Strength and durability
Strict quality control guarantees that the minimum cube strengths specified in BS 4721 or BS EN 998-2 are exceeded, while variability and standard deviation are reduced compared to site-mixed mortars. Details of typical characteristic strengths of Premix mortars are available on request.
When specified correctly and used in accordance with the relevant codes of practice, our mortars last as long as the structure. The admixtures are non-aggressive and cause no corrosion of embedded metal such as brickwork ties.
However, all mortars containing Portland cements may contribute to corrosion of zinc or aluminium components in exposed, continually wet conditions.
Air content
Air entrainment produces the desired plasticity, while eliminating the problems of bleeding often associated with high water content. Where relevant, the range in which the air content falls will be declared, as specified by BS EN 998-2.
Frost resistance
The frost resistance of masonry depends on the specification of suitable materials. It is also important that the composition of the mortar is to a consistently high standard, good workmanship and site practice are adopted and the correct joint profile is achieved (see below).
The entrained air in Premix mortars increases resistance to frost attack and improves long term freeze/thaw durability.
Rain penetration
Resistance to rain penetration is important to the durability of masonry and we recommend that the relevant codes of practice are always followed.
Fire protection
Premix mortars are non-combustible as defined in BS 476 Parts 4 and 8.
Exposure and mortar designation
When designing and detailing a building, it is essential the masonry materials are suitable for the expected exposure conditions.
The general degree of exposure of the site according to geographical location can be determined from BS 5628 Part 3. Consideration should be given to local conditions, such as the predominant wind direction, the exposure of individual components in the building and the likelihood of frost or sulphate attack.
Premix Mortars are available in all four traditional sand/cement mortar designations in general use and the new BS EN 998-2 mortar classes. Although the choice of mortar designation can be complex, the general suitability for mortars to be used in jointing exposed to different weather conditions is indicated below.
When masonry is to be constructed in exposed conditions, it is essential that the strength and other physical properties of both mortar and the units or background are compatible - see BS 5628 and BS 5262 respectively.
Joint profiles
The type of joint profile must be suitable for the degree of exposure. There are four pointing profiles in general use.
Weather-struck: Satisfactory for all degrees of exposure. The joint is ironed, closing the surface of the mortar, and inclined to the lower edge to shed water. The ironing produces a good bond between mortar and units. Good workmanship is required to obtain a uniform colour and texture.
Bucket-handle: Satisfactory for all degrees of exposure. The mortar surface is lightly ironed to obtain a close texture, again resulting in a good bond between mortar and units. Care is needed to obtain uniform colour and texture of joints. Over tooling can affect the surface colour of the mortar.
Flush: Suitable for moderate and sheltered exposure conditions. The joint is not ironed, resulting in an open texture. Good workmanship is necessary for a good bond between mortar and units, but produces a uniform colour texture.
Raked: Suitable for sheltered and some moderately exposed conditions only. A special tool such as a chariot should be used to rake the joint to a consistent depth, never more than half-distance between the unit face and any perforations. Gives excellent uniformity of colour and shade.
Note that the various types of joint profile will produce a different appearance in finished brickwork, particularly when coloured mortars are used.