We need a chemist: Portland cement and Lime.

[SteamyTea]

On another tread, I typed up a bit about Portland Cement.

Now I am not a chemist at all, in fact I am rather dismissive of them.  Having said that, 5 Chemists that I have chatted to informally have been very good at explaining what happens without relying on using memory test in Latin.

One Chemist, a recent PhD graduate was working in sales and explained long chain polymers to me, they are really quite simple, repeating 'units' that attach to each other.

Another one, again a PhD in chemicals, explained the electron orbits and how they are NOT 2D as drawn on paper, this is what governs, to a certain extent, the shape of molecules.

Another, PhD again, sat me down in a lecture theatre and explained the polarity of molecules and why that causes CO₂ to vibrate at certain frequencies and causes a disproportional amount of movement.  This principle of polarity is why a small amount of some molecules can cause a large amount of heating.

Then there was my old line manager, who also had a PhD in Chemistry who once said "when you design, or change a chemical formula to get the properties you want, you get what you are after, and something else".  It is that something else that is important.

Then there was our own @Jeremy Harris, who initially studied Chemistry then moved onto Physics.  He was brilliant as he was a practical man and understood the limitation of the 'something else'.

 

Now the above is just a way of asking if we have a decent chemist on here who can help out with a lot of the products used in the building trade, there must be at least one.

 

So getting back to the title, I had a look at Portland Cement and then Lime because of a question that @saveasteading asked about releasing and absorbing CO₂.

After a bit of googling I found a long, but easy to read article explaining how Portland Cement is made and then used.

http://matse1.matse.illinois.edu/concrete/prin.html

Basically, from what I understand, is that during the roasting, free water is evaporated and then elevated temperature drives out CO₂ that is attached to the calcium.  When water is mixed back in, a reaction takes place that causes a rise in temperature, and the hydrogen and oxygen are split up and combine with the Di and Tri Calcium silicates and aluminate, with some Tetracalcium aluminoferrite and Gypsum thrown in.  Di, Tri and Tetra I understand, the Ates and the Ites I don't, they need to be memorised.

I was going to show the changes in formula when Limestone, Clay and Ferric Oxides are roasted, but I can't find a decent explanation (why we need a Chemist).

The reverse hydration i.e. when water is added, is shown.

Tricalcium silicate + Water--->Calcium silicate hydrate+Calcium hydroxide + heat

2 Ca₃SiO₅ + 7 H₂O ---> 3 CaO.2SiO₂.4H₂O + 3 Ca(OH)₂ + 173.6kJ

And

Dicalcium silicate + Water--->Calcium silicate hydrate + Calcium hydroxide +heat

2 Ca₂SiO₄ + 5 H₂O---> 3 CaO.2SiO₂.4H₂O + Ca(OH)₂ + 58.6 kJ

If I understand the chemistry correctly, because the CaO is already attached to something the SiO₂.4H₂O chain and the Ca(OH₂) there is nothing for the carbon in CO₂ to attach to.

 

So then I had a look at Lime, wanted to know what happened as way too many people seem to think that it is the bee's knees and will cure all ills in a building.  I have been very dubious of those claims and can never find decent evidence to support it.

 

So Lime is made in a similar way to Portland Cement.  Get the right rocks, crush and heat them to change them:  CaCO₃ to CaO + CO₂.

Then the difference from Portland Cement happens, water is added, in the right proportion.  CaO + H₂O to Ca(OH₂). Calcium Hydroxide.

This forms a dry powder called Slaking.  Also known as Hydrated Lime, add a bit more water and you get Lime Putty.

Now, and this is where it is really different from Portland Cement, it absorbs both H₂O and CO₂ from the atmosphere as it wants to convert back to limestone CaCO₃ (calcium carbonate).

 

So come on Chemists, put me right and explain it better, maybe with a bit of basic theory as a grounding.

 

[SteamyTea]

Prompted by something @tuftythesquirrel said in another thread.

I went looking for the mechanical properties of lime v cement mixes.

 

I found this for concrete.

 

https://eurocodeapplied.com/design/en1992/concrete-design-properties

 

Copy to Clipboard

Concrete Design Properties according to EN1992-1-1 (γ_c = 1.50, f_yk = 500 MPa)

Symbol	Description	C12/15	C16/20	C20/25	C25/30	C30/37	C35/45	C40/50	C45/55	C50/60	C55/67	C60/75	C70/85	C80/95	C90/105
fck (MPa)	Characteristic cylinder compressive strength	12	16	20	25	30	35	40	45	50	55	60	70	80	90
fck,cube (MPa)	Characteristic cube compressive strength	15	20	25	30	37	45	50	55	60	67	75	85	95	105
fcm (MPa)	Mean cylinder compressive strength	20	24	28	33	38	43	48	53	58	63	68	78	88	98
fctm (MPa)	Mean tensile strength	1.57	1.90	2.21	2.56	2.90	3.21	3.51	3.80	4.07	4.21	4.35	4.61	4.84	5.04
Ecm (MPa)	Elastic modulus	27085	28608	29962	31476	32837	34077	35220	36283	37278	38214	39100	40743	42244	43631
fcd (MPa) (for αcc=1.00)	Design compressive strength (for αcc=1.00)	8.00	10.67	13.33	16.67	20.00	23.33	26.67	30.00	33.33	36.67	40.00	46.67	53.33	60.00
fcd (MPa) (for αcc=0.85)	Design compressive strength (for αcc=0.85)	6.80	9.07	11.33	14.17	17.00	19.83	22.67	25.50	28.33	31.17	34.00	39.67	45.33	51.00
fctd (MPa) (for αct=1.00)	Design tensile strength (for αct=1.00)	0.73	0.89	1.03	1.20	1.35	1.50	1.64	1.77	1.90	1.97	2.03	2.15	2.26	2.35
ρmin (%)	Minimum longitudinal tension reinforcement ratio	0.130	0.130	0.130	0.133	0.151	0.167	0.182	0.197	0.212	0.219	0.226	0.240	0.252	0.262
ρw,min (%)	Minimum shear reinforcement ratio	0.055	0.064	0.072	0.080	0.088	0.095	0.101	0.107	0.113	0.119	0.124	0.134	0.143	0.152

 

Has a lot of useful numbers.

 

I would like to see some for lime mixes as it would be really good to give a definitive, or at least well informed, answer to this long standing debate.

 

A bit more digging and I have found this.

 

https://www.intechopen.com/chapters/63429

 

It is a long read so may have to come back to it.

 

Mortar composition		fflex (MPa)	fcpr (MPa)	fccy (MPa)	GF (N/m)	ft (MPa)	Ecy (GPa)	Epr (GPa)	lch (mm)
NHL09C04M	Mean	1.3	3.2	2.0	12	0.39	5.0	5.2	390
	Std. dev.	0.1	0.1	0.2	3	0.02	0.2	0.5
NHL08C04M	Mean	1.3	4.2	2.7	13	0.51	5.4	6.0	260
	Std. dev.	0.1	0.3	0.3	1	0.01	0.6	0.2
NHL11C04M	Mean	0.89	1.7	1.4	4.9	0.24	2.8	3.8	240
	Std. dev.	0.04	0.1	0.1	0.8	0.03	0.7	1.0
NHL09C04W	Mean	1.7	3.5	—	—	0.57	—	—	—
	Std. dev.	0.1	0.1			0.05
NHL09C02M	Mean	1.1	3.2	2.0	12	0.49	4.6	5.1	220
	Std. dev.	0.1	0.2	0.1	1	0.05	0.2	0.6
NHL09R04M	Mean	0.96	2.3	1.5	10	0.38	4.2	4.4	280
	Std. dev.	0.06	0.1	0.1	2	0.03	0.2	0.4
NHL09C04MA	Mean	0.91	2.4	1.5	8	0.34	2.8	3.2	190
	Std. dev.	0.02	0.1	0.1	1	0.03	0.4	0.6

Table 3.

Mechanical properties of NHL mortars at an age of 56 days.

 

 

[Mike]

On 23/10/2023 at 22:20, SteamyTea said:

So then I had a look at Lime, wanted to know what happened as way too many people seem to think that it is the bee's knees and will cure all ills in a building.  I have been very dubious of those claims and can never find decent evidence to support it... ...So come on Chemists, put me right and explain it better, maybe with a bit of basic theory as a grounding.

 

I'm not a chemist either, but it's also a matter of internal structure and physical properties, not just chemistry.

 

For a good summary, see Lime mortars for the conservation of historic buildings, 2002, by Kerstin Elert, Carlos Rodriguez-Navarro, Eduardo Sebastian Pardo, Eric Hansen and Olga Cazalla . It's available to download (in Englsh) from the French Laboratoire de recherche des monuments historiques here .

 

To pick out one section in particular:

 

...the unfavourable properties of Portland cement mortars [include] brittleness, high strength, and a thermal expansion coefficient which can be twice as large as that of lime mortars and most types of brick and stone. Its low porosity, and especially the large amount of small pores, might hinder water movement in masonry and cause damage due to the accumulation of moisture behind cement layers or to evaporation and deposition of salts in adjacent stones or bricks. Moreover, soluble salts such as calcium sulphates and sodium salts might be present in Portland cement mortar, which can leach out over time.  Lime mortar, on the other hand, has a low efflorescence potential due to its relatively high chemical purity. Additionally, it has the advantage of allowing limited movement within the mortar joints and can undergo autogeneous healing due to dissolution and precipitation processes. Carrington and Swallow point out the importance of lime mortar being softer and more porous than masonry, acting as a sacrificial substrate where evaporation of water and associated decay from soluble salt crystallization could take place.

 

Although the paper recommends aged lime putty for conservation use, I'd add that other forms of lime are more suitable in some cases. For example you wouldn't want to use lime putty on a damp background, where regularly exposed to heavy rain, or on hard stone; hydraulic limes would be suitable instead. As a rule of thumb, hydraulic limes (and NHL 3.5 in particular) also seem to be suitable for most buildings built within the last couple of hundred years, as well as being easier to use.

 

Also not mentioned in that paper, the natural antibacterial and antifungal properties of lime can be beneficial in some circumstances - for example as a parge coat beneath natural insulation. It also doesn't mention that cracks in cement can facilitate water penetration (though, as above, it does mention that cracks in lime tend to self-heal).

 

Edited November 17 by Mike

[SteamyTea]

46 minutes ago, Mike said:

thermal expansion coefficient which can be twice as large as that of lime mortars and most types of brick and stone

Interesting.

 

A quick look at this paper about Portland cement shows it a thermal expansion of  3.84 × 10^-5 K^-1 so pretty small, halving that will not make much difference.

 

Brick has a thermal expansion of 5 - 7 x 10^-6 K^-1

 

Now I am not sure if the second one is volumetric expansion (top one is), but when there is a factor of 10 difference, of a tiny amount, it is still a tiny amount of difference.

 

One of the problems of research about lime is the lack of scientific evidence, but a huge amount of opinion.

This is a shame as I am sure lime 'mixes' have their place, but while it is marketed as a wonder material that will save the planet, cure damp in old buildings and probably save kittens from being stamped on, but nothing to back it up, I prefer to be sceptical of it.

 

As a test, if anyone is thinking of buying some, contact the manufacturer and ask for some data i.e. elasticity, moisture absorption, water vapour transmissibility, compression and tensile strengths.  Just the normal engineering properties.

Bet you can't get anything meaningful.

[lookseehear]

I like the approach of this thread. I think that as Mike points out it's the physical properties that matter more than chemical once set, or are at least perhaps higher on the priorities list. I come to this with a scientific background (albeit graduating 15 years ago, so a lot of hazy memories) but little building experience.

 

I saw this video recently and thought the outcome was pretty interesting, despite only really focussing on a very specific part of the physical qualities - the ability to transmit water vapour. 

 

I'm not a particular fan of Roger Bisby and think he's too close to 'clickbait' for comfort, but this simple experiment seemed to show that a 6.1.1 mix of sand, cement and hydrated non-hydraulic lime was the most vapour permeable of all the mortars tested, but because this contains both portland cement and lime, the physical and chemical qualities could be distinct from either in isolation.

[SteamyTea]

5 hours ago, lookseehear said:

Roger Bisby

Ah, the man that likes to perpetuate myths.

If a pipe fitter, that angry with the world, turned up at my works, he would last about 2 minutes.

[Roger440]

What exactly are you hoping to achieve/learn here?

 

If you ever feel the need to come to wales, ill happily show you a real life example of lime V cement on a wall with no DPC.

 

I was sceptical, i have to admit. But 2 houses later, real world experience tells me what i need to know.

 

None of it is helped by the "hardcore" lime-ists though, who would have you believe its the answer to every problem.

 

There was one on a group im in fitting a kitchen work top wanting to know what breathable sealant he should use where it meets the wall, as though a 5mm bead of silicone was going to make any difference to anything.

 

 

[SteamyTea]

16 minutes ago, Roger440 said:

What exactly are you hoping to achieve/learn here

Trying to cut though the BS mainly.

[Roger440]

7 minutes ago, SteamyTea said:

Trying to cut though the BS mainly.

 

Good luck with that!

 

You may be some time...................................................

 

 

[lookseehear]

1 hour ago, Roger440 said:

What exactly are you hoping to achieve/learn here?

 

If you ever feel the need to come to wales, ill happily show you a real life example of lime V cement on a wall with no DPC.

 

I was sceptical, i have to admit. But 2 houses later, real world experience tells me what i need to know.

 

None of it is helped by the "hardcore" lime-ists though, who would have you believe its the answer to every problem.

 

There was one on a group im in fitting a kitchen work top wanting to know what breathable sealant he should use where it meets the wall, as though a 5mm bead of silicone was going to make any difference to anything.

 

 

 

I'm sold on using Lime in solid wall buildings, but what I can't work out is do you have to go the 'whole hog' and use a hot non-hydraulic lime mortar for pointing and haired lime putty for plastering or is there a middle ground? The heritage crowd will tell you that anything with any cement in it is not to be used, but finding a good tradesperson is difficult enough without factoring in the extra cost of the time required to use these slow-setting mortars and plasters. I keep telling myself I should just learn to do it myself, but I know that these aren't the kind of jobs I'm very efficient at.

[Mike]

51 minutes ago, lookseehear said:

do you have to go the 'whole hog' and use a hot non-hydraulic lime mortar for pointing and haired lime putty for plastering or is there a middle ground?

If you're using lime mortar it's sensible to plaster with lime too, so both layers share similar properties in terms of movement & vapour transmission.

 

36 minutes ago, lookseehear said:

factoring in the extra cost of the time required to use these slow-setting mortars and plasters

One thing not often mentioned is to think about when you schedule the work - it's going to be easier to work with the seasons, at least outside. Stone-laying season for medieval stonemasons was apparently between Lady Day (25 March) & Michaelmas (29 September); the rest of the year was spent cutting stone for the next season. You don't need to go that far, but something to be think about.

 

 

[Roger440]

16 hours ago, lookseehear said:

 

I'm sold on using Lime in solid wall buildings, but what I can't work out is do you have to go the 'whole hog' and use a hot non-hydraulic lime mortar for pointing and haired lime putty for plastering or is there a middle ground? The heritage crowd will tell you that anything with any cement in it is not to be used, but finding a good tradesperson is difficult enough without factoring in the extra cost of the time required to use these slow-setting mortars and plasters. I keep telling myself I should just learn to do it myself, but I know that these aren't the kind of jobs I'm very efficient at.

 

Well, theres not much point in using lime for pointing, for example, if you then cover it in a layer of less breathable material. Anything with cement is less breathable. Likewise gypsum, though gypsum is a bit more complicated. Where it gets complicated is how breathable does it need to be?

 

There are plenty of armchair experts who will tell you lime isnt necessary, and, for example, gypsum will work as it is resonanly breathable. That statement, taken in isolation is of course true. But the problem with messing around with old walls is that no one really knows just how much moisture is moving through it. So at a practical level, if in doubt, use lime, is a pragmatic solution with the highest chance of success. There is no better performing material for this particular purpose.

 

If you ask anyone who specifies something else in an old, non DPC wall, they will not guarntee their idea/build up will work. Funnily enough, the onus is on you, not them, if, subesquently there are damp issues. Anyone wanting to spend money on alternative scheme, good for them, but ill spend it on the option most likely to succed.

 

Unless, and until someone comes up with a bullt proof way of analysing individual walls accurately, i cant see much change.

 

If you have established you need a breathable build up, and id make sure that you really do, then you have to understand the performance of each layer all the way to the wallpaper covering and glue. Or paint.

 

If it helps, working with lime is so much easier than cement or gypsum, mainly as you are not time limited in the same way.

[Gone West]

2 hours ago, Roger440 said:

If it helps, working with lime is so much easier than cement or gypsum, mainly as you are not time limited in the same way.

That's what I've read, and I do hope so. I'm going to try to lime plaster the window revels in a 600mm thick stone wall. If I get on alright with that, I'll try larger areas. I find it very tricky plastering with gypsum and get on better rendering with cement.