Paint problem

I have a shelf in my bathroom that was painted with white gloss. Part of this bubbled up exactly as if it had been treated with paint stripper only much more gradually (it took a few weeks or so to go ). Can anyone suggest why?
This may be sheer coincidence but it happened just after I fitted a new mirror and the bubbling occurred underneath the mirror, dead center and about 10cm wide. <chauvinist> And, contrary to my first thought, SWMBO hasn't been cleaning the mirror with anything except mild detergent.</chauvinist>
I have now stripped it back to bear wood and I'm about to repaint. I don't want it to happen again.
Any advice would be much appreciated.
A.
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[snip]

If you've stripped it back then you've probably eliminated a recurrence.
Steve.
--
Vehicle Painting Pointers: http://www.stephen.hull.btinternet.co.uk
Coach painting tips and techniques + Land Rover colour codes
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Loss of adhesion in this form really only occurs when something is trying to escape from the substrate through the paint coating film. This is usually moisture, but can also be natural resins and/or solvents still present after treatment.
The fact that you have noticed a relationship between the mirror position and the shelf looks like a reasonable area for investigation. It's difficult to diagnose without seeing the problem, but I would guess that the problem is moisture related, and that condensation could possibly be forming on the mirror and running off directly onto the shelf. Constant exposure to water lying on the horizontal shelf will shorten the effective life of the coating.
However if the shelf is fitted flush with the wall, its more likely that condensation is running down the mirror and either down the wall or dripping onto the back of the shelf, and the rear of the shelf (where it is fitted to the wall) has not been properly painted/sealed. Moisture is probably getting into the timber at this point, then trying to escape... with the consequent loss of adhesion you have seen.
Make sure the shelf is properly painted all over, even the parts that you can't see... if necessary remove from the wall and paint. You could also run a thin bead of white sanitary silicone along the rear of the shelf where it joins the wall for additional protection.
Regards
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Max Bone Decorating Direct Ltd
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Was this on old gloss? Some of the manufacturers at least used to include a silicone compound of some sort (remember SILthane?) to try to make soiling not stick to the paint. Of course this made new paint not stick, and although I do not know how exactly they managed this, the silicone migrated out to the surface with time, so that the initial two coats bonded together. Sanding, followed by sugar soap ought to get adhesion.
John Schmitt
-- If you have nothing to say, or rather, something extremely stupid and obvious, say it, but in a 'plonking' tone of voice - i.e. roundly, but hollowly and dogmatically. - Stephen Potter
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A.T. wrote:

Is the new mirror reflecting bright sunlight directly onto the affected area ?
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