Efflorescence?! unsightly colouration on sandstone - Slabs laid two years ago

[Dean85]

Hi There,

We had a largish patio laid in 2016 using pure mint sawn honed sandstone. The advice from the seller was that the slabs should be sealed on all sides to prevent staining with Geofix (I understand this isn’t very popular!). Our builder said his was ridiculous as would stop the slabs from adhering to the mortar underneath so he didn’t do it. He used marshals weatherpoint 365 For pointing.

Cue day 3...and the patio was covered in efflorescence, I can only assume from the sand used underneath. We waited several weeks to seal - but had to seal as the patio was so pale and showed up any blemish. We didn’t use geofix as the efflorescence was still an issue (despite jet washing several times and using Salt Away). Eventually we sealed with Pavetuf as this apparently is a breathable sealant which allows for the passage of efflorescence. It wasn’t perfect but there was little I could do and we thought in time the efflorescence would disappear.

It’s now two years later and the patio has unsightly white marks still on several patches. It seems really stubborn and it’s a real shame as detracts from what would be a lovely patio.

NOW, I’m assuming it’s still efflorescence (it definitely was to begin with as you could see the crystals of salt on the surface) but those in the know might have some other theories (acid wash used by builder!?) or ideas to get rid. I have a few slabs left in the garage so wondering if we are stuck with it and therefore the only option is to have the effected slabs replaced.

I have some photos (excuse the dirt and algae that needs to be washed off after winter!) will try and get these uploaded. Any advice gratefully received. Cheers, Dean

https://photos.app.goo.gl/6cd1yoo9LB16IXRu1

[lutonlagerlout]

firstly the patio looks pretty good Dean!

the blotchiness looks like a sealant fail
if in any doubt do NOT seal
Mint is a very soft sandstone and high maintenance, I avoid it like the plague
people still have it but they are warned
Roger might have some advice on sealants and should be along in a while
cheers LLL

[Dean85]

Thanks LLL...and thanks for the compliment, but yes- I wish someone had warned us re the maintainance!

I’ve looked at the page on sealant failure and it does indeed seem that that is a likely cause so thanks so much for pointing us in the right direction...unfortunately I see it’s a hard issue to rectify.

Any advice from anyone on getting rid of the sealant would be much appreciated (sand blast/chemicals?) - I have a company who specialise in cleaning and sealing patios who are willing to do the work. I just want to be sure that they have all the information they require before we start.

Cheers, Dean

[RAPressureWashing]

Dean
Only just seen this, you'll need a combination of items to remove the sealer, doe the company you are going to use have a steam cleaning machine as in either a Doff or Torik? a low speed rotary is also a possibility ?
Let me know what they have and I can then start to point you in the right direction of chemicals etc. Don't sand-blast it and no acids for the time being.

[Dean85]

Hi Roger- thanks for your reply. Have spoken to our guy and he does have an industrial Steam cleaner. Best wishes, Dean

[RAPressureWashing]

To remove the sealer, then Lithofin Wax-Off & the steam cleaner, he'll need to have it set for 120 degree. Apply the Lithofin on a dry surface, allow to dwell 15-20 mins you might need to give it a scrub to break the sealer depending on the thickness etc, then slowly start to steam the old sealer off, you sometimes have to do a second clean if any sticky stubborn bits hold on too the surface.
The Wax-Off is the closest to Mira-Strip (solvent) which isn't available in the UK anymore, shame as it was my stripper of choice for years.

[Dean85]

This is great Roger- thanks for your advice. Good to hear all is not necessarily lost. Will pass on.

Best wishes, Dean

[RAPressureWashing]

Dean
The info I have given will remove the sealer, as far as the efflorescence goes, I'd be inclined to remove the sealer, then let the paving breath and properly dry out of the next few summer months, and see if it stops coming through, Also with the steam cleaner, what the guy needs is high heat but low pressure, if he knows how to use it, he'll be fine.

[Tony McC]

For the three hundred and ummpteenth time, I remind everyone: When the daffodils are out, so is the efflorescence.

Follow Roger's sound advice. Clean off thye existing problematic sealant, let the summer work on the eff, and then look to seal in late August or early September.