I agree with Don, Steve, et al (fancy talk for "and others"). It's probably during washing that a lot of swirls occur. I think Steve nailed it -- the problem is you don't want to rub the paint when it is dirty, but washing usually involves rubbing a dirty car. If it was not dirty, there would be no need to wash it! A classical Catch 22. Here is how I try to get around the Catch 22. A part of this was previously posted to the "car wash" thread:
Washing a car requires a strict regime to avoid damage, as we all know. This is because any time you rub the paint you are at risk. I feel that whenever you are about to rub the paint, you should know why you aren’t about to damage the paint.
For me, this means I have to get as much dirt as possible off the car before I touch the paint. I rinse with a hose. I then spray using a hose attachment that mixes car shampoo in with the water. I rinse again.
My purpose for the actual washing (mitt to paint) is to remove film, smudges, etc., not dirt particles. The last thing I want to do is to try to rub off dirt particles, large or small. That is just going to abrade the paint. I do not wash in circles. I wash up and down, just like I was applying sealant.
Even with this 'pre-wash' technique, frequent and thorough rinsing of the mitt is vital. I feel that rinsing when you can see the dirt is too late. I assume that if you can see the dirt, it means you have already been rubbing the paint with a dirty mitt. I use a three bucket system -- adds about ten extra seconds to the rinse process.
I follow two earlier steps that I believe are key to the process:
a. I don't let the car get too dirty to begin with and,
b. if it does get dirty (despite garaging and covering), I don't let dirt get "caked and baked" on to the car.
The two points above mean:
1. keeping the car garaged and covered when parked out of the garage, and
2. checking-out the car when you come out from a store, etc., to see if you have any bird bombs or other contaminants on the paint (takes ten seconds) and removing them right then before they have a chance to set or dry on the paint. Now, in bad weather, mud, etc., it takes a lot more work to use this approach. I live in LA. If I lived in NY, I know the above appoach would be challenging and it might have to be modified.
Using the above approach does not mean fully washing the car everyday. It involves regular QDing to remove very light stuff and <em class='bbc'>spot washing[/i] to remove anything heavy. In this way, the car never gets real dirty to begin with and no dirt is allowed to set up, therefore when I do a full wash the swirl risk is reduced.
Spot washing involves carefully removing mud splashes, etc. immediately, before they harden and while they can be rinsed off. I think time is the key. Fresh dirt usually comes off easily and pretty safely. I suspect it's the encrusted stuff that leads to swirling as you scrub to remove it.
Now, if something has dried, if I did not get to it quickly enough, I try to hose off the junk with pressure. If that does not work, I let it soak in a sprayed-on shampoo solution. I call this a 'spot wash.' It's not QDing, because you don't QD a truly dirty car.
I just assume that if I have to forcefully rub, there is a significant chance I am about to damage the paint -- maybe a lot, or maybe just a tiny bit, but something. So I spot wash or QD depending on what is on the surface of the paint. Anything dried or gritty gets spot washed. Smudgy stuff or light dust, I QD. I just use common sense: "if I QD this instead of spot wash, will I run the risk of swirling the paint? Smudges, no problem, I'll QD with a little QD spray. Light dust, thin atmospheric fallout, OK, I'll carefully QD with lots of QD spraying for lubrication and pay close attention to my towel and the paint. Anything heavier and its a spot wash BEFORE the dirt can set up. Anthing that has set up, it's a soak and a spot wash."
The above sounds like a lot of work, but with the materials in the trunk, and the problem addressed right when you first see it, the dirt cleans up very quickly (as it has not set up). I SAVE time using this approach as the time to the next full wash is extended.
And, I believe that I reduce the chances of swirling, because when I do give the car a full wash, I am washing a smudgy car, not a dirt encrusted car. An added benefit is that the car looks great, all the time.
As I touched on, I know those in different climates may have trouble following this full routine, particularly in winter, but I think the general principles apply universally. For me, those principles are:
1. Try to avoid contaminents in the first place by garaging, covering, not parking under trees, etc.
2. If you do pick up contaminents, try to remove contaminents before they dry or set. QD or spot wash as appropriate.
3. If the contaminents are set, do a soak and a spot wash. Rinse if appropriate and possible. I then soak the dirt in appropriate liquid (car shampoo in most cases) first to soften the dirt, lubricate it, and reduce the amount of rubbing needed. I then try to rinse the dirt off. I repeat this process. Still no luck, I will carefully rub the shampoo-soaked dirt. I don't have to be at home to do this (by the time I get home, the dirt, bird bombs, etc. can set -- particularly if they are on the hood, where the engine heat will bake them on, a terrible thing). I have spray bottles of distilled water and car shampoo mixed with distilled water in the trunk, with towels. If I am near home and its not on the hood, I might wait and just go home them handle it. It's a judgement call.
4. QD regularly between regular washing and spot washings.
5. Ideally, full washings are to remove film, smudges, etc. only. Failing that, when we have (naughty, naughty) let the car go or been unlucky.
6. If we have let the car go or we are unlucky, the full washing should start with attempts to remove as much dirt as possible without rubbing.