Natural Roman Cement

[Martin 1958]

Hi

My first post. Hope someone can assist. We have a period property in Norfolk which is of brick and flint construction. We are currently waiting on an estimate from a builder to repoint some of the brickwork and flint panels. We have spoken tonight and he has suggested using Natural Roman Cementhttp://lincolnshirelime.co.uk/natural-roman-cement-18kg-2719-p.asp as an alternative to lime mortar. The reason given is that it dries quicker than conventional lime and he will be able to complete the job in a shorter time thus reducing cost. (He is planning on quoting on a daily rate)

I have looked online for information about Natural Roman Cement and it appears that it does perform like conventional lime based mortar.

Has anyone had experience of this material and can they confirm if it is a suitable alternative for this particular application?

Thank you.

 

[Abi Cott]

Interesting question

Bump

 

[88v8]

Hello and welcome.

It may have merit. But the composition over time and in different places, has been very variable.
Typically it was a constructional material. A defining characteristic seems to be large aggregate, and this is not really compatible with pointing applications.
I would ask him what mix of which materials he plans to use.

It is an important principle of stonework that the pointing must be softer than the stone. No problem with your flint, questionable with the brick, depends on the bricks.

I see that there is a quick-setting lime mortar available from Cornish Lime, here
http://cornishlime.co.uk/information/prompt-natural-cement/
The setting time may, if anything, be too fast, but for working during inclement weather I can see its potential merit.
Perhaps talk to them about it?

Ivor

 

[Flyfisher]

I'm not really sure, but I'd guess 'Natural Roman Cement' is some sort of lime mixed with a pozzolan material that makes ordinary lime mortar set quicker than normal. Or perhaps he means a mortar made with NHL lime? Hopefully a real lime expert will give a better answer.

But my real reason for posting is to ask why the builder thinks such a material would speed up the job. I don't quite understand why the builder would have to remain on site while the pointing cured.

 

[JanJonWestWales]

seems strange not to have some sort of comparison to NHL products - what is its equivalent?
surely if your builder wants a faster drying product then NHL3 or even NHL5 might work, and @ £7.50 vesrus £14 a bag seems a big difference
J

 

[Martin 1958]

I'm not really sure, but I'd guess 'Natural Roman Cement' is some sort of lime mixed with a pozzolan material that makes ordinary lime mortar set quicker than normal. Or perhaps he means a mortar made with NHL lime? Hopefully a real lime expert will give a better answer.

But my real reason for posting is to ask why the builder thinks such a material would speed up the job. I don't quite understand why the builder would have to remain on site while the pointing cured.

I think (am guessing) his logic in relation to the flint panels, which are quite tall, is that he can only go so high each day with the slower setting lime mortar without the weight of the flints starting to make things sag? So perhaps he would be able to achieve more with the quicker curing Roman Cement. Not sure if that makes any sense! Also I think he would only want to strip back what part of the existing flint panels he could reasonably expect to replace in a day to help preserve the fabric of the building during the job.

A few years back we had a new 5 foot garden wall built with flint panels by a different builder using lime mortar.It was, as I recall, quite a slow process building them up and they were much smaller panels than what is on the house.

 

[middi]

roman cement was the product of volcanic ash, mixed with "pozzolana" ( another very soft and powder looking by- product of volcanic eruptions) and lime . This sets quite hard when heated. It is not flexible but breatheable ( not exactly the same as our lime mortar).
The reasons why the Romans used it was because south of Rome there was, and still exists, the volcanic earthquake belt that crosses Vesuvius and in that part of Italy there still exists plenty of deposits of the above . ( some builders in Italy still use this mix today).
As to it been used in England, it does not appear to be a natural resource.

Only an observation !!

Middi

 

[livias]

I know lots about lime plaster but not much about consevatiion brickwork. I suggest you see if Gerard Lynch has written anything about Natural Roman Cement cos anything he doesnt know is not worth knowing

 

[plasticpigeon]

Since buying my money pit, I have done quite a bit of bricklaying, and have experimented with all sorts of mortars. i started with NHL3.5, but found that that set very very hard, so when doing the bricks at the front of the house I used 1:1:6 being one part NHl 3.5, 1 part hydrated lime, and 6 parts sand. this was quite soft to start but has hardened up, and is now probably about the same as the orighinal mortar, ie, a finger nail will leave a mark but not a gouge. This got me thinking, since the important point is that the mortar be softer than the masonry, then how about a weak cement sand lime, for example something like 1:1:8 or 1:2:8 with the 1 being cement, the 2 being hydrated lime and the 8 being sand. It woudl set quick and be pretty soft.

 

[MikeG]

.........Typically it was a constructional material. A defining characteristic seems to be large aggregate......

Not so. The Romans were quite sophisticated in their use of concrete. The aggregate used in the dome of the Pantheon, for example, changed the further you went up, and by the top was finely ground pumice. They were "horses-for-courses" in their approach to concrete.

 

[MikeG]

........ "pozzolana" ( another very soft and powder looking by- product of volcanic eruptions).........

Again, not-quite-so (you're not wrong, but you aren't wholly right). That is but one type of pozzolan. The Chinese used ground up bones from slaughterhouses. Broken bits of fired clay has been widely used in Britain for the last few centuries as a pozzolan, and this is still far and away the most practical solution for those wanting to speed up the setting of a lime mortar (indeed, it also works for a cement based mortar). Flint panels were traditionally built with broken bits of brick or tile embedded in the mortar away from the external face, allowing more courses to be done per day.

 

[livias]

PP
That sort of cement lime sand mix is a nono
It used to be popular but there were unexplained failures so English Heritage (I think it was) did some research
The problem turned out to be that the cement is v fine clogs the pores stops air getting to the lime so the lime doesnt set. So it relies only on the cement set. And it is a very weak cement mortar. Hence the failure

 

[Putters]

Are we sure about the product we're talking about here - as some of the comments appear to be talking about the mortar constituent of Roman concrete. Everything I'm seeing online about Natural Roman Cement appear to be talking about a very different product - and one that is quick drying (and doesn't work with aggregates as such) as per the original poster's question.

https://en.wikipedia.org/wiki/Roman_cement

If I've got the properties right from this PDF article it sounds horrendous for pointing (chiefly it being incredibly fast drying meaning an almost constant mixing required, it being highly waterproof which doesn't bode well for breathability - see the comment at the bottom of page 4, and it bonding so well to the brick that you'll never clean it off again if it does cause problems)

https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=17&cad=rja&uact=8&ved=0ahUKEwjJ5cyxu8vSAhUkBcAKHRVqBOc4ChAWCDEwBg&url=http%3A%2F%2Fwww.arct.cam.ac.uk%2FDownloads%2Fchs%2Ffinal-chs-vol.18%2Fchs-vol.18-pp.21-to-35.pdf%2Fat_download%2Ffile&usg=AFQjCNG_sPMqytvOiU9YkooOG4GzjWfYZg&bvm=bv.149093890,d.ZGg

 

[noj]

If it's just repointing then the only reason for not using a NHL or even a fat lime is the tending time required after pointing rather than using cement (Roman or otherwise) where you just bung it on and bugger off. You don't need a rapid set/cure for any structural strength.

Potentially you could do this part yourself (basically just stopping it drying out too quiclky, a bit of mist spraying, damp hessian if appropriate etc for a few days) once he's done the pointing?

 

[Chris-Burgess]

Roman cement is best used for repair jobs as it sets quickly, ratio for mix would be 2:1. Quite strong,

 

[TheRoost]

.........Typically it was a constructional material. A defining characteristic seems to be large aggregate......

Not so. The Romans were quite sophisticated in their use of concrete. The aggregate used in the dome of the Pantheon, for example, changed the further you went up, and by the top was finely ground pumice. They were "horses-for-courses" in their approach to concrete.

The product being discussed , Roman cement is a product name from 18th C. and bears no relation to mortars invented by the Romans.

Roman concrete is of course lime based , they also used it very cleverly to build structures in the sea, here the chemical reaction with seawater actually strengthened the mortar bond, these structures still exist after a few thousand years showing virtually no erosion! In contrast modern cement based concrete lasts only a few decades in seawater before it starts to fail.

As others have said, stick to your guns and use Lime mortar. I've found NHL to stiffen up in as little as 4 hours during the milder months of the year.