What is joint filler?
Joint filler is a filling compound used to fill and finish the joints between plasterboards, so that a wall or ceiling without visible joints is created. It is available as a powder that you mix with water, and as a ready-to-use paste. Major plasterboard manufacturers supply a joint filler matched to their boards. It is also called joint compound; in Dutch, voegenvuller.
The Dutch term is also used in concrete construction for a machine that fills the wide joints between precast floor units with concrete through a hose.
Method for plasterboard
- Preparation: make sure the boards are fixed, screw heads are just countersunk and the joints are free of dust.
- First coat: fill the joint with joint filler and press it in well with a filling knife.
- Reinforcement: press reinforcing tape (mesh tape or paper tape) into the wet filler. This prevents cracks along the joint.
- Drying: let the coat dry completely as stated on the packaging.
- Finishing coats: apply one or two thin, progressively wider coats to blend in the joint.
- Sanding: sand lightly flush with fine sanding mesh and remove the dust.
Board joints with tapered edges are designed to be filled this way. Straight butt joints are harder: feather them out wider so that no ridge appears.
Common mistakes
- Coats too thick: causes shrinkage and hairline cracks. Several thin coats are better.
- No reinforcement: without tape, a joint often cracks open after a few months.
- Working on too soon: a new coat on a wet coat sags.
- Screws countersunk too deep: if the paper face is broken, the board holds less well. Add an extra screw next to it.
- Wrong filler in wet rooms: in bathrooms, use products suitable for that purpose.
Related terms
- Plasterboard
- Plasterboard plug
- Sealant
- Joint
- Slab floor
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