Is this period "concrete"?

[a twig]

As per my chimney thread, I've started breaking out the 1980's concrete floor to put in proper footings so I can re-instate the chimney breast.

Upon breaking out the first section, I've found something a little unusual and hopefully the PP hive mind can shed some light.

Underneath the concrete, following the lines of the old chimney breast, appear to be some kind of footings, however, they are not particularly deep, nor are they particularly solid.

As far as I can make out it appears to be a mixture of clay, aggregate and lime mortar. I'm going to have to dig it out to put in proper footings anyway, but before I do I thought I would ask around here if anyone knows what it is/why it was there. Cottage dates back to ~1850s as far as we know, so could this be some kind of Victorian "concrete"?

I'll try and put a picture up later on.

 

[Zebra]

Clay wouldn't make very good footings, I don't imagine. Is it a clay soil where you are? Could it be some sort of loose backfill from when the chimney breast was taken away? Maybe even the sweepings of the old mortar?

 

[Penners]

Are you sure that the clay mixture does actually follow the lines of the old chimney stack? As Her Stripeyness says, I can't imagine anyone using that mix (sensibly) as footings. However, if it were simply a base for an old hearth, that might be a bit more credible. I could imagine any old rubbish being chucked into a shallow hole for a hearth to be built on top.

 

[a twig]

Well, I dug out another 6" or so yesterday so I could pour in the new footing.

I can say that it definitely follows the lines of the old footing, and consisted of clay with bits of stone etc. It really looks like someone had built a rubble wall into a trench but used clay instead of lime mortar. The clay isn't from the soil, as the soil around the "footing" is a completely different texture and colour, with no clay at all. Really odd!

Anyway, it's all dug out now, and some more solid footings put in place. Couple more days for that to cure then I'll do the other side. Then purchase some materials, book a couple days off work and crack on.

Quick question, I'm doing it in blockwork. this will be tied to the existing stone walls. The stone walls will then be boarded (as there are a lot of old water pipes etc which look pretty unsightly - planning on using that breathable wood/fibre stuff for the boarding) and then the whole lot will be lime plastered. Therefore should I use hydraulic lime for putting up the new blockwork breast or would cement mortar be ok?

 

[Zebra]

Interesting question! This relationship between block, mortar and plaster is one which I've been looking at in some depth, as I have a new kitchen extension in thermalite block, which I am planning to lime plaster, just because I want it to blend in better, and because I like lime plaster.
I am also using woodfibre boards and woodwool boards in various other areas.
Are you planning to use a fat lime plaster, or NHL? Because I am led to believe that using fat lime plaster over modern blockwork with cement mortar is not a good idea because the joints show through (although on the test patch I did about a week ago, I can't see them....). Perhaps, if you used a NHL mortar, then you could use a fat lime plaster straight onto the blockwork, although there might be other disadvantages to this system that I'm not aware of.
If you are going to use a NHL plaster, then I think you could get away with a cement mortar.
I started a thread on a very similar topic recently:
https://www.periodproperty.co.uk/forum/viewtopic.php?f=1&t=14923
The option I'm going for in the end is a NHL3.5 plaster. I'm planning on getting started just as soon as I get around to it, so I'll let you know how it goes.