I wouldn't recommend using a Dammar varnish over an acrylic painting. As a natural resin varnish, Dammar varnish will turn yellow over time. It only takes 20 years before Dammar varnish will turn noticeably yellow. Additionally, Dammar varnish will turn brittle and crack.

Plus, it is more difficult to remove dammar than it is to remove synthetic varnishes. Removing Dammar varnish requires very strong, toxic solvents, so it should only be done by a professional art conservator.

In short, you are better off using a varnish that is specifically suited to acrylics, and staying away from the Dammar varnish.

For art conservation purposes, it is best to use a varnish that is labeled "removable", in case your painting needs to be cleaned several decades down the line.

I use and recommend Golden Acrylic Polymer Varnish (this links to Blick Art Materials, and if you make a purchase I get a small commission that helps support this site). It's removable and can be diluted with water, which means you don't need any foul-smelling chemicals.