Moss and Algae Staining in Sandstone Paving

[mwjburton]

Last year we laid Buff Green Sandstone in our garden. I've been jetting it every few months to keep the surface dirt and moss off, but the stones have become stained despite this.

Its likely they were not sealed properly or we should have used some sort of algae deterrent. Either way, we'd very much like to clean them up and bring back their original colour and look as much as possible.

A local garden design company has advised that we try using Grundreiniger by Weiss to start with to try and remove the ingrained staining.

Then we could look at using something like Wet and Forget to try and help the surface stay moss and mould free for longer.

Has anyone dealt with a similar situation and can provide feedback on products worth using.

Many Thanks
Mark

Current Condition:

 

[r896neo]

Sawn sandstone is very prone to algae build up and really is best being sealed to make maintaining it easier.

Hypochlorite mixture is the best thing to lift heavy staining like that.

There are very good instructions on the paving expert website.

See here

http://www.pavingexpert.com/maintain_02.htm

 

[mwjburton]

Many thanks for the link. Once the weather settles down a bit (who knows when that will be!) we'll have a go at this on a small patch first and see how we get on.

Thanks
Mark

 

[geraldthehamster]

Last year we laid Buff Green Sandstone in our garden. I've been jetting it every few months to keep the surface dirt and moss off, but the stones have become stained despite this.

Have you been using a pressure washer? Tried it with the nozzle a couple of inches from the surface?

Cheers
Richard

 

[mwjburton]

Yes, we have a Karcher pressure washer, but it won't shift this.

 

[geraldthehamster]

Yes, we have a Karcher pressure washer, but it won't shift this.

OK. Don't know then. You could try brick acid (patio cleaner) but it has a habit of reacting with the oxide in sandstone paving and turning it bright red. I used it on mine to remove cement residue after it was laid - it had returned to its original colour within a couple of years! Probaby not very helpful, sorry.

Cheers
Richard

 

[mwjburton]

I've been talking to our stone supplier who have very good experience in addressing these issues and maintaining the stone and have been incredibly helpful in helping me with this. Below is the plan we've come up with. Its a lot of work and can really only be done once the weather improves somewhat, but my hope is that I can bring them back and then with the right care keep the stains away with proper management in future.


1 - CLEAN WITH BIOX
Use BIOX to remove biological stains caused by plants, algae or mould.
This is due to the fact the mould etc will be the top layer.

2 - RINSE WITH WATER
A mild soapy (fairy liquid + water) water scrub wouldn't hurt either with a rinse off afterwards.

3 - REMOVE OLD SEALER
After a week or 2 once all mould has gone, use Resiclean to remove old sealant.

3 - CLEAN WITH GRUNDREINIGER
To PH neutralise the surface again.

4 - SEAL WITH STAINPROTECT PROFI
Once fully cleaned & dry, finally seal the stones with StainProtect Profi.


I realise people are having good results with some types of bleach and that some of these products are expensive, but I feel this is a solid set of steps and makes sense to me in terms of the process. Have to see how it goes.

 

[r896neo]

Who supplied the stone out of interest?

I assume it was sealed before then using a solvent based sealer? I'm surprised its quite so bad if it was sealed, out of interest What was the sealer?

If an old sealant needs removed i would consider getting someone to do this for you the chemicals involved are no joke and if you don't do it correctly you will have a patchy surface which could give you mega problems when you come to re-seal.

Sealing of course is not worth considering til late spring at the earliest when you have a chance of dry weather for an extended period.

I would also forget the mega bucks for the biox and use hypochlorite instead its as, if not more, effective and seriously cheaper.

Pressure washers are not as effective as chemicals for cleaning porous paving like yours because they do not kill the moss and algae spores they just blast most of the visible stuff away. You will find that once cleaned properly with hypochlorite or biox it will stay cleaner for much longer.

 

[mwjburton]

Thanks for that. We don't have a very large area to cover, only about 30sqm, so won't need too much BIOX. Which hypochlorite product would you recommend though?

We're considering using a local landscaper to do the work, but I'm keen that they do a very thorough job, so I may end up buying the right kit and protection and making sure I fully understand the risks before doing it myself. Plus it will likely have to be spread over many days which is going to make it very costly with a contractor.

*edit - I see that you meant just have someone experienced do the final seal - good point, we should have someone do this.*

The sealer that was originally used was (I'm fairly sure) a cheap B&Q type product - we are no longer in contact with our original landscaper so don't know the exact product.

CED supplied the stone and have been great in offering advise and guidance for the fix up. They just delivered the stone though, it was our original landscaper who laid and sealed the stone.

 

[r896neo]

That's good news about the sealer, it was most likely a waterbased product like thompsons water seal which is pretty useless but much easier to get off than an impregnator.

Sealing is not the difficult bit its stripping the old sealant off. as if you don't get it right it could cause problems when it comes to re-sealing.

I'm not surprised at CED (who i think are rip off merchants) recommending the steintec stuff as its good but expensive.

If you wanted to contact someone you could do a lot worse than roger oakley from R&A pressure washing services. He at the very least could give you more detailed advice than me. You can google them.

Hypochlorite only comes in one form really and is about 20quid for 5 gallons. You would dilute it about 3:1 water:hypo then pour it on and let it sit for 10 mins. Then brush it a bit and leave for another 10 mins before washing it off. You need to direct run off away from plants or lawn.

There is a comprehensive guide on the paving expert website i linked to above.

Once its all done and dusted cleaned and re-sealed you should keep on top of it with something like 'patio magic' 3 times a year should keep it clean and clear and you just pour it on and leave it no need for brushing etc

 

[mwjburton]

Thanks so much for all your help and advice, it really is appreciated. I'll certainly look up Rogers details.

 

[mwjburton]

A month ago I tried the Wet and Forget on the patio and thought I'd update this thread as I have to say I'm pretty impressed.

The patio had been thoroughly jet cleaned, but was heavily stained with green algae etc. On 18th Jan, this is what it looked like:

I sprayed it with Wet and Forget (5-1 water mix). After 1 week it looked like this:

Today, after 1 month it looks like this:

The patches where there is still a bit of green are likely where the old sealer is still holding off the Wet and Forget.

Once the weather improves, I'll remove the sealer properly and give it a final clean before re-sealing using a proper sealer.

Anyway, for a quick and cheap solution, I though the Wet and Forget did a very decent job.