Advice on repairing an old chimney and bothy with lime mortar

[Tapster]

We have recently moved to rural Aberdeenshire, Scotland. Our property has two steadings (barns) and a bothy (a simple stone structure; in this case, it was used for pigs at one end, and the pig-man at the other: hence the chimney and fireplace).

You can see the dilapidated end of one of the steadings in the photo. We call this one Mordor as it is the steading from hell which we can't use for fear of death from falling masonry; it's a project for another day and another bank account! Amusingly, the term they use for an old roof like this is that it's suffering from 'nail sickness'!

Please see attached photos.

But I digress! The bothy is the problem for today. The pointing is in a terrible state: a mixture of very eroded hundred-year-old lime mortar and newer sand and cement repairs. The advice from a local roofer/mason is to rake it all out and replace it with lime mortar. I haven't done it before but the resources are all there on the internet, so I'll do that this year. Incidentally, the mason's estimate for the work was way beyond my budget, but he guaranteed it for a hundred years!!!

What I'd like advice on, please, is how to repair the chimney stack. Let's assume that I might use it as a chimney sometime in the future.

Crows have nested in the chimney stack and in the end wall of the bothy. They cleverly removed mortar to create access. You can see right through the chimney stack in one of the photos. There are quite large voids to be filled before the outer faces can be pointed. The stack has weathered three severe wind storms in the last twelve months but it won't last forever in its present state. The mason recommended that I collect stones to fill these voids but I don't know how to do the repair with these stones. If I place stones inside the voids, do I just cover them in mortar to secure them and restore the inside shape of the chimney, then build the chimney back out of the hole? How do I finish the outer faces?

Please help!! Many thanks for any contributions.

[ETC]

Get rid of that cement mortar for a start!

[Tapster]

On 10/02/2024 at 19:44, ETC said:

Get rid of that cement mortar for a start!

 

A good start, indeed!

Can you offer any advice on the chimney repair, please? That's the part of the job that I have least experience with.

[ETC]

Sorry no - I'm not a builder but I would suggest that a good start would be your local planning conservation officer.

[Gus Potter]

On 10/02/2024 at 17:30, Tapster said:

What I'd like advice on, please, is how to repair the chimney stack.

Copy and paste your post to Masons Mortar of Edinburgh and take advice.. these folk know their stuff!

 

Off my own bat. The stone you have looks like much what we encounter down the east coast of Scotland.. not well "sedimented" sandstones or more likely "conglomerate" in other words they tend to not weather well.

 

These houses were built by the gentry for workers, they were not good quality. You need to get your head round the fact that these houses are what they are.. they were built as cheaply as possible for the land / estate owner so they could extract the most they could from their workers.. they are basically shite structurally / in terms of workmanship and let water in! Get it out your head (if you have had that thought) that they are quality buildings...they are not. @Tapster my post is encouraging later.

 

You are trying to now make a silk purse out of a pigs ear!. The Scottish gentry lived say in Edinburgh / Glasgow and built in Ashler commonly ( oh! yes it was the Scots taking advantage of their own! nothing to do with the "English" or the "Welsh" or the "Irish" it was a "big boy" that done it and run away for those who are seeking factual history) .. faced sand stones.. the best.. I'm happy as an SE (and have done so) to convert these Edinburgh Ashler buildings all day long..

 

You'll see this in most Fife and Ayrshire coastal towns where the middle of the stone has weathered and the mortar is sticking out and that just drives water into the wall.

 

Sometimes with a bit of thought you can recover the situation and live happily ever after.

 

You need lime mortar.. you'll see often recommended a NHL3.5 lime mortar, bin that idea and go for a NHL 2 lime mortar which is supposed to be used for internal work only. But on this type of stone it's the angle of the pointing to shed the rain outwards that matters and acceptance that it needs regular maintenance. The idea is that you use a soft lime mortar that erodes faster than the stone.. you maintain that.. like cleaning your gutters. Eventually the stone will erode and need replaced.. hopefully it won't happen during your tenure.

 

 

 

 

[saveasteading]

To use stones, the principle is to minimise the volume of mortar. Have a collection of stone sizes to hand. Infill a void at the back with rammed-in mortar, then press in the biggest stone, or stones, that will fit. Repeat until at the surface.

This provides more strength and reduces porosity.

Granite uses harder lime than sandstone.

Stipple the finished lime surface with a brush, to give it more surface area for evaporation.

I knew none of this 2 years ago: it's findable with a lot of searching.

 

@Gus Potter is right about the landowner's intention. However this has been built with skill and the 3 skin construction has advantages too: it's still there after 150 years or so.

 

NB the foundations will be 400mm deep probably....leave them alone.

[Gus Potter]

On 17/02/2024 at 09:15, saveasteading said:

Stipple the finished lime surface with a brush, to give it more surface area for evaporation.

Great tip!

 

Very obvious once someone explains it so simply.