Solid concrete floor 1.5" below DPC - damp

[dormermike]

Hello

Original floor in 1920/30's bungalow, solid floor is getting damp patches at the wall/floor junction which is causing skirtings to rot where there is excess rubbish accumilated behind the skirting (saw dust from sanded parquet floors I believe). This is also causing woodlouce etc internally.

I've hacked off the skirting and cleaned out in another room to some succes but yet to tackle the worst room. In the past I used roofing felt adhesive.

I am going to tackle the last and worst room shortly, as it smells, but wondered if there is abetter product for lappgin the parquet floor adhesive (bitumen) up to the DPC (bitumen) as currently the wall/floor junction is exposed brick/concrete.

Thanks
Mike

 

[dormermike]

I found another post with exactly the same issue. //www.diynot.com/forums/building/floor-wall-junction-damp.363255/

Is it likely my bungalow had wooden suspended floor originally and is there a way to tell?

the bricks are noticeably damp at the floor/wall junction.

 

[^woody^]

Cavity walls?

Where is the DPC relative to the floor level?

 

[dormermike]

Yep, cavity walls. DPC is approx half a brick or 1.5 inches above the concrete floor. On top of the floor is parquet blocks mounted on bitumen. The blocks do not go all the way to the wall as there is approx 2 inches or so gap so the concrete is visible. The bitumen does not lap up to the bitumen DPC in the wall.

 

[dormermike]

Here is a pick, some of the blocks have been removed. DPC is visible the the wall.

Untitled

• dormermike
• 23 May 2012
• 2

 

[dormermike]

For woody or anyone willing to help please?

Out of interest I put a humidity metre on the floor near the damp..

Wondering now if the humidity could mean condenstation between the wall and floor which is showing up on the brick work and then making the concrete floor damp? There is a vent behind this section of wall which i guess could cool the bricks (vent doesnt appear on inside of wall).

I put a camera into the cavity recently and it appeared to be empty, or rather, wasn't obviously full of rubbish.

Wondering if the high humidity is caused by the damp, or the visa versa? This humidity meter is normally on a desk in this room, and has never shown this high... 76% at time of writing this.

Untitled

• dormermike
• 17 Jun 2013
• 1

In the pic above you can see the dampness on the floor - this exends to where the blocks originally were. The ones i'd removed from this section of floor were so wet i could squeeze moisture out like a sponge.

I am at my wits end with this and have contacted a CCTV drain company to check out the drains - there is a foul drain in the garden outside this wall, which AFAIK is original (1930's) though no actual direct signs of drain issues. Soil in the area is high clay content.

Any advise appreciated please.

Thanks
Mike

EDIT: now at 77%, so still climbing! BTW there is a radiator immediately above this which to confirm, is not leaking. And I know this damp is relatively minor (its concealed behind skirting) but this does actually extend all the way around the room. There is a smell of rotting wood in the room, small amount of fluffy mould at the base of one skirting (opposite side of room to this photo and actually an internal wall) and there are always woodlouce around!!!

I have ruled out internal leaks etc.

 

[^woody^]

If the walls are cavity and are clear, and there is that gap between floor and DPC, then rising damp my be the cause. Also, if there is no mould then rising damp would be the main suspect

If you have done the other rooms and this has worked then just carry on.

You can get bitumen based paint from the likes of wickes.

Or you can go for some professional products such as RIW, Superprufe or Ball Stopgap F75 or F76. All these may only come in quantities more than you need and may be relatively expensive to buy if you only have a small area to treat. These would be painted along the floor edge and up the wall past the DPC to form an internal surface DPM.

Then plaster down to 20mm above the floor and fit new skirting

 

[dormermike]

Hi woody, thanks. Do you think the humidity is a red herring then? Must admit the fact it is on internal walls as well as the exterior has had me going round and round between water getting into the gap and travelling round the floor slab, rising damp, through to condensation!!

Edit: forgot to mention, been watching this for over a year and the damp has no relationship to rainfall at all. During an extended dry period it was actually quite bad and equally have seen it bone dry during long wet periods. I realise this may not have a direct bearing on ground water levels, i guess anyway, but is part of the reason i am considering a cctv drain survey.

 

[^woody^]

Any moisture at that location is going to affect the humidity right there in the corner, so its not really an indication of the cause of any damp

Some readings of general room temperature, room humidity and local surface temperatures could be taken, as could a plot of a range of readings with a moisture meter, which would give a good guide if condensation is more likely than rising or penetrating damp, but you would need an experienced person to do that and make a correct interpretation of the readings and what is going on.

Limited use of a hygrometer or moisture meter won't be any good as correct interpretation of a wider area is essential.

 

[dormermike]

Ok cool, that makes sense

I dug a pit on the outside of the house, approx 1m deep and it didnt fill with water.

Just wondering where you think the water might be coming from, i know the ground, but is iy water table, or could drains be the issue? Water main runs outside the house but alongside that room.

Just concerned that as this room was worse than the other, painting/tanking the damp could cause it to come up in the middle of the room or something!? Saying that have removed loose blocks in middle of room and in fairness slab seems bone dry. The bitumen does still smell like bitumen though, oddly, considering it is 90 odd years old so if a put a book on the floor after a few days it takes on a bitumen smell?

 

[^woody^]

If you take off an area of plaster you should be able to see that the brickwork below the DPC is visibly wetter than that above.

All brick below DPC level and in contact with the ground will be permanently damp despite the weather

 

[tony1851]

Cavity walls?

Where is the DPC relative to the floor level?

You certainly earned your "thanks" on this one, Woody

 

[dormermike]

If you take off an area of plaster you should be able to see that the brickwork below the DPC is visibly wetter than that above.

All brick below DPC level and in contact with the ground will be permanently damp despite the weather

Ok nice one, didnt realise bricks below DPC are ok to be wet. I'll proceed with painting it up to DPC and if notthing else should protect the floor blocks from further damage.

Thanks for your help and advice, appreciated.

 

[dormermike]

BTW wierdly the damp always seems worse in the warmer weather - we are in a dry spell at the moment and i havent seen it this bad in a long time.. would have thought it the other way round

 

[^woody^]

One explanation could be the greater evaporation from the damp wall in warmer air, compared to even drier walls/floor/plaster etc around it.

Another could be more prevalence of condensation due to different relative temperatures, or even due to the dampness itself

If there is an underground leak or high ground water levels, then that too would keep the wall in a damper state as other things seem to dry out

There may be several things at play there, so without an actual proper investigation, it will be difficult to pin down

Have you got a general view of the external wall - from say 2m away showing the ground and wall, and one showing the elevation?