MPA Mortar provides a range of informative resources on mortar mixes and applications.
UPDATES COMING SOON - A new data sheet is to be released soon covering Sulfate and Frost Attack Data Sheet 25.
Files updated January 2024.
Factory produced lime:sand is a blend of sand and lime to which cement is added on site, to produce masonry mortars that can have a range of desired strengths and performance characteristics pre-determined by the specifier or user (For more information, see Data Sheet 18).
Factory produced ready-to-use mortars fulfil the requirements of specifiers and users seeking factory made materials. They are delivered to site ready-to-use in every respect and require no further mixing; no further constituents should be added. They have guaranteed mix proportions and overcome any potential problems relating to site mixing.
The incorporation of a cement set retarder into factory produced mortars makes it possible to produce materials with extended working life that will set normally when used in masonry. These mortars are now included in the range of products available from MPA Mortar members.
Factory produced silo mortars offer a range of mix proportions and overcome many potential problems relating to site mixing.
The transportable silo is filled by the producer with a pre-batched mixture of dried fine aggregate (sand), cement, lime if required and other admixtures or pigments premixed to the customer’s requirements.
The silo is delivered to site complete with integral mixer. Once power and water supplies are connected, mortar can be produced as required. The rate at which water is added can be controlled to achieve the required consistency.
The type of mortar used for rendering will depend on the background, type of wall and the exposure of the building. The information given in this data sheet applies to both traditional and coloured renderings.
Two coat work, an undercoat and finishing coat is generally required. In conditions of severe exposure three coat work is recommended, with the first coat relatively impervious to water and the others more porous
The use of lime and cement in plastering mixes, provides highly workable mortars which are easy to apply - durable - quick to dry out - and minimise the risk of efflorescence, condensation and pattern staining. In damp conditions where other plastering systems may fail, cement:sand and cement:lime:sand plasters are satisfactory. Finish coat plaster is generally gypsum-based and is outside the scope of this data sheet.
Paving slabs need to be supported continuously throughout their area to prevent rocking and cracking. The sub-base material supporting them should be easy to place and after placement develop sufficient strength to hold the slabs securely in place.
If the temperature of recently laid mortar falls below 0ºC there is a probability of some degree of frost attack. The water may freeze and expand thus disrupting the mortar by forcing the material apart and breaking the bond.
It used to be thought that this process was completely irreversible. However, the presence of free lime in the mix imparts to some degree the property of self-healing and any hairline cracks formed will tend to seal, over a short period of time.
It is obviously desirable to take precautions to minimise frost attack. Special precautions should therefore be taken when using mortar in winter conditions.
The inclusion of carefully controlled air entrainment under factory conditions in mortar increases the frost resistance in its hardened state and it is for this reason that MPA Mortar members supply specially modified factory produced mortars for winter usage.
The appearance of a building is enhanced by good quality bricklaying. After centuries of weathering, clay brickwork still has an attractive appearance. This can only be achieved if emphasis is placed on good detailing at the design stage followed by good workmanship.
Guide to Technical References in this data sheet
The methods of use and properties of cement or lime based plastering mortars are given in data sheet no. 5 of this series. This data sheet covers potential problems that, although rare, may occur and should be read in conjunction with MPA Mortar Data Sheet no. 5.
Plaster is applied to internal walling to cover varying backgrounds, correct irregularities and produce a surface suitable for final decoration. It is essential therefore that the final surface of the plaster should be of an acceptable standard with good adhesion to the substrate. Considering the amount of work carried out with plasterwork few problems occur. Nevertheless they do occasionally arise and are usually a result of incorrect specification and materials, poor workmanship, extreme site conditions or a combination of these factors.
This data sheet lists the most common causes of complaints and details remedies where appropriate.
In the UK factory produced mortar must comply with the requirements of the European Standard BS EN 998-2 Specification for mortar for masonry, Part 2: Masonry mortar. The standard, details the properties to be measured and the procedures that are required before a product can commence manufacture and be offered for sale. The tests specified in the standard are used during the Initial Type Testing (ITT ) phase after product development; this establishes the individual property values to enable a formal declaration of performance (DoP) to be made and the issue of CE marks. Values obtained during ITT are used for factory production control and for comparison against other future test results.
Mortar testing is undertaken on material in its fresh(1) state or on hardened mortar.
When subjected to persistent wind driven rain, the outer leaf of most masonry cavity walls will permit water to enter the cavity, generally through cracks at the interface between the masonry units and mortar. If the wall is properly constructed, water will flow down the inside face of the outer leaf and be discharged out of the cavity usually through weepholes.
Very often cavities contain defects which enable water to penetrate the inner leaf causing dampness to appear on the inner surface. Eventually decorative finishes may be damaged but before any repairs are undertaken, the underlying cause should be identified and corrected.
The diagnosis of rain penetration is rarely straightforward, particularly where insulated cavity walls are concerned. Various techniques are available to view the cavity; alternatively a number of masonry units may be removed. Once the cause has been identified, appropriate corrective action can be taken.
This data sheet provides a brief directory of simplified terms, descriptions and definitions in common usage within the construction industry in both UK and European markets
The method of use and properties of factory produced rendering mortars are given in data sheet no. 4 of this series ‘Factory produced mortar for external rendering’. This data sheet covers potential problems that, although rare, may occur and it should be read in conjunction with data sheet no. 4.
Render is applied to external walling to cover various substrates. The function of external rendering is usually to provide resistance to wind driven rain, but often it is also used to enhance the appearance of a structure. Problems with render can usually be avoided if the recommendations as to design, specification, materials and workmanship, as given in standards and guidance documents are followed.
Admixtures have been incorporated into mortars since ancient times. The practice of Roman engineers to add ox blood to building mortars, to enhance their physical properties, is a good example of this custom.
The use of hydrated lime and coloured pigments, as additions to mortar, has also been well documented throughout the ages and these materials are covered in other data sheets in this series
The use of ground granulated blastfurnace slag (ggbs) and fly ash in mortar has increased in recent years. Records indicate that blastfurnace cement was used for the mortar during the construction of the Empire State Building in the 1930s. Fly ash has been used as a constituent material of mortars for over thirty years, and in the case of some of the bagged proprietary mortars for an even longer period.
Mortars can be pigmented to highlight, enhance or tone in with the masonry used. The colour of the mortar joint can totally change the appearance of the finished masonry and a comprehensive range of colours and shades are available from suppliers of factoryproduced mortars.
Both lime: sand and ready-to-use mortars can be coloured by the use of pigments and the controlled manufacturing conditions employed by the factory producers will ensure that a consistent colour is obtained.
The benefit of using lime in mortar has been recognised by builders throughout the ages. The ancient Greeks and Romans produced mortar by burning limestone and slaking (mixing with water) the resultant product, then mixing this lime with sand. Many ancient buildings stand today as monuments to the efficiency and durability of these traditional lime mortars, and much of the lime used therein was hydraulic, that is, it gained strength by hydrating and setting.
BS mortar and associated test method standards were withdrawn and replaced by harmonized European Product Standards and common test methods. In addition a revised British Standard covering those mortar test methods that were not part of the new European Standards, but was desired to be retained, has been published.
All mortar mixtures, both wet and dry, are abrasive and alkaline and the following guidance is important to all users.
Hydraulic limes are a traditional building material that has been used for thousands of years, the Greeks, Egyptians and Romans all used forms of hydraulic lime.
Most pre 1920’s buildings were constructed using building limes, either hydraulic lime or hydrated lime.
Small lime kilns were located in many areas throughout the British Isles. However, as much of the available limestone contained impurities that would make it unsuitable for modern industrialised lime manufacture it was particularly suitable as a building material due to the property of hydraulicity present, in varying degrees, depending on the composition of the raw material source.
The type of screeding mortar used will depend on the required strength and end use. Levelling screeds are designed for a number of applications and to receive a final flooring, the thickness of the screed is governed by the method of construction being used. To achieve the optimum performance from a levelling screed a high standard of workmanship is essential.
The constituent materials and the proportions of those in the mix determine the properties of a masonry mortar in both the fresh and hardened states. The relationship between the fresh and hardened properties of mortar is complex; it being impossible to consider individual properties, in either state, in isolation.
Mortar in poor condition can lead to a loss surface wall strength, although this is unlikely to result in overall loss in strength.
Furthermore, the majority of relatively recent construction, utilises cavity work and therefore the inner skin and strength is less liable to be affected. The erosion of mortar may occur by the Incorrect use of pressure cleaning of fresh mortar in new masonry can also affect the strength of new construction and must be avoided. Note that pressure cleaning is dealt with separately in MPA Mortar Data Sheet 14.
This current data sheet sets out the assessment of the need for repointing, the choice of the mortar mix to be used and the application methods.