Everything about white cement

  About renovation plasters and mortars once again

The plaster restoration again A few words have been written about the plaster restoration, a lot of information you can learn being a guest at any fair-related construction. In mid-April in Krakow held another EGIR meetings. Talks long and usually interesting allowed emphatically and clearly see that in fact the bulk of modern plaster restoration of plaster, which were created at the turn of the century, there is basically nothing.

Currently, standards for restoration plasters say that the aeration of such plaster should be much more than 40%, some throwing in passing and 50%. In fact, this means that half volume of such plaster of air, more specifically a bubble, or so-called sealed. capillaries. On the question of why the answer is simple - because of efflorescence, or white-gray bloom, they like to appear on everything related to the cement, concrete, not excluding.

Concrete and cement industry long ago solved this Gordian knot is not playing in the details of how, what and why. For each pallet strapped is simply information that the white-gray lesions is not a defect of the product or does not constitute grounds for complaint, they do not alter the physical properties and durability of the product. They only affect the aesthetics. Usually they disappear after about two years.

Visiting the great cities easily find buildings from the early twentieth century - huge skyscrapers, buildings, bridges and monuments. In fact, on any of them you do not see these lesions, whether in terms of concrete, plaster or mineral (specifically cement - lime). The problem does not exist. Yes, you can see the degree of soiling, you can see how the water flows down the wall of a defective longer time gutter, window sills curves. But what is there is no eruptions.

What's interesting talking with people from the so-called. "Industry" can easily get the information - but is passed from the additional words as "estimate", "believe", "suspect" - the ready-mix low alkaline among the total available market could represent 1/5 of the total. Such a perspective can be said that this is a rather inflated number. It is very important information that really any problems with the eruptions, wysoleniami and colloquially speaking "syfem" on the walls depend on how clean and how good the quality of the cement. The general view is the one that the cleaner cement and additives, the less he possesses, the better. The above-mentioned aeration level of 40-50% means that any plaster is enough space in the capillaries to everything that has cement, what is necessary in the plaster there fit. Unfortunately there may be problems and it is important:

  • the necessity of sufficient aeration of mortar / concrete
  • flexibility plaster
  • sufficient strength and resistance

Unfortunately, these three conditions generally exclusive. I am writing in principle, because the aeration in the range of 10-20%, which is sometimes typical for ordinary mineral plasters, is so small that it can even combine all these three conditions necessary level.

Such high aeration, which is required in plaster restoration makes the mortar Recalls its structure rather honeycomb, not a "full" material, and this forces the large amounts of cement - by combining these were sufficiently consistent and durable. Plasticized mortar rarely achieved with lime - more often chemistry. As a result, plasters are either strong, but their flexibility raises some concerns, sometimes referred to are circulating as "hard" or plastic enough, but their strength is not sensational. This means that in fact the technology required certain conditions come - ad absurdum - to the wall. The confusion in all of this produces more information that can be easily obtained from the older date of conservators that even in the 90s mortar mixed traditional method - that was used simply white or gray cement, lime and sand sometimes waypoint (filler).

Now the question is where's the catch, or what's changed from the beginning of the twentieth century to the present. The answer is surprising. It is known that alkali to cause the eruptions appear or salting out on the walls. Of course, not without significance are also other components in the cement, but they are primarily to blame for what happens next on the wall or fugue.

As a reminder, below are presented by standards of (standard EN 197-1) for the individual components:

  • insoluble parts - up to 5%
  • losses ignition - up to 5%
  • SO3 (sulphur) - up to 3,5%
  • chloride - up to 0,1%
  • alkali - none, though too low alkaline cement shall be those in which the alkali content (of the type CEM I) is up to 0.6%

Cements of the addition of fly-insoluble parts can be as high as 30%. It is obvious difficulty that, the ash actually added in very significant amounts (eg. cements of type II can be 1/3 by weight) depends on from which carbon is derived, how was incinerated, which was the technology, or additions were described most often as a co-ie, those who have cause to european countries fulfilled "econorms".

An interesting and an object lesson about how to change the cement described very accurately by the standard is the same shape of the latter. In the 90s cements with the addition of ash or slag were the norm in the market and no one questioned. Changed most of their way to describe the classification, but not the same composition. What is interesting in the early '80s in America, there were no separate standards for ordinary cement, fly ash, or other. The former one, for just cement

Conversations with people, which know the Polish cement industry or concrete lead us to two conclusions: one more typical of contemporary Polish (and other East European countries) economy, the second - very strange for the current system. The first is that the use during the 70's acceleration additives - clinker substitutes. Powerful demand related to the modernization of the country require the production of huge quantities of cement and clinker. Replacement of pure clinker substitutes in the form of dust or slag allowed to increase the amount of the finished product delivered to market without changes in the production of the most important raw material.

The second conclusion - surprising - there are reports saying that cements with additives were truly equal, fair in the composition and the same. It was just due to the fact that each cement was associated with the same mines not modified processes, the batch was the same. This meant so much that it really that the charge was as even and constant composition, which was not without influence on the behavior of mortar, plaster or concrete-made on the basis of such a modified cement.

The study on the cement published in 1978 clearly mentioned is increasing the flexibility with which another state - cement producers - began to approach the alkali content in the late 60s was emphasized the need for a thorough examination of how alkalis and their size can affect behavior concrete. In the same paper it is described the way in which evolved standard speakers alkali content in the cement. In 1968 she already norm of up to 1.5% (a total of Na2O, American standards, unlike the European distinguish both alkalis as sodium compounds Na2O and K2O potassium, in a separate table specifying it as the equivalent of the former).

At the end of the 50s it was organized conference on the broadest sense possible additives and their impact on the liquidity of the concrete. By the way, the composition of a quantity of cement samples taken from various cement plants operating in the United States. The results were as follows:/p>

Cement - sample SO3 [%] Na2O [%] K2O [%] Alkalia na Na2O [%]
1 1,9 1,2 0,08 1,25
2 2,2 0,75 0,6 1,15
3 1,7 0,63 0,23 0,78
4 1,4 0,51 0,29 0,7
5 2,2 1,11 0,1 1,18
6 1,7 0,41 0,58 0,8
7 1,8 0,43 0,47 0,74
8 2,3 0,4 0,5 0,73
9 1,4 0,5 0,24 0,7
10 2,2 0,37 0,38 0,63
11 1,2 0,43 0,12 0,51
12 1,7 0,32 0,28 0,5
13 1,4 0,23 0,36 0,47
14 2 0,25 0,16 0,36
15 1,7 0,4 0,46 0,7
16 1,6 0,28 0,64 0,7
17 1,4 0,25 0,63 0,67
18 1,8 0,35 0,45 0,65
19 1,8 0,32 0,39 0,6
20 2 0,32 0,38 0,57
21 1,3 0,42 0,22 0,56
22 1,8 0,24 0,46 0,54
23 1,7 0,28 0,49 0,54
24 1,7 0,26 0,29 0,45
25 1,6 0,29 0,16 0,4
26 2 0,41 0,22 0,56
27 1,2 0,35 0,24 0,51
28 1,7 0,05 0,15 0,15
29 2,1 0,43 0,66 0,87
30 1,9 0,45 0,19 0,58
31 1,9 0,46 0,15 0,56
32 1,8 0,33 0,15 0,43

At first glance a very minor content of sulphates. In the late '50s, it was an average of less than 2%, and there were a sample where it reached 1.5%. At present, this standard is almost twice as high! On the Polish market, the vast majority of manufacturers determine their content in the range of greater than 2.5%, and there are those who define their content even above 3%. This means that in fact under the terms of the quality of the cement over the decades has significantly worsened, rather than improved.

With the alkali content in cement is a problem - at the moment there is no obligation to declare them, which makes it do so only single cement. Judging by the descriptions and what is the composition of the cement, you can suspect that at the moment there is nothing to brag about. Historically speaking, the change in the standards of 1968 had to be caused by what has happened with the cement. Most likely it has happened since the late '50s and throughout the 60s, which in turn was caused the observed changes. Suffice it to say that the average alkali content in different samples of cement is slightly more than 0.64%, the highest reach well above 1.2%.

Continue to appear, there is one very interesting table, this time for four selected samples of cement type I, available in Northern California.

Cement Sample A Sample C Sample E Sample J
SO3 [%] 2,21 1,95 1,78 2,1
Loss on ignition [%] 1,12 0,9 1,02 1,26
Insoluble parts [%] 0,14 0,16 0,19 0,27
Na2O [%] 0,57 0,09 0,28 0,35
K2O [%] 0,76 0,12 0,21 0,54
Alkali total [%] 1,07 0,26 0,42 0,71

A glance at this short table allows for an interesting statement:

  • The content of SO3 in the then cements slightly below or around 2% was the norm and not an exception
  • Ignition losses are surprisingly low and substantially oscillate around 1-1.2% for all samples regardless of the composition of the clinker, and the content of alkali. This suggests that these values ??are the contemporary norm, not the exception (recalling: currently this standard is up to 5%, and typical results are at a level between 2.5% and 3%, sometimes even surpassing even the higher value)
  • The insoluble parts was hardly; results do not exceed 0.3%, while remaining within generally less than 0.2%, with the current standard of 5% and the results of typical thickness greater than 0.5% and sometimes exceeding 1%; cements ash and "ones" because of addition can be as high as over 30%
  • The only important value without departing significantly from the currently accepted standards is the result of alkalinity cement, though, and so for many current manufacturers a score of 0.42% - is the pinnacle of a dream, and 0.26% - unattainable ideal, even if its meaning cements as LA - low alkaline .

These notes on the margins of both tables allow you to draw very serious proposal for changes in the composition and quality of the cement then - you suspect that these analyzes relate to the period at the beginning of what was probably a revolution of quality and technology; revolution which led to the fact that now in addition to cement clinker can be found in almost everything; revolution that made what was once an ordinary plaster applied everywhere, because of the composition of materials and raw materials used to create it, must now bear the name of restoration render. Plaster that in order to have those properties must have a special composition, with an enormous addition of a really strong chemistry.

If the assumption of these changes is right, the same right will claim that back a dozen years should see the real picture of cement, which was commercially available and its quality or composition.

In 1941, the American Association of Cement Producers issued a statement in which zaznaczało very clearly that the level of alkali at 0.6% or above should raise a strong suspicion as to the quality of cement. Two decades later - in 1959 - this call to limit the size is only optional to the next ten years to become the only limit for cements niskoalkalicznych.

At the same time, because only a year ago were defined types of cement:

  • Type I - general purpose cement (construction)
  • Type II - used under similar conditions as Type I, but in places where the concrete is exposed to moderate sulphate or in places where it is required moderate heat of hydration
  • Type III - cement, high early strength
  • Type IV - cement, low heat of hydration
  • Type V - cement with high resistance to sulphates

Such a description of the types of cement, the equivalent of today's CEM I to CEM V, and such and no other term for what proves the high quality cement, means only one thing. Even in the early 40s in their basic composition they were very close to each other, and for each parameter decided not extras like ash, and the composition of clinker and the firing method (adding in a timely manner corresponding compounds modifying these or other properties of the final product).

If you add to this information, that at the beginning of the Great Depression, there were many smaller cement plants, and not just in the US market, but also Polish (eg. cement plant in Klucze or Ogrodzieniec) producing cements on the market a regional or cross-regional (capacity of several tens of thousands of tons) we get very bright and clear picture of both the market and cement, which had to be of very high quality, with high-quality firing, in principle, no part insoluble, with alkalis at very low levels.

A composition and a cement properties make the problems they met most of the producers of concrete, mineral plasters or restoration at that time (the 30s and beginning of the 40th) essentially did not exist or were barely margin, which appeared in an extremely unfavorable conditions external. Sam does not divide according to the composition (as it is now), and the use or rather the destination clearly indicates that what was inside and what should not be there, it was so obvious that even did not have it in any description mentioning.

Performing on the cement plaster on historic buildings, fugując brick walls or putting received mortar is of the highest quality, which for many of today's products are unreachable - despite the fact that today is known chemicals, which in the 30s or later to be known could not. The same it just means that it really then plaster or mortar mixed by a plasterers at the construction site was better and had better features than the vast majority of today's products on the market referred to even as low alkaline mortar renovations.

The first standards for cement has been published in the United States in 1904. They concerned both types then encountered cement - that is natural and Portland. For the latter included the information that after calcination and cement manufacture can not be there more than 3% of other additives. For the record - at the moment for cement CEM I clean Portland this norm is 5%. This standard spread throughout the world with over 40,000 copies in just two and a half years. It can therefore be concluded that it has become, in a sense force. A few years later he added that the loss on ignition for Portland cement can not be higher than 4%. Standard with the same period to SO3 (sulfate) is 1.75%. Until 1929 standards distinguishes only two (!) Types of cement - Portland and natural. The ashes and any other "inventions" did not hear one. In 1917, two changes were introduced - appeared position insoluble residue of 0.85%, and increased sulfate content to 2%.

Looking at what is now accepted as a high quality, you can only sadly nod. Today, the remains insoluble cements clear is the level of 5% (sic!), And sulfates probably 3.5%. The standard of 1917 in our field of interest as follows:/p>

  • sulphates based on SO3 - up to 2%
  • loss of ignition - up to 4%
  • insoluble parts - up to 0,85%

Over the next three decades, it has changed only that, in the late 20s and 30s added margin of error of 0.15%, and in the 40s it increased to 0.75%. Even with the enlarged size of the margin insoluble residue generally oscillated in the worst case to 1.5%.

The alkali content of the cement develop wspominały three very important things:

  • features which have their hydrated compounds which act with the addition of water as a yeast cake, which after entry of it into the reaction and increase the volume
  • significantly lower the strength and other growth over time; the then standards provide strength test after a year or two, and even more years; at the moment the standards say about 28 days and on the day given class of cement

These two things made him at that time so important was the low sulfate content that may weaken the plaster or concrete - in a word blends, which are an important component of cement.

The alkali content of the cement develop was written three very important things:

  • their content in the material, which is preparing (calcined) cement should not exceed 1%
  • calcination process acts upon these alkali in two ways - some of them completely eliminate, therefore, that brings it to gaseous form, which means that in fact disappearing from the final product; the second group - the "only" reduced significantly, but properly conducted after the roasting process should not be a problem
  • information written in 1941 saying that really alkali content in the finished product at a level above 0.6% should be a cause for concern related to the quality of cement

All these, however, in places quite fragmentary information allows fairly accurately assess the quality of contemporary cements, even taking into account the following matters:

  • completely different methodology for testing the strength of cement and some of its parameters related to the results of these measurements
  • possible less accurate test results associated with a slightly different method, which was used in the early twentieth century until the Second World War

You can decisively conclude that the then cement was much better, and looking at its composition in terms of what is defined somewhat ironically as "the sugar content in sugar 'current products unless all the leading companies beats. There have been two very simple reasons:

  • Alkali - that is the main cause of problems (read: efflorescence) were at the basis of today unattainable and unusual - in fact they were not there; what's more, people connected to the same cement industry cared very much that they remained at the same, or a very low level; any ideas to increase their treated negatively, issuing recommendations
  • Insolubles parts - ie what is the attempt to dissolve the cement in the water - then they basically was not; They can also comprise various odd reactions associated with the bonding process, one or other of the external environment, whether the variety of compounds that produces human.

Only these two facts mean that then concrete, plaster do not need the then powerful chemistry to be without lesions in order to provide a plaster now regarded as the restoration and a restoration of the highest class, sometimes unattainable for many manufacturers. With the substitute is not done for a decent and reliable product.

Interesting summary of the quality of cements available in the different markets, the Swiss did. In the mid-20s they were assessed, among others, that:

  • loss on ignition does not exceed 2% in Europe than America where they amount to 4.2% (this is probably the information on the standard, as the authors state that it was in America 4% + - 0.25%)
  • insoluble part must be less than 2% (w America - less than 0.85%!), the Swiss emphasize that they are low particularly in the case of the French cement; lower limit, which was found at the time of the sampling size is 0.00%

Researchers assessed as "normal" Portland cements, bearing in mind that their classification was somewhat different than today, and the then "two" meant something other than the current "two". Assessment covered include cement from Egypt. Unfortunately, the researchers did not indicate what specific type was investigated. It was only contained information that they are "normal Portland cement." In this group, the insoluble matter was slightly more closed and the upper limit of the range of above 4% Swiss to just over 5% to "imported." However, given the fact that cements with such a high content of insolubles were evaluated last in the order, clearly pointing out that the norm for "insolubles" is less than 2%, it can be assumed that it can be about products from small or cheap cement plant that is not subordinate to national standards associations or they were not.

At the descriptive analysis are presented graphs and a variety of tables and they really give a full picture of the tested cements. Interestingly extremely high value of insoluble - more than 1.5% - are exceptions, even if the samples tested several dozen. Over 70% of the results in the range of 1% and is essentially independent of the country in which they were produced - from Egypt, through the whole of Europe to the United States.

Authors of the study gave the limits for the content of SO3 and they were then:

  • for Italy - 1,5%
  • for USA - 2%
  • for Germany, Austria, Czechoslovakia, Poland and Soviet Union - 2,5%
  • for United Kingdom - 2,75%
  • for France - 3%

Given that the American standards, and what happened to them was in those years a determinant of contemporary trends and the quality of the cement and the fact that significant differences occurred only in the content of SO3, and also considering the fact that none (!) the then standard was not worse than the current force and comments on alkali can be no exaggeration to state that the quality of production then was incomparably better compared to what today is on the market.

It is this quality of cement, basically no part insoluble - and it's still in the 40s, as a trace alkali content, which have a decisive influence on what happens with plaster or concrete, means only one thing - that if all the pores in plaster , including those used for the restoration of monuments, plastering or repairing contemporary buildings or townhouses created decades earlier, that in the nineteenth century, were the world simply unnecessary. Plaster on these homes, buildings that are now monuments are ordinary plaster c / a dyed in the mass (not scrutinize whether by means of fillers or pigments that time or not) and an equally exceptional plaster their restoration should be used.

Unfortunately, the problem lies in the low quality of current production of cement, which does nothing can replace those then used; which used as then fairly quickly lead to efflorescence, the white-and-gray raids; that enforce the use of aerators in large quantities; inadequate quality basically making such plaster, as formerly on the site. The method is simple: cement, lime and filler (call it revolved sand) in amounts known for years.

Currently, there are only separate brand cement, the quality is so high that the then exacting standards, meet without a problem, which the manufacturer in the existing conditions, then the quality would not have the slightest reason to be ashamed. Such a cement without any problem enables you to take restoration render, or plain plaster c / w quality restoration render directly on the construction site for a tenth of the price; cement plaster allows to perform the same quality as before, without the use of chemicals in such huge quantities that are used today to get what used to be the norm.

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