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European Standard for aircrete block marking

The development of European standards is a part of the European Union's Construction Products Directive to which the Greece has signed up to implement. The aim of the directive is to allow free passage of construction materials within the EU, removing any technical barriers. This process covers all construction materials and products. One of the other key aims of the directive is to allow any products that existed before the implementation to be able to continue to do so. The most visible sign of the new European Standards will eventually be the CE marking of all products. YTONG has taken the option to CE Mark, since it is the mark of conformity with our European standard and it denotes that our products satisfy certain requirements within European law.


EN 771-4 is part of a series of product standards for different types of masonry unit. For example, clay bricks are covered and specified in accordance with Part 1 and aggregate concrete blocks with Part 3 of EN 771. There is also a new suite of test methods, most covered by the EN 772 series of standards, as well as new product standards for mortars, lintels, wall-ties etc.
EN 771-4 specifies the characteristics and performance requirements for autoclaved aerated concrete masonry units available throughout the EU member countries. It aims to do so in product performance terms, avoiding as far as possible prescriptive requirements.

It should be noted that the declared value of a performance characteristic given for a masonry unit conforming to one part of EN 771 cannot always be directly compared with the same performance characteristic for a masonry unit conforming to another part of EN 771. This is particularly the case for compressive strength, where the test conditions vary considerably and this results in major differences in apparent strength across different types of bricks and blocks.



Scope of the European standard

The standard specifies the requirements for aircrete blocks for which the main intended uses are different types of loadbearing and non-loadbearing applications in all forms of walling including single leaf, cavity, partitions, retaining, basement and general use below ground level. It also includes walling for fire protection, thermal insulation, sound insulation and the fabric of chimneys (excluding chimney flue units).



The specification of aircrete units by length, width and height is retained. The term "width" is used as opposed to "thickness". Sizes of units have not been standardised on a European level. In EN 771-4, the use of thin-layer mortar is acknowledged and tighter tolerances on permissible deviations have been introduced for the units.



The density obtained from the new test method is virtually identical to the old, but a new permissible deviation between measured and the declared dry density has been introduced, limiting it to +/- 50 kg/m3.


Compressive Strength

The preparation and conditioning produces a higher test result by some 4% as a result of testing blocks in slighter drier condition. Strengths stated by YTONG will be the mean compressive strength of whole blocks.


Thermal Properties

EN 771-4 requires the manufacturer to provide information on thermal properties, predominantly thermal conductivity. YTONG products will have the same excellent design thermal conductivity (lamda) values as previous, but in addition a "lamda dry" value is quoted at zero moisture content to allow for comparison across the EU member states.



In EN 771-4, this is expressed as the freeze/thaw resistance. Until such time as a European test method is introduced, declaration is based on experience relevant to the intended uses of units.


Moisture movement

Drying shrinkage is a requirement given in the EN depending on the intended use of the unit. There is different moisture content range (6 to 30% moisture content) over which movement is measured, which better reflects the actual in-use conditions. The quoted value is therefore slightly lower than the previous value, which used a much wider range of moisture test conditions.


Water Vapour Permeability

EN 771-4 requires information to be provided on this issue when relevant to the uses of the units, and in all cases when the units are used externally. The value is declared from a generic set of tables obtained from EN 1745.


Water absorption

This is required by EN 771-4 and is declared when relevant to the uses of the units, and in all cases when the units are used externally.


Reaction to Fire

EN771-4 specifies that the reaction to fire classification be declared by the manufacturer when the aircrete units are intended for use in masonry walls subject to fire requirements. Independent tests on YTONG blocks have confirmed that they have very high classification of reaction to fire. Fire resistance tables are available (see YTONG technical information).


Shear bond strength

This is another new characteristic, which can be declared in terms of the initial shear strength and based on fixed tabulated values or values determined from tests.


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