Varnish Dilema - Silicone
Trying to get some new single pack varnish onto some existing varnish, and it looks like its been spotted with silicone - the varnish 'retreats' from certain areas if you know what I mean!
You'll need to get the new coat off first.
your varnish manufacturer will have a de greaser. sand back the affected areas, treat and try again. could also be airborne pollution ie diesel car or truck nearby or if you have used wd40 or something with oils or solvents within a several mile radius!
Was the old varnish two pack as they may not "agree"??
The general rule of thumb is that it's OK to put a one pack varnish on top of two pack (or an epoxy coat) but not the other way round. So it looks like it's a silicone type problem you have there and yes it really is a bugger to get it all away. One spot and you have this fish eyeing problem. There are silicon sealer removers for bathrooms that you can get and I have wondered if they would be any good.
Definately sounds like a contaminated surface. A rub over with thinners should remove any grease/grime prior to varnishing. I remember once chatting to Laurie Smart at his yard when he had just finished rubbing down a surface ready for varnishing subsequently followed by me running my index finger along the surface commenting on how smooth it felt, how he didn't lamp me I don't know as Laurie had to spend more to time removing the grease deposited off my finger onto the surface. Golden rule number one ......never touch the surface prior to applying varnish.
funny enough I once touched a brand new helicopter at the factory with my finger and got into trouble for the 'greasy' finger mark.
I'll be trying some of the solutions today, so I'll report back!
Reporting back that the offending contaminant almost certainly silicone) was indeed removed by a scrub with thinners followed by some 180 grit sandpaper. Varnish went on no problem afterwards, thanks to all who contributed.
Haaving survived the silicone ordeal, I've then proceeded to inflict another body blow to my finishing!
This one summarised from the SP site - also helpful