Why are my bricks so wet?

[Mike66]

I was concerned about a gap that had formed between my concrete path and the wall of my house. Over time the path has sunk and now slopes toward the house, so during rainfall I was worried that water might be running into the gap and potentially causing damage to the brickwork or leading to damp issues inside. (This was checked and no internal damp problems were found.)

To address this, I cut a channel and will be installing channel drains. Since doing this, I’ve noticed something unexpected: after rain, the bricks in that area are now becoming very wet, seemingly through capillary action. This never happened before, even when water was running straight down the gap.

I’ve now realised that the bricks below the original pathway level are exposed, and quite a lot of the mortar has come out of those joints. Could this be the reason the bricks are now getting so damp (as shown in the picture)?

I assumed installing a drainage channel would improve things, but it seems to have made the wall wetter. Any ideas why this might be happening? And do you think I am doing the right thing by installing the channel drains? Thanks in advance.

[Redbeard]

I don't know how likely this is, but try it:

 

Previously you had just concrete. I assume the top pic is 'before'. Now you have mud and broken concrete. It looks as if mud has splattered up the wall and has imparted a layer which absorbs water. So is it that the bricks area completely soaked through, or that the 'mud overcoat' is wet?

 

BTW, you said

8 minutes ago, Mike66 said:

(This was checked and no internal damp problems were found.)

As this is a cavity wall you might not see damp internally even if the ext wall was wet. This was, after all, the original idea of cavity walls, that a failure properly to maintain the external skin would not automatically result in damp internal conditions for the tenants ('tenant' used advisedly as experimentation with cavities started in 19th C when the private rented sector accounted (if I remember my Housing lectures properly) around 90% of the housing stock. (I accept, of course, that that cavity in your pic may well have been retro-filled if it is, as I guess, c1960s).

[Mike66]

Hi, it is definitely the bricks that are wet. And the property is 1970s and there is a cavity wall that is filled with a foam type substance. And yes, the top photo is before I decided to take the concrete up. I have attached another photo that shows the underneath bricks with a fair bit of mortar missing. 

[Mike]

I agree that it looks like water splashing, mostly below DPC level so nothing to worry about. No harm adding drainage channels - it should reduce the splashing.

 

1 hour ago, Mike66 said:

underneath bricks with a fair bit of mortar missing

They're just common bricks, intended to remain invisible below the ground level. The mortar was almost certainly never there in the first place, though if a tidier brickie had done it then it would be.

[elias837]

Yes, that’s very likely why. You’ve exposed bricks and mortar that were never meant to be below ground or regularly wet. Old mortar washing out makes it worse, as it lets water sit and wick up by capillary action.

Before, the path probably acted as a crude barrier. Now rain is hitting exposed, porous brickwork directly and soaking in.

Channel drains are still the right idea, but you’ll also need to repoint those joints and ideally add a small gap or drainage layer between the wall and path. Make sure finished levels stay below the DPC and water is directed away from the wall.

[MikeGrahamT21]

They look very much like london bricks, as were widely used at that time, which are quite a soft and porous brick.

 

Clear a bit more out of that trench, and then you're going to have to give it some real good time (and fine weather) to fully dry out, then it may be worth applying some brick protection, which allows the bricks to breathe, but essentially makes them water resistant. Of course also make sure the pointing is sound before filling the excavated area up with some gravel or a drain.

[Mike66]

I have had a linear channel drain cut into the concrete along the wall.

 

After this was done:

 

New brickwork below the channel became exposed

Some of this brickwork had missing/poor pointing and the builder didn’t repoint before inserting the channel.

After rain, the wall started getting noticeably wet low down, forming a horizontal band

The wetness appears above and below the DPC, is uneven, and is not splashback

 

 

There has now been over a week with no rain, yet the bricks have not fully dried, and the damp pattern has barely changed. This never happened before the channel was installed.

 

I think I have created a moisture problem that didn’t previously exist, possibly due to capillary action from the ground or the newly exposed brickwork.

 

 

Would removing the channel and reinstating the concrete be a sensible way to stop the wall drawing in moisture or is this new plan possibly making things worse. This is a classic example of leaving well alone. I should have ignored the original gap. The bricks were never wet. Thanks for all the replies. 

[MikeGrahamT21]

Looking at your original photos, it’s definitely an improvement how it is now. You will find the white powder appearing (efflorescence) as they dry out, and as they’ve been wet for so long this is bound to happen, keep brushing it off with a stiff brush to keep it to a minimum.

 

when I dug out to do external wall insulation below the DPC, I went all the way down to the foundation and it took around 6 weeks of fine weather for it to be completely dry, it will take some prolonged time especially at this time of year when it’s cold and damp most days

[Mike]

Yes, the white is efflorescence caused by the deposit of salts from the brickwork onto its surface as the moisture evaporates. Efflorescence is harmless but can take a very long time to disappear. It may also appear damp as the salts themselves can absorb moisture from the atmosphere. Bush it off every few months or, if you prefer, buy an efflorescence remover (a mild acid) from your local builder's merchant; it may require more than one application.