Screws, glues and labour: what you don't see in a joinery job

In joinery, the smallest details are often what determine whether a job lasts over time: the wrong screw or too thick a bead of foam can spoil an installation that is otherwise well done.

Screws: the right length according to thickness

As a general rule, the screw length should be 2-2.5 times the thickness of the piece it passes through, to leave enough thread driven into the destination piece without going through it. A screw that is too short doesn't grip well; one that is too long can poke out the other side or split the wood near the edge.

Plugs: solid or for cavities, they're not interchangeable

The standard nylon plug works in solid masonry. In plasterboard partitions or hollow brick, a specific plug is needed (umbrella-type or chemical), because the standard one doesn't grip in hollow material — using the wrong plug is the most common reason a piece of furniture or shelf falls months later.

Brackets: visible or concealed

• Visible, screwed: quicker to fit.
• Concealed / invisible: cleaner aesthetically, but requires routing a recess in the piece, which adds labour time.

Polyurethane foam: less is more

Polyurethane foam fills the gap between a door or window frame and the building work, fixing and insulating at once. Always apply it in thin beads without squeezing the can hard: the foam expands several times its volume as it cures, and a thick bead can end up distorting the frame inwards — a common mistake for someone who hasn't worked with this product before.

White glue: real yield

A 750 ml container of white glue (PVA) goes far enough to glue roughly 8-10 furniture joints or about 4-5 m² of edging/veneer, depending on the thickness of the layer applied.

How much a carpenter's hour costs

The average price of a skilled carpenter's hour in Spain is €30-50/h, depending on the area and whether the work is made-to-measure (furniture) or installation (doors, skirting). The assistant is usually billed 30-40% below the skilled worker — combining them with the skilled worker on wardrobe assembly or door installation lets you progress faster without making the whole day dearer.

Frequently asked questions

Why doesn't a standard plug hold in plasterboard? Because it is designed for solid masonry; in hollow material such as plasterboard it needs a specific plug (umbrella-type or chemical) to grip securely.

What happens if I apply too much polyurethane foam around a frame? The foam expands several times its volume as it cures, and a thick bead can distort the frame inwards — always apply it in thin beads.

How much does a carpenter cost per hour in Spain? Between €30 and 50/h for the skilled worker, depending on the area and type of work, with the assistant billed 30-40% less.

Conclusion

Choosing the right screw, plug and amount of foam for the material and real weight may seem a minor detail compared with the cost of labour, but it is what decides whether the work lasts over time or has to be redone. Quoting these items together with the skilled worker's and assistant's hours gives a complete and realistic breakdown.