The lumps in the paint were unfortunately straight from the can - hence the strain suggestion is probably right on. But really I would not expect the need to strain a brand new tin of anything!

Therefore the pimples I was getting were the lumps in the can being ejected from the gun tip.

Good suggestion on spraying in the sunlight - yes I did do that yesterday!

Never the less, the surface is sanding very easily and the result looks pretty good. I do think I'll apply one more coat to ensure I'm happy with it.

Thanks all