• Question: Why does paint dry on the wall but not harden in the tin?

    Asked by mollieK to Vicky, Scott, Jim, Gaia, Adrian on 15 Mar 2016.
    • Photo: Gaia Andreoletti

      Gaia Andreoletti answered on 15 Mar 2016:

      I had to look up the answer as I had no idea! In a sealed paint time the water in the paint will not evaporate, keeping it liquid. When the paint is put on the wall, the water can easily evaporate, leaving a dried film of solid paint on the wall.

    • Photo: Scott Lawrie

      Scott Lawrie answered on 15 Mar 2016:

      Excellent question! Things dry by evaporation. Like how a puddle will eventually disappear on a hot day. Paint is made of tiny specks of colour held in some water. In a paint can there’s no air or sun to evaporate the water, but in the wall there is, so only the solid colour specks are left after a while.

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