Pointing Archway

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Peter Mac

Can anyone tell me what sort of mortar mix to use whilst pointing up an old sandstone porch? A builder previously used portland cement with marigold tint. However, I've been advised that's not the right substance to use, and should perhaps use a lime based mix. Anyone know of a good combination? (The mix has to be fairly rigid) Thanks.
 
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Never ever use hard OPC mixes on old stonework! Mortars and grouts only act as binders in stonework, what holds the stonework together is the skill of the person who bonded and set the stones especially in random rubble. The use of coloured dyes by ill informed neanderthals should be banned.

Pointing old stonework is in two stages known as "tamp pointing" and "finish pointing" The joints must be raked out as deep as you can, at least three inches if possible (surface pointing is a waste of time). When pointing stonework always be aware of what is above and around you, do not cut out more than you can point in one day. Never cut out completely around a large stone in position as it might fall out and cause collapse af a large area.

Cut and rake out joints, remove growth and dirt, then brush down. Do not scour joints with a hose.

If there are small stones in and around joints, and they are loose or slack, remove them, clean out, and pack with your mix. Refit them in exactly the same position.

The mix for a tamp pointing sandstone is:

7/8 parts sharp sand

1 part lime (hydrated)

1 part OPC


For finish pointing (the last 1 1/2")

6 parts sharp sand

1 part lime (hydrated)

3/4 part OPC


To get the right mixes and make them uniform, you should buy a jug with measuring scaled on them and a decent stainless kitchen sieve, this is what you gauge your mixes with. Say you had a jug with a 1000ml scale and wanted some finish mix, well you would put 6 full jugs of sharp sand in, 1 jug of seived lime in and 750 ml of seived OPC. Stick with this and the mixes will be exact (gauged) throughout. The colour of the sand determines the dried colour of your pointing. It is always best to try and get local sand (can be hard nowadays as everywhere is closed down and bankrupt)

You will also need tamping irons, you cannot buy these anymore so will have to make some or get some made. Pieces of steel flat bar 16" long with a round steel handle welded on one end and another 2" piece of flat bar welded on the other end at 90 degrees ("T" shaped) these are what you use to push your mix into the joints with. Various sizes are obviously needed for the different sized joints in the stonework. You will also need a hawk, a thin alloy one is best as the edge is nice and thin and can usually be rested directly in the bed joint.

Dampen all joints with a hand held garden sprayer that has an adjustable nozzle to create a fine spray. make sure the finish point is slightly recessed, not brought out over the face of the stone. Let the mix dry for a couple of hours (depending on the weather) then go over them with your sprayer and a small pure bristle paint brush to remove the cement/lime skin, exposing the aggregate. This process also assits in sealing and cleaning the joints between the stone and the pointing and gives a good weathered surface. Great care and patience are required, do not use a strong spray of water and do not over water, as this has a tendancy to scour out the mix and start it running down the wall. Do small areas at a time, starting from the top and working down. Do not use a sponge to clean any of the stone faces because it smears, instaead use your spray gun and a small clean brush.
 
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I've seen the above reply on another site somewhere. You should give credit to the original writer.


joe
 
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I've seen the above reply on another site somewhere. You should give credit to the original writer.

I beg your pardon! Maybe you can add some meat to that odious and vile accusation?

Or do you want to delve deeper into the discussion about the stonemasons work and see who is the back-seat driver?

I challenge you!

Every forum seems to posses a poison dwarf who's spiteful and jealous attitude raises it's ugly head in the face of those who practice what they preach instead of hollow talking.
 
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There is good reason to use a lime only mortar rather than adding OPC, though the 20th century has tried to obliterate it from construction methods. This would be 3 sharp sand to 1 lime putty.
 
P

Peter Mac

Thanks very much!

I had given up hope for a reply before you appeared which is why I've taken so long to reply. I'm doing the job as a volunter, although I've done quite a bit of pointing before, this has to be very good quality work. If you're still around, could you maybe clarify for me what OPC stands for?

Cheers,

I appreaciate your effort,

Peter
 
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OPC = Ordinary Portland Cement, (spit!! horrid stuff, in the wrong place).

English Heritage did a recording years ago of an exercise reparing the joints at Fort Halstead in Kent, they may be able to provide a copy. It was a really good, detailed program. Well worth a look.
 
P

Peter Mac

I spent 1and 1/2 hours removing a metre square section of it.......all these nasty little slaters and undesirable creatures never seen before falling out from behind!
That's what I thought it stood for, but I needed to make sure I understood the jargon...Thanks
 
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Only a good shaped pure hydratic lime plaster will work well to use whilst pointing up an old sandstone porch. There are many technical reasons, here are some of them:

1st The thermal expanding of lime mortar and stone are very even (0,5-0,8 mm/m/100K), cement mortar will expand much more (~ 1,2) than the stone. Result: Cracks of the mortar, mostly seen outside, where is more thermal difference.

2nd The drying out capacity (after Cadlergues) of lime mortar is 0,25, cement mortar 2,5. Result: The lime mortar will dry out damp ten times quicker than cement mortar. No storeing of water, much frost attack will be avoided.

3rd The binding forces by drying out of the fresh mortar is low of lime mortar and very high of cement mortar. Result: No problems of binding from lime mortar on a 'weak' surface like an old wall, jointed normally with lime mortar.

4th The cement mortars have a lot of efflorescent alkalic salt deposits in it, which can make many problems. Only pure hydratic (not hydraulic!) lime mortar has no efflorescent salts in the receipt.

5th Its not a problem by receipting lime mortar by use of 'shovel method' 1part lime - 3 parts sand. To give in modern chemicals is of doubtful use. What modern alchemy has found out is often just the opposite what a good work needs. I do prefer traditional methods in this topic too. They are proved for centuries.

6th The pore volume and size can influence the capillary and drying out behaviour of mortars very much. So the walls behind cement mortars will be more damp than behind lime mortar. But rising damp by capillary activity is not possible to a remarkable level with cement render too. The reasons of rising seeming damp you can find in the salts and other natural sources, as mentioned here: Rising damp - the experts fake

7th The first layer of joint filling mortar should be grained 0 - ~2mm, the finishing 0-~0,8/1mm, depending of the original mortars nearby. So you can install a capillar pump, which will hinder water to came in and improves water to come out. Remember: Capillary transports are working only from big pores to small pores, so the fine grained mortar gets small pores, the rough grained bigger ones.

If you will know more details to this topic and can understand german, try this:
Masonry - a technical Guide
In english you will find info about mortar problems here:
Problems with lime mortars and others - my RILEM-lecture in the University of Paisley 1999

The problem is, that 'modern' craftsman are not more used to work with pure hydratic lime mortars, so they will recommend other things without respect of technical behaviour. Look for an old fashioned craftsman, there are many also in the UK. Perhaps ask the National Trust or Historic lime center or my fellow Peter Cameron from Historic Scotland at Fort George, there they know the good guys (and give them my greetings).

Good luck!

Konrad

My Tip: Never use OPC, it hurts masonry!
 
P

Peter Mac

Cheers - I'll hopefully be starting to repoint in the summer... so I'm making sure I know what mix is best now. I'm only going to remove the completely useless cement - hollow sounding patches - which are not actually doing any thing other than leveling the stone surface off - just now, then remove (repointing as I go) the major parts in the summer. There is a small amount of repair work to be done to decorative "stringing" so I presume the 1 - 3 mix will be ok.

I just want to thank everyone again just now who replied or who may reply as I really appreaciate the advice, and the help.
 
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OPC = Ordinary Portland Cement, (spit!! horrid stuff, in the wrong place).

If you don't add OPC to the mix it will not set, especially in damp or exterior work...try it instead of talking a good show! The reasons anyone who does actually practice this craft uses OPC, is because from trial and error they know if a small amount is not gauged (different amounts for different scenarios) it will not set. We think with all our technical babble we know everything, but sadly the opposite is true and a great deal of passed down knowledge that the craftsmen of the past knew is now lost. I do not know how the masons of the past practised their art fully, I do not know exactly how they worked, but I do know from the painful process of error that if I do not gauge OPC into my mixes, I will encounter problems. These mixes are well established and conform to British Standards; hence they are specified a lot. They are also accepted by English and Scottish heritage for use on listed buildings. Do not confuse internal plastering with external stone setting and pointing, because in that case Fat limes are better for plasters without a doubt.

At the end of the day, basically no-one really knows the methods the old masters used, all one has to do is look around and see the arguments for and against this and that. But we all like to stroll around with our noses up in the air thinking we are the bee’s knees, but after looking passed our bigotry we simply do not fully understand the old methods employed.

This is true for many a subject, not just stonemasonry. Take cast iron, well have a look at the old Victorian castings on say a fireplace then compare them to a modern one, there is no comparison in quality. They used to cast these things on the sand banks of the river where I used to live and they would come out crisp and clean, nowadays with all their so-called modern technology, they cannot replicate the definition or quality.

My Tip: Never use OPC, it hurts masonry!

True, if used for setting stone at the same ratio as for bricks and blocks, but if gauged at respective levels for stone masonry it is a tried an tested method.

my fellow Peter Cameron from Historic Scotland at Fort George, there they know the good guys (and give them my greetings).

He would obviously know that the arcade of the cloisters at Iona abbey in Scotland was completely rebuilt using hydrated lime and OPC about thirty-five years ago and is in as good condition as when it was done! The cills, stools, columns, caps and springers including the spandrel rubble are all set on gauged hydraulic lime and I must say are looking good for another hundred years or so. Mugdock castle in Scotland has also been restored in 1985 using hydrated lime and OPC gauged and is looking as good as new.


Only a good shaped pure hydratic lime plaster will work well to use whilst pointing up an old sandstone porch. There are many technical reasons, here are some of them:

I think you mean hydraulic Theoretical waffle. Number one the great craftsmen of the past never bothered with all this nonsense, instead they used the tried and tested method of what works, works and what doesn’t, doesn’t. Most sand was hand drawn from sandbanks (all the good is washed out of modern sand, I can still access freshly dug sand straight out the ground luckily) All the old buildings were built on the fly and everything was carried out on site, there was nothing technical about any of it, they used to add all manner of ingredients to their mortar mixes, it was pretty rough and ready from that point of view. Can you imagine a building site in 1780 with a squad of institutionalised, day-glow office boys prancing around talking b****cks? They did not need droves of these superficial types to build there cathedrals. They just knew their stuff from a practical sense and today the edifices they built stand testament to that and today we could not replicate it using their methods. One important factor is to always make sure the lime is new and has not had time to absorb any moisture before being hand mixed and banked. The best lime mixes are those that are left in the pits or banked the longest, the older the better. I also personally believe mixes using hydraulic lime gain strength as they age. One argument is that cement discolours the mortar, but it is the sand that causes colour change, that’s why local sand should be used if at all possible. In any case you can use white cement which is the same colour as lime anyway and is used on limestone as a matter of cause

A bag of hydrated lime bought at the builder's (Type-S, bagged lime) is quicklime that has been factory slaked only to the point that a powder is formed and not putty. The stuff in this country is high-calcium lime Hydrated lime is dried lime putty, there is no difference when mixed by hand and banked up for a week, there is no technical justification for requiring the use of lime putty for these applications. The reasons architects and others of this caste specify it, is because they do not have to execute it. And do not suppose as architects talk of the prime function of mortar is to bond masonry units into a monolithic mass as true, because it is wrong, a the skills of the mason bonding and tying the stones is what bonds the wall, not the mortar.

The first layer of joint filling mortar should be grained 0 - ~2mm, the finishing 0-~0,8/1mm

Way too fine. Sand this fine should be used for setting dressed stone regardless of the labours to their facings. All one has to do to prove what a silly statement that is, made by someone who I can guarantee has never dressed or set a stone in his life. is go up close to an old building and look at the joints to see the various sized binders that make up the finish pointing, they will be vastly larger than that and of a great range of sizes because if they are not they will not hold together during bad weathers.


spent 1and 1/2 hours removing a metre square section of it.......all these nasty little slaters and undesirable creatures never seen before falling out from behind!
That's what I thought it stood for, but I needed to make sure I understood the jargon...Thanks

The mixes you are talking about are completely different to gauged mixes I am talking about and are applied by dunces who know nothing of their subject. I too have spent far more time than you ever will removing their disgraceful desecrations. But by all means go ahead and do as you please, but you will only do it once.
 
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Oh, what a lot of text. I must be more shortly:

Belonging the grading all depends from the situation of the building, so my recommendation is meant 'about' and thus I wrote.

You refuse to go into the arguments, you spare out the facts of the opposite site and it seems you are singing a faithful hymn on OPC.

I have (after about 400 successfully finished monument restauration projects in whole Germany) some experience in the topics I post, so I restorated the historic facade of the Town Hall in Bremen only with pure hydrated lime mortars. Peter has seen this also last October. And also there I could learn a much about all the cruelsome attacks that cements can do. So pardon me, that I am not a fan of it.

2FA.JPG


But I must commit that its a big thing to get a good work done with hydratic lime mortars. Nearly all the mistakes I know I have published here: The common mistakes using lime products (in german).

Have you read my RILEM-lecture? The Mystery of historic Lime Mortars - can we solve it?. Whats wrong?

A little beg: Can you please declare me how and by which chemical process hydrated lime and cement mortars will set and get hard? By not so many words? That would be important to our debate. Maybe not everybode here in the audience knows it and will be interested too.

Best regards

Konrad
 
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Oh, what a lot of text. I must be more shortly:

It was far more painful for me, I can assure you.


Belonging the grading all depends from the situation of the building, so my recommendation is meant 'about' and thus I wrote.

Quite true my friend! So why you show me a German building whilst I am referring to this country is bizarre. I am working in the top end of Scotland where the wind and rain comes off the North Sea sideways at ninety miles an hour at sub-zero temperatures, your puny mixes would not last a night exposed up here. The building you show is dressed and squared dimension stone with very fine joints heavily protected by the arrises. Most of my buildings are random rubble of Caithness stone, completely different Kettle of Fish.

You refuse to go into the arguments, you spare out the facts of the opposite site and it seems you are singing a faithful hymn on OPC.

I think I have explained the practical aspects very thoroughly. “I seem to be singing a faithful hymn on OPC” Maybe you should re-read the first sentence of my first posting on this thread?

You seem as if you are on a crusade against OPC, as if you will turn to stone at the very utterance of it. There is nothing wrong with it, if used correctly. And once again trying to compare hard brick/block mortar mixes with mild stone mixes is extremely irrational, you need to withdraw from your tunnel vision and learn to differentiate between the two.

so I restorated the historic facade of the Town Hall in Bremen only with pure hydrated lime mortars.

I can tell you would have physically done nothing. When you say “I” don’t you really mean ”they”? You have never personally pulled a stone from it’s bed in a quarry, dimensioned a stone, dressed a stone or set one, you’re a theorist.

Can you please declare me how and by which chemical process hydrated lime and cement mortars will set and get hard?

As mentioned earlier, being practically orientated I do not need to know the boring minutiae of the chemical properties of lime. I draw my knowledge from practical experience of what my father learnt, from what his father learnt and from what their friends fathers learnt, exactly like my forefathers who built the great buildings that remain. All we need to know is what works on the buildings and looks after the buildings and protects them from the elements for a great many years. We know from practical experience and from the manner in which time has tested it.

We even add boiled linseed oil to our mixes for putty mastics now that will make all the pen-pushers hair stand on end. Chuck some crushed washed sea shells in with your mix as well and a bit of grated autumn leaves, makes a really stand-up mix.
 
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Ok, I suppose you're a craftsman, maybe a stone mason and you may or must have had some trouble with silly architects and conservators. I can follow you in some sense, but please believe me - and this will not be too difficult, that I can look to a horrible amount of bad experience with stupid 'craftsmans' too. But: That should not be our field of discussion, I argue.

Otherways, I do surely respect your familiar traditions but please give me the same honour. My father had also been architect for mostly building repair what means churches, castles etc like me and he did it from 1958 until 1979 in fully responsibility for the (~350) results so as mine ~ 400 since 1979. So we are no newborn Corbusiers, you understand ;)

I will not convince you by theories, that will not work in our debate (and did it never with craftsmans), I've learned. But you neglect the physical values of materials trusting only in your craftmanship. That may work good, but must not always and for everybody as shown by bad practise more as enough (and what would be the best planning without a good craftsmanship? Nothing, I commit it frank and freely because I experienced it often).

To finish: Please believe me, I am conscious of estimating good craftsmans practise, but as engineer and architect I am (and perhaps must be) interested in the theoretical background. This may be worth nothing for you, but my and my familys existence and the results of my planning depends just on this since over 20 years. So pardon my subjective point of view. And do you believe that f.e. the space rocket engineers did made every screw by their own hand inclusive their tools and must fly to Cassiopeia to prove their know how? That would be the result of your arguments.

If you would be interested to have a look on some results of my planning, try this: Some references - not in Scotland!

Best regards

Konrad

PS. I'm very sure, that the pure (and naturally improved by 'historic' but not hydraulic means) lime mortars I 'planned' and good craftsman used in harbour buildings in Bremerhaven, which can stand the water, salt and frost in pier walls (?, the walls which follow the harbour channel) and on other buildings exposed to hard climate conditions elsewhere in Germany can stand also scottish conditions. Perhaps some times we shall have a contest. Would it be an idea to ask Peter Cameron as a neutral expert to organize such competition? Could be a exciting challenge for us both.

2ZEMAU.JPG

Cementous craftsmanship in Italy after some years have passed

2DH2.JPG

Western exposed pure hydrated lime pointing in Bremerhaven Harbour after some years of climate change
 

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