Tanking Party Wall

[Shawld2]

We have just moved into a 400 year old semi detached grade 2 listed building. The owners of the attached property are undergoing major building works. I am unsure whether these are approved works or not. I am guessing not.
The owners have ripped out their kitchen including floors, walls and ceilings. They have replaced the walls with insulation, fireboard and standard plaster. They have replaced the floors with concrete. They have also tanked the walls and floors.
I am concerned that the works, especially the concrete and tanking, will cause moisture to be redirected into the party wall and this will potentially create a damp problem in our home and decay the wall. Also there is an oak pillar in the party wall that is supporting an oak beam, that runs through both houses. The pillar has NOT been sealed beneath the new plaster but has been plastered up-to. I am concerned that this pillar will rot from the additional moisture and from any other modern materials used near the pillar such as silicone sealant.
Has anyone had experience of such works in an old property and has it caused problems? Specifically tanking walls and floors.
Thank you for any guidance you can provide.

 

[TheForge]

We had, and to some extent still have, all of the stuff you've detailed in our house and yes it does cause problems. Cement floors will tend to push ground water sideways into the base of walls, destroying mortar and eventually eroding porous masonry and brick. Often the issue of water in the walls is then hidden with cement tanking up to about 3 feet. In our experience this then accentuates the decay of masonry towards the base of the wall and water travels up behind the cement until it can escape about 3 feet up the wall, where it collects and blows the plaster off. If you're really lucky and they then tank the wall with some form of sheeting (newtonite etc) without adequate means to remove the water you will then see damage even higher up, usually at junctions in the lathing.

Timber behind cement render will simply turn to cake in the presence of trapped moisture. We've even had brick turn to the same consistency, especially at the junction of cement and lime plaster.

Where we have removed cement tanking the wall is invariably damp behind.

We share a party wall where on the other side is a monstrosity of a 1980's cement fireplace - the wall on our side is continuously damp and leaches salts as this moisture is only able to escape into our house.

Just this weekend I removed (with great delicacy for fear of appearing in the neighbouring living room) gypsum and cement from our side of a blocked up doorway that previously joined the two houses. The doorway transpired to have been blocked up some time ago with a wattle and daub partition supported on an oak frame. Unfortunately behind the cement the base of the 3 supporting jams and the bottom most wattles had rotted completely to powder. A cursory prod with a screwdriver had to be abandoned when I hit the back of next doors skirting board!



I would try and meet with your neighbours and find a subtle way to discuss your fears without destroying neighbourly relations. If you believe inappropriate work is being done perhaps you should speak to your CO (if the properties are listed) but at the risk of damaging relations with your neighbours!

 

[Lime]

http://www.communities.gov.uk/publications/planningandbuilding/partywall

 

[Shawld2]

Many thanks for the reply. I guess my concerns were justified.

One point to clarify, I'm not sure whether it makes a great deal of difference but: The pillar between the 2 houses that is embedded into the party wall has NOT been plastered over. It is on show from within both houses. It also sits on a stone plinth that is about 6 inches off the floor in our house. The floor next door is slightly higher than ours so the stone is not visible from their side.
Also against the party wall we have a large radiator. Would that help at all to soak up the moisture and reduce the decay and damp?

 

[Shawld2]

It is a Grade 2 Listed building. I have contacted the Conservation Officer anonymously via email as I'd rather speak with the neighbours first and see if we can come to some sort of agreement (not likely I guess). I am awaiting his comments....
Thanks

 

[Penners]

Shawld2 - I think your concerns are well justified. Judging from your description, there would appear top be every chance that moisture could be channelled into the structure of the party wall, to its detriment.

A polite chat with your neighbours is invariably the stage 1 suggestion on such matters, but this is normally suggested at the point where they are planning their works. Given that you seem to be faced with a fait accompli, I can't see that they are likely to undo all the work that they've already done. So your contact with the CO seems wise - I just hope that he/she will observe your confidentiality request.

 

[TheForge]

The areas of the beam/prop/jam that are exposed to the air will be ok, at least initially, it is the areas in contact with damp masonry that will be the problem and I assume the beam dissects the full thickness of the wall.

If the wall becomes 'sealed' by impermeable finishes (gypsum/cement) then any moisture that is within it will have the potential to create a wet surface against the timber, thus promoting and accelerating rot. Eventually this rot may spread further into the timber, whilst a high moisture content in the timber will promote attack from other problems like beetles and funghi. If the wall is entirely dry however (highly unlikely) this won't happen.

The radiator on your side may aid the removal of some moisture from the wall, assuming you have breathable plaster on your side, but I doubt it would dry it completely.

 

[Shawld2]

Thank you for your replies TheForge and Penners. Really appreciated!

The wall on our side is open brickwork with (I have been told) lime mortar. So I guess this will allow the moisture through? Do you think this would also stop the moisture getting trapped within the wall and therefore the beam?

 

[Penners]

That's very difficult to say. Clearly your lime plaster will help, but it all depends on just how much damp is likely to be in the wall and whether its migration through the plaster on your side is enough to handle this.