Zinsser BIN is a shellac based primer and sealer. it is suitable for use on many, many surfaces. But you are here because you want to know whether it will work on top of varnish, arent you? Well, there is only one way to properly know, test it!
Can You Use Zinsser BIN Over Varnish
Yes, you can. From my testing, Zinsser BIN covered really well when painted over varnish. It also adhered to the varnish exceptionally well and there was zero peeling or scuffing in my scratch test.
The below graphic has been created from information directly from Zinsser themselves. You can see that BIN is the only one of the three primers that Zinsser actually recommend for use on varnish.
For the test, I varnished some untreated pine. Then after the varnish has had plenty of time to dry I painted over it with Zinsser BIN.
You can see in the image above that I am not just testing Zinsser BIN. I will also be testing Zinsser Bulls Eye 123 and Zinsser Cover Stain. This way we can compare how each of the primers performs when painted on top of varnish. For those of you wanting more information on which Zinsser primer to use read my dedicated article here.
The BIN painted onto the varnish really well and also covered the varnish really well. So far so good and no problems at all.
I then left the samples for around a week. Giving them plenty of time to dry and fully cure.
You can see here how well the BIN and the Cover Stain have covered the wood. Both of them doing a better job of covering the wood than the Bulls Eye.
Now comes time for the real test. The problem with painting over varnish with any paint is always adhesion. because varnish is such a glossy surface it can be really hard for paint to stick to it.
So without further ado let’s see how well the BIN has stuck to the varnish. For this, I used a piece of rough-cut c16 timber.
I like to use this method as I feel it is a thorough test for the paint while not being overkill. I don’t want to use something too soft which is not representative of the challenges the paint will face and I also don’t want to use something too hard. If I used a really hard material it would just scratch every paint and not give me any usable results.
Below is the BIN after the scratch test.
You can see that there is zero peeling, chipping or any marking at all really. The BIN has definitely worked really well here and has had zero problems being used on top of varnish.
This just shows why Zinsser recommends using BIN on top of varnish, it works amazingly well.