Joints going/gone green - Sandstone paving with mortar joint

[jimbob88]

Hi I layed a sandstone patio in my garden on top of a concrete base. The mortar joints have gone green. If I have to rake out what is best to rejoint with and prevent them from going green??

[lutonlagerlout]

try sodium hypochlorite
roger has a mix on a cleaning page where you mix the above "swimming pool bleach" with water and baby shampoo

apply leave 20 minutes then hose off

be aware you need to wear PPE for this and it may bleach grass
no good for round ponds etc
cheers LLL

[Andy Meechan]

I'd be tempted to try cleaning it with a pressure washer first before you try to remove the pointing. I've seen green pointing in a few of the gardens I look after and I reckon it's usually caused by patios that don't drain well and water hangs around in the pointing.
To my knowledge water runs off the slabs and into the pointing (lower than slabs) and then zig-zags through the patio and leaves the patio at the lowest point. Your patio is possibly laid without enough of a fall.

Hope this helps.

PS - if you do try pressure washing it don't hold the lance too close or you'll maybe wreck the pointing.

[RAPressureWashing]

Can you post a photo of the "green" pointing?
From this I should be able to advise.

[Azpects]

The reason the pointing will have gone green is almost always down to Algae which thrives in moist conditions

As said, if the patio is not draining properly it will only encourage algal growth further

We offer two solutions at Azpects, Algae Remover and Black Spot Remover (Black Spot Remover would be over the top if this is merely Algae but will kill the most stubborn infestations)

http://www.azpects.co.uk/products/easy-algae-remover.aspx
http://www.azpects.co.uk/products/easy-black-spot-remover.aspx