Ask a Tradesman
QuestionIs a damp proof course really worth it?
OK, I have a bit of building experience helping out my mates when I was younger. I was always suspicious of DPC. What I'm talking about is the black plastic sheets that are put in between the bricks/blocks/stone a few courses up from the foundations. I understand that it's to stop the damp from the ground from rising up into the wall, though I'm not sure really how big of a problem this actually is.
Anyway, I always cringed about the structural integrity. If you've ever accidentally bumped the wall when it's being built a few courses up from the damp proof course, you'll know what I mean. It shifts very easily - it's obviously a weak spot in the wall. Maybe when everything is built up and the roof is on, you don't have to worry about it, but you still have to admit that you are compromising the strength of a wall with a DPC, versus one without. And the risk is that it gets so ingrained in a bricklayers habits that people overuse it. I mean I've actually seen garden walls and exterior pillars with a DPC. One pillar had shifted 3-4 inches at the DPC and it was supporting a roof, covering a walkway at a supermarket. That one was obviously a forehead slapper and really dangerous, but does anyone share my general DPC scepticism?
Dpc should be bedded on mortar, and not dry laid.
I have never seen any walls move using this method.
If you have seen that pillar moved 3/4 inches out side the super market it was probably a ram raider had hit it with his car.
B J D BUILDING/ROOFING 20th Feb, 2011
I do a lot of plastering and rendering and you can definetly tell the difference between a wall that has damp course and a wall that doesnt.
A wall that doesnt have dpc within 12 months will start to turn green with moss and constantly be wet, render doesnt stand a chance on a wall with no protection from damp, within 12 months or so it will start to bubble and fall off the wall.
If there is no damp proof on a wall for example a garden wall and it needs sand and cement rendering for example, it would need to be suitably prepared with either a felt backing, damp proof membrane and then meshing fixed with mechanical fixings to create a key or application of a sand and cement tanking system to stop damp penetration into the sand and cement.
If it is not being rendered you will still have problems in years to come with the mortar breaking down and just starting to crumble and worse still the face of the bricks blowing.
If a wall is being painted again this will start to bubble and peel off.
A lot of builders overlook dpc on garden walls etc but for how much it costs and the time it takes to apply it saves a lot of expense in years to come.
Bayley Property Services 19th Feb, 2011
reading your question with interest & thought i would share this with you.
I've lived in a 1940's ex-council house for nearly 10 years which has a plastic damp proof membrane.
It's a big,solid well-built property practically covered in god knows how many tonnes of roughcast but the whole house at some point in the past has shifted to one side about an inch on the DPM!
Not sure how commonplace this is a whole house moving on it but thankfully though ever since i have been here it hasn't got any worse and no problems with damp!
The mrs keeps saying one day were going to wake up above next doors driveway! HaHa
Some food for thought for you ;)
carl melady 19th Feb, 2011
Id say a damp proof is a defo for any building project. As long as its beddded down i dont see it moving. Ive come a cross a lot of bricklayers who dont bother bedding the the dpc and that in my eyes is a defo no no, an obvious weak spot. As other people have mentioned with out a dpc in time the face of the bricks will blow and the motar joints get eaten away as damp travels up the wall.If fitted properly its doing its job with out weakening the wall. plus the weight of the structure above pushing down on it isnt going to let it move. With regards to garden walls etc i normally use 2 course of engineering bricks to act as the dpc as they dont let the moisture travel up the wall.
hope this helps
JNR Building and Maintenance LTD 20th Feb, 2011
Dpc has two functions, it stops damp ingress/progress which is vital; and it allows the building to move (expand/contract) on the dpc, crazy I know, but the weight of the building keeps it in place. You would imagine it would just slide off but it doesn't.
A.T.Brickwork 18th Apr, 2011
I dont think this is an issue with housing because of the way it is laid, there is always a key on the bricks and mortar above and below hence no compromise on the strength and stability of the building. However, with garden walls it can be an issue due to their height and chances of being knocked/shunted by pedestrians or vehicles. You should always use two courses (150mm) of engineering bricks on a garden wall to stop the damp rising instead of dpc. A lot of brickies dont do this and it should be standard practice!
R.Hughes Building and Conservation Ltd 20th Feb, 2011
i used to question a old bricky about this. so we got a brick put on muck then dpm then more muck then another brick. left it over night and then tryed to pull it apart and, yes do do stick quiet well. i was surprised...roy
northview property mainenance 19th Feb, 2011
in the old days slate and lead are used as dpc but if you want to have a wooden floor in your house i sugest putting in a dpc it will also comform to building regs ?and also stop the smell of rotting wood.(molurios lacromons)if anybody can spell it better shout
Winstanley Joinery & Construction 19th Feb, 2011
Just built a garden wall last month. Used 2 courses of red engineering bricks as the dpc.With Buff coloured bricks they look good to the eye. customer was pleased.
Lee bell 11th Mar, 2011