White salts on bricks below the dpc

[Jenniehorner]

Hi
I am attaching pictures of our wall which has a lot of white and black salts on the bricks below the dpc. No cavity.
We’ve replaced a row of paving blocks with gravel and scrubbed off the salts but they come back. There is no damp in the house. It is unsightly and wondered if there is anything we can do? The wall above the dpc has been treated with Stormdry and we wondered if it was worth treating the bricks below with Safeguard Multi surface biocide and then Stormdry them? But worried we might stop the wall breathing and cause problems.
Advice very welcome

 

[Cubist]

Sorry to disabuse you but there is no DPC per se in that wall. At some time in the past a chemical agent of some kind has been injected to create such a barrier but few, if any of these were/are effective. In addition the chemicals used can and do degrade over time to become even less effective than they first were. The salts and moulds you are seeing may be due to either or both descending damp from rainwater running down the external walls or damp rising from the footings/foundation. In your shoes I would consider a close examination of all the entry holes originally drilled to inject the DPC chemicals and repair any/all found to be allowing water entry. I would also consider increasing the width of the stone gravel filled channel to around 30cm and excavate below it to a depth of about the same with a view to enhancing the drainage away from the surface of the wall - a search of this site for French Drains and the Zebcolm Trench would be useful to you. Beyond that anything you may be able to do to enhance airflow around and along the foot of that wall will also be a big help,

 

[Jenniehorner]

Dear Cubist
Thank you so much for your advice that all makes sense. The wall was originally the end of a barn and converted over 30 years ago at which point the chemical damp proof plugs were likely to have been done. I like your advice on checking the plugs and we will repoint the bricks at the same time. We recently had to dig a trench about a metre away from the wall and were surprised to find no excess water so I think your thoughts on water running down to the unprotected bricks makes sense. We can certainly widen the french drain and go deeper. It is all open around the wall so nothing to improve there.

What do you think to sealing the bricks with Stormdry after cleaning or would that cause other problems?

 

[noj]

It seems to demonstrate that the injected dpc could actually be working! Damp is only rising to that point and no further. But if the internal floor level isn't above the height of the holes then you've got the perfect recipe for internal damp...

Alternatively the Stormdry above that point is making the area under the holes the only place moisture can exit the wall, concentrating the damp.

Additionally, if it was originally a barn that housed animals there simply could be a high level of salts at the bottom - many years of urine seepage.

 

[Cubist]

Hi Jennie, I'm not a great fan of masonry sealants as I believe these can operate to trap moisture generated indoors and reduce the opportunity for air movement to carry it away from the external surface.

 

[Jenniehorner]

Hi Jennie, I'm not a great fan of masonry sealants as I believe these can operate to trap moisture generated indoors and reduce the opportunity for air movement to carry it away from the external surface.

I am with you on your view which is why we have hesitated in applying it to below the row of plugs. It wouldn’t do any harm in cleaning the bricks with the biocide would it?

 

[Jenniehorner]

Hi Jennie, I'm not a great fan of masonry sealants as I believe these can operate to trap moisture generated indoors and reduce the opportunity for air movement to carry it away from the external surface.

It seems to demonstrate that the injected dpc could actually be working! Damp is only rising to that point and no further. But if the internal floor level isn't above the height of the holes then you've got the perfect recipe for internal damp...

Alternatively the Stormdry above that point is making the area under the holes the only place moisture can exit the wall, concentrating the damp.

Additionally, if it was originally a barn that housed animals there simply could be a high level of salts at the bottom - many years of urine seepage.

So presumerably all we can do is clean and re mortar the bricks?

 

[Jenniehorner]

So presumerably all we can do is clean and re mortar the bricks?

So presumerably all we can do is clean and re mortar the bricks?

So presumerably all we can do is clean and re mortar the bricks?

Cubist
It looks like the internal floor is one course lower than the row of plugs. So if chemical damp course treatment is hit and miss what can we do about it? There is no apparent damp on the inside wall.

 

[Jenniehorner]

So presumerably all we can do is clean and re mortar the bricks?

So presumerably all we can do is clean and re mortar the bricks?

So presumerably all we can do is clean and re mortar the bricks?

Cubist
It looks like the internal floor is one course lower than the row of plugs. So if chemical damp course treatment is hit and miss what can we do about it? There is no apparent damp on the inside wall

 

[Cubist]

I am with you on your view which is why we have hesitated in applying it to below the row of plugs. It wouldn’t do any harm in cleaning the bricks with the biocide would it?

Nope.

 

[Cubist]

Cubist
It looks like the internal floor is one course lower than the row of plugs. So if chemical damp course treatment is hit and miss what can we do about it? There is no apparent damp on the inside wall.

Sorry, missed this. That's, odd to my mind but then my mind works differently to most Chemical DPC installers. Nevertheless its good news that theres no damp evident indoors and this may underpin @noj assertion that the chemicals did some good. Frankly theres not a lot more you could or should do in that regard in my view, just keep an eye on it.

 

[Jenniehorner]

Thank you

 

[a twig]

Squinting at the photos through rose tinted glasses there might be an original DPC in the mortar at the level of the gravel - could be worth investigating by very gently chiseling away a small bit of mortar and see if you can see any slate there.

That said if the property is dry internally then I’d be inclined to let sleeping dogs lie

 

[Jenniehorner]

I will investigate - thank you