Damp course and plinth (duplicate threads merged)

[Gasplumber]

Hello guys I’ve got damp above my skirting board all around the living room external walls.
It’s a solid wall 1930 house with suspended timber floor.

I dug up outside and broke off the cement render plinth and there is a damp proof course about 90mm below the external ground level the bricks are knackered.

what can I do to stop the damp should I just remake the plinth all around the house.
And assume water must of got in through where the plinth meets the wall.
Or do I have to dig down a further 150mm and fill with gravel? I’m thinking the damp cours would still be bridged tho! So not sure what to do.
Thanks

 

[HERTS P&D]

Welcome GP, you have answered your own question. dig around the house and fill with gravel.

Andy

 

[Gasplumber]

Thank you. With the gravel does the top of my gravel ditch have to be 150mm below damp course?
Also would you just sand cement render a plinth starting above damp course to seal the bad bricks?

 

[HERTS P&D]

Yes to all of the above.

Andy

 

[Nige F]

Hello guys I’ve got damp above my skirting board all around the living room external walls.
It’s a solid wall 1930 house with suspended timber floor.

I dug up outside and broke off the cement render plinth and there is a damp proof course about 90mm below the external ground level the bricks are knackered.

what can I do to stop the damp should I just remake the plinth all around the house.
And assume water must of got in through where the plinth meets the wall.
Or do I have to dig down a further 150mm and fill with gravel? I’m thinking the damp cours would still be bridged tho! So not sure what to do.
Thanks

Before you start digging - locate the airbrick inside the house - is it above or below the wood floor ?

 

[Gasplumber]

The air brick is about half and half
The top of my 6” skirting is at the top of the plinth.

 

[Nige F]

Thanks , so how is the underfloor ventilated - other lower airbricks ?. It's a strange setup with the dpc low as it is . Maybe others have opinions on the validity of a new dpc injected , as digging out etc. is a lot of work.

 

[Gasplumber]

It’s ventilated by only half the air bricks.
If I dig it out I’ll end up with probably a 300mm drop from external floor height to top of gravel line as I can’t lower mine and the neighbours drive haha.
Gonna look crap.

I’m wondering if they put the plinth there as they knew they were going to cover the dpc and that somehow worked for years.
Only lived here a year!

 

[Gasplumber]

Like the title says I’ve got a 1930 semi and a bit of damp in the walls above skirting board internally.
Upon digging outside the damp course is below floor level and bridges by this plinth of render. why would they of done this

is this how they used to dampproof.
As I don’t know what to do

 

[bobasd]

Your wall looks to be a cavity wall?
No headers to be seen?
You give a 1930's date but even with a 1930's date most properties had cavities by then.
If there is a cavity then maybe its blocked and bridging moisture?

The bottom half of the air brick is blocked off - why?
Can you poke a screwdriver through the openings in the upper air brick - how far does it go in?
Do you have air bricks around 3-sides of the property for through ventilation?
Why not remove the affected, living room skirting, & lift some floor boards to see whats happening below the suspended floor? Esp any air bricks or rotting joists?

A French drain below the DPC might help or might make things worse - worse case you could end up with an open slot
or a water filled moat - it needs someone on site to see all round conditions eg. such as the slope of the drive.

Plinths are nonsense and cause much damp damage.
Esp the using of cement in the plinth mix - a 4:1 sand and lime is your best re-render mix.

Whatever happens outside you will have to hack off the interior plaster to 300mm above damp signs and render with a 4:1 or 3:1 sand and lime mix, and a Remedial finish - dont use anything Gypsum.

 

[Safety First]

Looks to me as though they have tried to mitigate the damage of raising ground level by creating a a bitumen coated plinth that will shed water. Water that hits it from splashing on the ground will indeed be shed, but it will of course also draw moisture from the ground. I am presuming location of dpc, can you confirm exactly where you have found it?

 

[JohnD]

The cement plinth was an attempt to cure or conceal damp at the bottom of the wall. Unfortunately it has the opposite effect.

You seem to be badly damaging your brickwork.

Where is the DPC? Are the floors wooden or concrete? Why does your airbrick look blocked?

The paving appears to have been laid by a numbskull who doesn't care about the damp caused by raising the external ground level.

 

[Gasplumber]

 

[Gasplumber]

Wooden floors and that’s where I found the dpc. Looks like painted on bitumin and it’s stuck well to the brick.
Under it’s rendered still. Not sure how many more courses down as didn’t dig more.

 

[Gasplumber]

To be honest I sealed the bottom of vents to stop rain getting in as I was seeing damp. mill take a brick out and see if it’s got a cavity