Remedial action

[Penners]

My daughter's C16th timber-frame Norfolk house has significant damp in the brick plinth in one corner of the kitchen. Internally the damp rises up about a 12 - 18 in from the floor.

Outside the wall, there is a french drain. It's filled with gravel, which over the years has got very polluted with soil. About 6in below the surface of the gravel is a line of filled holes in the brick plinth, indicating that a chemical DPC has been injected at some point. The brick plinth has also been painted with some sort of black, bitumastic-type of paint.

My instinct is to tell her to dig the soil-polluted gravel out of the french drain, down to well below the line of DPC holes. Also to strip off the bitumastic paint. I also feel that she should leave the french drain empty of gravel for a good few months, to allow the brick plinth to have a good circulation of air.

Does anyone have any comments on that proposal - for or against - please?

 

[middi]

When you specified 17th cent. cottage Penners, with signs of damp on the "plinth" wall internally, I immediate envisaged the possible original construction method used in your aerea.

6 or 7 in square sole plate beam with full length studs, infilled with wattle and daub, sitting on a lime rich large flint base, rammed in just below soil level, with the sole plate protruding a few inches or more above ground level. Sometimes a row or two of bricks ( if lucky ! ) was used above the flint. No chance of permanent damp there, and if there was it would have been no big deal.

There are very very few cottages left in their original base construction condition, most have been" repaired" or " updated" mostly because of poor earlier maintenance where the sole plates were allowed to rot away, mainly due to the high soil level allowed to build up around the base.

It is quite possible that your daughter's cottage has suffered similar fate where the original construction has been altered, including a nice " modern" solid floor, with possibly a rendered exterior.

What you are suggesting to do in trying to ascetain and alleviate the cause of damp, is the best course of action, remove as much of the external accumulated soil and debry including the black stuff and let the base breath as much as possible.

Make sure that the external surface covering , regardless of its construction materials, will shed the water clear of the brick plinth .

The situation can then be monitored , and futher decision can be made at a later date.

It will cost nothing, will require a fit person and a shovel.

 

[Gervase]

Sounds like sound advice to me.

 

[Penners]

Many thanks for your thoughts, Middi and Gervase.

Middi - you have exactly described the house! 20th century "improvements" have included internal concrete floors, plus - as far as I can see - extensive replacement of the brickwork in the plinth, using cement mortar. And the external rendering is cement. Hey ho.

On the plus side, the house has a wonderfully massive oak frame, apparently in very good condition, including some beautifully moulded king joists, and some very beautiful old oak windows crying out to be properly restored to their original condition.

Thanks for confirming my thoughts on letting the plinth breathe. Fortunately the bottom edge of the rendering is quite well "bell-bottomed" so it ought to throw water well clear of the plinth. Ideally I'd like to be doing this at the start of summer, rather than winter, but there we go.

Also fortunately, I have a fit son-in-law to wield the shovel!