Have I left any varnish behind?

[Geoff_S]

I'm using Polyvine water based varnish with a wax finish and am very pleased with it on the door frames.

However, I am now varnishing the veneered door panels and I cannot get the brush marks out. So first coat, then 300 grit, another coat another 300 grit and then a third coat and a 300 grit.

Each time I sand it down I stop as soon as the brush marks disappear. But my question is, how do I know if I have actually left any varnish behind? As I say, as soon as the peaks of the brush marks have gone, I stop.

I plan to wax the panels with clear Liberon.

I have tended to avoid varnish in the past and have always used sanding sealer and wax to great effect. The big advantage was that the sanding sealer dried solid in less than an hour and was easily sandable. It's at least 4 hours between coats of varnish and it's still a bit sticky 12 hours later so clogs the sanding discs.

 

[AndyT]

Just guessing here but I think I spotted a clue in your last word - "discs" - it sounds like you are power sanding this step. The difference between taking off the peaks of the brushmarks and taking off all the varnish is going to be tiny. If I were you I'd do the intermediate sanding by hand - just one or two passes, with fine abrasive on a cork block. (Or even better, fine Abranet on a perforated hand pad and a hose to the vacuum cleaner.)

 

[Phil Pascoe]

If your abrasive clogs quickly the varnish is not dry.

 

[Geoff_S]

Thanks Andy & Phil.

Looks like I might have taken the varnish off then. Just how long should it take for the water based varnish to dry before it can be sanded? It's been at least 12 hours in 18+ degrees.

Yes, I did use a power sander, very delicately if that's possible. I tried my Abranet but I've got acres to do.

I think I might go back to sanding sealer & wax.

 

[ED65]

Geoff, the rule of thumb for this is you leave it as long as necessary for it to harden.

Depending on a few things (the moisture content of your wood and the humidity are probably the two main ones) this may take longer then a day. For a not-dissimilar product the time necessary for a full harden was given as 48 hours and this was for North America, which would generally have much better drying conditions than over here.

There's another possibility unfortunately, and that's that the finish you have just isn't hard enough to sand properly.

So looking at it from the other side of things, isn't what to aim for not having bad brushmarks in the first place? You can do various things to help water-bourne finishes settle out, but I'd just switch to using a foam roller personally.