Liquid damp proof course - does it work?

Discussion in 'Builders' Talk' started by diymostthings, Oct 11, 2018.

  1. diymostthings

    diymostthings Well-Known Member

    We have a 100 year old cottage made of stone - walls about 420 mm thick but this includeds a cavity. Obviously no DPC but I've seen these adverts for pressure injection of DPC liquid (presumably some sort of silicone?). We have always had signs of rising damp (only on one wall) which can't be "decorated out".

    Does anyone have any experience of these systems - either the actual injection process or whether they actually work in the long run?
  2. dobbie

    dobbie Well-Known Member

    After the injection the walls are usually then rendered with an integral waterproofer to a metre high.
    This would be no good for a stone wall as it needs to breathe.
    KIAB likes this.
  3. fillyboy

    fillyboy Well-Known Member

    No, can work well in very old brick buildings, but the pressure injection stuff relies going into a mortar course, it wont usually impregnate the stone (depending on the stone).
    Tanking and waterproof render up to a metre high will help, alternatively, do what they did 100 years ago.

  4. Dam0n

    Dam0n Active Member

    Rising damp is a bit of a myth... There are usually valid reasons for damp in an old house such as yours. Rising damp isn't one of them...

    The injection dpc is a waste of money at best and damaging to the building at worst. Have a good read up before you decide on what's best.

    Search "period property" in google and ask the same question on the forum it sends you to. No disrespect to any one here but most builders haven't got a clue when it comes to old buildings and more often than not make the problem worse.

    Stay away from any "damp proofing" firms. They always have a vested interest and will just try and sell you some totally unsuitable tanking or injection dpc.
    KIAB likes this.
  5. KIAB

    KIAB Well-Known Member


    And use lime mortar,not cement based mortar.
    Richard_ likes this.
  6. Richard_

    Richard_ Active Member

    I'd get rid of the source rather than tanking. Old walls need to breathe not be sealed. As others have said, rising/penetrating damp are misleading.

    • Check the ground levels outside, is it 150 below the DPC? There will be a DPC, either slate or bitumen paper.
    • It could be rubble in the cavity - there will be one, albeit not very wide and often bridged. Your walls are likely to be stone outer and brick inner with a gap between. Do you know if someone's put in cavity insulation, that can cause a lot of damp problems on an old house.
    • It could be poor roof drainage or window details.
    • Is it near cooking or washing?
    • Use lime mortar and plasters, they let the walls breathe.

    Interior and exterior photos would be useful.
  7. stuart44

    stuart44 Active Member

    I agree that using lime mortar is usually the best solution, but I can't understand why Jeff Howell and Peter Ward claim that it's only in the UK where there are companies using the injection system. It's used in many places in Europe and the USA. As is using a roll of DPC.
    I tried a bit of Thermalite block in a tray of water last week, and it took about 2 days to reach the top, so I reckon you need a DPC on the inner skin.
    Jord86 likes this.
  8. Jord86

    Jord86 Well-Known Member

    You may need to find a hobby, mate :)

    I don't believe rising damp is a myth at all, granted a lot of the time condensation and poor ventilation are mistaken for damp, but there's many properties I've been in where they've had obvious signs of damp for example at the bottom foot or so of the party wall, with no radiators, bathrooms, chimneys, guttering, pipe work under the floor in that house or the neighbours etc anywhere near for there to be an explanation other than it was coming up through a damaged original slate DPC.

    Another place quite recently my mate was renting, the original house had been turned into a business on the ground floor, and a separate flat above, accessed from the rear of the property via a forty year old single story extension/ utility. Where the original back door would have been which was now an arch at the bottom of the stairs leading into the extended part was, again, ten inches or so from the floor, flaking paint, damp and cold to the touch, again nothing near it to give any indication other than it was rising damp.
    stuart44 likes this.
  9. Richard_

    Richard_ Active Member

    If an injectable DPC works, then why tank as well?

    As for the need for DPCs, many old house don't even have slate but stay dry. It's not just old houses. I've worked on new build straw houses with no DPC or DPM, just engineering brick, lime mortar and leca/foamglass under the slab. Yup, we can keep straw dry without plastic but brick walls need plastic and tanking?

    What a DPC allows us to do is speed up construction by using cement. They guarantee dry walls without having to worry about ground conditions, brick/mortar porosity, or maintenance of render and pointing.

    Back to rising damp problems - My recent project seemed to be a clear case of rising damp with a 750 high tide mark on the inside wall. It turns out the cavity was filled with mortar brick debris to that level. The cracked cement render was trapping water in the wall - the wall was wet when we took the render off. So the damp was most likely a combination of damp bridging the cavity, plus the wet render making the wall cold which caused condensation.

    An injected DPC and internal tanking wouldn't have fixed it, it would have blocked the damp from sight. That would make the problems worse in future.

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