Micro Blisters

[JonE]

I guess the biggest issue is whether its original paint or not! If it is, then "just maintain", for Chris's reasoning above. It's a steel car, if its the one in your header?

If it is a B3 car, I can check whether it is original paint colour or not from the ledgers, if you contact me direct....

[Adam Brown]

Were any of the affected areas covered with a sheet or something that could trap moisture between that and the paint, if so - that would also do the job.

[PDavies]

Yes Adam the car was covered in a dust sheet . How does this caused a problem ? Will the old paint absorb any moisture ?

[Nick Lettington]

I thought this common knowledge, so sorry for delay responding.

A number of years ago I atttended a course on maintenance painting of steel structures. You will all know, when steel rusts, small deeper pock marks appear. Often when a car is half restored and left in primer, these small marks appear all over the surface. Over time, the rust pits develop and hydroscopic ferrous salts form that litterally pull water through most paints. It is very difficult to fully remove them when refinishing rusty panels, so without a full strip down it is likely that any microblistering will reappear. 
Now it's probably 20 years since I did the course. I believe I may still have the notes in a box at work but if I remember correctly, it is possible to minimise the problem by scrubbing the surface with water after removing the visible rust as these salts are soluble in water... A second clean up would doubtless be necessary, but it would reduce the risk of blisters.

I have never applied this to car bodywork as I like cars I can drive all year and take kids and rubbish and Christmas trees in... But the science applies equally to any painted steel.