Updated: Apr 4, 2020
So today I thought I would talk about adding clearcoat to 2K direct gloss. I have heard many painters adding 2K clearcoat to their direct gloss for the final coat. We're going to take an in-depth look at what the pros and cons are.
Firstly, direct gloss consists of the below chemicals (roughly)
* Flow agents
* Catalysts (sometimes)
* Fillers (sometimes)
* A single type of UV absorber
Secondly, Clearcoat consists of the below
* Flow agents
* Catalysts (most likely)
* Two types of UV absorbers
We have a few differences here. One being the filler in the 2K Direct gloss. This could be a talc or clay (there are technical terms) but for us Talc and Clay sums it up.
Fillers are used in 2K gloss for many reasons, some being to add a bit of build to the product. Sometimes 2K gloss can be low in viscosity but have good build have you ever noticed? Also, adding fillers to 2K can help keep pigment dosage levels correct for example if you use straight Black it doesn't need much carbon black to get full coverage.
Say our direct gloss needs 30% pigment to be ready to mix and then it can be mixed with hardener. Well if we add only 15% black to the binder what happens with the other 15%? This extra 15% can be made up of fillers which Isn't a bad think so please don't go to your local factor and tell them Jordan said you're adding fillers to my Direct Gloss! haha...
If you read my last post about hardeners and how the groups in the two products need to be the same to cure this kind of applies to direct gloss and is why fillers are sometimes used to make sure the ratio is the same.
Now that we understand a bit about what is in the 2K direct gloss and how it is made up lets look at why people add clearcoat to direct gloss.
People that add clear to direct gloss report that it flows out more, gives higher depth of gloss and makes it easier to polish up.
In my honest opinion I would say if you have to add clear to the last coat of direct gloss to get the above results then the direct gloss is not the best quality. A good quality DG (direct Gloss) will have reasonable flow and depth of gloss but the thing is most DG colours today are designed to have slight peel to match commercial vehicles paintwork as that is what DG is most commonly used for. If you are wanting a good quality DG try a UHS direct gloss. This should be compliant and will have better characteristics.
Another reason why some people clear coat over direct gloss is they will blend out into the adjacent panel with direct gloss and then apply clear coat over the blend area... This in my opinion is no better than using base coat and clear coat but this is my opinion.
Here's how adding clear coat to DG makes it easier to polish. Adding clear will alter the curing of the paint usually making it softer and take longer to cure (hard) so yes doing this will give you the above results. a very very small amount wouldn't cause any major issues as the resins used in DG are usually compatible with clear coat resins. In some cases they may be the same but you are altering the paint which can cause issues. However I would always advise doing a spray out and leave it outside for a month or two.
In my honest opinion if you're wanting the above results just base and clear the job or apply direct gloss, allow to cure, Sand and apply clearcoat.