Oil based varnish over water base???

[goaliedad]

I like to use water based poly- easy clean up, fast drying. I did some knotty pine trim several years ago- there was other knotty pine in the area that has old school varnish and has yellowed. Can I put old school varnish over the water based or do I need to shellac it first? Trying to get some more yellow hoping to more closely match the old stuff?

[mikefm101]

Letting the water base cure thoroughly the varnish should stick OK.  It is a few weeks though, from what I understand, to cure thoroughly.

I've done something like this, specifically with water base poly on top of BLO so the reverse of your need, but should be the same principle. 

Shellac would certainly work and be quicker although I've never done that that I recall.

[fredhargis]

Oil based varnish tends to yellow more over time so I doubt you will apply the oil based and have instant color match (it will adhere, though). You might want to consider using some tinted shellac to match the color...or just wait a long while.