Aircrete Blocks and Products – Glossary of Aircrete Terminology

Celcon manufactures a wide range of quality aircrete products, available in a variety of grades and dimensions, and all conforming to BS 6073. This is the excellence of Celcon aircrete.

Glossary of Terms

Aircrete Lightweight: loadbearing and thermally insulating building material - most commonly available in block format.

Agrément Certificate (BBA Certificate): Certificate of a product’s performance issued by the British Board of Agrément.

Autoclave: Vessel in which aircrete blocks are steam cured under high pressures and temperatures.

Autoclaved Aerated Concrete (AAC): Original name for the material now known as aircrete.

Bed Joint Reinforcement: Light metal reinforcement available in both roll and strip form. Laid in the mortar of bed joints as the wall is built it helps prevent cracking by distributing the high stresses that can occur from point loads. Also used instead of (or in conjunction with) vertical movement joints where wall lengths are long enough to otherwise crack due to normal daily and seasonal thermal and moisture variations.

Closure Blocks: Special shaped units for use at ends of floor beams at the floor/wall junction.

Concrete Spreaders: See Padstone

Co-ordinating Face Size: Physical measurement of the face of a single block including the surrounding mortar joint measured to the joint centre line. Total joint thickness is taken as 10mm.

Coursing Units: Brick size blocks used primarily in closing cavities and levelling course heights.

Damp Proof Course DPC: A device usually comprising a layer or strip of material placed within a wall, chimney or similar construction to prevent passage of moisture.

Diffusion Resistance: Factor ratio of the permeability of air to that of the material under consideration.

Fair Face: Description of the appearance of an exposed wall surface where mortar joints are neatly finished. Depending on location and purpose the wall surface can be left unfinished or painted. For a description of the surface of a block within a wall see ‘Smooth Face’.

Flanking Walls: The wall (normally the inner leaf of an external wall construction) which runs at right angles to and across the ends of a separating party wall.

Lean Mix: A weak concrete mix used below ground level to in-fill the cavity from the top of foundations to below DPC level.

Padstones and Concrete Spreaders: A cast concrete unit built into a wall to carry a concentrated load (e.g. a beam) bearing directly onto it. When imposed loadings are such that would cause local over stress, the use of a padstone spreads the load over a larger area of block work reducing stresses to an acceptable level.

PFA Pulverised Fuel Ash: One of the major ingredients of some aircrete blocks - a waste product from coal fired power stations. Using PFA enhances Celcon blocks environmentally friendly status.

Plain Face: See Smooth face

RMI:  Repair, Maintenance and Improvement.

Semi-Exposed Elements: Walls separating a heated space from an enclosed unheated space are referred to as Semi-exposed (or Sheltered) walls. The most common example is the wall between the house and an attached (integral or adjacent) garage.

Separating Party Walls: Walls with a specific sound insulation requirement separating dwellings of different occupancy. Building Regulations Approved Document E refers.

Slip Plane: A slip plane is a sliding joint. Usually of two courses of smooth dpc type material or building grade polythene it is used to separate parts of the structure which have different movement characteristics. For example, the combined effects of drying shrinkage and the thermal movement of a concrete roof slab cast directly onto a brick or block wall could cause cracking in the upper courses of the wall. The use of a slip plane between the top of the wall and slab would help prevent this. The most common use for slip planes is under the bearings of long lintels, precast beams and slabs.

Smooth Face: A block with an exposed face without any markings. Such blocks can be used without any applied finishes internally or externally depending on the type of block.

Tanking: A membrane or coating applied to the vertical surface of masonry, usually at or below ground level and under certain conditions where it is necessary to prevent moisture migration and/or where contaminated ground conditions exist.

Thermal Bridging (also known as cold bridging): Where a material of higher thermal conductivity, such as mortar or a concrete lintel, bridges a material bearing better insulating properties, such as Celcon blocks.

Thermal Conductivity (k): The measure of the ability of a material to transmit heat W/mK.

Thermal Resistance (R): The measure of the resistance to heat flow of a material of a given thickness (m² K/W).

Thermal Transmittance (U): The amount of heat which will flow through one square metre of a wall of a structure for every degree of temperature difference between the inside and outside environment (W/m²K).

Thin Joint Mortar (Celfix): A strong, fast setting sand/cement mortar designed to be applied in a thickness of 1-3mm to bond aircrete blocks and panels

U-Value: See Thermal transmittance.

Vapour Permeability (Diffusivity): The inverse of vapour resistivity.

Vapour Resistivity: Vapour transfer characteristics of a material.

V-Key: A physical marking on the face of blocks formed during the production process and as an aid to identifying different types of blocks.

Work Face Dimension: Face dimension of a single block excluding the surrounding mortar joints.

This information has been sourced, reviewed and adapted from materials provided by H + H Celcon.

For more information on this source, please visit H + H Celcon.


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