Exterior Pre Wash Guide Estimated reading: 5 minutes 13710 views Summary: A deeper dive into prewashing for all levels of detailer What’s is the hype around pre-washes? Do I really need a pre-wash? Let us start with how a good pre-wash stage is usually done: Apply pre-wash to the dry car without rinsing first (exceptions listed below). Foam it only if necessary. Let sit for the given dwell time, but never let it dry on. Rinse off Control your pre-wash. If some areas still have contamination that is to be removed before the contact wash, do a second round, this is also the point to use a bug remover if needed. Go on to your contact wash. Why do a pre-wash? There are 3 major advantages of a prewash- safety, efficiency, and thoroughness. Safety: The basic idea here is that dirt that isn’t on your car can’t damage your paint. Without using a prewash, it is much more difficult to safely wash as there is a higher chance you will wipe dirt across the paint, leaving behind scratches. Prewash uses chemical cleaning power and doesn’t rely on physical contact (except the rinse of course) to clean the surface of your paint, allowing you to remove most of the dirt without touching the paint. This greatly reduces the likelihood of damage caused during the contact wash. Scratches can be caused by debris regardless of the shampoo used if a certain level of dirt is reached, which can only take a few days in some cases. If you wash your car every other day, for example, you may not need a prewash. Even for weekly cleaning, a prewash can be very beneficial- everything depends on your specific scenario. Efficiency: Safely cleaning without a prewash is possible, but it is a big hassle and adds a lot of time to a detail. The basic method without a prewash is that you have to use a new side of the microfiber each time you wipe, which is both tedious and requires more microfibers. For most people, this extra time is not worth it when you could just add a pre-wash to your routine. Thoroughness: Most prewashes are able to get to surfaces of the paint that you will be unable to with a microfiber or wash mitt, such as the curves in between panels, or by emblems (brushes are not the most ideal solution here anyways- without a prewash they just agitate the dirt and cause scratches). There are also areas you miss or forget during a contact wash. A prewash helps prevent debris from these areas from dripping out onto the rest of the paint during a contact wash or rinse phase, which results in both a cleaner and safer wash. A Good prewash also does a very good job at actually cleaning these areas. Some notes on Pre-washing: Should I rinse before the pre-wash? No, in general, you should apply the prewash chemical to a dry and cold surface. A pre-rinse before the actual pre-wash would dilute the chemical further and could also stop the foam from bonding correctly. There is one exception to this, which is excessive mud. Mud can stop a pre-wash product from actually working on the paint. Foam or no foam? Foam itself offers no added cleaning power. However, it allows longer dwell times and is safer against drying out, which can be a benefit in hotter climates or on sunny days (although it is always best to avoid washing in extreme heat when possible). Also, depending on your available equipment, it might be quicker to use a Foam Gun vs. Spraying down the whole car with a pump sprayer. Rinse top down or bottom up? Both can give the same results, so if you are already happy and set in your working ways keep doing what you are doing. If you are just starting out rinsing, bottom up has a lot of benefits as it makes it easier to verify that you have rinsed everywhere with the pressure washer/hose. Even if you don’t have a pressure washer you can still do a pre-wash, rinse with the strongest nozzle of your garden hose. This will not be as good as with a pressure washer but still a big improvement When to actually rinse? You rinse after the product has done its work, either by a manufacturer-given time or when the foam has run down. You should always rinse before the product starts drying on the paint. A rinse is one of the most important parts of a pre-wash, allowing you to take contaminants off the car that would otherwise pose a scratch risk – what is not on the paint can’t scratch the paint. Before we end a quick overview of the types of pre-wash there are and for what you best use them What types of Prewash are there? Rinse Almost always an option Will get dirt off, to an extent Least cleaning power, good against mud pH Neutral Better cleaning power by increased dwell time Surfactants remove some dirt and help dissolve it by dwelling over time Takes a lot of dwelling time Result likely better than just Rinse but a lot less then pH Basic (alkaline) Often available at a Self-Serve The same product can often be used for both prewash and contact wash pH Basic (Alkaline) Strong against organic contaminants Can remove a lot of Traffic Film Results are likely the best Various products differ both in strength and material safety Particularly strong products can be hard to use correctly Same product cannot be used for prewash and wash pH Acidic Strong against mineral contaminants Often a follow up after a pH Basic prewash Not all that good on its own Can rejuvenate some coatings by removing mineral deposits clogging the coating A Pre Wash always ends with a Rinse and so does this guide.