Lime, water and stone

[biffvernon]

Biff

As someone who is more used to brick and timber I do not claim to be an expert on stone. My understanding is that if lime in a very watery solution is applied the water evaporates leaving particles of lime to fill voids, etc - hence consolidating the stone. This is of course a very simplified (simplistic!) view, but generally a non scientific explanation of how lime watering should work. However, I have been told by colleagues that in their experience it does little to assist in the slowing down of degaradation. Not sure why and it would be useful to have more information and scientific backing or counter-argument to the use of lime watering. A few years ago I suggested lime watering be considered for some fragile carved stone and was told that the powers that be do not consider it a suitable method because it had been used on this particular item before and had done little or nothing to help prevent deterioration. I suspect this could make an interesting separate thread whereby others share their knowledge and experience of this method.

Penners

Big Guns can do a lot of damage if used too frequently or indiscriminently!!

And so to a separate thread.

I think the clue may lie in your phrase 'water evaporates leaving particles of lime'. If you mix hydrated lime with water you mostly have a suspension of lime particles (calcium hydroxide) and when the water evaporates these particles will slowly carbonate to form particles of calcium carbonate which may, or may not, be bonded to a greater or lesser extent to the stone.

When the stone is watered with lime water we have a different situation. Most of the lime is in solution rather than in suspension. As the water dries the calcium has to come out of solution, forming crystals which may, or may not, be bonded to a greater or lesser extent to the stone. I suspect the bonding in this case will be much stronger. But, like I said, it's very complex; it only takes a small proportion of other ions such as magnesium to alter the chemistry, and thence the physical properties, significantly, and there has not been a great deal of scientific work done on it.

 

[Schoolmarm]

So, if the surface of a stone does in fact become harder/stronger will this increase the likelihood of the face spalling?

 

[biffvernon]

It might. There again it might not. In a porous stone I would expect the limewater to soak in and consolidate the stone to some depth rather than form a surface crust. But don't blame me if your house falls down.

 

[Jon Maine]

To throw my tuppence in on a subject i know only a small amount about but that is hearsay from my local masons, many of whom served their apprenticeships on Wells Cathedral.

Firstly, they question the use of the lime water, its consistency varies, say 50 lime waterings are called for on the same stone. So If one day there is an insufficiency of water on top of the putty lime what do they do?

Secondly, The most active limewater is said to be drawn from the water upon the top of freshly reacted quick lime. Not many have access to this.

Thirdly you are reliant on the operator, it is a very tedious job encouraging shortcuts as stated by the men who were responsible whilst boys to undertake such tasks ( although given Wells is stated as a success this could be seen as a contradiction).

I still say until it has a proven track record that on common stone my feeling is to replace like with new like, in the scale of things this is the natural thing our predecessors would have done.

I am not convinced that we would try to consolidate a piece of rotten wood unless it had a unique historical value. I feel exactly the same way about stone.

If you have to spray a piece of stone 50 times to make it last 40 years more, yet in twice the time you could let in a new stone to last 200 years what is the obvious solution? Realistically we need to consider the ongoing maintenance costs of these buildings and I do consider anything but a thorough repair as shortsightedness. Are we looking to preserve the last ounce of the original structure at all costs? Or are we looking to preserve the building looking good with honest repairs for the long term?

I am interested in debating the above mentioned points.

 

[skier-hughes]

I still say until it has a proven track record that on common stone my feeling is to replace like with new like, in the scale of things this is the natural thing our predecessors would have done.

Would this be the case in all scenarios?

Wells cathedral, the church had lots of money, it could afford a like for like repair.
Your poor country farm worker, tasked with looking after his homestead may favour a repair that he could undertake at his convenience and within his capabilities.

I have absolutely NO knowledge on this subject at all........

Graham

 

[biffvernon]

Let's think about the theory a bit deeper. Lime water is a solution of calcium hydroxide. It is clear. Remember the old school experiment? Blow bubbles into it through a glass tube and the clear limewater goes milky. That's carbon dioxide from your breath reacting to produce insoluble calcium carbonate, which precipitates out of solution forming microscopically small crystals of calcite.

Sandstone is often made of quartz grains cemented together with a matrix of calcite. Acid rain dissolves the calcite leaving, eventually, a heap of sand. The limewater treatment needs to be done before we get quite that far. When the stone is soaked in limewater and the water evaporates what we want is for the calcium hydroxide to react with CO2 from the air and for calcite crystals that form an interlocking matrix holding the quartz grains together.

But there are quite a few things that might go wrong.
If the stone is already saturated with water your limewater isn't going to get far in.
If the stone is not very porous the limewater is not going to get far in.
If it's a hot day the water will evaporate before it has got far in.
If the water evaporates too quickly there will not be sufficient time for the calcium hydroxide to carbonate - you just get dry calcium hydroxide which isn't much of a bonding cement.

So you need to limewater the stone in such a way that all the dissolved calcium hydroxide carbonates within the stone and you need to do it again and again until all the pore spaces are pretty much filled with new calcite crystals. This gets progressively more difficult as the stone becomes less porous. The limewater will take longer to penetrate and so will atmospheric CO2.

Any excess calcium hydroxide should carbonate eventually, but I wonder whether extra CO2 might be delivered by adding sugar and a high pH tolerant yeast or bacterium to the mix - that's what happens in rock diagenesis, the process of turning mud into rock at the bottom of the sea.

And then there is the physical makeup of the new calcite cement to consider. Calcite crystals are not particularly strong, not like quartz, but they produce an interlocking matrix that is good for consolidating the sand grains. The actual shape and size of crystal that form this matrix is probably significant. It will be determined by several factors, such as concentration of anions and cations (including cations other than calcium) in the solution, temperature, pH, rate of crystal growth, nucleation sites and more.

As I hope you can see, it is complex business. Theory says it will work, but the conditions have to be right. Some of those conditions may be under the influence of the man and his boy. Others may not be.

 

[Jon Maine]

Great idea for mildly friable, accessible stones in my opinion that can be monitored and replaced at a later date with no huge expense. Certainly good for someone who has little skilled practical ability as they could certainly manage to apply by spray or otherwise on a regular basis mainly for the minimal cost of a sprayer and some putty lime.

It would be interesting to repeatedly soak some falling apart stone in a bath of limewater to see if over a period of time it does hang together back to the core. It could even be possible to apply the damp proof course injection equipment to apply limewater to the core of the affected ares from the inside out, would require a 10mm hole.

Great in theory, couldn't agree more about the theory. But whilst it is not nailed down it could be a lot of effort spent on some masonry to little affect? Could it actually damage the stone if like Coniophora puteana and wood all you end up with is a veneer of sound material on the outside but rotten in the core?

My feeling as as two stones will behave differently from day one of being quarried within a few feet of each other that the potential is that there are far to many variables to understand and make allowances in application of limewater.

 

[Lime]

Let's think about the theory a bit deeper. Lime water is a solution of calcium hydroxide. It is clear. Remember the old school experiment? Blow bubbles into it through a glass tube and the clear limewater goes milky. That's carbon dioxide from your breath reacting to produce insoluble calcium carbonate, which precipitates out of solution forming microscopically small crystals of calcite.

Let's think about it deeper still.
From memory of that same experiment of blowing bubbles in lime water the liquid would turn first cloudy white then, with more blowing, would become clear again.

I think lime watering and it's efficacy is much more to do with the stone it is applied to.
Stone itself consists of many chemicals, some almost inert some quite reactive.

 

[DaveBrigg]

This discussion reminded me of a childhood visit to Mother Shipton's Cave. Apparently, a teddy bear hung up as shown in the picture will 'turn to stone' within three months. I can see two problems with this process though: a teddy bear is more porous than most houses, and no-one is going to want their house to end up looking like the cliff face below.

 

[Gareth Hughes]

This discussion reminded me of a childhood visit to Mother Shipton's Cave. Apparently, a teddy bear hung up as shown in the picture will 'turn to stone' within three months. I can see two problems with this process though: a teddy bear is more porous than most houses, and no-one is going to want their house to end up looking like the cliff face below.

|I understand that the two protruberances halfway up the cliff face are a straw bonnet and a riding hat that were left in the 1870s and never collected. But the overall effect is just the "Flintstones" look that some people apparently go for...

 

[skier-hughes]

But all tastes are different and why shouldn't some people like the flinstones look?
Some like timber frame, some like brick, some like straw bale, some like georgian, some like tudor, some like victorian and some even like Barratt.
A house that was supposed to be covered in lime at least hasn't been destroyed by not being covered if it is looked after and can be covered in lime when the next person buys it and wants to "do the right thing".
Whereas if you say the houses should be covered as that was how it was in the beginning, I'd have to knock down my lounge and bedroom, the kitchen and bedroom, utility, remove the upstairs and live in two rooms which is how most people believe my house was like in the beginning, or we could go right back and just have a giant moat with a mound :wink: :lol: :lol: :lol: :lol:

 

[Flyfisher]

A moat? We used t'dream of 'aving a moat . . .

 

[Jon Maine]

A moat? We used t'dream of 'aving a moat . . .

Buy a building plot on a flood plain put your house on stilts and in the monsoon season you will have a hell of a moat.......