Pebble-dash causing damp?

benssson

Hi,

We've recently bought a 1970s bungalow and noticed the front bedroom seems to have a damp issue. We contacted a firm to come and take a look and he reckons its the pebble-dash letting rain soak in.

He said the pebble dash was "destoning" in that when he rubbed his had against it some of the pebbles would fall off. He then did a "test" where he poured some water over the pebble-dash and watched the quantity of water that dripped off the bottom (probably about 10-20%) to show how the pebble-dash wasn't working effectively. His recommendation is to replace the pebble-dash with a new render.

This is setting off all sorts of alarm bells and seems very "scammy" to me. The pebble-dash doesn't have any obvious cracks or sections where there are no pebbles. My gut feeling is that its a condensation issue rather than anything to do with the outside render.

Am I right to be wary?

Thanks in advance!!

stator

What type of wall is it?
A 1970s wall should have a cavity

benssson

stator wrote: »

What type of wall is it?
A 1970s wall should have a cavity

Our building survey says its 9-inch solid brick construction.

stuart45

Are you sure it's solid brick and not AAC blockwork under the render? Solid 9 inch brickwork didn't meet the U values introduced in the 1965 building regs, although some did still get built after that time.

Whitterbod

Have you checked that the gutters and down pipes are clear ,mine had a blockage and ran down the wall,

benssson

stuart45 wrote: »

Are you sure it's solid brick and not AAC blockwork under the render? Solid 9 inch brickwork didn't meet the U values introduced in the 1965 building regs, although some did still get built after that time.

Not sure - this is from our building survey -

The external walls appear to be of 9-inch solid brick construction, generally finished with a pebbledash render.

benssson

Whitterbod wrote: »

Have you checked that the gutters and down pipes are clear ,mine had a blockage and ran down the wall,

Yeh, they're all checked and seem ok.

benssson

I had another damp specialist come by today and he said the problem is caused by the render being made of concrete allowing the water to bridge the dpc (the black render in the photo) with the recommendation to strip it off and re-render with a silicone based render like K-Rend. Now I'm not sure what to believe :huh:

Also worth noting that there is no mould growth on the walls. Again, from our building survey

Some evidence of damp was found to the front bay in bedroom one. The problem did not appear to be serious, however, we would recommend you arrange for this area to be inspected by a timber and damp specialist and you should budget for some treatment and repairs.

benssson

stuart45 wrote: »

Are you sure it's solid brick and not AAC blockwork under the render? Solid 9 inch brickwork didn't meet the U values introduced in the 1965 building regs, although some did still get built after that time.

Ahh, I mis-typed. its a 1930's bungalow.

Doozergirl

Two 'damp specialists' with completely different ideas.

The black render is not a DPC, in fact, it's possibly the problem. The DPC is horizontal, between brick courses. The front of it and the areas around it need to be kept clear, otherwise water can travel vertically up the render, straight past the horizontal DPC and into the bricks above.

The picture isn't good, but one wouldn't usually render below the DPC. You stop the pebbledashing just above DPC and use a bell bead to kick it out slightly at the bottom, allowing water to drip away from, not down, the wall.

Below DPC you leave the brick/block uncovered. If you do render it then it's imperative it stops before the DPC and that there is a clear break.

You shouldn't have paving right up against the wall either as water can run towards the wall and settle there. There should be 150mm of clear air between DPC and the ground, and sensibly, paving should be around a foot away from the house. Lots of people fill the space between paving and wall with gravel, which allows better drainage.

What is actually happening inside the house and where though?

FreeBear

I would agree with much of what Doozergirl has said... The cement plinth at the base of the wall is a common "feature" of 1930s construction (I have one on my house). With a cavity wall, it doesn't generally cause too much trouble. With a solid brick wall, it will provide a path for moisture to track above the DPC and penetrate the wall.


Cut the cement plinth back to just above the DPC (it should be just under the bottom of the door frame, maybe slightly lower). Cut the paving back from the wall and install a french drain, and let things settle down for a few months. Stripping off the existing cement render and slapping a coat of K-Rend on isn't going to fix anything.


Although they claim that K-Rend is "breathable", I have yet to see any data to support this claim - It is a cement based, polymer modified coating (quoted directly from K-Rend datasheet), so no better in terms of breathability than the existing pebbledash.