What is vol en zat (fully filled joints)?

Vol en zat is a Dutch trade term indicating that a space has been filled completely and without voids. You come across the term in specifications and application instructions, mainly for masonry. The term is used in three ways.

Vol en zat bricklaying

In bricklaying, vol en zat means that all the space between the bricks is completely filled with mortar, both the bed joints (horizontal) and the perpend or head joints (vertical). No air may be trapped. This has clear advantages:

• the masonry lets less rainwater through;
• less lime or cement washes out, which reduces the risk of efflorescence;
• the wall transfers the load more evenly.

With jointing as you go (Dutch: doorstrijken), where the bedding mortar is finished straight away as the joint, vol en zat bricklaying is a requirement. It also applies with normal pointing: hollow perpends behind a neat joint are a well-known cause of penetrating damp.

Note for cavity walls: on the cavity side, you specifically do not want mortar that bulges out or falls into the cavity. Mortar residue on wall ties or insulation forms mortar bridges, along which moisture can run to the inner leaf.

Vol en zat in plastering and floors

• Plastering: a bead, such as a corner bead or plaster stop, must be fully embedded in the mortar, without hollow spots behind it.
• Floors: a broadcast material (for example sand in a synthetic resin floor) is scattered in excess into the wet bonding layer. After curing, you sweep away the loose material.

In practice: practical tips

• With every brick, also put mortar on the end (buttering), so that the perpend is full straight away.
• Press the brick down and tap it into line, so that the mortar gets into all the corners.
• At handover, spot-check whether the perpends are filled: you can often hear hollow joints when you tap them.

Related terms

• Jointing as you go (doorstrijken)
• Bed joint
• Perpend (head joint)
• Mortar bridge
• Cavity wall
• Efflorescence
• Mortar

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