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meirman
science forum beginner
Joined: 11 Jun 2005
Posts: 4
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 Posted: Sat Jun 11, 2005 9:12 pm Post subject:
humidity and partial pressures
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Why is it that even oil-based paints and all other non-water-based
paints take longer to dry when the weather is humid? Since only the
level of water in the air is higher than average on such days, I would
assume that only water-based paints would take longer to dry.
Last time I took Physcis, they spent a lot of time on partial
pressures and evaporation, and afaicr the rate of evaporation
increased the less gas of the same subsance was in the air. I either
was told or presumed that that was because there was no equilibrium
between the puddle of the liquid and the sparse level of the gas.
Meirman
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o�in
science forum Guru
Joined: 05 May 2005
Posts: 408
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| Posted: Sat Jun 11, 2005 9:52 pm Post subject:
Re: humidity and partial pressures
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| Quote: | Why is it that even oil-based paints and all other non-water-based
paints take longer to dry when the weather is humid?
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How do you know that is true? I am not convinced. |
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meirman
science forum beginner
Joined: 11 Jun 2005
Posts: 4
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| Posted: Sun Jun 12, 2005 12:41 am Post subject:
Re: humidity and partial pressures
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In alt.sci.physics on Sat, 11 Jun 2005 16:52:09 -0700 "oðin"
<oðin@ragnarok.com> posted:
| Quote: | Why is it that even oil-based paints and all other non-water-based
paints take longer to dry when the weather is humid?
How do you know that is true? I am not convinced.
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A friend of mine experienced it today.
Also, why would every can of water and non-water based paint say it if
it weren't true? (Yes, that's not a physics quesion.)
Meirman
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Setanta
science forum beginner
Joined: 12 Jun 2005
Posts: 3
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| Posted: Sun Jun 12, 2005 4:48 am Post subject:
Re: humidity and partial pressures
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"meirman" <meirman@invalid.com> wrote in message
news:slrma1h45rm4mhfrpoikshlfscb9oa9mus@4ax.com...
| Quote: | Why is it that even oil-based paints and all other non-water-based
paints take longer to dry when the weather is humid? Since only the
level of water in the air is higher than average on such days, I would
assume that only water-based paints would take longer to dry.
Last time I took Physcis, they spent a lot of time on partial
pressures and evaporation, and afaicr the rate of evaporation
increased the less gas of the same subsance was in the air. I either
was told or presumed that that was because there was no equilibrium
between the puddle of the liquid and the sparse level of the gas.
Meirman
--
If emailing, please let me know whether
or not you are posting the same letter.
Change domain to erols.com, if necessary.
|
Thoughts
I suppose the drying of the paint could be described with reaction
kinetics - where some volatile is given off - and heat - during drying - I
can imagine that the formation of droplets on the painted surface could
potentially slow drying through cooling and possibly skin formation leading
to trapped volatiles (paint layer assumed to be semi - permeable (to the
solvent)). whether this is the same mechanism that describes the induced
drying delay in waterbased paints is questionable as the paint is initially
solulble in water.
Setanta |
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