Problems with Valejo water based varnishes

[vaddoc]

Dear all

 

I moved away from enamel varnishes and initially used the Valejo water based ones. Somehow they never worked for me. I recently used the Valejo polyurethane Varnishes and they gave a good result, although adhesion to the substrate looked poor. Also they come very thick, I did not thin at all but still came out fine.

 

Just a few days ago, I used the polyurethane varnishes again but this time I thinned with the Valejo acrylic thinner and also put some retarder. The varnish became milky, left horrible brush marks and when dry started pealing off the surface. Strangely, the mat varnish over the red colour was fine.

How should the Valejo varnishes be thinned? No info on their website.

What water based varnishes you use and have good experience with? What do you use for thinning?

Could I use enamel varnish over the acrylic paint and how long should I wait for the paint to cure/dry?

 

Regards

Vaddoc

[druxey]

One can use solvent based paints and varnishes over water based ones, but not the other way around. Perhaps that is why you have the adhesion issue.

[vaddoc]

On 4/28/2019 at 12:31 AM, druxey said:

One can use solvent based paints and varnishes over water based ones, but not the other way around. Perhaps that is why you have the adhesion issue.

I used water based varnish over acrylic paint Druxey. But indeed it is "fat over lean"

[vaddoc]

Dear all

 

Let me share what I found out from the internet

 

Acrylic paint may take 30 days to cure and some say it might release some water vapour during the process. Probably best to wait a few days before applying enamel varnish.

 

Water based polyurethane varnishes can be thinned with just water, no special fluids needed. However, there seems to be a rule not to use more than 10% water. Also, these varnishes should be brushed and maybe go over just once. They dry incredibly quickly. The surface will look terrible, full of brush strokes but this is alright. Polyurethane varnishes shrink as they cure and have an incredible levelling ability so it will be alright in the end. This has been my experience so far. I used Valejo polyurethane varnish over my very large hull with just a brush, unthinned and the result was excellent.

 

I actually did a few trials with the Valejo water based varnishes, both the acrylic and the polyurethane in gloss and satin, thinned with water and unthinned. The results were pretty much the same, consistently very good irrespective really of how much they were thinned. They dry out incredibly quickly though, there is barely time to go over a second time. For satin, unless there is very little material on the brush, there will be brush marks not from the varnish but from the media within. Especially the gloss is very forgiving. Generally best to lightly load the brush.

 

I went on and used the plain acrylic varnish on my rudder, not really being particularly careful. The result was pretty good and this time adhesion was good. I think the previous failure was either due to the retarder I used or due to some kind of contamination.

 

 

I hope this will be of help to others

 

Regards

[druxey]

Um, you never mentioned adding retarder before....

Edited April 30, 2019 by druxey

[vaddoc]

8 minutes ago, druxey said:

Um, you never mentioned adding retarder before....

It was either the retarder or some contamination. I read that polyurethane varnishes have a bit of a fragile balance, keeping the polyurethane suspended in the water. If you thin too much or add funny chemicals, the bonds can break and the polyurethane becoming insoluble. Probably this is what happened in my case.

[cog]

Interesting, as I had problems with the Vallejo varnishes, all, whilst using it for airbrush, both with, and without retarder. Thanks Vaddoc