Random Stone Wall - cladding options?

Rural_Puppy

Hello all
In process of total refurbishment of a Victorian stone cottage. Scotland, coastal location. Walls are very thick, about 2 ft, and built out of some very random rubble, Basically a pile of stones held up with gravity, so very uneven. May have originally been a byre or similar barn for animals.
Over the years, it is clear that various repairs have been undertaken, including using cement render in some places, and topped off by plastic masonry paint over the lot.
The paint is flaking, and clearly moisture has been held in the stonework. the interior has been completely stripped out, as it was also damp, unsurprisingly!
I started by stripping back the plastic paint, and as I go am discovering quite how bad the walls are. Most of the mortar is falling out, and some of the faces of the stones are disintegrating and turning back into sand. So large holes are appearing on the wall surface.
On the plus side, the cottage is quite small, single storey with interior footprint of only around 40m2.
We plan on rebuilding the interior floor and walls, with appropriate tanking and damp proofing materials to ensure that water is kept out. The exterior ground levels will also be reduced, once we have tied in the building to the new floor (just in case the very weak foundations decide to give way). We intend to pack in lots of insulation in floors, walls and loft. Heating will be via GSHP and UFH as part of a district heating system (we have 4 cottages altogether).

We are thinking about how to finish the very uneven and now holey exterior walls. Our builder is suggesting an exterior insulating cladding with render over the top.
I assume we will have to at least try and stuff some lime mortar into the holes beforehand.
My concern about external insulating cladding is potential for dampness and how the walls can continue to breathe and dry out.
Has anyone successfully clad dodgy stonework? What did you use? Any hints and tips that may help us?
Thank you!

gollum007

Cladding that is a terminally stupid idea.


The cement render and plastic masonry paint are the cause of your current problems.
Dig out and replace any missing or damaged stones with proper lime based mortar & fill in the gaps.



Inside, you want proper breathable plaster and no tanking or anything.


Trying to use modern building or anti-damp methods on this sort of construction will kill it.

Rural_Puppy

Thank you - I am inclined to agree! However, the whole thing looks dreadful now, more holes than mortar / stone in places. The "tanking" inside would be a pvc membrane as part of the suspended floor structure to stop water penetrating up.
The wall construction would include something like permaguard (eggbox type stuff on a roll) to provide a route for moisture to evaporate rather than transfer to the internal walls and cause a dampness issue.
We did wonder about covering the external stonework with marley eternit or similar to help it look a bit better. Trouble is the walls are very uneven, so may end up with voids behind it, which might not be a great idea.

Rural_Puppy

Hello again. I am still researching what might be possible to use to render / clad the random stone walls once I chip off the existing concrete render, poorly performing lime mortar and modern plastic paint over the top. I have come across this product - anyone used it? or recommend something else that might be appropriate to cover the walls once the mortar is picked out and replaced with lime mortar.
https://bauwer.co.uk/
Thank you!

FreeBear

Couldn't find an MSDS sheet for the Bauwer products, but I did find this in their general information doc.

BAUWER is a dry pre-blended, ready to mix powder. It’s based on cement, lime and volcanic glass such as perlite.

So, a cement render with a bit of lime thrown in.... The insulating properties will also be pretty low at the coating thickness quoted (25mm). For a solid stone wall, I would look for something else. Have a chat with Ty Mawr or Mike Wye and see what they have to recommend.

Rural_Puppy

Thank you - had a look at Ty Mawr. Their products look good, but far away in Wales - we are West Coast of Scotland. Wondered if anyone had come across these chaps? https://www.masonsmortar.co.uk/shop/