Replacing old mortar around indian sandstone - What is the right technique & mix?

[ricardo596]

I have a large terrace laid with untreated Indian sandstone flags. They were laid, 10+ years ago on sand or, it transpires, on a sort of rough concrete mix, which hasn’t set. Both allow the flags to be lifted which, for the most part, I have tried to avoid. Over time the concrete pointing between the flags has disintegrated. In some areas it was applied more thickly and this is generally sound. Elsewhere it was thin and poor quality so has come away.

I have begun to remove the old mortar and to fill in the gaps between the flags with a 4:1 mix of white cement and sand using a trowel. My mix errs on the dryish side as it’s easier to manage. As the flags are mostly bevelled inwards from the top I use a spatula to press the mix well into the gap to ensure the void is properly filled. Being no expert, my early attempts left a thin layer of ‘muck’ on the rim of the flags leaving an unsightly ‘beard’. Over time I have reduced this to a ‘moustache’ (!) either side of the joint, but even so it doesn’t look great. Even with a dryish mix it is virtually impossible to avoid it getting onto the edges of the gap and 'staining' the stone. I am approaching the area with most pedestrian traffic so want to get the best finish possible.

My questions are these:
• What is the best way of getting rid of the beard/moustache? Brushing only makes a small difference. Might I have to use a chemical?
• Am I using the right mix/technique? I worry that slurry or poured mortar will stain the sandstone. The gun system appears better, but with which mix?
• Lastly, my current mix is quite yellow. The present grout is much greyer. At this juncture I might want to stick with what I have done so far, but I’d be interested in alternatives.

Any advice would be most welcome - thank you.

[London Stone Paving]

If you are using a dry mix then it shouldn't really be staining the edges of the slabs, so I am confused to the actual type of mix you are using.

A dry mix is not recommended for pointing. The pointing will need to withstand a lot of pressure and a dry mix just aint got the guts for it

Whenever you are pointing it always pays to keep a bucket of clean water and a sponge close to hand. You can then wipe off any mortar spills immediately. This is the best solution to avoid staining the slabs. Answering your questions specifically:

1. It depends on the level of staining. You may need to use a chemical but I wouldn't like to advise anything until I have seen the affected area. Can you post a picture on the site? If not email me the picture and I will post it for you

2. There are loads of different methods for pointing. Some use a wet mix, some people swear by a tacky mix (that holds together if you compress into a ball. Either way it shouldn't cause you any issue with staining as long as you keep a bucket of water and sponge to hand. If I was pushed I would go for the tacky mix as you will find it more forgiving than a wet mix, however you need to strike it hard to get the mortar compressed properly

3. in my experience mortar dyes are very temperamental and never give the desired look. You could go down the route of a Larsen or easy point (these are coloured mortar mixes, google them there will be loads of info on the www). Otherwise try and get the desired look with a few trial mixes. Worth going to the merchants to see what colour sand they have got. Anything that's extremely red or yellow would be a no go.

Steve

[ricardo596]

Steve

Thank you. I've sent an e-mail with the photos to your londonstone address as I can't see how to attach them to this!

Regards

Richard

[London Stone Paving]

Got it. Will upload them v shortly.
Btw, it was definitely not a dry mix

[London Stone Paving]

Here are the pictures:

[London Stone Paving]

As I said, definitely not a dry mix. It looks like its been installed by a seal :;):

On the plus side the fact that you have used the wet mix means that you will have a strong joint.

What you should have done was to use a trowel to scrape off the bulk of the excess mortar and then used a sponge to give it a final clean down. If you follow that process going forward you wont go far wrong.

A far as removing the excess mortar you are going to have to use some kind of chemical. I know you said the stone is Indian Sandstone but do you know what type it is?

Steve

[Tony McC]

It's always hard to teach DIYErs how to undertake mortar pointing. It's something which takes time and practice to get right, but they rarely have enough time to learn - they are often just getting the hang of it by the time the job is completed - and there's not usually enough of an area to get sufficient practice.

The key is to *carefully* feed in the mortar using a small trowel to push the mortar from a larger trowel or hawk held parallel to the joint itself. Try not to overfill, as execess can be messy to remove, and clean any stains or spills as soon as possible after striking (smoothing) the mortar.

Some people will use masking tape, a perishable oil, or even a pre-sealer, but these all add to the time and the costs. The most important thing is to have patience and take your time.

[lutonlagerlout]

hydrochloric acid time!

if you use HCI make sure and use full PPE and prewet the area to be cleaned with it
always have a large bucket of clean water to hand

LLL

[ricardo596]

Steve, thanks. Sorry, I don't. Multi-coloured and pretty but that's about it!

Tony. Likewise thanks. Yup - got that now! The latest efforts reflect more care but there is still room for improvement, hence the posting the question. When pressing down with the spatula to get the mix well into the gaps there is still some overspill, no matter how hard one tries. If Steve's advice about using sponge doesn't do the job then it may be a case of having to use tape on the sides.

LLL. Thanks too. I'll look into that, especially as you say, I'll need PPE.

Richard

[KAMIKAZEE DIY]

During my garden fun last summer I did a lot of pointing.

Getting the mix correct is crucial. 3/1 sand/cement and then it's fine tuning how much water - too much and it's easy to stain, not enough and apparently it'll be weak crumbly and won't stand test of time.

My AMATEUR advice is that if the slabs are soaking up moisture from pointing mix it's too wet and will stain. Apparently what happens is whèn the water evaporates it leaves the cement behind leaving the horrible stain marks.

Once you have right mix is half the battle, as you point there will be excess squeezers up from joint as you pack it to the max.
Flick excess to side with trowel, then strike with brick jointer. The excess crumbs you have flicked to side shouldn't be swept up till next day as by then they'll be dry and no stain potential.

DO NOT BRUSH FRESH CRUMBS ASIDE - ALL YOUR DOING IS BRUSHING CEMENT STAIN DEEPER AND WORSE INTO SLAB!!

Hope this helps.

If I'm gibbering rubbish tony m will hopefully correct my errors.

Good luck

[ricardo596]

Kamikazee. Thanks. It's a fine balance....