Advice on locating source of 'rising damp'

[RomanAbramovich]

Situation:

detached bungalow built 1958, concrete floors, hall and lounge floor covering is original wood block parquet, remaining rooms 'marley' type tiles.

property has been uninhabited for several months.

noticed there are no airbricks anywhere in the structure.

cavity wall construction.

plot is on a slight gradient, the fall from front to back of structure (30ft run) with a drop of approx 2ft.

rising main enters vertically thru concrete floor in toilet room.

structural engineer advised there "might be sulphate attack" a couple of months ago, due to some loose marleys and white deposits along seams of some tiles, predominantly in the two rooms at front of property, but that a "core sample" was reqd for analysis to prove/disprove.

consequently i investigated/priced up digging out floors, new dpc etc etc....

however, on stripping the property back to a shell yesterday, noticed the folowing:

parquet wood blocks lift easily (looks like bitumen adhesive).

The loose marleys i've scraped up here and there are bone dry underneath, as is the floor underneath.

some internal walls show damp patches (damp wallpaper) up to 18 inches above skirting, all such patches are on walls just off or against the central hallway.

none of the rooms external walls have damp patches.

none of the outside brick skin show damp patches.

pulled some skirting away from directly below a damp wallpaper patch, it was clearly damp/rotten, noticed the finished surface (appears 2 be sand and cement render) runs right down to the floor. throughout the entire property the wall surfaces are rock hard, even kicking internal damp patches it's obvious the render/plaster is not even slightly blown.

racking my brains as to the source: sulpahte attack, damaged rising main, damaged sewer pipe closeby, due to the gradient of the plot.....

not sure where to start digging!

has anyone experienced a similar scenario and what steps did u take to invesigate and remedy?

 

[^woody^]

If you have rising damp then you either have no DPC, or a failed DPC.

The source is either ground water, mains water or drain water, and excess water is also the cause of sulphate attack - although I don't know how your engineer managed to conclude that there might be sulphates on the basis of loose tiles and white deposits .... if the properties in that location have ash floors then there "might be" risk of sulphate attack for that reason alone.

If the floors are not significantly uneven then they can be left alone

You can CCTV the drains, and test the incoming mains

If this dampness is rising, as opposed to other possibilities, then you need see if an injected DPC will resolve it - but you need to identify the cause first

 

[RomanAbramovich]

"You can CCTV the drains, and test the incoming mains"

i'll kick off with these two items on monday. hopefully will be able to cross them off the list of possible causes.

"If the floors are not significantly uneven then they can be left alone "

two floors have a slight dip in the middle, another has a slight bulge.

The engineer made his assessment based on the age of the property and the fact that red ash was often used for sub-bases at that time. although he did repeat MIGHT be sulphate attack (nothing like sitting on the fence when a client is paying a sizable fee eh???!!!)

seems like identifying the root cause will be a process of elimination.

out of interest, how deep were concrete floors/subfloors constructed back then?

 

[^woody^]

The infill will normally be a bit less than the foundation depth, about 2-3 ft, and there wont be a DPM and the slab will be 4-6 inches

If there is a risk of sulphates, and if the floors have dipped/bulged/cracked, and if there is a suspected high ground water content (the cause of your damp), then it may be worth considering floor replacement while the place is empty

 

[RomanAbramovich]

yes this is the worst case scenario, which tbh i am prepared for.

will research costs re getting a floor core sample analysed.

assuming the floors are replaced, how are the internal walls treated? is a chemical compound injected into the base of internal walls once the slab and infill have been excavated?

(assume if all floors are replaced, dpc membrane to regs etc etc, water will still attempt to permeate up thru the internal walls)

 

[JohnCo]

We have found a major cause of damp appearing from the base of an interior wall to be the plaster making contact with the finished floor! Always eliminate this as a possible cause by cutting it away at least 25mm above FFL. Damp has been known to travel under the floor covering for this reason as well. Regards JohnC

 

[RomanAbramovich]

drain cctv was ok, water meter reading not budged for 2 weeks while away over xmas period. rules out 2 possible causes of damp!

i have been made aware (by a local tree surgeon) that the neighbourhood has a high water table, which peaks in february. There are known to be underground springs, and the soil is (soggy) clay.

6 of the 8 rooms have sound floors, little deviation in level. in the 2 rear rooms (site is on a slope) the slab has dropped 30mm at the far end. as a result, the brick partition wall seperating the 2 rearmost rooms has been affected by subsidence. i can see thru the floor level horizontal crack to the room next door!!!

all external walls show no signs of subsidence.

assuming the brick partition wall is built directly off the floor slab, what are the underpinning options here? I can't visualise how the task would be approached in this situation - any ideas?