Fibo 850 Concrete Datasheet
Side view of a Fibo 850/950 Block.

Fibo 850 Concrete Block

Fibo 850 super lightweight concrete blocks are available in 100mm and 140mm thicknesses. They are suitable for general-purpose walling applications and provide a strong background for applying plasters, renders and fixings. Fibo 850 blocks are easy to handle and provide great thermal efficiency values. 

Manufactured to BS EN 771-3, they consist of expanded clay aggregates and a mixture of other naturally occurring raw materials and cement. The clay aggregate is produced from carefully selected clays, which are bloated through heat expansion to create a low density, porous aggregate with numerous cavities. This makes Fibo 850 incredibly light and thermally efficient.


Specification & Application

Weights & Pack Sizes

All weights are approximate and subject to normal variations in raw materials.

Table 1 – Block Weights and Pack Sizes

Thermal Properties



Block Wall Ties

Under normal conditions, wall ties should be embedded 50mm into the mortar on each leaf, staggered in alternate courses and spaced in accordance with the following.

Table 5 – Wall Tie Spacings

Leaf Thickness
Cavity Width
Horizontal Spacing
Vertical Spacing
Ties per m²
Less than 90mm50 - 754504504.9
Over 90mm50 - 1509004502.5

Block Mortar

Generally, the mortar type for work above ground level should be designation (iii) / Compressive Class M4. Designation (ii) / Compressive Class M6 mixes should be used for work below ground in conditions where there is a risk of saturation with freezing.

Table 6 – Mortar Mixes

Mortar Designation
(as per BS 5628-3)
Compressive Strength Class
(as per BS EN 1996)
Recommended mix proportions of materials by volume
(iii)M41:1:5 to 6 - Cement:Lime:Sand.

1:5 to 6 - Cement:Sand with or without air entrainment.

1:4 to 5 - Masonry Cement:Sand (with non-lime filler).

1:3½:4 - Masonry Cement:Sand (with lime filler).
(ii)M61:½:4-4½ - Cement:Lime: Sand.

1:3 to 4 - Cement:Sand with or without air entrainment.

1:2½:3½ - Masonry Cement:Sand (with non-lime filler).

1:3 - Masonry Cement:Sand (with lime filler).

Site Practice

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The Whiteley: Bespoke Blockwork For A Unique Restoration

Mixed Use

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Construction photo of The Whiteley.