Rotten joist and wall plate replacement

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Hi,

I'm in the process of replacing my ground floor floorboards with 22mm t&g chipboard. This is as a result of having to rip the previous floor up to remedy issues with various services.

During the process I've discovered evidence of an historic damp issue which has left a joist end, and the portion of wall plate it was sat on, rotten.



This joist is situated under the area where the sink was located, by the rear wall. I need to replace that portion of the joist to ensure adequate support of the chipboard. The rest of the joist runs the width of the kitchen and seems fine. It is supported at intervals by dwarf walls.



I'm no builder so I'm looking for advice. I think my options are;
  • Run a new piece of timber in parallel from the dwarf wall to some concrete blocks placed on the oversite - possibly using mortar to get the appropriate levels.
  • Cut the existing joist at the dwarf wall and butt join a new piece that runs into the void in the wall where the previous joist was positioned. The issue which this option is that the wall plate at this location has rotted leaving a void. There is enough remaining, I believe to support a replacement.
I was planning to treat all the wood with woodworm killer as a precaution.

The other issue I have is that the mortar under the brick in this area has crumbled, effectively leaving a brick floating in mid-air as shown below.



The lime seems to have been washed out leaving just sand which has crumbled out.

I was planning to fill the void with gravel, as the void is around 120mm deep, and then pack it out with a sharp sand and lime mix. I've never worked with lime before. I haven't even seen it at the merchants before but my understanding that since these are solid walls, l should be using lime mortar rather than cement, especially near ground level.

As ever, advice based on experience is welcomed.

Cheers(y)
 
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I'd solve the first issue with blocks on the oversite, like a mini pillar...
The second, I'd whack a few cut bricks in there and mortar the gaps.
I wouldn't bother with lime for such a small repair, it won't impede "breathability" and will be set solid fast.
I'm sure you'll gey lots of decent advice here, however, that's how I'd do it.
Minimal effort, same outcome.
 
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OP,
Why not post pics of the joist tails and the plate they are on across that whole wall?

If you drive a screwdriver or chisel into the two joists shown so far you might find that they have been hollowed out with rot.
Start probing about 150mm from the plate, & keep probing back until you reach the knee wall.

There's no DPC under either main wall or knee wall plates, and no DPC capping of the joist tails - plus there's maybe limited through ventilation in that sub-area?

Air bricks should have been installed every 1.5m to 2m.
Ground level outside should be lower than any existing DPC.
The pockets and lack of mortar are not important & are easily dealt with - they are not your problem!
There are signs of numerous remedial plastering attempts - besides the leaking sink perhaps there was or still is rising damp in the walls?

Dont ever use woodworm chemicals as a precaution - only use on active woodworm infestation.
Active means you must actually see the little mechanics.
 
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Build a block sleeper wall with dpc on mortar.

Blup
 
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Have you def resolved the leak? My guess is the waste was leaking on the corner, as the water seems to spread from below it.

Blocks with damp membrane underneath and on top, then some timber to bring it up to height.

Any timber that is flaky from rot, remove and replace. Soak it all with triple action wood treatment.

That's pretty much what I have had to do.
 
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