Repointing around old DPC

Discussion in 'Builders' Talk' started by Rob Denness, Dec 2, 2019.

  1. Rob Denness

    Rob Denness New Member

    I am repointing a bungalow, circa 1960's. I have chased along each side of the dpc, (which looks like bitumen), but most of it has been pointed over solid and the remainder is in pretty bad shape - either very brittle with a raggedy edge, or already crumbled away.

    My question is what is the best course of action for repointing, considering most of the outside edge of the dpc is between 5 to 25mm back from the face of the bricks?

    I was planning on using a 3:1:1 or 4:1:1, but now wondering about using waterproofer in there also? It is going to be difficult to joint each side of the dpc as it is now.

    Attached Files:

  2. gadget man

    gadget man Screwfix Select

    Looks similar to a pic posted yesterday...:confused:
  3. Multiskillmaster

    Multiskillmaster New Member

    Anything below damp is 3:1 mortar (supposed to be no feb..) everything above not stronger than the brick.. generally 5:1
    I would look into getting a new dpc injected, that would guarantee the water is kept below. your mortar looks as if when they were built, the lads whipped the cement! The ground make up is encroaching..the regs are FFL to be 150 below dpc or you could put in a French drain or Aco’s suffice nowadays.
  4. Rob Denness

    Rob Denness New Member

    Thanks for your reply multiskillmaster. Yes, I would always go 3:1 below damp, but like you say: the original pug looks very lean, so I wasnt keen on going too strong with it (to allow for some movement). Also the fact that even if I did go 3:1 as per regs, obviously it's only the first 15-20mm of the joints that would be stronger anyway. So I suppose my only option might be to just fill the bed solid across the dpc and inject a dpc? (In which case it wouldn't matter about going slightly weaker with the mortar anyway)?

    I know what you are saying re outside ffl, so maybe a aco type drain or French drain might also give any dpc a fighting chance
  5. Multiskillmaster

    Multiskillmaster New Member

    You’re welcome.. the stronger the mix the more chance of the pointing staying put...I point patios with 2:1 full depth and never had the joints blow with frost.
    Your bricks LBC dapple lights..have a moderate frost rating and a pretty good strength rating... modern houses shouldn’t move, they are built rigid...obviously there is minimal thermal movement, but if there was ‘movement’ this would need to be a lime mortar per Victorian properties, as these had minimum foundations and moved with the ground..and as such flexed and didn’t crack. Yes you are spot on...the efflorescence on the course below damp shows they are saturated, water is being fed into the brick from the soil against the brickwork. If you bridge the DPC water can travel across the mortar, especially weaker or leaner mixes, if you could rake out further under the existing carefully I would slide a slither off new DPC in and point that top and bottom, the lateral lap isn’t the best but it will stop the water, and looks right from outside. I don’t know how many lineal metres you have to correct.
    Mogzy1985 likes this.
  6. Rob Denness

    Rob Denness New Member

    Yes I have considered lapping a new bit of dpc in there, but I wasnt too keen on undermining the brickwork too much more, but also worried about capillary action due to the small overlap that I might achieve. Do you think tanking as it is now with blackjack or similar, then forming a plinth might be the way to go?
  7. Multiskillmaster

    Multiskillmaster New Member

    You can take all the mortar bed joint out up to 1 metre...with no support (as long as there is not an opening very close above ) nothing will happen. So you can take out 50mm deep mortar safely and lap the dpc under by 25mm..will be effective synthapruf is a messy job. Keep it clean and simple
  8. Rob Denness

    Rob Denness New Member

    Thanks for that. I sent the picture to a building inspector today, and he said an asphalt plinth could be made to go around it. However, if going down this route I'm sure it would be worth reducing the FFL immediately around the walling beforehand. Just think it's going to be an expensive way to do it..

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