How far apart should movement joints be?

Movement joint spacing depends on the masonry material: clay bricks maximum 12m centres, concrete blocks maximum 6m centres, calcium silicate blocks 7.5m centres. Joints should also be placed at changes in wall height, thickness or direction (corners on long walls). Closer spacing may be needed for very exposed walls.

Why do clay and concrete block have different joint spacings?

Clay bricks expand slightly after manufacture (irreversible moisture expansion), so joints accommodate growth. Concrete blocks shrink as they cure (drying shrinkage), which means more joints are needed. Clay: 12m max centres for expansion. Concrete block: 6m max centres for shrinkage. This is specified in BS EN 1996 and PD 6697.

How wide should a movement joint be?

Movement joints in external masonry are typically 10-15mm wide. The mastic sealant depth should be twice the joint width for proper adhesion (e.g., 12mm wide = 24mm deep sealant). A compressible filler board fills the rest of the joint behind the sealant. The filler board should be wider than the joint to ensure compression.

What sealant for movement joints?

Use a low-modulus polyurethane or polysulphide sealant rated for +/- 25% movement. Silicone is not suitable for masonry movement joints. The sealant must adhere to both faces of the joint. Apply a bond-breaker tape at the back of the sealant to prevent three-sided adhesion, which reduces the sealant's ability to stretch.

Do internal walls need movement joints?

Internal blockwork walls also need movement joints, typically at the same 6m centres for concrete blocks. Internal walls are less exposed to temperature changes, but drying shrinkage still occurs. Movement joints in internal walls are often simply filled with mastic and decorated over, as visual appearance is less critical.

TradeCalculator.co.uk

Movement Joint Calculator — Spacing, Mastic & Filler Board

Calculate movement joint positions, mastic sealant and filler board for clay brick and concrete block walls.

Wall Length

Wall Height

Wall TypeMax spacing: 6m

Sealant Price

Filler Board Price

Joint Width

10-15mm typical

How We Calculate This

This calculator determines the number, spacing and material quantities for movement joints in masonry walls.

Joint count

Joints = ceil(Wall Length / Spacing) - 1
Clay brick: 12m, Concrete block: 6m, Calcium silicate: 7.5m.

Sealant

Mastic Depth = Joint Width x 2
Filler board fills the remainder of the joint behind the sealant. Sealant volume per joint = width x depth x height.