Rendering and dpc

[loscurrie]

Hi,

I too am thinking of replacing some external rendering at the back of my house myself. All my queries have been answered on previous posts bar one.
I want to replace the rendering which has blown below the damp proof course. surely the reason it blew was because it was below the dpc. It also made the internal plaster damp and smelly.
Since I knocked it off the walls are now dry but how do I render the bottom of the house without bridging the dpc?

 

[anobium]

Hi,

I too am thinking of replacing some external rendering at the back of my house myself. All my queries have been answered on previous posts bar one.
I want to replace the rendering which has blown below the damp proof course. surely the reason it blew was because it was below the dpc. It also made the internal plaster damp and smelly.
Since I knocked it off the walls are now dry but how do I render the bottom of the house without bridging the dpc?

Your quite right that this is what caused your internal problems.
You form what is called a bellcast at the base of the render just above the dpc. As it's name implys it , is shaped like the base of a bell and throws the water away from the brickwork.
It's quite a job but a good plasterer should be able to fill you in on the finer details.
PS Don't tell softus I told you this !

 

[loscurrie]

Thanks Anobium,

What you say is good advice for above the dpc but what about below?
when I render the bottom , is there a gap between it and the top. The dpc stops at the edge of the brick so will not protrude past the new rendering.

 

[noseall]

dont render below the dpc. if you can, re-point the brickwork joints, and if you really have to, give it a coat of bitumastic paint.

 

[JohnD]

I don't know if this is considered a good way to do it, but this is how I once did a similar wall with a rendered plinth:

Hacked off the rendering above and below the DPC (trenched beside the wall so I could go below ground level) and loose pointing/soft mortar and patched in.

wire-brushed the slate bed so it was well exposed and clear of any bridging

Tacked a pice of 15mm x 30mm batten over the DPC line

Rendered down to, and up to the batten

After render hardened, removed the batten; I now had a render plinth with a slot in it and an unbridged DPC

Painted the mortar bed, and slate edges, top of the lower render and bottom of the upper render with Aquaprufe, applied sand blinding

Filled in the "slot" with render leaving only unobtrusive lines of Aquaprufe visible. the DPC is still unbridged because the Aquaprufe seals the slate and bed from the render, and the render is discontinuous between upper, lower and slot sections.


(I actually painted the lower render with Aquaprufe down to the footings before refilling the trench, thinking this would protect the brickwork from water pressure penetration, but have since learned that it doesn't actually work like that, as the water gets in from the underneath)

 

[Softus]

Your quite right that this is what caused your internal problems.
.
.
.
PS Don't tell softus I told you this !

anobium you scamp!

BTW, the job of forming the "bellcast" shape can be made easier with bellcast render beading. You can get lengths of it in galvanised or stainless steel, and even polyester coated galv steel

 

[loscurrie]

Thanks all of you. I'd been searching for a solution to that problem for ages and lo, just one day on this site and the answer appears.

I have to say, some of your names seem to appear all the time. Thanks for taking time out to help us plebs but, don't you do any work? I think i might become a plasterer .

BTW my attempt is actually going to be hidden by decking so only the top will be seen but you may see a new post re:decking.

Cheers