Tanking and internal blockwork walls

[TheForge]

Happy New Year All, a little bit of advice/opinions required!

We are still trying to remedy some damp issues in our living room which remain despite reducing the exterior ground level, constructing a French drain, repointing exteriorly in lime, removing chipboard and bitumen floor coverings (to find nice old flags) and removing several layers of plasterboard, cement render and 1970's Newtonite sheeting from the walls.

The front wall (ashlar stone, rubble interior, solid wall c.1700) remains damp in places at low levels on the inside. Now, while I expect this is probably the result of condensation, we had suspected that there may have been an interior 'skin' built inside this wall (as the wall is 9 inches thicker downstairs than upstairs and plastered in very flat gypsum).

We removed the plywood and plasterboard 'boxing' that had been constructed around the window reveal the other day and, as expected found, a single skin light weight, thermalite style breeze block wall built from floor to ceiling with a token cavity (breached by debris) between it and the inside of the original wall.







Obviously this must have been an attempt to both damp proof and insulate the wall and, whilst not very 'traditional, I was inclined to leave it in situ for its additional thermal performance. However, on closer inspection, the inside of the original exterior wall has been lined with Newtonite tanking sheets (I only know its Newtonite as the application instructions were stuffed in the cavity!) inside the cavity. The wall behind the tanking seems to still have old lime plaster on it. Based on the experience of removing this material from other walls it will only trap moisture behind it and within the fabric of the exterior wall (and may explain why the plinth is so wet and covered in algae on the outside).

The block work wall finishes just below the original lath and plaster ceiling and should come away without damage to the ceiling.

My initial reaction is to take down the block work wall, remove the tanking entirely, assess the state of the wall and repair the lime plaster/replaster as required, leaving the wall functioning much as originally intended, this will also add an additional 9 inches to the room.

Does this seem like a sensible course of action? Will the thermal performance of the wall be significantly reduced without the blockwork skin or will the difference be negated by the (hoped for) reduced moisture content of the wall. What would others advise? Any thoughts would be appreciated.

 

[Zebra]

I'm no expert but would think that was a very sensible plan and that there are other ways to provide the same level of insulation. My walls were tanked with cement and removing it has made a huge difference. I haven't recreated an inner layer yet but was planning on using either a hemp-lime plaster, which is supposedly quite a good thermal insulator by itself, if applied in thick layers. http://www.lime.org.uk/products/mortars-and-plasters/ty-mawr-lime-hemp-plaster/
or alternatively a wood fibre based breathable internal insulation, http://www.natural-building.co.uk/pavadentro_renovation.htm.
I haven't done it yet, so can't say how good either product is, and the walls do have to be dry before applying either, with no further risk of penetrating damp or rising damp.
I suppose you can't pull a corner off and have a look because that would break the tanking?

 

[stuart45]

The problem with your walls is that you have a vapour barrier on the cold side of an insulating block, which could cause condensation on the tanking.

 

[Lime]

Isn't this a good example of how ineffective modern damp solutions really are?
It makes me cringe just to look at it.

My initial reaction is to take down the block work wall, remove the tanking entirely, assess the state of the wall and repair the lime plaster/replaster as required, leaving the wall functioning much as originally intended, this will also add an additional 9 inches to the room.

Does this seem like a sensible course of action?

Of course it does.

 

[MdB]

I think I would answer with probably.

Your wall has been turned into modern wall with a cavity (be it narrow and bridged) so should behave somewhat like a modern wall with a damp outer wall and a dry inner wall. This obviously isn't happening and I would want to find out why before doing anything.

The Newtonite type of systems have been suggested here before for dealing with damp in cellars and if installed correctly should have left you with a dry internal wall (though the outer would still be damp) so it is interesting to note that it hasn't worked for you. Stuart45's comment on condensation forming on the cold side of the insulation block might well have something to do with it.

Now that you have opened up the cavity, the extra ventilation may well help matters though not something you would want to do long term.

For what it is worth, I removed tanking from one damp wall and dry walling from another and both dried out once back to bare stone (+ reducing ground levels outside) so it worked for us.

 

[TheForge]

Thanks all for your replies.

Right, off to start taking the blockwork down...

 

[Zebra]

Let us know how you get on!

 

[stuart45]

I'm sure taking the blockwork down is the right choice. If I built a cavity wall like that on a new build I would be expecting damp problems.
A properly built cavity continues down below the DPC to allow any moisture to run down below. When you add a new skin on top of the existing floor, any moisture will collect at floor level and cause dampness.

 

[TheForge]

Reporting back with a progress update!

We made a start on removing the breeze block wall earlier in the week and revealed about 7ft high Newtonite sheeting all along the wall, draining onto the flagstones at the bottom. The flags were all very damp under the breeze block.



Careful removal of the nails fixing the tanking sheets revealed sodden wall paper predominantly intact behind it! The paper was some form of woven paper/fabric but so wet that it disintegrated to the touch and simply fell off the wall. Damp was visible up to the top of the tanking to the right of the window and black spores were visible all over.



At low level to the left of the window the damp and mould were even more pronounced.



Unfortunately the old lime plaster underneath has blown and delaminated badly at the junction of the two tanking sheets about 3 feet off the ground and in a few other spots, whilst around the window reveal it has been hacked off entirely in the past and some repair work will be needed. A couple of bricks in the quoin around to the right of the window have spalled and disintegrated in the damp as well.

 

[TheForge]

Below the window there is clearly a bricked up window seat - another dilemma now as to what to do with that! Any thoughts?



There was much newspaper and brown packaging paper stuffed into both the cavity and gaps around the door frame/window as rudimentary insulation, the date of which suggest the tanking work was done in October 1976. (along with a retro Bounty wrapper which I neglected to photo!)

Anyhow, thanks for the advice, I think we certainly made the right decision to open it up, the wall was completely sodden behind the sheeting and was an object lesson in why not to seal up old, solid walls! An awful lot more to do this weekend now to tidy everything up and finish the rest!

 

[FamilyWiggs]

Excellent work Tom and very exciting.

Those floor tiles look similar to some "Heather Browns" I discovered under chipboad and polythene too... and cleaned up you will be amazed at the depth and richness of colour. I was also lucky that the 70s makeover had not destroyed the underlying fabric, just tanked over the top. Not you've had a poke about, are there other hidden delights to find in other rooms?

Great website too - once I found the house one!

 

[tobydog]

That must have been very satisfying and I'm sure the sigh of relief from the house could be heard all around. It's interesting though that, if your newspaper dates are in with the works, a previous owner chose to Newtonite and insulate a complete wall only a month or so after one of the driest summers on record (1976).

You make mention of a bricked up window seat, however, is it possible that there was a bigger window there originally and a previous owner simply fitted a smaller one and bricked up the gap? It looks too shallow for a seat.

 

[TheForge]

The house was sold from the nearby estate in September 1976 (it had previously been the estate forge, carriage works and lodge) and it appears the new private owners got a builder in straight away to 'modernise' what was probably quite a run down building as almost all evidence points to all work being done in late 76 with a second more cosmetic phase in 1982 when the house changed hands.

Unfortunately the builder doesnt seem to have had any knowledge of traditional methods!

I'm fairly certain the windows are 'original' sized as there is no external evidence of alteration and I have a selection of photos showing them similar to today in the 1890-1920s. The 'window' apparent in the photo is actually an aluminium framed secondary glazing unit which sits about 12 inches in from the actual oak casements. Unfortunately these windows are modern reproductions as the last owners ripped out the historic windows to install PVC! After CO intervention and a court case later they were forced to replace them with wood. Unfortunately they are not a patch on what the original windows look like in old photos. Even taking this into account the seat would be relatively shallow but I can't really see what else it would have been.