I found your varnish, when thinned according to instructions, to become very thin and run when I applied it to my mural.
Varnishing can be tricky. Overly thinned varnish on a large vertical surface is harder still. We suggest thinning varnish in a clear container you can mark with a permanent marker.

• Pour in the varnish first. Only fill about half way. It makes mixing much easier.
• Mark the jar and divide the amount of varnish into quarters and mark the half way level and then mark halves of them. Then mark the same 1/4 mark above the amount of varnish.
• Add the appropriate solvent depending on the kind of varnish. This is a 25% addition, and about the thickness we use. From there thin slowly. Add another 1/8 at a time to continue thinning.
• Mix the varnish with an old spoon for at least 1 full minute. This will ensure the mix is homogenous.

Test the varnish on a scrap material that has been coated with at least a layer of gel or medium to mimic the feel of the varnish on the artwork. We like the varnish to have just a bit of drag to it. Others prefer it much thinner, but for a wall mural especially, the thicker varnish offers more control and less tendency to run or sag.

Don't dip your brush into the container; use a tray. The porcelain coated butchers tray works really well for this, but even a low cut plastic milk gallon container can work as well.

A good varnish brush is vital to varnishing. It should be 3 to 4" long, have soft ends such as a split-hair china bristle brush. It should be flat and thin. A house paint brush is a poor choice because it loads up with too much varnish and can apply too much material. You want to apply thin coats evenly.

Only load the brush about 1/2 way at the most. Start more at the 1/4 mark. If you load the brush too much, it drips varnish near the ferrule and creates foam. Try to work quickly, and stop only at visual edges of the artwork. If you have to stop to adjust the ladder or scaffolding, leave off at the edge of the skyline for instance, rather than in the middle of the sky. Satin and matte varnishes can leave a noticeable line as two coats overlap.

What is the best protective coating for an exterior mural/artwork?
The best system GOLDEN has is the MSA Varnish. It provides protection from the elements and the ultraviolet rays of the sun, which can cause fading over time. It is also removable if the work needs to be cleaned.

If you wanted to paint over a mural inside a house can you varnish it and then paint over it with Latex house paint?
We normally warn people not to apply paint over varnish. With the Polymer Varnish, there should be good adhesion, but we would suggest applying 2 coats of paint, and the first one should be applied thinly so it dries quickly. The second coat can be applied normally.