How to avoid cracks between painted wood and painted plaster?

Question

A wooden piece is screwed against a plastered block-wall. Both, the wooden piece and the plaster, are primed and painted.

Problem. I expect that there will be a thin crack between the wood and the plaster in a few months.

Question. How to finish the wooden and plastered surfaces, such that the cracks between them are less likely to form?

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What I thought so far. Leave a 3mm gap between the wooden piece and the plastered wall, then fill the gap with silicone. Let the silicone have the same paint as the plastered wall. But a problem with this approach is that the light reflection might not be the same. E.g. the silicone area might be more shiny.

Answer 1

You need an elastic caulk that can be painted. It should be applied in a wide enough bead to be able to stretch while staying stuck on both materials as they each do their own thing according to ambient humidity and temperature.

Basically don't fill a 1mm crack with caulk and expect it to stretch to 2mm when the crack widens.

Some silicones can be painted, but they're pretty are.

In your case the ideal would be acrylic caulk, which is available pretty much everywhere and very easy to apply. It's water based so all you need is a wet finger and a wet sponge. It can be painted with acrylic paint without any trouble, although you should of course wait for it to dry and cure before painting it. For other paints, read the docs to make sure it's compatible.