How can I reduce moisture in stone walls? Possibly insulate at the same time?

[Gary1111]

Hi all, I have an old stone terraced miners cottage in Derbyshire with damp walls at the back.
They are very exposed to the rain.

It's mainly noticeable in the bedroom and adjacent bathroom.

It's a rental property, if possible would like to improve the epc rating at the same time.

I wondered if there is some external render that would be suitable?

next door has a stone chip render and they say they don't get the same problems, although everything I see online says not to use a cement render.

I did see people saying Thompson's water seal helps, it does say it's breathable.

I guess I can try that on a small area of maybe a square meter to test it without any drastic repercussions?

My other idea might be to use a water barrier internally such as the mapei shower area membrane?

Or insulated panels that you tile on, although the thickness needed may be a lot of work as I would need to move the toilet.

I don't have an extractor fan in the bathroom, the tenant says he opens the window for 10 minutes a day.

Any advice would be greatly appreciated.

Thanks

 

[a twig]

An NHL based lime external render would be the obvious option but wouldn’t add much in the way of insulation.

First though try and find the causes of the damp (external ground levels, faulty rainwater goods, poor internal ventilation etc) and fix those rather than just treating the symptoms.

Wood wool or wood fibre boards are the best options for internal insulation, there are plenty of good posts about using them on here

 

[Kearn]

Get some forced ventilation so you have dry air internally - humidity triggered extraction. Moisture is a killer. 10 mins isn’t enough, if they actually do it. Rule of thumb is 30 a day for an old house, but that needs cross flow not just one room/window - so bedroom and bathroom possibly depending on your layout, or better still from to back / side to side of house depending on sheltered sides etc. And I’d go for more time when it’s a bathroom.

Something that seals doesn’t breath. It’s a load of b0ll0cks that you can write on your tin of snake oil and get away with due to the ways in which things are, or aren’t in this case, defined.
external line render will help with managing the wetness - it will absorb then release, rather than having the stone soaking up and holding onto damp.

 

[aockenden]

You could try an internal insulating lime plaster with a non-biological insulating aggregate like pumice or LECA (not sure if appropriate sized LECA pieces for a plaster are available out there). If the wall is super wet it’s probably risky to use insulating bio-aggregates like hemp or granulated cork.

But I also definitely agree with “a twig” that you should be trying to pinpoint the root cause of the damp in the wall firstly, not just blundering into the dangers of playing whack-a-mole with symptoms.