On an old 2” cav', with half inch of damp protrusions into the cavity from both sides and a tie wire helping catch the snots, a blocked cavity is a very real possibility.
Last edited:
DPC Mortar - Look ok?
- Thread starter Signor Bob
- Start date
They definitely built my old estate in the 1970s with "outie" DPCs, but my current house's 1990 extension has an invisible one.
I guess that at some point in the 1980s someone worked out that you could point over it without the world ending. Plus this way you don't get the crumbly bits above and below as shown in the photo in this thread.
Arguably the outer skin's DPC is hardly necessary anyway, the brickwork above gets pelted with driving rain so it's fairly pointless, and it may even trap moisture above the DPC by preventing it from wicking into the ground. Perhaps using a wider "outie" one on the inner wall could be a sensible precaution though, where appearance doesn't matter. But if protruding inside the cavity it could catch dripping condensation and hold it against the wall.
The bumps in it stop the house sliding away! You'd need a heck of a sideways force to lift the entire house by the 1mm needed to clear the bumps.
I guess that at some point in the 1980s someone worked out that you could point over it without the world ending. Plus this way you don't get the crumbly bits above and below as shown in the photo in this thread.
Arguably the outer skin's DPC is hardly necessary anyway, the brickwork above gets pelted with driving rain so it's fairly pointless, and it may even trap moisture above the DPC by preventing it from wicking into the ground. Perhaps using a wider "outie" one on the inner wall could be a sensible precaution though, where appearance doesn't matter. But if protruding inside the cavity it could catch dripping condensation and hold it against the wall.
The bumps in it stop the house sliding away! You'd need a heck of a sideways force to lift the entire house by the 1mm needed to clear the bumps.
Jeezus.
You might want to google capillary action. Absent of a DPC the ground moisture can wick upwards by upto 1.2m. And that is not a function of rain hitting the bricks.
Have you never been in a property with rising damp on the party wall between the two properties? That has nothing to do with rain hitting the internal walls. They are internal walls and not subject to rain.
Most of the houses that I work in are Victorian 9" brick walls. When it rains, in most cases, the water evaporates outward. Capillary action is not the same thing as penetration. Gravity only works in the vertical plane.
I'm yet to see any issue from rising moisture from capillary action due to DPC being set back slightly from the external face.
In fact that's not even an issue in terms of rising damp, but gravity is an issue as much, much more water actually soaks down the external face and settles on the DPC.
So perhaps a DPC set-back is advantageous as it will allow the DPC to drain? I'll write to the NHBC and get the standards bought up to the 21st century.
And after all, rising damp on the external leaf of a cavity wall is not even an issue in the first place. It's actually the whole point of a cavity.
In fact the one and only reason that DPC is left projecting, is so that lazy inspectors can see it from the car park one month after the wall has been built.
In fact that's not even an issue in terms of rising damp, but gravity is an issue as much, much more water actually soaks down the external face and settles on the DPC.
So perhaps a DPC set-back is advantageous as it will allow the DPC to drain? I'll write to the NHBC and get the standards bought up to the 21st century.
And after all, rising damp on the external leaf of a cavity wall is not even an issue in the first place. It's actually the whole point of a cavity.
In fact the one and only reason that DPC is left projecting, is so that lazy inspectors can see it from the car park one month after the wall has been built.
I wouldn't actually omit a DPC from an external wall, my point is just that its presence is vastly less important than the internal one.
I'm fully aware that there's an internet conspiracy mob who think rising damp doesn't exist, alongside flat-earthers. Sadly some assume you're one of them if you mention anything about them!
I'm fully aware that there's an internet conspiracy mob who think rising damp doesn't exist, alongside flat-earthers. Sadly some assume you're one of them if you mention anything about them!
Nonsense. Not all bricks above damp are FL rated.
Interesting! That looks like bitumen backed fabric, hence melting it in. Our 1950s place is built on something similar, what looks like a cotton bandage in bitumen. It definitely works, but we now have black drools on the side that faces the sun.
DIYnot Local
Staff member
If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local
