Algae forming on 6 month old Indian Stone with Rompox Easy

[twixx]

First of all, forgive my ignorance when it comes to terminology, I'm out of my depth

Basically, we had Indian Sandstone installed back in March. We used Marshalls Indian Sandstone - Grey - 22mm Calibrated, from Travis Perkins.

It was laid on to mortar on top of a limestone sub-base. We used Rompox Easy in basalt for the joints.

Sure enough, as soon as the weather has turned, we've seen a rapid onset of algae both in the joints and on some of the slabs.

Why might this be?
Will it clean up?
Can this be prevented?

Some of the stones appear to have formed a halo type thing in the middle, which I find strange. Is this simply where the mortar IS not?

 

[r896neo]

Yes the halo effect is because they are spot bedded. It's a classic case unfortunately for you. The dark spots don't dry out as the mortar stays damp. The light spots dry out fast as there is a void underneath.

The rompox is green because it stays constantly damp as it's a porous product laid on a non porous mortar base. it's not a great product.

Cleaning is easy, best thing is hypochlorite bleach and water mixed about 4 parts water to one part bleach. Put it on with a watering can and Rose and give it a light brush. After 20 mins hose it off. The run off will damage plants so only use this method if there is a way to keep it out of flower beds and lawns.

Your pointing will deteriorate prematurely because of the spot bedding but you can cross that bridge when you come to it.

 

[twixx]

Thank you for your response.

Is there a "fix" to the spot bedding (I appreciate it wont be easy/pleasant).

What would be a good replacement for Rompox?

Would cleaning and then sealing be beneficial?

 

[r896neo]

To be honest lifting and relaying on a full bed is the only definite fix. You can try grinding out the pointing and pouring a mortar slurry into the open joints but its penetration will be patchy at best.

Sealing will help keep it cleaner but most paving needs a couple of treatments per year. I have the same paving at home and haven't sealed it.

I would leave the pointing until it starts to crumble out and then decide if you want to relate or try just repointing.

 

[twixx]

Disappointing considering it's only been down 6 months, but hey ho. Hopefully it scrubs up in the spring.

Say we did decide to relay on a full bed, wouldn't the algae on the Rompox still remain and return, what with it being porous and the bed not? Or are you suggesting relaying without the Rompox and using another non-porous jointing compound?

 

[r896neo]

Yes use another jointing compound or even sand and cement.

The alternative is to drop the bedding mix strength way leaner to make it more porous. Something like 8:1.