Algae forming on 6 month old Indian Stone with Rompox Easy

Vini123

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?

magn8p

@Vini123 - We have Indian sandstone as well in our patio but the beige version. It was installed by the previous owners and when we moved in, it needed some cleaning.

I used Wet&Forget Mould and Algae remover (http://amzn.to/2jtHDXz) so this helped me get rid off even the most tough mould especially from the joints.

Try this and you wouldn't be disappointed!

The halos in your case suggest that perhaps you had standing water for too long which in turn suggests that the handyman who laid the patio didn't add sufficient gradient for the rain water to naturally drain away - I may be wrong on this but I am sure you will get to hear a lot of other views as well.

All the best.

Vini123 wrote: »

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?

Furts

Two thoughts come to mind. Water is hanging on the slabs and the algae is the result. But the circular dabs are fascinating. Many slab layers put down a mortar dab and bed the slab onto that. Not good, but it happens. It looks like the clean spots mirror the dabs underneath. Why? I do not know. Logically water is trapped underneath yet you say you have a limestone sub base.

But Travis are reputable, as are Marshalls, and I am a fan of both. If you raise a polite concern with Travis I am reasonably confident a Marshall Rep would take a look at your issues. A fly in the ointment could be if you did not use a Marshalls Approved Contractor, but give it a try and see where you can get.

EachPenny

Furts wrote: »

Two thoughts come to mind. Water is hanging on the slabs and the algae is the result. But the circular dabs are fascinating. Many slab layers put down a mortar dab and bed the slab onto that. Not good, but it happens. It looks like the clean spots mirror the dabs underneath. Why? I do not know. Logically water is trapped underneath yet you say you have a limestone sub base.

At a stretch I'd speculate that where the slabs are bedded there is better thermal conduction of heat from the ground keeping the slab surface slightly warmer in those areas than the surface areas above voids.

That marginal difference in temperature might be enough to make the difference between the formation of dew or not. If the area above the voids has dew forming more frequently/heavily then those areas will be damper for longer and more likely to develop algae growth.

I've seen a similar thing with plastic coated steel roof sheeting (without any insulation) fitted to purlins. As the temperature drops below dew point you can see dew starting to develop in pattens following the layout of the purlins. That is a good indicator that it is time to stop walking around on the roof and get down the ladder asap before you go slipping and sliding over the edge of the roof. Been there, nearly did that

Vini123

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

Apparently its common, and caused by spot fixing/dot dabbing. http://www.pavingexpert.com/stain_reflective_01.htm

Apparently Indian Sandstone is better laid on a full bed of mortar. You live & learn!

Furts

Vini123 wrote: »

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

Apparently its common, and caused by spot fixing/dot dabbing. http://www.pavingexpert.com/stain_reflective_01.htm

Apparently Indian Sandstone is better laid on a full bed of mortar. You live & learn!

All slabs and all paviors should be fully bedded, just like bricks and blocks when building a wall. It is not rocket science but corners get cut. You could try going back to the installer and complaining, something might get done about matters.