| Differences between EN 771– 4 and BS 6073–1:
The standard contains a National Annex informing users of the differences between EN 771-4 and BS 6073-1. Some of the main issues are summarised below. Dimensions:
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. As a result, blocks from our ‘Plus' and "Jumbo Plus" range are manufactured and declared to the enhanced tolerance class of ‘Thin Layer Mortar A', which includes a tolerance on the bed height of ±2. Density:
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 test method used to determine compressive strength is completely different in EN 771-4 compared to BS 6073-1. The preparation and conditioning produces a higher test result by some 4% as a result of testing blocks in slighter drier condition. Thus, regulatory requirements have been amended in line with the apparent increase in strength. This is the case for Approved Document A of the Building Regulations for England and Wales BS8103-2. The strength categories in BS5628 have also changed to reflect the differences. Strengths stated by H+H UK 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. H+H UK products will have the same excellent design thermal conductivity (lambda) values as previously, but in addition a ‘lambda dry' value is quoted at zero moisture content to allow for comparison across the EU member states. Durability:
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. The British Board of Agrément has assessed Celcon Blocks for use above and below ground level DPC, confirming their fitness for purpose in these locations. Moisture movement:
Drying shrinkage is a requirement given in the EN depending on the intended use of the unit. There is a 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. Whilst we have quoted values available, the inclusion of the property is at the request of the French Regulators and it appears to have very little meaning in the UK. 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 Celcon Blocks have confirmed that they have the highest classification of reaction to fire. Fire resistance tables are available elsewhere (see H+H UK 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. This has little bearing on the design of structures in the UK and H+H UK has opted for tabled values obtained from EN998-2. Thin-layer mortar attracts a significantly higher declared value. Flexural bond strength:
This has been introduced for a legal requirement for Finland only and there is no requirement to declare a value in the UK. To determine the products and applications we have available, follow the links on the Left hand panel or follow the Library link to download information on our products and services. | 
