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will Venning


Post by will Venning » Tue 28th Mar, 2006 2:26 pm

I purchased a Devon longhouse about two years ago. The building has evolved over the centuries, so there is no definitive "style".
The walls are mainly constructed of stone. However, on the north side there is cob from first floor height. Some of the internal walls are cob too, but again at first floor level.
There was much damp in the house. Concrete floors of various thicknesses were laid directly onto the dirt. Plaster on the walls was coming away.
I relayed the entire ground floor incorporating a DPM. After removing the plaster from the walls i rendered them in limebond. This had been recomended to me as it is a breatheable product. Since doing this the dampness and musty smells disappeared.
I know that there is a well somewhere under the house. Also, because the house is sited halfway down a valley it is possibly susceptable to run off.
I duly decided to tank the walls internally. This was done to a height of 1.5m and then onto the floor about 200mm from the wall. I did this about three months ago.
The weather has been unusually dry since. Then, a couple of days ago we had quite a lot of rain.
To my horror, when i went to check the walls, all the area that was tanked on the north side of the house was damp. Above the tanking the limebond render was dry.
I am wondering if the recent weather may have affected the water table beneath the house and that the tanking has somehow exacerbated the problem.Does anyone out there have any suggestions?



Re: damp

Post by Laura » Thu 13th Apr, 2006 4:27 pm

Hi Will,

I have no expertise whatsoever in this but am currently researching damp problems in my own property. Have you consulted http://www.handr.co.uk - I am not voucing for them but found some of their info interesting. I have posted some extracts from their website below for your perusal.

"A relatively common example of the effect of inserting a damp-proof material into a structure is the appearance of fresh 'rising damp' in walls following the laying of a new concrete floor with a damp-proof membrane. This is most often done when a suspended floor structure is replaced by a solid floor, or when a breathable stone slab floor is lifted and re-laid. Before the alteration of the original floor, moisture would have been able to evaporate off a large surface, without affecting internal finishes. However, a new impermeable membrane allows the water to accumulate beneath, forcing it to the sides of the room and into the base of the walls. This causes damp and decay problems unless appropriate ventilation has been provided at the floor/wall junction. These damp problems are then often used as justification for the injection of a moisture-barrier and the removal and replacement of plaster with remedial mixes. In fact, the more cost-effective solution would have been to allow the floor structure to continue to breathe. This can be down with a suspended floor, or by re-detailing the floor/wall junction in such a way as to allow moisture to dissipate, for example with a vented skirting detail.

A damp-proof barrier is always vulnerable to local failure and will tend to concentrate moisture and damp problems at these points. This is a general characteristic of all impermeable materials, including those used in tanking systems, which are generally found to fail at some point or at some time. This results in more 'concentrated' moisture at the points of failure, and hence more severe damp problems locally when they fail. Because of this, the more robust, fail-safe, and traditional building techniques rely on the use of permeable materials and ventilation systems in order to dissipate moisture and prevent it coming into contact with vulnerable materials or interiors."

continued on their website....this may or may not help....



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