Working wet-on-wet means applying a new layer before the previous one has set or dried. The two layers then bond into a single mass, rather than the top layer merely gripping the surface of the one below. It is one of the simplest ways to prevent delamination — it costs nothing and only requires the right sequence and planning.
Where it is used
- Screeds — a cement-based screed laid onto a still-wet bonding slurry, making it a bonded screed rather than a floating one
- Tiling — bedding tiles into a mortar bed that has not yet set
- Plastering — a second coat applied to a first that is still damp, so no separation forms between the coats
- Concrete and paving — placing successive layers wet-on-wet so no cold joint develops
- Painting — rolling out a coat within its open time so laps and edges do not show
Why it works
With a cement-based layer that has already set, adhesion is mechanical: the new mortar keys into the roughness of the substrate. Apply the second layer while the first is still plastic and the cement reactions continue across the boundary, producing a far stronger bond. With paint it is about the still-wet edges flowing together, so the film dries out evenly without visible joins.
Points to watch
- Plan the logistics. Wet-on-wet only works if materials arrive on time and there are enough people. If supply stalls, a joint forms anyway
- Weather and temperature. Sun, wind and heat shorten the open time considerably. In hot weather work in smaller bays and shade the work
- Not always wanted. With floating screeds, load-distribution layers over insulation and deliberate separating layers, a bond is exactly what you must avoid
- Misapplication. Wet-on-wet is not an excuse for applying a second layer over a first that cannot yet carry it
- With paint, keep the wet edge ahead of you and work a wall or ceiling corner to corner in one go
Related terms
- Screed
- Bonding slurry
- Plastering
- Cold joint
- Setting
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