Reusing Lime Mortar for Plastering?

[Flyfisher]

Did anyone watch the Victorian Farm on BBC2 this evening?

I didn't see it all, so might have missed some important context, but there was a bit where a chap was going to plaster some walls with lime plaster. It was explained that old lime mortar could be reused for this purpose after crushing it down to a fine powder and remixing it with water (and hair, of course).

I thought that lime mortars and plasters "go off" by a carbonation reaction with atmospheric CO2. I don't see how this can happen twice so what's the point of crushing old lime mortar into a powder and using it for a plaster mix? Is the end result a different type of plaster?

Unless I've misunderstood this lime alchemy stuff?

 

[Gervase]

No, you haven't misunderstood. The programme was utter b*ll*cks. Or rather, the edit was b*ll*cks, and the 'talent' was singularly lacking in such.

 

[Schoolmarm]

:lol: :lol: :lol:

 

[worms]

I didn't see the programme and I am quite happy to accept the b*ll*cks description.

Perhaps, though there is an underlying point that:

a) old mortar could potentially be useful instead of digging and carting new aggregate

b) in many situations there might be less than 100% carbonation and therefore old mortar might retain some useful properties

c) in the context of a Victorian building site, old mortar could have been mixed in with the limestone on the fire and converted back to quick lime

d) on a Victorian farm, c) could apply if they were using their own lime kiln

I guess with c) and d) it would partly depend on the relative availability and cost of limestone and in some parts of the country, the work involved in salvaging old mortar might have been worth it.

 

[biffvernon]

a) very true
b) can't be much left un-carbonated after a century
c) it would have to be a VERY hot fire!!!
d) if they have a lime kiln it would probably be more hassle than it's worth to reuse old stuff - you only find lime kilns within handcart distance of limestone quarries.

So I reckon a) is the winner.

 

[Gervase]

I reuse old plaster and mortar if it's available when knocking up new stuff, but I wouldn't fancy breaking it down by hand or with a log as they did on the programme - mine just gets pitched into the roller mill and ground down in seconds.. As Biff says, though, it doesn't have any reactivity and is only really of use as aggregate. You do have to add lime, otherwise all you'd get would be a sloppy bucket of wet sand!

 

[worms]

Biff,

I'm not trying to argue that the programme was right in any way, but...

in b) above, I thought the concept of old walls "healing" after subsidence was on the basis that the mortar deeper into the wall did not carbonate completely unless/until air managed to reach it (and that there was evidence of incomplete carbonation in analysis of some Roman buildings).

in c) did Victorian builders not sometimes make the quick lime on site? That is the fire I was meaning.

For d), while I acknowledge your much greater knowledge of geology in general and lime in particular, I am not (yet) convinced that you are correct. Surely quick lime and hydrate could not be transported as easily as limestone? So for the parts of the country with no ready supply of limestone, would the normal practice not have been to ship the stone to local kilns?

 

[Gervase]

You find incomplete carbonation where mortar has been completely shielded from the air - commonly under impermeable slabs - but in walls it does tend eventually to carbonate fully, even with granite or dolorite stone.
Limestone was shipped to local kilns, but the the production of lime was a pretty specialised affair, and you'd be lucky to find even one in every parish or community. From the kilns it would be transported as quicklime and slaked when needed, although a hot mortar was often made for stonework and agricultural brickwork which was made with quicklime and wet sand mixed together and left to self-slake under tarpaulins.
Once the rail network became widespread, then local kilning began to die out, as quicklime could be moved in bulk around the country. It was then that engineers began to be able to specify different types of lime for particular projects; as in Smeaton insisting on blue lias limestone with its naturally-hydraulic qualities for lighthouse building.

 

[worms]

Thanks, that's interesting!

 

[biffvernon]

And you might find this article interesting too:
http://www.hullcc.gov.uk/pls/portal/docs/PAGE/HOME/PLANNING/CONSERVATION/LISTED%20BUILDINGS/LIME_POINTING.PDF

There's a bit on page two about reused lime mortar.

(Hat tip to an old ghost haunting the forum.)

 

[Schoolmarm]

She is an angel not a ghost 8)

 

[Moo]

Angels don't haunt, surely?

 

[Schoolmarm]

Only if you missed church last sunday.

 

[skier-hughes]

Oh Sh**

 

[Schoolmarm]

:lol: :lol: