White Sprit takes off new gloss paint, WHY???

Hi,

I have recently been doing some window woodwork gloss painting with crown one coat gloss, decided I needed to do anothe coat, as the brush marks at the stat of the stroke were showing. Sanded and rubbed down with white sprit, noticed some parts were blistered, rubbed with the cloth a little more and large amounts came off. The paint had been applied about 60 hrs before.

Any idea what migh have gone wrong?

Thanks

Reply to
James Salisbury
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AFAIK there is no chemical reaction occuring when gloss paint dries. All that happens is the oil evapourates. Therefore soluble in white spirit before == soluble after.

When emulsion dries a polymerisation chemical reaction occurs. Just like the formation of many plastics, so what you get after is not just a solid version of what was in the tin. Although it is water based, the product of the polymerisation is not water soluble.

HTH

-- Mike W

Reply to
VisionSet

Hiya Mike. Thanks for that, I think I'd figured the first part myself, but that last bit I didn't realise.

jim.

Reply to
jim.

You must have run the top of the paint off when you opened it and not stirred it all in. I can't think of a reason for what you have had happening. You aught to know that a skin forms on a part tin of paint and that it is insoluable. It oxidises into a thermosetting plastic on contact with air.

Paint consists of an oxidiser, powdered colourant and a vehicle. The oxidiser is often tunge oil or a synthetic resin like it and the vehicle is solvent -usually white sprit. The powdered colour is often metal salt or oxide. It can also be organic dye.

There is no way that a full compliment of the above from a reputable source will behave as you say it has.

Reply to
Michael Mcneil

Don't get this....so why doesnt gloss come off whenever you rub it with white spirit ? We'd all be using it as stripper wouldn't we ?

Reply to
norm

Okay, so I'm wrong, more certain of the emulsion description though.

-- Mike W.

Reply to
VisionSet

Er, don't think you're 100% right about that either :-). Dispersible in water before = water sensitive after i.e. won't stand prolonged contact with. If they could get the emulsifiers to disappear during drying, water based paints would truly have arrived. Ammonia does that but would be worse than solvents for the user. IIRC they dip some new cars in acrylic paint but in the kind of controlled environment that isn't possible for d-i-y.

Reply to
stuart noble

Oil-based paints contain linseed oil which has unsaturated (ie double) carbon bonds. These react with oxygen in the air and slowly cross-link forming a polymer. That's why you get a skin in a partly-used tin of paint. The air-gap will be fully saturated with solvents within minutes of replacing the lid (so no more evaporation occurs) but there's enough oxygen for the surface paint to react with.

I've never known white spirit to dissolve dried oil paint. Maybe it was brush cleaner?

Reply to
Laurie

Untrue. As the solvent evaporates there is a polymerisation of the polyurethane content of the gloss paint.

Reply to
Steve Firth

After 60 hours (OP said) this seems extreme. The evaporation of the solvent (White Spirit, Water or Xylene) is what makes the paint become touch dry. The polymerisation is what makes the paint film permanent. This is hours for Vinyl and Acrylic. This is a day or so for Polyurethanes and Alkyds This weeks for the resin in Hammerite.

-- Ed Sirett - Property maintainer and registered gas fitter. The FAQ for uk.diy is at

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Reply to
Ed Sirett

I was overpaiting old gloss. The previous top layer of old paint came off very very easly, ie with the push of a filling knife it came off in big sheets. I suspect that I may have found a patch that had'nt taken to the old paint undeneath, and the mechanical action of the cloth (tescos cheap dishcloth) helped it off.

Reply to
James Salisbury

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