As is the way of things, a simple(-ish) rewire and light redecoration has rapidly escalated to a full-on gutting and remodel.

Cottage is in Scotland, approx 250-275 years old, built using local stone. We are leaving exposed this interior stone wall (and another one). Historically the wall has had some damp issues from a cracked chimney pot, but we believe they’ve been resolved in the last decade or so, and the wall seems dry.

My question: what pointing should I use? From internet searches and local builders I’m getting mixed advice – either NHL 3.5 lime + sand, or cement + sand. I see both on the wall – appears to be mostly lime-based pointing with some cement repairs.

Hive mind thoughts?

I’ve used Tradiblanc (a lime and white cement blend) with sharp sand a lot. Masons mortar in Edinburgh do it.

@Vader is your man who will know.

Yes NHL 3.5 will be fine for that. Mix it 2 or 2.5 parts sharp sand to 1 part lime.
Clean off all loose material and damp the wall before pointing, make sure the shine has gone off after wetting the stones.
Ideally cut out the cement. If you are repointing the whole wall, you need a couple of centimetres minimum joint depth. Don’t be surprised if under the mortar you find what looks like mud, it is very common to find buildings of that age built in clay and pointed in lime, as lime was expensive. Clay is great but needs to be pointed.
Once pointed up cover it so it doesn’t dry out-lime needs to be damp to cure. You will need to scrape the top 1 or 2mm off the surface as part of the curing process. Do this after a couple of days but if the mortar is sticking to your scraper, leave it longer until the scrapings fall to the ground.

Tradiblanc mentioned above is a good product but far to hard for internal pointing. It’s for chimney work or exposed locations such as haunching or harbours

You can get everything you need from mason’s mortar. I’d recommend you get a small tool and scraper, use either st astier or Otterbein NHL 3.5

Any questions feel free to ask

Ideally cut out the cement. 

Be careful. I was repainting the back of my fireplace and had to cut out a broken brick. I didn’t realise how thon the wall was and knocked through into next door’s lounge🙈

@Vader – awesome stuff, huge thanks for the detailed input. I didn’t realize I need to cover the pointing indoors. Will plastic sheeting be OK, or am I supposed to use the proper Hessian fabric?

Also – didn’t realize I needed to go a good 2cm of joint depth; I’ve generally been scraping until I got to relatively good mortar. And yeah – interesting mix of stuff in the mortar – don’t think I’ve found any clay, but have found bits of straw, twigs, and coal within the aggregate.

@andrewh – hah! No chance of that here – walls are over two feet thick!

@krixmeister yes a sheet of plastic is fine, you just want to stop any drafts or air moving across it and drying too quickly. If it slows curing too much you can always remove it. If working outside always double cover, Hessian then plastic sheeting. Drying too quick is the No1 route to mortar failure and nasty white pointing.
Re the depth, shallow mortar is going to dry out quickly so bare that in mind. A smear of mortar will just crumble off. But at the same time try to avoid cutting out really solid old mortar if you can. It sounds like you have the original, so it’s a balance at the end of the day.
You do often see inclusions of coal and wood ash in a mortar, it’s usually from the lime kiln when the limestone was burnt but may also have been added as a pozzalan

2 1/2 century old cottage in Scotland. That sounds lovely.