my block paving 

its a yearly job as everything goes green , black or red with the air being so clean here,

I can get 20 years patina in one year on things

The only thing I hate about Jeye's Fluid is the nasty persistent smell of the cresol and phenol in the stuff.  I used to use a power washer to clean the paths here too, but it's really slow when compared to brushing some bleach over it and just hosing it off.  The other snag with using the pressure washer on sandstone is that I've found it tends to damage the surface of the sandstone paving, although it's fine on the drive pavers.

 

 

44 minutes ago, JSHarris said:

hypochlorite

 

Would a highly concentrated solution of this work as a weedkiller on gravel? 

3 minutes ago, newhome said:

 

 

 

Would a highly concentrated solution of this work as a weedkiller on gravel? 

 

Possibly, but it wouldn't be as effective as toxins that specifically target plants, plus it would pose a risk to beneficial organisms in the underlying soil. Unfortunately, persistent weedkillers have all been found to be too harmful to the environment, and I'm not aware of any that can legally be used now.

37 minutes ago, epsilonGreedy said:

Just another irrational neurosis of the first time self builder.

You're not alone. At the end of last winter I bought algae remover and used on a large section of wall that was unpointed flint blocks, largely shaded over winter and looking green.  The algae remover (from TP I think ??) wasn't sufficiently expensive for me to engage with home-brew ideas, and it worked well enough.

Aldi patio cleaner concentrate:

 

https://www.aldi.co.uk/doff-path%2C-patio-%26-decking-cleaner-/p/069689272573901

Edited March 4, 20197 yr by Onoff