How to get rid of mold on limestone?

Hi folks,

I've got a lot of mold on my limestone driveway and reconstituted limestone retaining walls, anyone know of a solution that kills the mold?

A high pressure sprayer works on the driveway to a point but doesn't do anything on the retaining walls.

The driveway has tiny black spots within the limestone and the retaining wall appears slightly dark and greenish, neither of these can be pressure washed off.

anyone got any solutions?

thanks
Dave
 
Buy a buttload of exit mould from woolies?

Also, are you sure it's mould and not some sort of moss? The black mossy stuff seeping through limestone retaining walls is kinda standard, isn't it?
 
One quarter teaspoon Oil of Cloves in a 500ml spray bottle of water. Shannon Lush recommends this. Bleaches only "bleache" the mould but Oil of Cloves kills the spores.
 
i have a limestone house, i have been told to try napisan by the company that sells limestone but didnt work for me
-pressure washing it at no more than 900psi
-wire brush
- rubbing another limestone block against it rubs off the weathered surface


im pretty sure its a mossy build up and then from the rain and weathering it goes black, dont think its mould
 
Bleach doesn't actually kill all the mold, it mostly just bleaches things to make them look whiter. Pressure hosing is even worse because it etches the surface making it more porous which subsequent mold will love.

Use these products which will actually kill the mold, moss & algae etc:

SPRAY AND WALK AWAY (quite cheap at bunnings $35 for 5L, mix with water 1:5)
or
WET AND FORGET (from memory same ingredient but much more expensive)

The active ingredient is Benzalkonium chloride.

Simple to apply. Mix with water in a spray pack, apply later in the day so sun doesn't dry it out too quickly and let it go to work without any further effort from you. Time and weather does the rest. Plus no destruction of the surface that occurs with pressure hosing.

Vinegar has proven to the be the next best product (diluted with water 50:50 from memory) to treat mold. However I would not use on surfaces such as limestone as the acid may attack the surface. But for tiles etc vinegar works well and actually kills the mold unlike bleach.
 
Hey folks,

I'm resurrecting this post. The reconstituted blocks now are almost luminous green.

I've tried WET and FORGET, waited for 4 weeks then pressure washed and it doesn't work on the limestone reconstituted blocks.

I've tried pure chlorine and left for 24 hours then pressure washed and it doesn't work either.

The reconstituted blocks actually look green, as if the green mold/moss/whatever it is has discoloured the blocks.

Anyone got any other ideas?
 
Have you tried all the ideas in the thread?

Oil of cloves, vinegar and Napisan were the other suggestions. I would be giving them a go - can't hurt to try.

Any photos?
 
I've tried WET and FORGET, waited for 4 weeks then pressure washed and it doesn't work on the limestone reconstituted blocks.

WET and FORGET is not supposed to be used like that. You spray it on and leave it alone. Each time it rains it gets reactivated. It takes longer than 4 weeks to work - more like 4 months in my experience. Now you've pressure washed it all off.:(
 
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