Spouse asks "Why does paint stick?"

Factual Questions
1

Spouse was painting a asks “Why does paint stick?”

She’s of keen mind and likes good academic answers. She probably had first year physics and chemistry as a pre-med student.

2

I think it would primarily be van der Waals’ force.

3

Coulomb’s law.

4

To put it simply, paint is made partially of glue. The most basic kind of paint is just protein-based glue, plus pigment. We used to make paint that way in our theater shop, using this nasty protein glue made of boiled down bones and hides. Similarly, Milk+rust powder gives you the cheapest way to paint a barn red. You can also use eggs, latex, and many other bonding agents as a base for paint.

The BASF Chemical Reporter explains why glue sticks here in a kind of a basic way, and SDMB Staff Reporter Una speaks on the topic in more detail.

5

It’s going to be a combination of factors:

  1. Porosity. On porous surfaces paint soaks into holes, and when it dried it is physically held to the surface.

  2. Shrinkage. Paint shrinks as it dries, causing it to cling tightly to any surface imperfections, much like saran wrap.

  3. van der Waals’ forces as **Napier ** mentioned.

  4. Air pressure. Paint forms a tight seal with the underlying surface, so removing it is even worse than trying to lift a sheet of paper directly off a smooth surface. The residual oil layer under the paint adds to this effect.

Small patches of paint on non-porous surfaces such as polished metal will often peel off as readily as saran wrap, because with no surface imperfections, corner or pores to cling to it’s only the pressure differences and van der Waals’ forces keeping it in place.