“Soily” mortar in Garden store

[Rrs93]

Hi all,

We inherited a poorly-built single brick garden store built at the back of our Victorian terrace. While removing some of the concrete render (white in the pics attached), I’ve discovered this black mortar which I can only describe as having a soily texture/smell. I’ve taken a wire brush to the area and it is just flaking off (like soil would!!). The black “mortar” does not extend the height of the wall but is rather in a particular spot. 

This wall is the adjoining garden wall with our neighbours and they don’t have this on their side (albeit they don’t have a bricked structure at all, it’s just garden), so presume it’s a result of our space and the construction thereof. 

I’ve had limited success on the web and I’m trying to understand what it is, whether it’s a concern and how to deal with it? Ultimately we only really want to board on top to create a utility / gym space so doesn’t have to be perfect, but wouldn’t want to board on top of issues. 

Cheers

[ProDave]

That looks to me like the bad patch has been infilled, different brick and coursing.  Was there a window before?

 

Is the mortar wet?  or dry and crumbling?

[Rrs93]

Thanks Dave - it is wet.
 

I’ve removed the render and discovered this patch. It’s possibly been trapped behind the render for decades so hoping it can dry out now I’ve removed it. is there anything else you can think of?

[ProDave]

What does this wall back onto?  Can you see the outside?  Or is this the outside I am looking at?

[Rrs93]

This wall is the boundary wall with our neighbours - it’s an external wall on their side but they’ve used it to create a single brick store room on our side. Sorry just noticed your question re. Window - no I doubt this would have been given it was an external boundary wall.

 

neighbours have said it’s not the same on their side but will check further in daylight 

[Redbeard]

Looks a bit *too* black to me, but here in S Yorks (and I am sure other areas too) we have 'Black mortar'. The (lime) mortar was made using an aggregate of mixed sand and steelworks or colliery slag. It's awful stuff to hack out, as it was also used  in basecoat lime plaster. 

 

I think as a theory that does not stand up, though, as if I understand you correctly the render was over the lot, and from what little I can see the render looks like sand/cement and thus probably much more modern than to date from the 1920s/30s heyday of 'black mortar'. Oh well, it was worth a thought!

[Rrs93]

2 minutes ago, Redbeard said:

Looks a bit *too* black to me, but here in S Yorks (and I am sure other areas too) we have 'Black mortar'. The (lime) mortar was made using an aggregate of mixed sand and steelworks or colliery slag. It's awful stuff to hack out, as it was also used  in basecoat lime plaster. 

 

I think as a theory that does not stand up, though, as if I understand you correctly the render was over the lot, and from what little I can see the render looks like sand/cement and thus probably much more modern than to date from the 1920s/30s heyday of 'black mortar'. Oh well, it was worth a thought!

Cheers. Yes the render basically covered all of the black area and below (I.e. not above the black area). 
 

the mystery continues, the mortar is so soil-like if someone told me in isolation to guess what it was, that’s what I’d guess!

[larry]

Scrape some into a pot and try to grow some tomatoes in it?! 

 

Does it look like the soil in the garden? Random idea but could you do one of those soil tests compare pH levels etc. Random thought. 

 

There were lazy trades even in the 1920s... It's a small area right? And it would have been dark so that would have limited growth? 

I mean literally no idea but if it quacks like a duck...

[larry]