Cob walls - damp, plastering and tiling

[roripori]

Hi there,

This is a double pronged topic.

I'm in the process of buying a house, it's not listed but it is probably about a hundred years old and not standard construction. At first viewing I noted some what looked like old damp issues in two bottom corners of the living room downstairs. I assumed it would be easy enough to replaster, but after a second look underneath the plaster where I was expecting to see brickwork I noticed that the walls are made of some cob like material. This patch has become quite soft and flakey, presumably because of previous/ongoing damp issues. See attached photos.

My questions are:
1. Is this in fact cob?
2. The plaster on top, which looks like standard gypsum and is all over the house - does this need to be ripped off and replastered with lime plaster? I say this because it sounds like cob doesn't work well with gypsum plaster.
3. How would the issues pictured be fixed?
4. Related to this, can you tile over and grout cob? I would like to put a WC and shower upstairs in a room that isn't currently a bathroom.l, however if cob needs to breath then presumably tanking and tiling a shower enclosure wouldn't work?

Many thanks

 

[roripori]

Sorry, attachments this time!

 

[Gareth Hughes]

If I recall correctly you were house hunting in East Anglia in which case it's unlikely to be cob but may be its relation, clay lump. Or another earth-based material like clunch.
Not only does the interior surface appear to be gypsum plaster, but the outside looks like it's got a nice suffocating coat of cement render. Which would suggest that all sorts of other nasties may be lurking in the floors too.
Earth construction needs "a good hat and a good pair of boots" as they say in Devon, but a gypsum plaster and cement render sandwich will not be doing any good. A fair degree of breathability (one tiled shower room might not make a difference, but a completely impermeable building will) is vital, and without it, this sort of thing happens:
https://www.bbc.co.uk/news/uk-england-devon-36926950
Others here are more technically adept at possible solutions.

 

[roripori]

Yes, I knocked the previous house on the head, was too much hassle what with one thing or another.

Whilst I'm happy to do a load of renovation work which is required, if this property has as you say been suffocated in its entirety then I'm guessing all of the render and plaster would have to be removed and rerendered and replastered? I'm guessing a 4 bed house of this size would not be cheap to do?

 

[Easrow]

A house in our village was bought last year. It looks like they had the same issues and good intentions to restore. I'm not sure what happened but they had started work when the corner of the house collapsed. After looking at it I would say they too had the sandwich of cement and when they took it off it gave way. The whole cob part of the building was demolished and they are now rebuilding in brick. I'd say be careful.