Mortar on indian sandstone slabs

[xtianaudio]

Hi all - First time post, coming here for a bit of advice.

 

I'm having my garden landscaped by a local company, and as part of that have had sandstone slabs laid.

There have been lots of delays due to weather and other bits, what was originally going to be done over a couple of weeks has taken a couple of months.

The owner of the company i'm using seems to be a nice bloke, but I've got some concerns with the slabs. Originally he had another company coming in to lay the slabs, but they cancelled last minute so he got someone else in. When laying the slabs I noticed a lot of the mortar going on the slabs.

 

I've been away on holiday and they did the pointing (looks to be with sand and cement), and more mortar has got on the slabs and not been cleaned off. This has obviously now dried very hard.

The guy is currently away on holiday, so I wanted to give the slabs a rinse off to get rid of the dust and see what they look like, and when wet the scale of the mortar staining really becomes apparent. When dry it looks grey and hazy around the edge, not great but less visible. When wet it really is obvious.

 

I tried the pressure washer, doesn't make any difference at all.

 

I have some brick acid (Sika 10% stuff), so done a few test pieces from off cuts, and it did not damage the stone, so tried that. I'm aware that brick acid could cause staining hence the test and only trying it on 1 slab. First of all 50/50 which didn't seem to do much, then applied neat with a paintbrush onto a damp slab. The mortar fizzed, I left it for 20 mins (kept checking and didn't let it dry) and then used a very stiff nylon brush. Made a small difference after about 5 minutes of scrubbing. To get the slab cleaned up with this method would probably take me 4 or 5 repetitions and quite a lot of time.

 

Personally I can't see a way of getting this up with any sort of ease, but I'm *hoping* there is a way of doing it. I'm not going to bring it up to the guy whilst he is on holiday but hoping you can push me in the right direction of how I should approach it when he's back to finish up. Am I worrying about nothing, is this standard procedure and they will get it cleaned off no bother? Or is it a serious issue and I need to bring it up as early as possible?

 

I've attached a few pictures of both wet (after pressure washing) and as they were drying out.

[Alan Ambrose]

Worth trying a mechanical method imo. Stainless or brass brush (not steel) by hand to begin with - may need some experimentation to find the right method. Do wear eye protection.

 

You could just wait until the contractor gets back and ask them then. It won’t get worse over a few weeks.

Edited July 3 by Alan Ambrose

[LA3222]

In all honesty, it looks a right mess IMHO. I would suggest the slabs will have to be replaced, I can't see how those Mortar stains are going to come off sandstone - not what you want to hear I expect and I may well be wrong. Hopefully some with more experience of sandstone slabs will be along to give their thoughts.

[twice round the block]

This Indian sandstone in the photo has been down a few years that was repointed using easy joint on Sunday.

 

Who ever laid your slabs hasn't got a clue.

They never should have been jointed with a strong cement mix as they have been, which looks like it was applied wet, via a watering can and has ruined lot's of the slabs, as sandstone is porous.

 

Two options to joint up sandstone are: Easy joint

or

A mix of 1 cement and 2 sharp sand is brushed into the joints as a dry mix and pushed down using a jointing iron or a length of blue water pipe depending on the size of the joints.

 

The patio can then be sprayed with a fine mist nozzle or if rain is forecast in the near future. Let nature take it course, and that will set mix.

 

Can't expand your photo, but have they constructed a step from cut slabs?

[xtianaudio]

28 minutes ago, twice round the block said:

This Indian sandstone in the photo has been down a few years that was repointed using easy joint on Sunday.

 

Who ever laid your slabs hasn't got a clue.

They never should have been jointed with a strong cement mix as they have been, which looks like it was applied wet, via a watering can and has ruined lot's of the slabs, as sandstone is porous.

 

Two options to joint up sandstone are: Easy joint

or

A mix of 1 cement and 2 sharp sand is brushed into the joints as a dry mix and pushed down using a jointing iron or a length of blue water pipe depending on the size of the joints.

 

The patio can then be sprayed with a fine mist nozzle or if rain is forecast in the near future. Let nature take it course, and that will set mix.

 

Can't expand your photo, but have they constructed a step from cut slabs?

They have laid slabs over the existing concrete steps at the back of that’s what you’re referring to? I did say I want all of the existing hard standings replaced with sandstone. Should they not have done this?

 

I was actually reasonably happy with the slab work. It was square, evenly laid without any bad transitions. Replaced a manhole cover with inset and followed the grout lines etc. so looked like the slab layer had some idea of what they were doing. Do you see problems with the slab laying itself?

 

The pointing however… I could’ve done a better job myself with 10 minutes on Google.

 

Do you think there’s any chance of them fixing it, or should I be going straight in with it needs all new slabs and relaying by a third party that we both agree on? They will of course want to do the most efficient (aka cheapest and quickest) way of fixing it but I can’t even see how they’d manage it.

 

They’re back tomorrow to clear the left over building materials and prep the soil areas for top soil and turf. I just want to ensure my expectations are clearly communicated and hopefully get on the road to recovery.

 

They are a local firm, been going for years, lots of good reviews and no bad ones. So hopefully their reputation will ensure they commit to getting it sorted.

[Moonshine]

They look bad, i would have used easy joint as above, and its what was used on our porcelen tiles.

 

How about a small sample area, with brick accid and an angle grinder with a wire brush to remove the mortar.

 

May damage the tile under neath but could weather in.

[Gone West]

58 minutes ago, twice round the block said:

Two options to joint up sandstone are:

I think there are three. We used a Roughneck Mortar Gun successfully and cleanly on our sandstone slabs.

[xtianaudio]

I thought I should follow up with this as so many posts are left with no resolution! Long story short I owed them a few quid for a raised bed/sleepers they did for me. Agreed to not pay that and I sorted the slabs myself (yes, a big risk on my part but I just wanted them gone!).

 

I used (actually got through x2!) crimped wire cup angle grinder attachments (check your angle grinder RPM), and a load of very strong brick acid. Ensure you use appropriate  PPE (I didn’t, I know a should have). Body totally covered, eye protection and quality mask.

 

Got all of the cement off with a few hours of relative heavy work (bent over with a grinder and loads of brick acid).

 

Expected it to badly rust. It did. Give it a good long cooling off period - preferably 2 weeks of mixed weather. That makes all of that rusting appear.

 

Next step was 2 large bottles of LTP rust remover in a few steps.

 

1. Paint or spray on rust remover. Leave to settle and do its thing.

2. Before it dries, spray off with pressure washer, then wash slabs with a paving cleaner (NOT acid based).

3. Leave another week and same again. Most rust deposits should be gone within 2 treatments. Clean again as above.

 

FYI the trust remover bloody stinks like rotten garlic. But it works.

 

After that let it fully dry out - the slabs are likely to look a bit tired from all the acid.

 

Assuming your slabs are good few months old (I’d suggest open to elements for at least 4 months), give them a good clean then a seal.

 

I used Lithofin stain stop plus. Google paving expert sealant trials for a great test. I found that to be the best balance between mild colour enhance, sealant properties and price. 1 large tub and I have some left overs for a top up coat next summer.

 

Yes it was a lot of work, but I was in the (somewhat) fortunate position of the slab laying being OK, and the cement staining being the main problem. If there were major issues with the slab laying I wouldn’t have bothered and gone for the nuclear option.

 

Pics attached. No doubt if we have a serious few freezes this winter or next, the pointing will need redoing. But overall I’m happy with the result I achieved and it might give those with a particular interest in DIY and elbow grease and option for fixing theirs:

 

 

[twice round the block]

Looks better now.

Re-grout next year and it will be as good as new.

I use Algon patio cleaner every spring and it restores the natural sandstone colours.

[xtianaudio]

1 hour ago, twice round the block said:

Looks better now.

Re-grout next year and it will be as good as new.

I use Algon patio cleaner every spring and it restores the natural sandstone colours.

 Exactly my plan! I couldn’t face trying to grout it again after the work of getting cleaned up 😅. Thanks for the advice - looking forward to picking a nice colour rather than my cement patchwork, depending on how much sharp sand or builders sand the labourer put in the mix 😂