Damp

[Doug789654]

Hi All

Standard damp question here...

I live in a 1890's terrace house and seem to have a small damp issue at low level on an external and party wall corner. It has been like this since I moved in to the house about 4 months ago (surveyor missed it as there was a bookcase in the alcove).

The main problem area is only about 30cm high and about 30cm wide. Here the lining paper was very slightly damp to the touch and came off easily. This is on the external wall. This is the photo with the sockets in.



On the adjacent internal wall there is some slight discolouration to the paint at about 20cm high, but it feels the same as the rest of the walls and the lining paper isn't going anywhere. See the other close up photo.



I'm assuming this is rising damp, although there seems to be a damp patch on the outside of the wall but higher up. Perhaps this is a red herring?



The house had extensive treatment in the mid 90's that seems to be working everywhere else.

What can I do to resolve this? Any thoughts?? I am planning in decorating this room soon so would like to get it sorted before starting.

Thanks

Doug

 

[vinn]

1. Is the floor solid or suspended? It appears to be level with or lower than the ground level outside?
2. The wall is solid and the Remedial treatment company should have used a render not gypsum plaster in any re-plastering work.
3. If you probe the mortar beds you might find a slate or bitumen DPC behind the smeared on pointing.
4. Notice that some attempt was made to point up the lower brickwork (probably the Damp company's idea of Remedial work) - all that rear elevation, and the adjoining yard party wall, need raking out to 25mm and re-pointing.
5. The party wall is butting up to the main elevation and most probably bridging penetrating moisture into your rear wall.
6. Why not show pics of the whole rear elev. and the top of the party wall?

7. All affected/stained plaster will have to come off to say 600mm height and be rendered with a sand and lime mix. Plaster/render should stop 50mm shy of the floor - no contact.
8. Skirtings will have to be removed.
9. The outlet is at risk of damp arcing - (& its overloaded).
10. Is the chimney breast ventilated top and bottom? Was it swept before blocking up?

 

[Doug789654]

Hi Vinn

Thanks for taking the time to answer and happy new year. I'll answer your points in order.

1. It's a solid floor throughout the house. I believe it was done in the 70's when the front and back rooms were knocked through - this is based on wiring age. It is roughly the same level as the outside. The dpc rods are in the lowest course.

2. It was a specialist damp company that did the work. I have the original scope of works in the attic so I will have a look into what they used. My surveyor identified very low damp level in a small bit of the kitchen and recommended re-plastering with a special plaster (namely "Sovereign Renderlite" or "Thistle Dri-Coat") - are these any good?

3. I'll have a look at this when it stops raining but I haven't noticed anything like that on the untreated/unrepaired walls.

4. My surveyor did not comment on the pointing but did look at it as he mentioned some areas that need repairing above windows.

5. It does look like that. There are signs of a vertical barrier in the edge of the wall, but this ends in the middle of the damp looking patch on the external wall - does this need extending up?

6. Photo.



7/8. OK I'll look into getting that done. I have some other plastering to get done anyway.

9. I understand the damp arcing but not the overloading? At the moment it just has a table lamp and a set of xmas lights on a 24hr timer plugged in.

10. Chimney is in use as the flue for a gas 'log burner' - this was professionally installed about 4 years ago so I can only presume it was done properly. All other chimneys are vented top and bottom.

Thanks a lot.

Doug.

 

[^woody^]

In order of likelihood, I'd put my money on
1. That garden wall causing lateral moisture movement.
2. A leaking gutter
3. The stack - with or without nr 1
4. The paving level - associated with nr 2

And potentially the pointing above the damp area

 

[vinn]

1. The lowest course in the pic is half buried so any chemical DPC (FWIW) should have been inserted in the higher bed or brick - allowing for the re-pointing, there's no sign of any holes in the pic?
As above, the external ground level appears to be too high esp. if the solid floor doesn't have a membrane (DPM).
If you remove the skirting in pic 2. then any membrane will be revealed.

2. DriCoat and Renderlite are fine - but what the D&T Co. specify & what they use are often two different things.

5. As above, the yard wall is a probable cause of penetrating damp - there are ways of isolating yard walls from main walls.
Besides re-pointing it needs coping stone cappings.
Matching vertical injected DPC's can be taken to the top of the yard wall (injected both sides of the wall is best) and the main wall - but again, its a matter of what they are worth?

10. The neighbour's external chimney breast is bleeding dark sooty chemicals - these have spread on to your brickwork - making it possible that you will have to hack off and render higher up on the inside surface.

 

[Doug789654]

Evening,

There is a membrane beneath the solid floor (can see it in other areas).

I haven't noticed a leaking gutter on either my or neighbours house.

The dpc holes are in the same course of bricks all the way around the house. Could I put a step in it? I'm getting the impression Vinn that you are sceptical about injected dpcs. Are they generally not good or just overpriced? What about the diy ones?

The vertical dpc is in my back wall as opposed to the garden wall/neighbours house wall. Where would the optimum place for it to be?

It's not the neighbours chimney joining the house at the garden wall, his whole house is a brick longer. Not sure why some of the bricks are black though.

Thanks a lot for your help,

Doug

 

[vinn]

With a membrane in place then its likely that the damp is a combination of penetrating damp from the outside and rising damp coming up in the wall through the remains of any previous damp courses.
Can you point out on a pic exactly which bed or course of bricks the injection DPC holes are in?

But to get the chimney breast business clear:
You have an internal c/breast with a gas log effect appliance.
Your neighbour has an external chimney breast which (as above), because of soot chemicals in their unswept flue is leaching these chemicals into your brickwork.
Can you post pics of the other side of the yard wall?
And can you point out on a pic showing exactly where the property boundary line is?

If the yard wall stays in position then vertical DPC's will work best in both the yard wall and the house wall - on both sides of the yard wall - however, its obscure exactly how the yard wall abuts the house wall and c/breast?

Chemical DPC's have a very poor record of effectiveness in my experience - however, some people report good results using DryZone.

 

[Doug789654]

Hi Vinn

I have added an arrow to the photo above showing the dpc. It is only in this corner that the it is half covered.




I don't think I've been explaining the chimney/wall interfaces well, so I've drawn a quick sketch on the computer showing a plan of the walls. This should clear it up.



I'm thinking as a plan of action:

1. skirting board and plaster off to 600mm AFFL.
2. re-pointing low levels outside.
3. injected dpc to yard wall and extend on the house wall (to level with the yard wall?).
4. injected dpc to bottom of house wall above the existing one?
5. replaster with appropriate plaster.

Seem suitable? Whats a guide for allowing the wall to dry out before replastering?

I'm guessing that this must be affecting my neighbours house too? I will have a chat with him this week if possible.

Thanks for you ongoing help!

Doug

 

[Gerrydelasel]

Injected DPCs don't work.
The outside ground level is clearly too high.

1) Lower ground level by 8 inches.
2) Wait a year to dry out.
3) Replaster if necessary.

 

[Doug789654]

Hi Gerry

To lower the ground level would involve excavating a lot of concrete and to be honest I don't have the budget to do that.

The issue is confined to about 30cm of the wall where the ground level is at it's highest so I could excavate locally here? As long as I ensure there is still a slope so the water runs away from the drain that could solve the issue?

Thanks

Doug

 

[Gerrydelasel]

The issue is confined to about 30cm of the wall where the ground level is at it's highest so I could excavate locally here?

Yes that would do in a pinch. You could then expand your excavations little by little over time, however much you can fit in your wheelie bin at a time! No need to break your back over one little damp patch.

 

[Doug789654]

How would I go about doing this?

The whole yard slopes to the drain which is on the kitchen wall. The area in question has quite a sleep slope so I could convert this to a gentle slope by taking about 100mm off the top corner and gradually making the reduction smaller until it there is no step over about a 500mm square. Does this make sense? I've sketched it out below:



This would make it so the outside was at least 1 course lower than the inside all round.

Is this something I can realistically do myself?

Thanks a lot.

Doug

 

[Gerrydelasel]

I don't see why not.

Could you live with gravel instead of concrete?

 

[^woody^]

Any damp from raised paving can be dealt with by coating the wall externally with a water repellant, rather than messing about with paving levels.

The position of that damp patch higher up the wall in the lastest image, shows that the issue is not related to rising damp or splashing. And the apparent dampness of that boundary wall supports this.

 

[Doug789654]

Could you live with gravel instead of concrete?

Definitely - I only moved in at the end of last summer and have been thinking of easy ways to hide the concrete as the yard is pretty big and all covered in it.

The position of that damp patch higher up the wall in the lastest image, shows that the issue is not related to rising damp or splashing. And the apparent dampness of that boundary wall supports this.

The damp on the inside of the house is below the visible damp patch on the outside wall. It extends from the floor about 30cm up (about 20cm above the top of the skirting board) in a rough semi circle. I've added where it roughly is to the external photo. It was raining when I took this photo so the whole thing looks wetter than it usually does.



I'm not sure if these are separate or related issues or if one is a complete red herring. I don't mind work so am happy to try different solutions I can do myself if possible.

Thanks, Doug.