At One Place

Can you mix water-based paint and oil-based paint underneath?

Water-based paint and Oil-based paint underneath
No — it damages something or fails
Not directly. It will look fine and peel off in sheets later.

What actually happens

Emulsion has almost no adhesion to a cured oil-based gloss, because the old surface is hard, slick and non-porous. The new coat dries, looks perfect, and then lifts in sheets months later, usually taking a fingernail to start it. Oil over water-based is far less troublesome and is generally acceptable on a sound, keyed surface.

What to do instead

Abrade the gloss to a dull finish and use a bonding primer. Skipping the primer is what causes the failure, not the paint choice.

Paint, glue and materials

Combination Verdict Why
Superglue and baking soda Fine Yes, and it is a genuinely useful trick — but it gets hot.
Expanding foam and water Fine Yes — polyurethane foam needs moisture to cure, and misting the gap helps.
PLA filament and abs filament Do not They will not bond to each other, and they want different temperatures.

Common questions

Can you mix water-based paint and oil-based paint underneath?
No — it damages something or fails. Not directly. It will look fine and peel off in sheets later.
What happens if you do?
Emulsion has almost no adhesion to a cured oil-based gloss, because the old surface is hard, slick and non-porous. The new coat dries, looks perfect, and then lifts in sheets months later, usually taking a fingernail to start it. Oil over water-based is far less troublesome and is generally acceptable on a sound, keyed surface.
What should I do instead?
Abrade the gloss to a dull finish and use a bonding primer. Skipping the primer is what causes the failure, not the paint choice.

Related pages

Sources

  1. Official vendor product documentation — At One Place

How these figures are compiled and checked