Damp course and plinth (duplicate threads merged)

[Safety First]

We are certainly at the limits of my knowledge. But with the same problem (though with poured concrete rather than bricks) I cut about 1' from the wall and removed the concrete. Exposed the old dpc. Replaced the air bricks that were about 1/2 covered. Filled with membrane and chunky washed gravel. Then build a 5 m lean to across the exposed wall as the above is no substitute for a proper soakaway/ French drain.

A dpc is usually or mainly horizontal laid down between courses of bricks/ blocks rather than applied to a vertical surface.

 

[Safety First]

Also, if you have wooden suspended floors the air bricks need unblocking to preserve the life of the timbers, aside from what cosmetic signs of damp exist on the interior walls. Air is your friend!

 

[JohnD]

I don't understand where you mean the DPC is.

Why does the airbrick look blocked?

 

[JohnD]

Welcome GP, you have answered your own question. dig around the house and fill with gravel.

Andy

Cobbles or pebbles are better than gravel. The larger and cleaner the stones, the more air, and the less capillary of water.

 

[Gasplumber]

That’s my damp proof rubber there

I’ve removed a brick it’s a cavity wall. No insulation tho.

 

[Gasplumber]

I’ve now removed a few bricks the cavity is full of crap aswell
Guess I’ve got to empty this for a start.
Then I’m still left with what to do with the plinth.

 

[bobasd]

OP,
your cavity is blocked and bridging moisture across to the inner wall and its decorations.
Given that you will have to hack off interior plaster then you could clear the cavity from the inside skin.

Just saying but:
Without any more digging you could break the plinth contact with the brick drive - cut off say 50mm of plinth, & then drill and gun in DryZone into the most accessible bed?
Cutting the plinth ground contact isolates capillary action behind the plinth, & the chemical DPC will hopefully inhibit rising damp in the outer wall?

Remember that the Plinth/DPC are on the outer skin of a cavity wall - which, in the scheme of things, is not all that important once the cavity is cleared.

 

[JohnD]

hurrah, you've found the DPC!

IMO you need to excavate and expose the wall so that the DPC is at least six inches above ground level. This will leave you with quite a trench. Unless you are able to remove that paving and restore the original ground level, you could dig your trench and back-fill it with clean cobbles or pebbles. These will allow drainage and because the are so big, do not support damp by capillarity. If the ground is not free draining, dig a little deeper so the trench will never fill with water. Don't allow dirt, mud, earth or sand into the trench because any of those will support damp. You can use landscape fabric to isolate the trench fill. Water rises higher by capillarity when the gap is smaller.

You can have a sunken gravel path beside the house if you want. The purpose of the cobble backfill is safety, to prevent you falling into the trench.

It's easier to clean out a cavity by removing a brick at the quoin and raking out. I've had good results using a powerful builders vanister vac and feeding the hose or metal tube along, where it sucks out loose material such as sand, wasp nests, and small mortar snots. Large bits will clog the pipe and need raking out. As Bob says, the cavity rubbish is bridging damp to the inside wall.

 

[Gasplumber]

I’ve being raking the cavity out.
If I clear the cavity then am I right in thinking even tho the damp proof course is bridged externally with the render I could leave that in place and get no more damp inside.
Because the bottom bricks are knackered anyway.

 

[noseall]

hurrah, you've found the DPC!

Suspended timber floors will likely have DPC's at differing levels.

 

[bobasd]

The outer skin DPC was shown in photo number one.
But why and how it was brought out from the brickwork into the sand & cement of the lower plinth is a mystery, unless the original builder's were parging as they brought the founds to DPC level?

I dont understand: "DPC's at differing levels"? Do you mean all suspended floors or just this particular property?

 

[HERTS P&D]

Suspended timber floors will likely have DPC's at differing levels.

We now have an expert on the case!

Andy

 

[bobasd]

OP,

Given how you've gone about opening up the cavity in the last pic, if you continue like that you will end up damaging large sections of the Plinth
Why did you choose to open up from the outside?

Whatever - under no circumstances open up at a corner - dont touch any inside or esp outside corners, & stay about 1000mm away with any other openings.

I did ask you for pics of the interior damp signs but not heard anything since?

 

[Gasplumber]

 

[Gasplumber]

The top of that plinth lines up with the top of my skirting.
I chose outside as weather is good and I’m going to repoint the bottom 6ft of the wall so made sense to stay outside.
The damp inside isn’t that bad either just a scrape and a paint needed I reckon.


From the top of the plinth externally I’m raking out 2 ft worth of crap