why are 1930's brick buildings ok with cement?

[michael]

We are always hearing about the advantages of lime over cement based mortars and how the latter can do more harm to brickwork than good. So why is it that more modern brickwork buildings appear to be surviving quite well with their brick and cement structures?. I’m thinking in particular of the many thousands of 1930’s estates of semi detached houses that still dominate many suburbs across the UK today. Whilst they may be a bit uninspirational in their design, they do never the less seem to be quite sturdy structures, the choice of middle England, and still standing not only having survived their cement mortars but also the Luftwaffers efforts to destroy them. I know that some more recent brickwork structures and perhaps those of the 1930’s are cavity walled and so damp can’t pass through the second skin as long as the cavity is not bridged but what about the outer skin? Why is the cement not forcing water to escape through the bricks and causing the face of the bricks to crumble. Were the industrial manufactured bricks of the 1930’s and of more recent structures of a higher quality in that they don’t deteriorate with water saturation and frost?

 

[inwood]

My understanding about bricks vs. mortars is that as long as the mortar is softer than the brick the moisture will be absorbed by the mortar and prevent the (or stones) from spalling.

Modern bricks are fired at very high temperatures to make them very hard. In fact cement used nowadays is so hard that the bricks have to be fired at an even higher temperature! - seems nonsensical to me.

I would suggest that 1930's bricks and mortars are matched accordingly i.e. mortar softer (even if it is cement) than the bricks.

 

[Flyfisher]

Is this more of a porosity issue than one of absolute 'hardness'?

Any water/moisture coming into contact with a brick wall must surely come into equal contact with the mortar and the bricks. If the water is absorbed by either material then it becomes at risk of freeze/thaw damage. I'm not entirely sure how the characteristics of one material can affect any damage to the other.

But if a brick can be made to be so strong (by higher firing temps?) that it can resist freeze/thaw damage, or be made so impervious that it doesn't absorb any water in the first place, then I don't understand how it can be damaged by freeze/thaw cycling, regardless of the type of mortar used.

Perhaps 'hard' and 'soft' is being used in a special architectural way that I'm not used to - I'm certainly no expert so the above is only my own conjecture.

 

[chuckey]

I think that the case for lime is overstated, the main advantage is that as lime is softer and tends to be self healing, when a building settles it is less likely that huge cracks will appear.
The main advantage of cement mortar is that it is cheaper.
Where I live, the victorian bricks are very soft and porous, my neighbours house was re-pointed using 2:1 cement mortar mix over 38 years ago, it still looks immaculate. Two houses down a friends house had to be under pinned, about 60% of the bricks in their side wall had diagonal cracks in them, caused by settlement stresses, and with lime mortar and no cement!
A modern developement of £500,000+ houses near my brother were buillt using lime.
I think you have to be careful about mixing "hardness" and "non-porous". I believe that my bricks are so porous that the walls are self draining, i.e. the water just runs straight through them, and the balance can evaporate through the pores. As modern bricks are denser, they are less porous, but still contain cracks and fissures due to the firing process. These can retain water but it can't evaporate.
Frank

 

[Nemesis]

A modern developement of £500,000+ houses near my brother were buillt using lime.



Presumably hydraulic, much rhe same properties as cement but much more eco friendly.

A growing trend.


Far better to use a non-hydraulic lime for a historic building for many reasons - including the fact it is a 'sacrificial' element, and a great deal more aesthetically pleasing than cement. Too much at stake to risk cement really. Can't see any advantage and many disavantages.

Basically though - yeas modern brick is far harder.

 

[Flyfisher]

Where I live, the victorian bricks are very soft and porous, my neighbours house was re-pointed using 2:1 cement mortar mix over 38 years ago, it still looks immaculate. . . . . . I believe that my bricks are so porous that the walls are self draining, i.e. the water just runs straight through them, and the balance can evaporate through the pores.

If the bricks can absorb so much water, I wonder why they have not succumbed to any freeze/thaw damage over the decades?

I don't understand how soft bricks can be protected from weathering by the type of mortar that is used - and chuckey's example suggests that cement mortar need not be damaging. Perhaps 38 years is not sufficient time for damage to accumulate? (also, it's only one example so perhaps not representative?). Or perhaps a lime mortar would actively 'wick' the water out of the bricks?

So much to learn, so little time!

 

[middi]

On this forum we are always going to hear about the advantages of lime over cement, simply due to the fact that when most of the properties we discuss about were built before the cement age. As the majotity of these discussions focus mainly on restoration and repairs, damp or sloping ceilings, the use of cement would in many cases destroy the delicate balance of porousity, flexibility, and the need to "breath" which is associated with traditional or historical buildings. Cement is neither porous or flexible.

 

[michael]

Thanks everybody - Yes as far as I understand it, lime acts like a wick drawing the water from the brick and allowing it to evaporate away without any damage to itself. Cement on the other hand can trap water. Looking at your comments above I guess the brick buildings from the 1930's onwards must have been designed with a very strict and delicate balance between 'type of mortar mix' Verses 'brick selection' to allow minimum water penetration but sufficient water evaporation properties. Are there any old Builders/Architects out there that can confirm the philosophy of that time?

 

[Craig]

1930s walls were built to be more waterproof and more rigid than in older buildings. Though the article below talks about why lime is good, in doing so it also touches on why cement works in a more modern setting.

From
http://www.buildingconservation.com/articles/prtlndcmnt/prtlndcmnt.htm

The strength and density of mortars made with Portland cement also cause problems where used on historic masonry. Strength is critical because to be suitable, the mortar must be weaker than the stone or brick it is used with, so that if stress in the wall leads to failure, fracture lines occur in the mortar, not in the brick or stone itself. Lime mortars are more flexible and can tolerate a greater degree of movement without failure. This in itself makes cement mortars and lime mortars disastrous bedfellows, particularly where a traditionally constructed wall has been repointed in a lime mortar. In this case the core remains flexible, but the surface is now rigidly bound by the new mortar, and seasonal movement causes stress in the surface, commonly resulting in spalling brickwork or stonework.

The density of the mortar or, to be more specific, its vapour permeability and porosity, are also critical because traditional construction methods rely on a porous surface to remain dry. In modern wall construction the cavity which separates the inner and outer leafs ensures that any moisture that enters the wall is unable to reach the interior. However in a traditional construction, whether a lime rendered panel of wattle and daub, fair faced brick or ashlar, or a solid masonry wall with a coating of render or limewash, the surface absorbs moisture readily, but it also dries readily, so damp does not penetrate far it into the wall. Preventing this natural evaporation with a dense waterproof coating of cement will trap moisture, risking damage by frost action, and salt crystallisation damage can occur wherever cracks in the coating occur.

 

[Nemesis]

I can testify to seasonal movement - old buildings of course in the main do not have the sort of foundations which modern ones do.

We have doors which close and then don't close or not so readily as slight movement occurs with winter and summer.

Modern building methods are meant to keep all weather out, the building is designed to be rigid, with physical DPC etc, period buildings were built, as stated above, with materials which allowed them to 'breathe'.

I've seen many an old wall with cement pointing which has suffered damage - far too risky to try and I can see no advantages at all.

 

[rogerh]

Regardless of its effect on the building, the production of cement is far more environmentally damaging.

 

[JohnB]

I was told by someone, I think it was on a cob/lime course, that the houses in London that collapsed during the blitz tended to have cement mortar and the ones with lime mortar survived. Not sure how true it is.

 

[inwood]

It's true that lime mortars are more forgiving and do 'self-heal' (although I wish we could find a better term as I think that term is too inflammatory sometimes).

I have a friend with a 6' wall built using lime mortar. The neighbour has a huge climbing plant on their side which they rarely cut back. The result is a wall with a significant weight of planting on it at the top.

The wall has simply moved over time to accomodate the weight to such an extent that the top two foot of the wall curves away from the vertical by about 1'6". It's quite a sight and something that would have failed a long time ago had it been cement.

 

[Flyfisher]

In what circumstances is cement actually better than lime?

While I appreciate this forum is going to be biased towards lime rather than cement (purely because of the age of the typical properties, not because of any dogmatic flag-flying), I'm curious to know in what circumstances cement-based mortars would actually be better than lime-based ones - if any.

I'd not trying to start a 'bring back cement' wing of PPUK (fat chance of success anyway :wink: ), just trying to get a better understanding of these things because it seems that lime is so much better than cement, in so many ways, that I'm wondering why cement is still used at all - especially since it is 'greener' than cement. Maybe it's just a cost issue?

 

[Lime]

Many 1930s houses were built using lime.
Most houses of that era also had proper foundations.
The big drawback with lime is that it takes a while to harden sufficiently for further work or alteration to take place.
Using cement allows for quick building and the use of the hammer and chisel in just a few days.

 

[Nemesis]

Well - Castle House is an example of where cement was considered better than lime - although I have to say it was still all alittle experimental at the time, and that's caused some problems:

http://www.architecture.com/go/Architecture/Also/VandA_5185.html


The Stummerville thing didn't happen in the end, but Vivat is now hopefully taking it on.


The SAVE 30 exhibition (first seen at the V and A) begins this weekend at Upfront Penrith. On until 21st JULY not August!


http://www.savebritainsheritage.org

 

[Flyfisher]

I can understand why Castle House was built with cement as a sort of 'technology demonstrator', but I can't see that cement gave it any inherent advantage over a similar structure built using lime. I was looking for examples where cement was instrumental for a structure.

There must be example where cement couldn't be replaced with lime. Motorway bridges perhaps?

I take Lime's point (this is getting confusing!) about lime mortars taking longer to set. This is clearly important in these days of 'throwing up' buildings very quickly when 'time is money'.

 

[Nemesis]

Well heaps of 20th century buildings... Luder's Gateshead Car park for example.

http://www.riskybuildings.org.uk/docs/04gateshead/index.html

http://www.c20society.org.uk/index.html

 

[Gareth Hughes]

Nemesis is that better for you? are you a "special constable" by any chance?

How about you spend your time posting real life experience information to users instead of nit picking on my post.

Maybe you would like me to post you photographs of my new oak framed building & house so enable you to sleep tonight.

Incedently on looking at your history i see you have posted company/website names in the past. Has anyone told you about "people in glass houses" ?

Go and bother someone else please!

You arrived here, posted a clear advertisement for a firm (recommendations on this forum are generally given as a response to a request rather than out of the blue), called Nemesis a "little Hitler" when she cast doubt on whether your post was anything but advertising spam, and when then thread was (rightly) removed, you turn up here to continue the abuse. All in a total of three posts from starting out.

 

[NT]

Popular Victorian brick was extremely soft - so soft they can sometimes even be carved with bare hands if determined.

When cement mortar eventually comes away it pulls a layer of brick off with it. Loss of brick fireskin often results in ongoing total deterioration of the bricks. Stone is also damaged by cement.

Then there's damp: old building walls with no dpc and no cavity have higher water content, and cement mortar reduces wall evaporation, sometimes causing bricks frost damage, and sometimes damaging salt deposition in the brick faces. Lime evaporates water well, and sacrifices itself rather than the brick.

Then there's movement: old buildings often have not a lot in the way of foundations. Eg 13" brick strip founds were common in Vic times. So the house walls move a little. Lime, being softer than the brick, cracks, then grows crystals across the crack to self-heal. Cement otoh is harder than the brick, so the bricks break. No healing occurs. Result: structural damage.


AIUI the pluses of cement are:

* quick setting makes for faster building
* quick setting makes building during frosty times not too much of a problem unlike lime
* higher compressive strength needed for high rise buildings, concrete beams etc
* Harder finish makes it vandal proof.
* Slightly lower material cost


NT