Damp / Slate DPC / Render Breaching

[DampDan]

Hi!

Recently purchased a C1856 settlers cottage that was assessed as having rising damp during the pre-inspection. Got an "expert" out to check and they confirmed rising damp, which they can fix for bulk coin. Been reading this forum and I am 100% certain I can do something about this without having old mate come and inject my walls. Looking to get some confidence boosting recommendations, and confirmation of actions, before I start regretting my life choices.

There are a few spots that show physical signs of damp internally, and I am focusing on the largest spot for this post. The internal damage is minimal, but I suspect renovations occurred prior to our purchase so unsure what has been covered up. Below I have included a picture of the skirting and wall that shows rotting of the board and a very slight patch coming through the paintwork.

The outside wall that corresponds to the internal skirting picture is 1cm think render which is hollow in a lot of places. I removed a portion of the render, and it was mildly wet. Kept removing render until the hollowness was gone. You'll notice there are some nice Knapen tubes that have been inserted post render, in what I imagine has been a lifelong attempt to fix the damp issue.

The render extends the complete wall and goes into the ground to ensure a good amount of water can be wicked up (assuming). The bottom of the wall has a rendered lip which I removed and found what I think is a slate DPC. Picture below. Can anyone confirm? You can also see that the slate DPC (??) is at ground level, with the concrete path perfectly in line.

Now, I am looking for some confidence boosting remarks that let me know I am doing the right thing by removing the hollow render and the render that covers the DPC bridged to the ground. As I remove the DPC render covering lip it is moist so I figure this is a good thing to be doing. I also intend to remove the concrete and drop the ground level, maybe putting in a french drain as they look pretty nice.

Any words of wisdom or feedback that I am an idiot for anything I have done so far, please do let me know.

PS. The house has a musty smell that I have determined is coming from the gap between the skirting and floor. There is one particular spot that is nearly 1cm that has a good draught coming up. If I place a candle in front of that gap the house smells lovely. The subfloor ventilation seems poor, especially since two extensions were added to each side of the house. The back wall, in these pictures, has had two air vents added, which were done poorly and have the smallest hole behind them. I will fix these.

Dan.

 

[^woody^]

The musty smell is mould spores, and if that mark on the skirting is rot, then your problem is more likely to be rising damp or the high paving level, and not necessarily the render issue. Is the floor void properly ventilated? You may need to check the void for rotten timber joists.

Those ceramic tubes for damp control are a discredited system, but should be open regardless.

 

[DampDan]

I'm completely lacking knowledge in this area but I would say the subfloor ventilation is poor. The front of the house has 2 vents that are fully open with a quality install. The two at the rear, that I am replacing, look to be a rough knock out approximately 3cm wide and 10cm tall with a metal grill glued on. I've purchased some terracotta vents to match the front and will be making the cavities sized to suit.

I'm guessing the sides of the house had vents, but the extensions on either side have blocked them in toto.

Over the last few days, with the metal grills removed, I do notice a less musty smell. There is airflow that can be felt by hand, but it's by no means a forceful breeze. I do hope that it is working.

We had bulk rain last week that is not usual for this time of year so I thought that could be related. The previous owners did not mention anything, but who would as it's not really a great advertising campaign. "Best musty smell in Aus!".

There is no room to get under the floor. I'll pull the skirting sometime but opening up the floor is not a planned event this side of Christmas.

I plan to continue removing the render and opening up the slate DPC just because it is damp when I remove it. There is a smell to the wall when I pop off the render but whether it is similar to the musty smell is difficult to call. Your mould spores definately sounds like something I need to look at further.

 

[DampDan]

Today I got around to removing the skirtingboard. It had turned to what I would describe as cork. The wooden supports behind the board were basically dust that once resembled wood.

There is a smell, as one would expect, but I'm not sure if it's the musty smell I am getting. I've been inside too long now that I'm just use to it. Hopefully it's linked. The floor joists I can see below look solid with no dampness. The skirting supports to the adjoining bits are also still wood (not dusty wet nastyness) which I am glad.

Any rough timeframe I should leave this all exposed to air dry and become fresh once again?

Cheers,

Dan.

 

[DampDan]

Had a bit of a break from working on this issue but slowly getting back into it. The internal skirting board has been off since December and seems to have dried out really well. The external wall where the hollow render was removed has also dried out nicely over the last 9 months so next will be looking to do a proper render with materials suited to this kind of wall.

I do have a question regarding the lower part of the wall though. The photos below show that the left corner of this wall has sandstone (?) that sits on the ground and not on top of the slate DPC. To the right of these blocks the slate DPC starts approximately 5cm higher than the base of the stone. Is this a thing for a 1860s build? I find it odd that the rest of the wall is on slate, but this corner is not.

I've cut back the path and dug down to match the lower level of the sandstone to let that dry out. The ground was fairly wet but after one day is drying out nicely. Hopefully this is a good thing, and I can now consider options of how to stop these blocks from continuing to sit in a damp environment.

If anyone knows if this type of corner, having no slate under the blocks, is a thing please do let me know. I'm looking for ideas on how best to move forward with this one.

Regards,

Dan.

 

[George_engineer]

While it probably was built with the thinking that the slate will keep the sandstone from wicking up groundwater, it wouldn't have been built with the more modern concept of a continuous DPC. So it's no surprise it jumps around. Could be the ground was much lower in the past, or there was a lean to there or a doorway etc etc.

Directing water away and lowering the ground level is absolutely the best thing to do. Possibly even to the extent of some minor underpinning.

 

[DampDan]

While it probably was built with the thinking that the slate will keep the sandstone from wicking up groundwater, it wouldn't have been built with the more modern concept of a continuous DPC. So it's no surprise it jumps around. Could be the ground was much lower in the past, or there was a lean to there or a doorway etc etc.

Directing water away and lowering the ground level is absolutely the best thing to do. Possibly even to the extent of some minor underpinning.

I suspect the ground was lower and many owners ago th concrete path was laid. I plan to remove the path, look at possibly a French drain to add some elegance and then pace on the side of that.

Your comment regarding underpinning concerns and excites me. I've added a picture below but there is a definite crack directly above where the DPC ends that extends the full height of the wall. Would underpinning be able to correct/stop that from further cracking?

Thanks for your reply. Really appreciate it.

Dan.