Does VOC-free paint require VOC-free undercoat?

Question

I have been asked to paint a room with a paint that has no or low VOCs (volatile organic compounds) such as the Dulux Ecosure paints.

I was originally planning to use a plain white paint as the first coating to give me a clean, uniform surface to paint on with the new colour (I'll probably still do two coatings of the new colour). Would it defeat the purpose if I didn't use a low-VOC undercoat or is it the top coats that matter (the purpose being better air quality, in case it wasn't clear)?

Dulux actually sells an Ecosure undercoat (https://www.duluxtradepaintexpert.co.uk/products/picker#details/dulux-trade/ecosure-undercoat), which is why I started wondering if I need to worry about more than the top coatings.

More background info: the room is in a 20-year old house, though I'm not sure when was the last time it was painted. It currently has some stains and dirt on the walls, and I already fixed some cracks and holes with plaster (so it definitely needs some sort of paint job).

Answer 1

VOC solvents are used in paints because they are volatile; they will readily evaporate at room temperature. When someone wants low-VOC paint, it means that they don't want (for health or environmental reasons) to release VOCs as the paint dries. Since the undercoat would need to dry before the finish coat is applied, using an undercoat that is not low-VOC would defeat the purpose.

Answer 2

The part of paint that evaporates is called a solvent or diluent. The main one used in a latex paint is water, though there are others too.

Not all solvents are VOC's - that specifies certain ones which are a problem for smog, and so are regulated by the local air quality management districts. They have been driving the paint industry to eliminate VOCs and reqire architectural coatings to have ever less VOCs in paint.

Random citizens consider "paint" to include primer, wash, etchant, etc.

Citizens don't like VOCs because they stink, and because there's a belief that such solvents will harm you and that the house will off-gas solvents for many months.

If the requirement is to paint the house with low/no VOC paint, then the person will expect that to apply to the primer too.