Lime mortar grouting to York stone slabs

[Nick303]

Hello and I’ve just joined the group.

We have a kitchen floor, part of a new oak framed extension built by others 25 years ago.
The slabs are reclaimed Yorkshire stone and the previous owner has told us the are 5-6” thick.
We believe lime mortar was used to grout the floor and it has deteriorated now.
I intended to grind out the mortar to a depth of an inch or so, and then re-apply mortar.
Can anyone offer advice on the correct mix for a heavy traffic kitchen with dogs, the depth, and perhaps how to clean back the stone after application?
Many thanks in advance.
Nick

 

[Itchinfilth]

I went for a pre mixed NHL 3 for ours. Trying to keep it as neat as possible when forcing it in. As you are applying the mortar downwards into the gaps I found it easier than applying to joints on a wall.

Most efficient way to keep clean after doing 3 large areas was using a damp cloth for bits that clearly went over on to the stone being careful not to touch the joint. Then a few more final passovers as it becomes more obvious to the eye as it lightens and becomes easier to notice. Don't forget to wet the joints well before you start.

Don't underestimate how much mortar you will get through. The gaps take some filling depth wise.

 

[Robola]

I would be avoiding grinding. The mess it will make indoors is massive plus any damage to those flags will be obvious.

 

[jamest]

Definitely avoid any power assisted grinding. I used lime putty mortar to grout my flags, which were newly laid and only about 3 cm thick. I've also used it to grout terracotta tiles. The advantages of lime putty mortar is that it is less brittle (more forgiving of movement) and more vapour permeable than NHL. What IF says about avoiding spreading the lime over the flags - I even tried taping along the edges to make the process quicker. You should use a fairly dry mix - same as you would for pointing brickwork - and with lime putty it's probably worth damping it with a mister twice a day for 4 or 5 days after finishing it to make sure you get a good cure (that's what I did and it worked well, but I don't know what would happen if you didn't do it).

 

[Flyfisher]

I used NHL2 at about 1:2.5 for grouting clay pamments and it seems to have held up well over the past 15 years or so. Fortunately, the pamments were newly laid so I didn;t have to worry about removing old grout but I would echo the above advice about avoiding power grinding, or at the very least being very, very careful because the slightest slip will damage the flags and remain visible forever.

A dry-ish mix will help to minimise staining of the flags due to the inevitable grout spillage. Remove as much spillage as you can at the time but don't worry too much as any staining can be easily removed when dry using brick acid or diluted 'spirits of salts' - at least it was easy for my pamments.

 

[Kearn]

In terms of ongoing clean up, an old paint brush and plentiful supply of clean water will allow you to twitch as you go, cleaning off any residue while wet and cleaning the stone.

Once it’s dry, it’s a case of re-wetting and/or having to brush off with something more aggressive such as a soft wire brush/churn brush . However, this may damage your stone surface, but also any mortar that’s found it’s way into pits and pockets will be a pig to remove once dry!