Damp! Re-point, gravel strip, or french drain?

Discussion in 'Builders' Talk' started by hadfield, Oct 22, 2021.

  1. hadfield

    hadfield New Member

    Hello folks - thanks in advance.

    Just moved in to a property built c.1930 which was renovated by previous owner. "As new" when we moved in. Damp signs appearing above skirting on the inside of solid stone wall. Caused by overflowing drain we suspect. Picture below. [​IMG]

    On the outside of this wall, concrete pavers have been laid (not recently) and the pointing is totally shot. Picture below.

    [​IMG]

    We noticed when we arrived that the drain level was too high, blocked, and would spill over and in between the flags after the washing up or washing machine had emptied etc. We believed this was the root cause of the damp. Overflowing drain & pooling water in poor condition pointing against house, possibly above original DPC which may be bridged by pavers. Since the drain was unblocked, which used a load of water and caused some serious pooling in the process, the tide line in the kitchen raised about half inch BUT has settled.

    We've had poor weather in the north lately and during heavy rains this exterior wall is battered by prevailing wind and rain. I suspect the shot pointing is allowing more water to seep in, albeit less than the overflowing drains. So, I want to address it.

    My options (as I see them - where I need your help..)

    1. Repoint with a "breathable" lime mortar and seal the flags against wall
    + Seals out most water
    - Potentially seals water seeping in elsewhere, less breathable than gravel strip
    - There is what looks like a modern injection chemical DPC 1.5 bricks above paver (in pics later on), but sealing with mortar does not address the potential bridging of original DPC which I suspect is below the pavers.

    2. Cut away narrow strip in pavers, dig shallow trench, line with geotextile and fill with 20mm pebbles.
    + Allows wall to breath
    + Any pooling water happens lower down the wall
    + Reduces splash off concrete pavers during rain
    - Not sealed like option 1
    - Water cannot run off anywhere, might pool closer to footings and still above DPC.

    3. French drain - Cut away pavers 6" from house, dig trench, lay geotextile, 20mm gravel and perforated pipe, knock through drain surround below ground and feed pipe into surface water gulley.
    + Water can drain away below DPC
    + Gravel prevents splash back
    - It's invasive, there's the gas supply and a cable running parallel to wall
    - Knocking through drain to feed pipe in is not ideal

    Now more pics to help:

    The wall in question, can see what appears to be chemical DPC injected 1.5 bricks above pavers:

    [​IMG]

    Shot pointing:

    [​IMG]

    Close up, lifted shot pointing to reveal cable, and gas supply to right (I think).
    [​IMG]

    Close up of modern DPC, which looks to be working on the exterior as it appears dry above the line of bore holes:

    [​IMG]

    I'm a handy lad and could tackle most options but your advice would be massively appreciated. Of course my preferred option would be the least invasive but concerned this only fixes the issue in the short term. Option 1 might get me through the winter and mean I can address properly in fair weather come spring.

    Happy to explain more and share more pictures. Cheers.
     

    Attached Files:

  2. Robot Enthusiast

    Robot Enthusiast Active Member

    Hi, just saw you post on my French drain post so thought I would reply.

    Questions:
    Your house was built in 1930, this is the time when portland cement started being used rather than lime. Suggest one of the knowledgeable folk on here confirms your cement is in fact lime before you arrange any pointing?
    Digging the trench is fine and will take the moist soil away from the brickwork with gravel allowing some breathing. There are some other things to consider though...

    Just be careful about how you deal with the water though. A true French drain should route to a soakaway, not just seep into the ground next to the house - although I never got this confirmed if it was okay or not. We have London clay so the water just pools and I would need to route it to a proper nearby soakaway but this is very difficult in my case as there isn't one. Maybe if we didn't have clay this would work. I live in suburban area and my place is right on the corner of a main road and junction.

    For my place I'm actually going to carefully smash out all the concrete around the house and relay a concrete base that is below the DPC, and ensure that it falls away from the house. More aggro and money to do this but as the soakaway is not an option I don't have much choice.

    Good luck.
     
  3. Wayners

    Wayners Screwfix Select

  4. hadfield

    hadfield New Member

    Thanks R.E. Good to know about the mortar, I’ll hold off the pointing for now as I’m likely heading down the trench route. I will firstly dig the trench, line and gravel, but no perforated pipe leading to drain. I will see how this goes and decide, if the damp worsens, to then take further steps with a pipe and perhaps connect to drainage. I suppose I am lucky that the surface water drain is only a couple of yards away. It’s breaking through the drain housing beneath ground level that is the tricky part.

    On your point about lowering levels all round, that would be the ultimate long term solution but is out of budget for now, and given that the damp is isolated to this single wall, I think I can focus my efforts on this problematic spot. Tomorrow the work begins, I’ll keep this thread updated, thanks very much for the pointers.
     
  5. hadfield

    hadfield New Member

    Cheers Wayners. Appreciate it and have looked at those aco drains as an option. Shame they’re so bloody obvious. Plus I’d have to break through the rain water drain housing below ground level to connect the aco drain, and if I did that, I’d rather take the more discrete french drain option. Again, cheers, well worth considering.
     
    Wayners likes this.
  6. CGN

    CGN Screwfix Select

    lower ground level and take skirting off, hack plaster off and let it dry.
     
  7. hadfield

    hadfield New Member

    Thanks CGN. I didn’t think to remove skirting or plasterboard. Good advice.
     

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