This may answer your questions.

BLISTERING.
RECOGNISING THE DEFECT :

1/. Air or water-filled blisters in paint film .

2/. In the advanced stages paint comes away from the substrate .

3/. Size may vary with the weathering factors.

4/. Long periods of humidity and wet weather promote the phenomenon

5/. In extreme cases rusting occurs.

POSSABLE CAUSES:

1/. Spraying over rust.

2/. Undried previous material sanded too soon.

3/. High relative humidity or condensation generated by variations in temperature during the spraying process.

4/. Condensation during spraying .

5/. Residues of sanding dust.

6/. Sanding water not dried off.

7/. Topcoat too thin.

RECTIFYING THE DEFECT:

Having determined the extent of the damage , sand down the areas to sound substrate and respray.

As I pointed out all these can change, ie effect, time period , etc due to chemical reaction.

There you are Geoff that should help you out.

Last edited by Jack The Lad; 16/02/13 09:54 AM.