Spraying clearcoat is an art in itself, for the most part spraying experience is the best way to learn this skill. However, having an understanding on what it does and establishing good routines will go a long way in how your paint job holds up.
So first off lets have a look at what clearcoat does exactly.
It provides UV protection for the layers beneth, mostly your basecoat. Much like the sun will burn your skin, it will burn your basecoat if its left unprotected. Basecoat with too little clear applyed (which can happen from overreducing or not applying enough) will typically fade with a chalking effect, the only remidy at which point is respraying.
Clearcoat also provides resistance to chemical splashing, mostly noticably against gasoline. It provides a durable finish that protects from stones chips and road fallout. It is worth noting that it is not soley the clearcoat that provides the holdout but the primer and basecoat under it, in a nutshell its only as strong as the weakest link. Lastly it creates a shine for your basecoat, it takes your dull looking basecoat and creates a lustre to compliment the vehicles finish.
So what to expect when you buy some clearcoat. It will look something like this:
You will always get 2 parts, the clearcoat and its corresponding hardener/activator. Sometimes you will require an additional reducer used to thin it out further but it will depend on the brand of clearcoat you get. You will also get to choose a fast, normal or slow hardener. You decide on this based on temperature combined with the size of the job which we will discuss further below. You will require the technical data sheet (obtainable from the manufactures website), this sheet will provide you with information that tells you how to mix the clearcoat to get it ready and what size gun tip is ideal for the particular product.
Modern clearcoats are urethane based products that rely on a chemical crosslinking process (polymerization) to cure the clearcoat. It works like this:
The clearcoat is mixed with the hardener and polymerization begins. You will have anywhere from 1-4hrs typically (check your tech sheet) to spray it once activated. This crosslinking network is used because it creates very strong film, cures fast and provides optimal holdout.
you can see that the clearcoat once cured will not only get its strength from adhesion, but also from the surrounding area. So as we can see below, modern clearcoats differ from old lacquer based products because lacquer does not cross-link. Lacquer also remains soluble when cross-linked urethane does not,
what this basically means is paint thinner will remove lacquer but not urethane cross-linked clear.
So when it comes to actually spraying clearcoat, you want to start by spraying your off-sets first and then move on to the bulk of your panel(s). You will want to maintain about 50% overlap with each pass of spraying. Clearcoat has got to go on wet and maintain a wet edge to work properly, starting out you should
intermittenly look down your panel to verify your applying well.
(sorry typo in this next picture, should say 1st pass and 2nd pass, not coat)
This is where the speed of your hardener comes into play, the slower your hardener the easier it will be to maintain a wet-edge which is why on larger jobs you will need to use a slow hardener. The clearcoat starts to skin over very quickly and the mist (overspray) from your continued spray will land in areas youve aleady sprayed and give a textured look if you have used a too fast of product.
You will typically require two coats of clearcoat to provide proper holdout, however on small jobs you only need to apply two coats over the basecoat itself. You are able to apply your first coat over only your basecoat and the second coat over the entire panel,
So why should you apply clearcoat to entire panel? While we mentioned the sun will fade your basecoat, it can also cause the thin edge of your clearcoat to chalk and fade too. Thats probably the easiest explanation i can think of but heres a picture anyhow:
So while I hope this works to provide a basic explanation of what you should know before spraying clearcoat the best advice I can really give is follow the information on your technical data sheet. The most common mistakes I observe from new painters is not keeping the gun straight to the panel, new painters tend to angle it. The gun distance is to far away and the product goes on dry, it should be approximately 6 inches from the panel.
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