Tiny bubbles in water-based Satin

[allthebuttons]

I’ve just had MDF under-stairs cupboards built, but when they went to paint the door, they’ve been finding that tiny bubbles are appearing as it dries. It’s Ronseal water-based Satin paint, and it’s being used all over the house (including similar MDF) and everywhere else it is fine.

They have been using Dulux quick-drying undercoat, so I thought I would have a go myself With Zinsser BIN. I sanded it down smooth and painted over two coats of BIN… still the same thing. The attached picture shows the BIN.

I’m really surprised it’s happening with Shellac, which normally works with everything. I’m guessing something is wrong with the MDF itself, or an earlier coat?

Can anyone explain what is happening here, and what they/I can do? Does it mean sanding all the way back to the MDF?

Thanks!

 

[DiyNutJob]

Your MDF must be reacting to the paint producing a gas. If you sand all the way back, you will increase the chance of more reactions. I would just spot repair the bubbles.

 

[allthebuttons]

Do you know why that would be happening? The same paint is being used on MDF from the same batch elsewhere without problems.

 

[DiyNutJob]

Probably just manufacturing variations. Some boards may have more of a chemical in the bonding agent. Of course, I am only speculating.