Concrete Blocks

Using our concrete blocks means there is no need to wait for mortar to dry, meaning you can place the blocks and start building straight away.

There is no real difference; breeze block is an old name that people still use for any grey building block. The original breeze blocks were made with cinders and ash from coal fires, and that is where the name comes from. Modern blocks are all concrete, but they come in three types. Dense aggregate blocks are heavy and strong, lightweight aggregate blocks such as Plasmor Stranlite and Fibolite are made with expanded clay to cut the weight, and aircrete blocks such as Celcon have air bubbles set into the mix, which makes them light enough to lift with one hand and good insulators. People also say cement blocks, which means the same thing. 

Yes, by a wide margin for the same area of wall. One standard 440mm x 215mm block covers the same face area as six bricks. At around £2.40 including VAT for a Celcon standard block, the materials cost less than six facing bricks, and a bricklayer lays a block wall far faster with less mortar, which is where the real saving sits. The trade-off is appearance. Blocks are meant to be rendered, clad or hidden inside a cavity wall, so for a wall you will see, facing bricks or a block wall with render are the choices. For garden walls, garages and the inner leaf of a house, blocks are the economical answer. 

We sell blocks individually rather than by the pack, with a minimum order of 10, so you only buy what you need. Per block, prices run from around £2.40 including VAT for a 100mm Celcon standard block to around £5.40 for a 215mm hollow block. A full pallet varies by block type: a pallet of 66 solid dense 7N blocks comes to roughly £165, and a pallet of 120 Celcon Hi-Strength 7 blocks to roughly £415.

The number is the block’s compressive strength in newtons per square millimetre, so a 7N block carries roughly twice the load of a 3.6N block. For most houses and extensions up to two storeys, 3.6N blocks are strong enough for the inner leaf of cavity walls and internal partitions. You step up to 7N where the loads are higher: below the damp proof course, in foundations, under beam and block floors, in piers and the lower storeys of three-storey buildings. 7N blocks are also denser, so they cut sound better but insulate less. The price difference is small, at about £2.40 against £3.50 per block, so when in doubt the stronger block costs little extra. 

Use a 7N block below ground. Our solid dense 7N block is the usual choice for foundation walls and below the damp proof course, because dense concrete resists water and frost and takes the weight of the walls above. The Celcon Hi-Strength 7 and Plasmor Stranlite 7.3N blocks are also rated for use below ground and are lighter to lay. Standard 3.6N blocks should stay above the damp proof course. If a soil report shows sulphates in the ground, check the block manufacturer’s guidance for that ground class, as some blocks are not suitable. We do not stock wide trench blocks, so below-ground cavity walls are built as two leaves of 100mm blocks or in 215mm blocks. 

Use hollow blocks when the wall needs reinforcing steel and concrete inside it. A 215mm hollow 7N block has open cores that are filled with concrete around steel bars once the wall is up, which turns a block wall into a reinforced one. That is the standard way to build retaining walls, free-standing garden walls over about 1.2m, gate piers and agricultural walls that have to resist sideways push. Hollow blocks are also lighter to lift than a solid block of the same size. For ordinary house walls, partitions and infill between floor beams, solid blocks are simpler and cheaper, and they take fixings anywhere. 

Yes, at the same strength rating. A Celcon Hi-Strength 7 aircrete block and a solid dense 7N block both carry 7N/mm², so they are interchangeable for load-bearing walls. The differences are elsewhere. Aircrete is light enough to lay one-handed and insulates about six times better than dense concrete, which is why it is used for the inner leaf of cavity walls. Dense blocks are better at blocking sound, take screws and bolts without special fixings, and stand up better to knocks and to damp ground. Lightweight aggregate blocks such as Plasmor Stranlite sit between the two. Choose by what the wall has to do rather than by weight. 

We stock concrete blocks in three thicknesses: 100mm, 140mm and 215mm, all with a standard 440mm x 215mm face. The 100mm block is the everyday size for cavity wall leaves, partitions and beam and block floor infill. The 140mm solid dense block suits single-leaf garage and garden walls where a 100mm wall would be too thin. The 215mm size, in Celcon standard and 7N hollow, builds a solid wall in one leaf and is used for piers and reinforced walls. We do not stock 75mm or 300mm trench blocks; for a 75mm partition most builders use a 100mm block instead.