Discoloured sandstone paving

[rajan2004]

Hi all,

We have had some light grey Indian Sandstone paving installed in our front garden.

The paving has now been in for a couple of months but within a couple of weeks of it being put in, yellow marks started appearing on it. Some marking was darker, others lighter. There is clearly something wrong - luckily we have withheld a sum of money from the contractors until it is all fixed.

Basically, none of the slabs were sealed and the manufacturers of the stone think that the cement & Mortar mix has leaked through. They did suggest trying to use Rustex to clean it up but I have a feeling that won't work.

There are also a couple of slabs which have an orange 'gravel' type mark on them. I'm not sure what these marks are but the contractors say this is just the natural colouring.

I'm not sure how to attach photos of the damage to this post but if anyone can help then I could email them to you. I'm hoping there might be a way of cleaning the slabs up. The only other option is to replace all the affected slabs but we're talking about half of the path!

Thanks
Rajan

[DempseyLiverpool]

Suppliers push blame on contractor saying mortar staining then recommend rustex

Sounds like natural markings from iron oxides found naturally in the stone. Not all natural stone needs sealing and it doesn't sound like cement staining.

If the paving is well laid on a full mortar bed with no rockers and pointing is solid I can't see why you have withheld money ? Why hadn't the contractors been paid on completion if all was ok ?

[rajan2004]

[quote]

The problem is that all isn't ok - the staining is actually very very bad. I wish I could post a picture of it to show you how bad it actually is. It definitely doesn't seem natural...

[mickg]

send me or any of the moderators a photo and I will post it for you, lets have a look before jumping to any conclusions

my email is mick@crystalclearideas.co.uk

[DempseyLiverpool]

As Mick says would need to see some images. I only mention payment as you say these markings appeared a couple of weeks after completion. Was there any other issues with the work ?

[rajan2004]

Hi Mick,

I've just sent you some photos via email - it would be great if you could post them so I could canvas some opinion.

Dempsey, the marks actually started appearing during a 2 week gap in the work. The path was laid down, then there was a short gap, before some brick edging was laid down next to the path. The path was then cleaned (I think with some type of acid) and the marks have been there ever since.

I'm not sure when the gravel type marks started to appear - I think they were there from day one but seem to have got worse as time has gone by.

[mickg]

photos sent by Rajan

[DempseyLiverpool]

Acid and most imported sandstone/limestone don't mix !!

Personally I don't use acid to clean any paving. If there is a fix then Roger from R AND A Pressure Washing is your man. But i doubt there is.

[lutonlagerlout]

hard to say from the pics but could just be natural variation
who bought the stone and what is it specifically?
LLL

[RAPressureWashing]

This is about the 5th or 6th paving this year that has had this all Kandla Grey, there really isn't a fix for this, one I did work on I was able to remove the staining where an acid was used to clean them by the laying company so they looked like acid burns, I got the surface totally free of the staining, then after the first rainfall around 2 weeks later they came back, there was also an area that had not be cleaned in any way at all and the staining started to appear on these as well, paving hadn't been pointed either, just seems there is a lot of iron content that comes to the surface really quickly after laying? & something triggers it to show, I do know that on a couple of the pavings I looked at, they had been bought off the internet, so not seen before delivery etc, so really cheap imports ? maybe I don't know.

[rajan2004]

Hi Roger,

Yes this paving had been bought from an internet company who actually have very good reviews and have been very helpful with our enquiries.

Two questions - if the remaining slabs haven't developed any staining in the 3 months since being laid, do you think they will be ok or is there a likelihood they could stain in the future too?

Also, the paving company suggested trying to use Rustex to clean the affected areas - what do you think?

[RAPressureWashing]

Hi Roger,

Yes this paving had been bought from an internet company who actually have very good reviews and have been very helpful with our enquiries.

Two questions - if the remaining slabs haven't developed any staining in the 3 months since being laid, do you think they will be ok or is there a likelihood they could stain in the future too?

Also, the paving company suggested trying to use Rustex to clean the affected areas - what do you think?

To answer your first question, again this is what I have seen before some pavers stained & some not so very random, will the rest stain over time? difficult to say as if it is natural iron staining it could or can appear at anytime.

Question 2
I Don't think the Rustex is going to remove this permanently, as it isn't rust as such but possibly the natural content of the stone. The Rustex might remove the surface appearance of staining for a while but I feel it will come back as it's in the stone and not a man made stain.

[rajan2004]

Hi everyone,

Just an update on this issue. I used Oxalic Acid last week and the yellow staining has almost disappeared. I reckon if I apply it a couple more times, the stains will completely go away.

One question I had is that the path generally tends to stain quite easily. If it's raining for example, you can clearly see footprints etc on the path. Would having the whole path jet washed and sealed solve this problem?

I am planning to eliminate all the hardened yellow stains with the Oxalic Acid and then to perhaps wait until the weather picks up next year to get the whole path jet washed and sealed - what do you think?

[RAPressureWashing]

Oxalic will remove the surface stain for a while IMO, but you need to be careful using it to much as it is a bleaching agent/chemical so I'd be very careful using this endlessly, what strength are you using it at?
If I was you, I'd leave the paving to where you have got it for now, then see if the staining has stayed away after the winter.

[rajan2004]

I'm using 3 teaspoons to 100ml so I guess around 18g to 100ml. Is that strong enough do you think? It has made a huge difference - does its effectiveness prove that rusting had taken place?