Damp issues

[sw19ric]

Hello,

First time forum user, I'm looking for some advice on whether a chemical DPC is necessary.

It's a circa 1900 mid terrace house. The survey showed high damp readings on the front external wall and the recommendation is the standard chemical DPC and replastering with a waterproof sand and cement render.

The thing is, there was a blocked drain outside the wall right where some of the highest readings were. It was blocked solid with soil and roots. There was also ivy climbing up the front wall all the way up to the roof, blocking the gutter and causing it to overflow and water to run down the wall. It seems highly likely this was the cause of the damp.

It's all been cleared now and rainwater is flowing properly into the drain, but there are still high damp readings in some areas of the wall.

On stripping away the wallpaper, I see a tide mark on the plaster under the bay windows. This is about 2 metres away from the drain, so probably not likely source. The shape of it doesn't look like rising damp (see photo), it seems to be coming down from the corner of the bay window and spreading out to either side, could this just be condensation from the window, or a leak perhaps? I wouldn't have thought 'rising damp' would make a mark of that shape.

Any advice would be gratefully received, I'm trying to avoid injecting any chemicals or using sand + cement if possible!

Thanks!

 

[JohnD]

I'm looking for some advice on whether a chemical DPC is necessary.

No.

What has happened to the original (presumably slate) dpc?

the recommendation is the standard chemical DPC

never invite anyone into your home who sells chemical injections.

On stripping away the wallpaper, I see a tide mark on the plaster under the bay windows... it seems to be coming down from the corner of the bay window and spreading out to either side

show us the outside. It will be a building defect, perhaps a roof or gutter fault, or gaps around the windowframe.

the thing is, there was a blocked drain outside the wall right where some of the highest readings were.

I expect this is a brown, salt-glazed clay gulley. What town are you in? It was cracked in 1940 and has been leaking ever since. You will need to dig it out and replace.

It's all been cleared now and rainwater is flowing properly into the drain, but there are still high damp readings in some areas of the wall.

A wet, 9" brick wall, takes about 9 months to dry out. You can speed it up by chipping off the plaster and render, and setting a desk or room fan (not a fan heater) to blow air onto the wet area.

Clearing your airbricks and digging out any rubble so there is a good airflow under the floor will encourage water to evaporate off in the void.

 

[sw19ric]

Thanks for your reply JohnD,

Here are a couple of photos. The first shows the air brick - the bottom row of holes is blocked by the plinth. Do you think it would help add more ventilation if I hack away some of the plinth to expose the holes? I presume they've done that to keep it a certain distance above the ground level.

The second picture shows the same air brick from the inside, only two rows are visible, I think the top two are open, just blocked from view in this photo. Do you think this gives enough ventilation? This is the only air brick in the front wall. There is another at the back of the house, which was partially blocked by debris (soil, rubble) on the inside.

 

[tell80]

OP,
You dont know what you want because you dont yet know what's caused your problems.

You have rising damp.
You might also have sub-area condensation damp due to lack of through ventilation.
There has been previous work in the bay - neither wall render nor skirting are original.

The latest pics show extensive rot damage to the joists and probably to the floorboards.
The single air brick is inadequate. You need a number of air bricks at the front and rear of the house to provide through ventilation.

How far damage from rising damp is present on the front elevation isn't shown in your pics?
Can you take pics of any interior damage and pics showing the front elevation at ground level including the gulley(?) that was blocked?
Show on a pic the location of the DPC - scrape the mortar beds for it to show.

You will have to remove the bay skirtings - take care of the cable clipped to them.
Hack off all the render/plaster back to the brickwork.
Lift a number of floor boards to expose the rotting joists below.

Its a simple matter to test a gulley and drain for leaks.
A pic of the rear airbrick location would help?

 

[sw19ric]

How would I check the gulley/drain for leaks?

 

[tell80]

Why not respond to whats been suggested above before getting into "How to advice?"

 

[sw19ric]

There has been previous work in the bay - neither wall render nor skirting are original.

Yeah I thought that, why are parts of it grey - is that a cement render from a previous damp proofing attempt? It feels much colder to the touch than the lighter areas.

The latest pics show extensive rot damage to the joists and probably to the floorboards.

Yes there is a lot of damage to the joists, not so much in the floorboards though. Mainly in the corner of the external wall opposite where the drain is.

How far damage from rising damp is present on the front elevation isn't shown in your pics?

do you mean how far up the wall? it's patchy, so in some areas there is no damp, then a few inches left or right there are high damp readings. so it's not at a uniform height across the wall.

Show on a pic the location of the DPC - scrape the mortar beds for it to show.

I can't see the DPC on the outside - I think it's covered by the plinth. Should I be able to see the DPC from the inside under the floorboards?

 

[tell80]

Your first question ref previous work doesn't matter: whatever was done hasn't worked. The reason I mentioned it was to show you that the damp problems had been around for a while.

Next question. The particulars dont matter - all should be revealed when the floor boards are lifted.

Next. No, I mean across the interior of the wall, & the exterior Why not remove all obstacles, and, as best you can, take pics showing the rear elevation at low level - do the same at the front elevation. Clearly show air bricks and plinths.

What I'm looking for on the interior is bubbling wallpaper, and discolouring to the decorations.



Yes the DPC should be just visible when viewing from under the floor.