08-16-2013 01:03 PM
I am making a small project with maple and walnut. I prefer to keep the maple color as natural as possible thus I like using water base polyurethane but on the walnut I prefer to use oil base. Since the project is already assembled is it possible to apply water base poly on top of oil base poly? I'm thinking of putting on one or two coats of oil base poly on the walnut and then adding water base poly on top of that.
I'm trying to have both preferences without having to tape off the different woods during the finish process.
08-16-2013 02:07 PM - edited 08-16-2013 02:10 PM
… and then see if what you propose will get you where you want to go. You wrote:
“I prefer to keep the maple color as natural as possible thus I like using water base polyurethane but on the walnut I prefer to use oil base. Since the project is already assembled is it possible to apply water base poly on top of oil base poly?”
Let’s stop here and address the issues raised so far. First of all, so-called water based polyurethane bares absolutely no resemblance, chemically or functionally, to oil-based Polyoneverythane. “Water based poly” is more properly described as a water-borne acrylic finish with acrylic being the dominant resin and with only a very small amount of urethane resin added. In some products the amount of urethane resin is less than 1% by volume. By comparison, oil-based poly is varnish made from linseed oil and urethane resin (frequently in combination with alkyd resin). Functionally, the oil-based varnish offers more resistance to moisture and to household chemicals.
You asked if it possible to apply a water-borne acrylic over an oil-based varnish. Yes, it is. But, it would be a good idea to allow the oil-based varnish to cure for a few days first.
You then wrote:
“I'm thinking of putting on one or two coats of oil base poly on the walnut and then adding water base poly on top of that.”
Now, we have a problem. You said that you wanted “… to keep the maple color as natural as possible”. Please understand that as soon as any oil based poly is applied, however many coats you apply, you will lose the natural look you want to achieve. Oil-based varnish, particularly those made from linseed oil, will immediately impart an amber color to your maple. Applying a water-borne acrylic finish over the Polyoneverythane will do nothing to alter the yellow created by the linseed oil/urethane resin varnish. Moreover, as time goes on the oil-based poly will “yellow” even more…Polyoneverythane is the most prone to yellowing of all varnish types available. In other words, you will gain nothing by applying the water-borne acrylic finish over the oil-based varnish.
Further, taping the seams between the maple and the walnut will yield limited success. The oil-based varnish will migrate through the cell structure of the semi-ring porous walnut and bleed into the adjacent maple under any tape you apply. This will result in an irregular border where the maple joins the walnut.
You don’t say what you have made; but, a better approach may be to change to a totally different finish option. Since the project is small you may want to consider lacquer applied from an aerosol can…
08-16-2013 04:29 PM
Thanks for your reply. I appreciate your suggestion. I have never used lacquer but this might be the project to do so. The one or two coats of oil based poly was only going on the walnut not on the maple. I realize that to put oil based poly on the maple first would cause it to have the amber color. I was wondering about putting the oil based poly only on the walnut first and then doing the whole thing with the water based poly.
It is a very small project so maybe lacquer from a can is the way to go. From your answer I am assuming lacquer would allow the maple to remain as white as possible, but would it cause the color in the walnut to be similar to what the oil based poly would?
08-17-2013 10:46 AM
Maybe it would be possible to apply some BLO to the walnut, without getting it on the maple? Let it sure, then topcoat the whole thing with whatever you choose to use. That should give you the color I'm guessng your after on the walnut, and leave the maple natural (if it can be done).