Pure lime makes poor mortar?

[Anonymous]

Hmmm... I think mud and hay may be OK for VERY rural and vernacular type of buildings, but I don't think it would suit all!

My house certainly is a lime plaster house.

 

[Anonymous]

After you've added a few layers of lime wash you might not tell the difference between lime and mud plaster. Cob Buildings by Jane Schofield & Jill Smallcombe (who, I believe, both live in Devenshire mud huts) is a good starter on this subject. Buy it from jane@blackdog.ukf.net or elsewhere.


Cob Buildings

 

[Anonymous]

Well, ours is certainly lime plaster not mud! Far too posh a house for mud!

The cob buildings book is available from SPAB. The authors are SPAB members.


http://www.spab.org.uk

 

[Anonymous]

I can't speak for anywhere else because I have not got the hands on experience. But in Devon mud plasters are virtually the norm. I don't care how posh or non venacular you property is - the builders used what was readily available and if that was mud it was mud. Without digging a hole in the plaster to find out no one would know. I have to admit that in the more upmarket houses the mud backing coats are skimmed with lime finish but this is merely a veneer to give a smooth surface. In more basic dwellings mud plaster was just limewashed. After years of redecoration it is often difficult to work out whether the walls were skimmed or the finish is just a build up of limewash. I have also found cob walls that were worked up to such an extent that no plaster was necessary - the surface being smooth enough to not require plastering.
As I said, I have never had the time to play with mud plasters but I would be willing to bet a substantial amount of money that I could produce a very posh finish indeed without any lime whatsoever. Mike.

 

[Anonymous]

I had a go at plastering with mud onto lath during a course run by Mike Wye & Associates last month. Lovely smooth stuff it was - like melted chocolate.

Surprisingly, it was both much easier to apply to the wall and also easier to get a smooth consistent finish than it was with lime mortar.

 

[Anonymous]

I know ours is lime with hair - there are holes in it! The nouse is built with it too.

In the north, there are very few 'ancient'dwellings left really - apart from churches and cathedrals - and what there is is built mostly from stone, as we have a great deal of it around. The 'harrowing of the north' after the Conquest didn't help. Then we had the Border Reivers - and houses had to be strong and fortified - bastles and towers.

Following peace, and Inclosure Acts, more substantial dwellings were built - again, stone is the main material. Our house is most certainly an early example of what became the 'traditional' Northumbrian farm building once peace finally arrived - three bay two storey, central staircase, with a later addition T on the rear giving a cross passage and stable with hayloft. All built from very local stone, with simply dressed stone door and window surrounds. The poshest bit of stonework is inside with fireplaces - again, very simple but very well done. Originally the roof would have been stone slab but it was re-roofed in Welsh slate I suspect in the 19th century when the extension was added. The railway helped to make slate a common 19th c roofing material all over the north, taking the place of sandstone and ling thatch round here.

It's an interseting juxtaposition with bastles nearby.
It's also interesting to compare with the Landmark Trust's Causeway House at Vindolanda - only a few years earlier, but with more of a transition fron rough bastle construction about it - and with 'black thack', ling thatching. Only three such buildings now survive in this area - sadly, one of those is currently sprouting a swathe of reed repair and lots of blue placcy. I think things are moving on that however - EH seems to think that this is a very early failure of the thatch (14 years) which was grant-aided.

 

[Anonymous]

All right, thank you! Plastering and limewash is well covered - what happened to the "mortar" element of this thread? Mortar is used for more than just rendering and pointing and bedding bricks you know!

What about external haunching or fillets and roof bedding?

 

[Anonymous]

Now I think we've argued this one before!

What was traditionally used then before the advent of Portland cement?

Me, I'm thinking of a hydrulic lime for re-bedding of ridge tiles. The cement is cracking off anyhow and falling down onto the roof and into the gutters. The cement around the chimney did the same - came off in lumps when we had the chimney replaced (cracked and rather dangerous).

Wasn't there something similar in the other evening's Restored to Glory?

 

[Anonymous]

Who's Vicker?

Still baffled by what you meant by this ...

"This is a good bright start to a debate me lads, what we don't want now is blinkered enthusiasm clouding the question - please carry on you two (and tell us what you 'really' think!). "

Perhaps you could enlighten us with your experiences? All contribution most welcome, tell us what you 'really' think, now!!! <IMG SRC="http://www.periodproperty.co.uk/discussing/smileys/smile.gif" BORDER=0 ALT="">

I don't know the exact composition of the lime mortar used to build my house. I'm pretty sure it was sourced locally, and didn't come from France or somesuch other place, like some of the hydraulic limes that are now readily available to me. Neither was it pure, mature lime putty, supplied neatly in tubs from Rydedale. Even if I knew the exact composition of the mortar, it is unlikely that I'd be able to go to the expense and touble of reproducing it precisely . Very unlikely. The choice is either cement based mortar, or some sort of lime mix.

I'd have to try and pick a mortar that's suitable not just for the soft standstone masonry, but also the position in which it's used (exposed chimney stack, sheltered wall, interior wall etc), the present state of decay of the masonry, and the environmental conditions that it has to perform in.

I was advised to use eminently hydraulic lime (St Astier NHL5 to be precise) to repair and repoint the exposed chimney stack. This seems perhaps to hard and inflexible to me, perhaps it would damage the surrounding weak stone? Or I could use a fat lime mortar, but maybe that would be too puny to withstand the climactic extremes?

Maybe I should go for something in the middle - a feebly or moderately hydraulic lime for example?

Decisions, decisions. Perhaps it would be better to keep on endlessly pondering the various options and not actually doing anything to the chimney. It might be decades before it collapses.

What do yoo reckon, then?

 

[Anonymous]

Ian - Geoffrey had a similar chimney dilemma at Knedlington. One was simply collapsing and the mortar had perished to the point of no return. It needed careful disassembling and rebuild.

Lots of discussion - on and off forum - and I can recall the end result, even though, in the overall scheme of the work at Knedlington, Geoffrey can't! (he's getting on well by the way - just so much to do!).

Normal non-hydraulic fat lime was thought not suitable for a chimney. Too soft. SPAB thought feebly hydraulic, Mike Wye moderately. Both would not be too harsh for those soft old bricks, but tough enough to stand the weather in such an exposed spot.

In the end I recall the Mike Wye mortar suggestion was chosen.

I presume you saw the problem on Restored to Glory last week in taking down (not sure why it wasn't fixed in situ as was suggested) the chimney which had been built with Portland. Lots of damaged bricks as the mortar stuck to them and the brick face gave way. Many then not usable.

Thw other half is slinging the Ryedale putty and sand mix onto the fireplace back as I type. Lots to do as it's so rough. I think we will be without heating for a long time!

 

[Anonymous]

Add a soupcon of ce**nt.

 

[Anonymous]

He did finally - for the flaunchings and fillets (as winter was drawing on, frosts had set in and lime wasn't suitable, he needed rid of the expensive scaffolding etc) ) but I'm not sure that it was any better than the lime would have been.

I only hope that we can remove the cement from our ridge tiles (stone) without damage as I doubt I can replace them easily.

 

[Anonymous]

"I was advised to use eminently hydraulic lime (St Astier NHL5 to be precise) to repair and repoint the exposed chimney stack. This seems perhaps to hard and inflexible to me, perhaps it would damage the surrounding weak stone? Or I could use a fat lime mortar, but maybe that would be too puny to withstand the climactic extremes?"

If you gauge a non-hydraulic lime mortar with a suitable pozzolan then you can easily vary the hardness to suit the particular circumtances. I've been using the same 3.5/1 non-hydraulic mix for harl coat, backing coat, general building work and repointing and even on the roof. Shame the winter's here now - still so much more pointing to do!

 

[Anonymous]

Ta Evelyn, that's very useful to know. I will go with that.

Probably too late now for even the NHL - still needs time to achieve a good set (a few weeks I've heard) and it's already frosty!!!

Roll on Spring 2006!

Cheers

 

[Anonymous]

Perhaps, mailman.

The only concern I've got with that is the stuff I've read saying that the cement can affect the set of the lime in the long term, and the results have not always been too good.

 

[Anonymous]

Do not mix cement in with proper lime! Adding a bit of lime into cement as an extender is different. Not actually sure why it's done!

Where historic stuff is concerned (unless Castle House) DO NOT USE CEMENT!!! DO NOT ADD A BIT OF CEMENT TO LIME!!!

Thw Smeaton Project and personal experience...

Interested in your hydrate experience though, for scratch coats...

 

[Anonymous]

Ta for that Richard, it is something that I will consider.

I'm slightly concerned that I will need to guess the correct amount of pozzolan to add, and may not get it right. It would be a shame to experiment on the chimney itself - could be a costly mistake.

I could get hold of some pozzolan and try a few experiments with setting over the winter - perhaps bonding a few stone blocks in my frost free cellar to see how strong the mortar sets with various proportions of pozzolan.

I generally use 1 part fat lime to about 3 parts sharp sand for mortars. My mixes are not precise proportions, and vary according to how wet the sand is. I just keep on mixing until the mortar looks and feels right. If necessary I let it stand and drain off the excess water, or add more lime. I suppose adding the pozzolan could be treated similarly, given sufficient experience. I doubt that the men who built my house agonized over exact proportions and faffed around the way that I'm doing.

 

[Anonymous]

Having never felt the need to use hydraulic, and therefore having no experience, I am confused.
If a hydraulic mortar is breathable how come it can be used for ridge tiles? Water will run straight through a lime putty mortar but presumably not through hydraulic??
Incidentally, I have heard it argued that pointing should be viewed as sacrificial. If one takes that view then perhaps putty is better on all occasions bearing in mind it's other attributes. Mike.

 

[Anonymous]

Good point, I'm not sure just how breathable hydraulic lime is.

I suppose the main thing with ridge tiles is that you want them to stay on the ridge. Perhaps a fat lime mortar would not be strong enough for this application.

Is there some compound in the cement that also accelerates erosion under certain conditions?

 

[Anonymous]

I have just done a baby brickying course at the college where I work and I asked the Q about why hydrated lime is added to cement mortars and had 2 answers.

The first answer was that it is added as a plasticising agent, but we shouldnt worry about it because everyone uses febmix or fairy liquid now, the next instructor said it was to keep the mortar workable and to slow down the set - they knock up vast quantities of muck at a time which may hang about for an age before being used, also they need to knock down the walls built in class and clean off the bricks ready for use by the next lot, without the lime the set would be too great and they would lose too many bricks.

Hope that bit of anecdotal trivia is of interest.