Morrells waterborne primer issue?

[Tomber]

Has anyone had an issue similar to this whilst using a waterborne primer? See attached image.

Process:

- 2 Coats of primer sprayed onto MDF, denibbed with 320 paper in between. The 1st coat was left to dry overnight before second was applied.
- Cleared off with air and tack cloth before applying morrells waterborne lacquer.

After about 15mins of drying time small pimples began to appear as per image.

Does anyone have any ideas whats caused this? It looks like raised grain to me but that seems usual considering I applied 2 good coats and even tried 3 coats on a test piece with same results.

Thanks,
Tom

 

[custard]

Are you sure the lacquer was sprayed in thin coats? With waterborne you want the absolute thinnest coat possible commensurate with the surface becoming visibly wet. Try again keeping the air turned high, spraying thin coats, and not overlapping too much.

 

[Tomber]

This was after the first coat of waterborne lacquer, it was sprayed very thinly.

I think the issue is the primer coat. I treated the edges of the shelves with a PVA solution prior to spraying the primer and these treated edges remained dead flat.

I tried applying a 3rd coat of the primer without denibbing before applying the lacquer and the same problem occurred.