Copied and pasted from FB from a well respected detailer. I don't see how you can dispute the dry or rinsed panel method, the photographed results are clear to see.
Having also tested this myself off the back of this post, I can't argue it and now pressure rinse my car prior to foaming. My test was with Bilt Hamber Auto Foam as well.
"Warning lengthy post: Something that seems to come up often, most of the time on a weekly basis, is "Should I rinse before foaming/ pre wash?" My reply is always the same and I spoke to many pros about this and the majority are of the same opinion....... "YES"
While there's no right or wrong answers in detailing methods it's really what works for you however taking variables like time and cost out of the equation then there is more effective / safe ways of working.
So why do I say "YES" to pre rinsing? Well for me it's a no brainer; here in NI water is free, I want to use the no cost option to shed all loose dirt from the surface before applying product. My thinking is that the loose dirt could be covering some of the bonded dirt making the product work on the easy to remove stuff rather than working on the problem areas. In short I want the product to work on the difficult stuff.
What are the arguments against? Well some will suggest that a powerful water stream could push the dirt into the paint and flaw the paint. For me I'd have to argue that point, granted if a power washer is sprayed directly onto a grain of dirt the pressure could force it deeper but in reality we should all be using a power hose at an angle anyway allowing the pressure to flood the area carrying dirt away. I've tested this a little by inspecting corrected paint and power hosing when dirty, I've yet to see any evidence to show that presser washing dirt will actually inflict damage.
The other argument is that a wet surface is diluting the product; that I can agree with. It does but to the point where is makes the product ineffective? No. If using foam and u want a dwell then a wet surface can shorten that dwell time, however a good snow foam doesn't need 20 mins dwell.
When your passionate about car cleaning you start to question each method you use and look for ways of bettering what you do, this is why I've tested pre rinsing and it is why I will stick with pre rinsing. For those who are on the fence I had a white car in recently and decided to test the theory again and picture the results.
Below is my test, two panels which are equally as dirty, both with a line drawn in the dirt. Rear door is rinsed with pw (8 - 10 vertical passes and 8-10 horizontal passes) and front isn't. Both then foamed using kkd blizzard force and allowed to dwell for the same length of time. The foam is then rinsed using a pw at the same distance for each and 8 - 10 vertical passes and 8-10 horizontal passes (both as near the same as I could possibly achieve) however it was repeated on the drivers door to 'make up' for the Rinse, they have therefore saw the same amount of water and only difference is the sequence. Not surprising to me but the rinsed panel is much cleaner, almost a contactless wash. It was evident how much the foam softened the remaining dirt on the rear as u could see the dirt rinsing off with ease. I'll let the pics do the talking, thanks for reading."
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