Contractors in Cambridge area/Damp

[Jackied]

Hi, we have damp (of course) in our Grade 2 listed building - see full details below. Previous works (ie what we did when we moved in 10 years ago) following the surveyors advice was to construct a land drain across the front of the house and reduce the soil height by two feet (!) at the back, and then see what happened. This was done by a specialist historic building company, not regular builders.

There is a small area of wall at the front of the house that is still damp, although the levels are lower than they were at one point. This is at the base of the wall - bubbling disintegrating plaster, interior bricks along the bottom crumbling away etc.

We have had two builders suck their teeth and say 'don't know about that' and a damp survey that suggested just taking the wall apart just to see what is going on. When I phoned them the conservation officer was not happy about that idea! What we probably most need is a recommendation for a specialist contractor in our area that can actually work out what best should be done, propose a plan for the conservation officer, and execute it! I've contacted quite a few with no success.

Tips on things that should NOT be done would be helpful. (We know it shouldn't have a DPC put in!)

MORE INFO
It is a timber framed house approx 1600. The walls are very thin, the outside is inappropriately cement rendered and the inside covered in plasterboard as far down as the sole plate. The exterior base of the wall on the non damp areas is brick painted black with bitumen (presumably). The base of the wall on the damp areas is of unknown construction and much lower in height than on the brick base side of the house. The whole of the front of the house is probably a few inches below ground level; it is gravelled outside. There are no plants close to the house by the damp area. The floor inside is slate slabs,we don't know what they are laid over, I'm guessing concrete. it's a dining room with lots of ventilation (via a massive chimney).

A friend who has done restoration himself says the rainwater goods look OK to him as far as he could see without a ladder, there are no cracks or staining on the exterior render, and the exterior bitumen paint on the base of the wall looks OK. He thinks that the timbers are OK at the moment.

One possibility that occurs to me after reading the FAQ on here is simply reducing the height of the soil outside. But by how much, and how long should we leave it to dry out before repairing inside? And then should it be with breathable materials on that area of the wall?

 

[Flyfisher]

Reducing the height of the outside ground is generally a good idea, preferably to at least six inches below the inside floor area.

A rule of thumb often quoted in these here parts is to allow one month per inch of wall for drying out. Lots of variable involved of course - wall saturation, aspect of wall etc - but it gives a rough idea and highlights the fact that it will almost certainly need more than a few weeks.

Bitumen paint won't allow the wall to breathe and is generally a very bad thing. As is cement render, for the same reason. Ideally, both should be removed and replaced with lime render. If you wish to retain a black plinth you could try black limewash. I've used 'Blackish' limewash from Ingilby paints in Sudbury, Suffolk.

 

[MikeG]

......the exterior bitumen paint on the base of the wall looks OK.........

I'd suspect that this is your problem.

 

[Jackied]

Thanks v much for the quick replies.

We were told by one builder that it was bitumen paint, but I don't know for sure. How can we tell? I bet it's a PITA to get off!

Replacing the possible bitumen with black limewash (I am sure the listing people would insist on retaining the colour, we aren't allowed to change the window paint colour) - would it be pointless to try just that without re-rendering the whole house as well?

When we moved in 10 years ago we were advised that removing all the render would be difficult and potentially damage the underlying wall, and that we should wait until it needed to be replaced anyway and only then re-do it with lime. That may have been bad advice though!

Interestingly, the black paint on the back of the house is a lot more uneven and chalky looking than at the front - so maybe that is a more appropriate paint.

I

 

[Kearn]

Sounds like in describing your situation, you've effectively answered your own questions...! Get rid of the modern materials and rebalance the levels, see what's what, then remedy.

One of the first jobs I undertook on our house, similar to yours, i.e. age and timber framed, was to strip the outside to see what we were dealing with. Concrete render off, plastic paint removed and same with the bitumen paint. Some of the bodges you'll find masquerading as timber where joints have failed etc, any old rubbish has been stuffed in then painted black, are frankly terrifying.

What we then could see (and smell!) was the condition of our structure. We were relatively lucky, but still had quite a bit to deal with. Our sole plate had long gone at least a century ago and been replaced by bricks, but the later additions of concrete to fill gaps in the frame and in contact with the timber as patched render, then covered in paint had caused water retention and we ended up having to scarf in a foot or two of oak to each of our posts. You'll see wet oak start to dry before your eyes once it's back in the air, but thorough drying will take time, I forget with ours but we're talking months. However, with the correct materials put back on, this isn't an issue really and as long as it can breathe it will find it's equilibrium eventually.

We chose not to render or limewash the lower level, leaving our oak as it should be and the brick in fills without covering - original lime pointing still present and correct. Up above we had blown original 400+ year lime render due to plastic paint added in the last 50 years. Here we replaced what was required with lime plaster and actually have left as is as the colour is lovely.

Spalling brick faces imply the mortar/pointing isn't lime and allowing moisture out through the joints. Plasterboard won't be helping, mostly in hiding issues and the presumed gympum skim internally will add to to the breathing barrier.

A chimney isn't going to help the problwm if the moisture can't out of the wall into room correctly, but once it can, the draw should help.

What is your subsoil make up? Where are nearby water courses/table height?
If the ground isn't bone dry, then moisture will find its way up, and if your floor base is indeed concrete, this will push damp out to the walls.

What happens when it rains - is there splashback against the house / which side takes the brunt of the rain / does the fall on paving run away from the building?

The wrong grade of gravel, with no water runoff can be very good at retaining mositure!

What not to do: ignore it if it's bad enough as what you see may not be the full extent, inject any kind of snake oil into the bricks to make them a 'moisture barrier'', apply tanking or waterproof coatings inside or out, use concrete, gypsum, anything non breathable, including for pointing and modern vinyl paints, have the groundwater runoff towards the house even if you have a trench/French drain, have internal ground level equal or below external...

 

[Jackied]

Thanks Kearn, We are on a free draining chalk, a half mile or so from the nearest water - a fen/watermeadow

I don't know the actual table height but when they have dug holes in the road outside they haven't obviously filled with water.

The wall faces roughly SE - it is the SW wall that gets the brunt of the rain. I will go and stand outside in the next daylight rainfall! I've done it before but could easily have missed something. The house is probably lower than the pavement but the land drain is between the house and the pavement.

I'm interested that you did things that changed the appearance - is your house listed? We've been led to believe that this is virtually impossible. (It may not help that we are also in a conservation area.)

 

[Kearn]

Interestingly, the black paint on the back of the house is a lot more uneven and chalky looking than at the front - so maybe that is a more appropriate paint.

quite a bit of ours could Have be described that way, but it was the doing of the underlying fabric rather than the paint... try the pen knife test...

 

[Abi Cott]

My conservation officer has been quite accepting of changes to the structure that are low key visually and prolong the life of the building. I'm not wood, I'm stone, but I'd guess the key is the same.

Tell them you are going to keep the aesthetic appearance as close as possible the same. Tell them you are going to use lime and authentic materials and fill out the listed building consent application. I'd be very surprised if you got a no.