Damp Advice

[Ydraiggoch]

Hi,

I'm hoping someone can advise whats the best way to approach a small damp problem I have. And tell me if what I'm planning is correct.

First of all the dampness seems to be just in one corner of the room. There are 3 things I've noticed that could be causing it.

1) Under the floor there was a pile of debris (Soft sand / cement stuff) bridging between the floor and the wall over the DPC.

I've removed the pile of debris in this pic, but you can clearly see the DPC.

2) On side of the wall there is about 1m where it looks like no DPC has been installed.

You can just see where the DPC stops just to the right of the middle of the photo.

3) The path outside is on a slope and on the wall where the DPC stops (as bove) the path is higher than the DPC Level

DPC line is the lower mortar line at the corner

4) The final issue I see is that the Cavity wall is filled with those grey insulation balls. These must surely be acting as a bridge across the 2 walls (Outer & Inner)

So, my plan to fix this is to use a chemical DPC in the area where there appears to be no DPC. For the outside path, rather than lower the whole path which is a major job, I was thinking of cutting a channel between the house and the slab ~12" and digging down to below the DPC Level. I would then fill the channel with Chips (hoping that any water would drain away better??)

This doesn't solve the bridging problem, but will hopefully improve the situation considerably. And knowing that the damp problem isn't a major one, I'm hoping my ideas will clear it?

Any suggestions to further help this problem will be much appreciated. Thanks in advance.

 

[bobasd]

Your first pic shows a joist sitting on a wall plate. the wall plate doesn't seem to have any DPC, unless that bit of black stuff below the plate is the DPC?
Probe the joist and the plate looking for softness and rot.
I dont see any black DPC material only a thick bed of mortar where you say the DPC is?

are we being shown a DPC concealed in a mortar bed in pic 2? whats covering the long ledge? whats dangling down - is it a spider's webs or vegetation?
i dont see any air bricks in pic 3 - how is the underfloor ventilated?
How do you know its a cavity wall with cavity insulation?

There's no Bellcast at the bottom of the render - the metal stop-bead should be cut out and replaced with a plastic Bell Cast.
You should have Bell cast's over all openings in the render.

Would you please post pics showing the damp signs inside the house?

 

[Ydraiggoch]

hi bobasd, Thanks for the response.

To try and answer your questions....

The Black Stuff under the wall plate is the DPC (Plastic roll stuff)
The Joist is solid, no sign of rot on that. There is a small area (~3") of wall plate that has gone soft, which was where the pile of debris was that was bridging across the DPC.

Pic 2 - The DPC looks like it stops where I have marked DPC in the picture. The rest is as you say a solid line of mortar.
The Ledge at the bottom is covered in dust (Not sure why I have ORA in the box). The Ledge itself is covered in a black tar like substance (As is the rest of the floor)
No vegetation just spiders webs and all dry too.

There are Air Bricks out of Picture. Plenty of air getting in as you feel the breeze when you lift the floor boards.

I can't send you pics of the damp areas as I've now taken the plaster off in that area (full room renovation). But there was no real staining as such, just slightly damp to touch and loose wallpaper along with a distinctive damp smell.

The room also had polystyrene tiles ~3mm glued to the walls too (not sure if this could have contributed?)

Hope this helps

(I'm not sure what the Bellcast is, so will look it up)

 

[bobasd]

Any staining, damp touch, loose wallpaper and distinctive smell means its damp - typically rising or penetrating damp.
Polystyrene tiles are often used to cover over damp signs. remove them, they create bad smoke in a fire.
It looks like serious attempts have been made in the past to do something about the damp in the walls and on the oversite soil - are you on a hillside?
Joists on masonry must sit on a DPC - joist ends going into a wall must b capped with DPC material.
Maybe your best bet is to cut the concrete and make a French drain - but will it have to return around the rear of the house, and hopefully discharge under the concrete at the front elevation corner?

 

[Ydraiggoch]

Apologies bobasd, you'll have to forgive my ignorance to some of your terms.

When you say about 'serious attempts have been made to do something about the damp' are you referring to the black tar stuff? If so, I assume this has been done at the build stage (1970s) as its all over the underside of the house. The house is built on a hill side though. Infact the part of the house we are looking at here is actually upstairs, but when you get to that part of the house its next to the back garden and so is on another 'ground' level (if that makes sense?)

I'm not sure what a French drain is, but will look it up. Could you explain where you think it would need to run again for me? I'll try to post a layout of that section of the house
Thanks again

 

[Ydraiggoch]

Hope this helps with understanding the layout?

Oh, and I have removed all the polystyrene tiles!

 

[bobasd]

The bitumen then was a pre-emptive attempt to "waterproof" the footprint of the house.
It wont work and you might have to live with a certain amount of damp.
The ground floor should have been built higher say with a couple of steps leading up to the external doors.
That would have made the front of the house much higher and cost the Builder more.
why they would use slate as a DPC in the 1970's i dont know?
where the letter D is thats the outside corner - you would just have to let the French drain moisture discharge under the concrete around there.

 

[Harry Bloomfield]

I'm not sure what a French drain is, but will look it up.

It just a pipe, with plenty of holes in it, to hollow water to enter it easily, usually surround by gravel or similar which would it easy for water to drain into the pipe. The pipe then drains to wherever suitably lower. You can buy the pipe ready made, or make one up by drilling the holes yourself.

 

[Ydraiggoch]

So, I think I'll crack on with my plan then.

Inject the Chemical Damp course where I think there is none.
Cut the slabs closest to the house and install a French Drain

Hopefully that will help reduce any Damp that is there

Once again, thanks for the responses. I have learnt a lot using this Forum over the years and continue to do so!