Parging/Concrete skirting causing damp?

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Clearlight
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Parging/Concrete skirting causing damp?

Post by Clearlight » Sun Mar 10, 2019 10:53 am

Hi,

I'd really be grateful for any advice you can offer on the possible cause of a damp issue. I have a 1933 semi with original bay window (Picture 1) which is showing signs of damp in the two external corners of the bay.

There is a concrete skirting (parging?) around the base of the house which you can see at the bottom of the bay, which I am wondering if it is some sort of damp proofing thing that is perhaps no longer working properly? This extends all around the property and is the same next door.

The 'skirting' is not in very good condition and is cracked away from the wall in some places so I'm wondering if the deterioration of it may be causing the damp, or whether this 'skirting' is purely cosmetic and the damp is coming from elsewhere? Picture 2 shows the location of the highest moisture readings on the external brickwork (highlighted)

There is no damp elsewhere in the property and the ventilation bricks you can see in the pictures are clear and air is definitely flowing well under the property. From looking under the floor of the property there does seem to be some damp course under the main part of the building, but I couldn't tell if it extended to the bay - it isn't visible outside and was difficult to check inside.

The final picture (Picture 3) shows the damp inside. It wasn't noticed for a while because it was behind a seating unit in the bay window, otherwise it would have been dealt with sooner.

Any advice on what the concrete skirting is and whether it might be the cause of the problem would be very much appreciated. If it should be repaired, what sort of mix should be used to replace it?

Many thanks,
Andrew
Attachments
Bay3.jpg
Bay Window (Picture 1)
Bay3.jpg (303.34 KiB) Viewed 591 times
Bay2.jpg
Centre of damp area outside (Picture 2)
Bay2.jpg (300.18 KiB) Viewed 591 times
Bay4.jpg
Damp inside (Picture 3)
Bay4.jpg (258.89 KiB) Viewed 591 times
cotswold builders
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Re: Parging/Concrete skirting causing damp?

Post by cotswold builders » Sun Mar 10, 2019 1:58 pm

Its not serving any real purpose, and moisture is getting trapped behind the plinth and transferring across the wall , which is most likely an add on bay constructed in sold brick.
With no air circulation behind the boxing and a cold external wall will cause damp.
I'd cut the concrete away clean of the bricks and apply a couple of coats of synthapruff.
Lower the ground level a bit to avoid splash back.
If you want to replace the plinth use a 3\1 plastering sand with added water proofer, prime the wall first with neat SBR., with a chambered top.
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sammy.se
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Re: Parging/Concrete skirting causing damp?

Post by sammy.se » Sun Mar 10, 2019 6:07 pm

I'm in the middle of dealing with damp.
Couple more things to check for:

Is your guttering all OK and flowing well into the gully with no leaks near that area?

Are there any mains water pipes under that area that might be attracting condensation?

Is that window sill getting rain on it, and is it the flowing or splashing down the wall?

Those airbricks are at floor level - water is probably getting in through there... Digging a channel there is probably a good idea.

Sent from my Nexus 5X using Tapatalk
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Re: Parging/Concrete skirting causing damp?

Post by Clearlight » Mon May 06, 2019 8:22 am

Thanks very much 'cotswold builders' & 'sammy.se'.

After your posts I had a look and you are both spot on!
The nearby rain drain was blocked causing standing water in heavy rain which was I'm sure contributing to damp in the wall, and also there is a crack between the plinth and wall in close proximity to the worst of the damp on the inside so I suspect rain driven agains the wall is running down and into this crack.

I have cleared the drain and filled the crack temporarily to confirm this is the cause and then will do as you suggest 'cotswold builders' and replaced the plinth treating the wall beforehand.

Thanks again for your advice, it was really helpful.
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Re: Parging/Concrete skirting causing damp?

Post by wes56 » Mon May 06, 2019 9:59 pm

find your DPC by poking with a small screwdriver - when youve found it, mark the line on your pics.
the air bricks and joist tails should be sitting on the DPC.
examine the joist tails for rot.
the walls are cavity walls so take a few bricks out here and ther, and look for cavity blockages bridging inside the cavity - especialy at the bay damp area.
skirtings and flooring in the bay might be wet rotted.
the plinth has to be removed clean back to brick - right round the house.
dont try an replace it.
best practice is for a gap of 150mm below the DPC to ground level or the ground will bridge the DPC.

the paint should be removed from that panel of bay brickwork - but thats another story.
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