<VV> Car Covers and Dew

Tue Mar 10 17:22:12 EDT 2009

Hi Doc

Lots of good sense here and I agree with most of it.

However, the bit that I would question slightly is that the moisture only 
comes through the cover - yes, most covers are porous, and are designed to 
let moisture both ways, but I have several scrap cars here which are covered 
with completely waterproof tarps (on some of the I use builders' damp-proof 
membrane), and they still get moisture under the cover, whatever the surface 
they are on (usually tarmac or gravel, here). That's why I only keep scrap 
cars outside.

Apart from that, as I said, not much to disagree with. Bt it underlines what 
will be the first paragraph of Book 2 of the Got Rust? saga, that I am 
currently writing.

That is going to say that the most important thing you can do, bar none, as 
soon as you get a classic car, is secure good, dry storage for it. And if 
you have to pay a rental for the storage, the money you pay will be saved 
many times over by the repairs you won't have to do to the car and the 
depreciation it doesn't cause.

Cheers

Alan

----- Original Message ----- 
From: <RoboMan91324 at aol.com>
To: <virtualvairs at corvair.org>; <alan.wesson at atlas.co.uk>
Sent: Tuesday, March 10, 2009 8:58 PM
Subject: <VV> Car Covers and Dew

> Alan,
>
> While there is moisture in the ground that can rise up, it is more 
> difficult
> for that moisture to rise through concrete which is what most of us park 
> on.
> If you park on dirt, that would be the worst situation in regard to ground
> moisture.  During a rain, water will soak into the concrete and slowing 
> evaporate
> out which could condense on the underside of your car if it is cool.  A
> sealed or painted concrete surface is best unless there is a depression 
> where you
> park and a puddle forms.
>
> Dew generally comes from the air.  Hot air holds more moisture.  (This is 
> why
> politicians are all wet.)  As the air cools during the night, it reaches 
> what
> is called the "dew point" and water vapor will condense on any surface. 
> This
> generally happens on the cooler surfaces first and most.  Since most car
> covers are porous to let moisture out, they will also let moisture in. 
> During the
> night, the moisture will soak through to the car's surfaces which are
> typically cool.  It probably seems to you that the moisture originates 
> between the
> car and the cover because the moisture on the surface of the car cover
> evaporates first in the morning sun and the moisture below the surface 
> evaporates last.
> Of course, the cover will lengthen the time it takes for any inside 
> moisture
> to evaporate.
>
> The worst case would be covering your car with a cover that reaches the
> ground.  Any moisture from the ground, rain flowing under the car or dew, 
> will be
> trapped there longer because the cover prevents air circulation and thus 
> slows
> evaporation.
>
> Doc
> 1960 Vette; 1961 Rampside; 1962 Rampside; 1964 Spyder coupe; 1965 
> Greenbrier;
> 1966 Corsa Turbo Coupe; 1967 Nova SS; 1968 Camaro ragtop
> ~~~~~~~~~~~~~~~~~~~~~~~~
> In a message dated 3/10/2009 12:21:20 PM Pacific Daylight Time,
> virtualvairs-request at corvair.org writes:
>
>> Message: 2
>> Date: Tue, 10 Mar 2009 18:29:11 -0000
>> From: "Alan and Clare Wesson" <alan.wesson at atlas.co.uk>
>> Subject: Re: <VV> Car Covers
>> To: "Ron" <ronh at owt.com>, "mike hicks" <mhicks130 at cox.net>,
>>     <virtualvairs at corvair.org>
>> Message-ID: <C303FCFA02A6435EBC9AB5E5B23528E9 at ALAN>
>> Content-Type: text/plain; format=flowed; charset="iso-8859-1";
>>     reply-type=response
>>
>> I am prepared to take your word for it, but personal experience indicates
>> otherwise! I have had several very unfortunate experiences with
>> micro-blistering, on cars that were left outside in *dry* but dewy
>> conditions, and because extremely micro-blistered where the cover was in
>> contact with the paint. When I removed the cover the contact surface 
>> where
>> the cover touched the paint was wet, as were various places under the car
>> where the moisture could only (apparently) have risen.
>>
>> And I have just done a quick web search on the subject, and the best
>> explanation seems to be that dew is formed from moisture that condenses 
>> from
>>
>> air close to the ground, as the ground has harboured heat in the daytime, 
>> so
>>
>> when night falls the vapour nearer the ground condenses more.
>>
>> That in itself strikes me as a good reason to avoid car covers, because 
>> the
>> dew is going to be condensing under your car where it is near the ground,
>> and wetting it (this is certainly what happens). So whatever the cause of
>> the dew (and I'm prepared to believe what you say about dew, and I stand
>> corrected) I still wouldn't touch a car cover with a ten foot pole, 
>> except a
>>
>> dust cover on a car kept in a very dry atmosphere.
>>
>> Cheers
>>
>> Alan
>
>
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