Preventing damp in wall of Victorian Malthouse

[thomatkinson]

Hi everyone,

 

I have a couple of connected questions about damp, drainage gravel and soil up against a wall. Can anyone offer some advice?

 

I’m attaching some pictures of the areas in question. And in case useful: my building is an early Victorian Malthouse conversion made from brick and stone, with solid walls 2-3 foot thick at the base. The original foundations are stone but there is a concrete slab underneath the basement floor. The basement is half below ground and half above. The soil around us is mostly clay along with some rubble from various demolishing in the site’s past.

 

Firstly, we have some problems with damp in one area of the basement wall (see pictures with potted tree and interior cill). The problem is pretty much at the ground level and slightly lower,  causing bubbling in plaster on the internal cill (the window frame pictured is probably rotten due to another separate reason, though the damp may be a joint cause). We don’t have this problem in other areas of the basement walls and, with a bit of investigation, it seems most outside areas are well drained with gravel going down a good 30cm or so before you hit soil. I’m thinking of digging out this wet clay against the wall, allowing the wall to dry out in the sun for a couple of weeks, repairing any major cracks, perhaps waterproofing the wall under the ground with Storm Guard (which is already coating the same wall above ground), sloping the base of the trench to make water flow away from the wall, then filling it back in with drainage gravel of some sort, with a top dressing of shingle to match the current. Does this sound like a good plan? Any suggestions for improving it or things to look out for / best materials to use?

 

Secondly, in one area in this same trench around the building (see picture with basement window and black metal steps at right - we would build this between window and steps), we would like to create a level base for a 4x3 or 3x2 foot garden storage cabinet. I’m thinking to dig out the trench at the base a little to lay some pressure treated timber ‘walls’ spanning the shorter width, perhaps concreting or pegging them in place; build these walls up to the ground level, sloping the base between the wooden walls away from the building; fill the space between the timber with drainage gravel of some kind and compacting it down before dressing the top with matching shingle again, perhaps with a weed proof membrane under it. The depth of this platform would be about 25-30cm. Would this work as a base for my cabinets? Would I need to put something between the wall of the building and the new gravel, such as water proof sheeting or perhaps a third pressure treated wall at the back spanning the length of the platform? Any advice about materials or this design would be appreciated!

 

Thanks,

Thom

[Susie]

I read everything through and initially thought a French drain would work and unless your cabinet is plastic it will rot if wood sat on gravel. 
but then I came to your interior picture which looks more like a plant pot had at some time been placed in centre of window and the poor plant overwatered perhaps there was a hole in the pot. 
do you have any other damp areas?

[thomatkinson]

Hi Susie, 

 

Thanks for your reply. 
 

We definitely plan on a wooden cabinet and we don’t want it to rot - good point! Depending on the cabinet design it would either be clear of the floor and only touching the gravel at the four corners, or if in full contact with the gravel I guess we could put down a water proof membrane between. I have also seen those plastic snap-together shed bases, which contain the gravel and go some way to keeping it dry. Not sure!

 

The damp in the interior picture does seem to be caused by exterior damp. Each time we have fixed it, it comes back. And there are a few other areas in the nearby wall which aren’t pictured. No damp elsewhere in the house - just by this wall under the window. And no plant pots have been kept there. 
 

Thanks,

Thom