I have used oil based clear finishes for many years and are now required to use water bourn clear finishes. Ok, I can do that but I have many pieces that have been created with oil based finishes. Some now require a refinish and the oil finish is still good but I want to refinish before the existing finish fails. Can oil based finish be directly covered with the new water bourn clear finish or are other steps required?

The pros should answer this soon. I've always heard that you can apply a water base finish over an oil base,but not the  other way around. A light sanding is recommended before applying the new finish.

Wecome to the forums Jim, I think you'll really like it here. I suggest you go to the top topic on the forums page and introduce yourself. We have a great group of guys here. Always friendly, and the management is here to serve you.

Yes you can, but be aware that problems may show up due to other reasons than the 2 finishes involved. The oil finish may have some silicone contamination on it, guaranteed to cause "fish eye" with almost anything you put over it. So unless you are 100% absotively, posilutely sure there's been no pledge or whatever used you might want to consider a barrier coat of dewaxed shellac. For the record, I'm not one of the pros here, they'll be along shortly.

Edited July 26, 20178 yr by Fred W. Hargis Jr

Fred, would a good wipe down with lacquer thinner get rid of any Pledge like contaminants?

7 minutes ago, Gene Howe said:

Fred, would a good wipe down with lacquer thinner get rid of any Pledge like contaminants?

No, it won't.   I've had silicone oil remain after stripping, wiping with acetone, and sanding,  Lacquer thinner can also damage the oil-based finishes.  If the piece has ever been waxed, you have another issue with bonding.

 

"Oil-based finish" is a rather broad category.  If it's an oil or oil-varnish blend, you can just clean (as below) and apply another coat of same.  I guess the other question to ask is why do you want to change over to w/b finish now?

 

I think I'd go with a thorough cleaning first with Dawn & water to remove the water-soluble (polar) dirt, then with mineral spirits or naphtha to remove the  oily (non-polar).  Light abrasion, followed by a barrier/bonding/sealing coat of shellac.  Then apply your w/b finish (or another coat of oil-based finish).

 

Reading:

http://www.woodcentral.com/bparticles/save_finish.shtml

 

 

I'm planning to cover w/b finish in the next TGIF.   It may not be on Tuesday though as I'll be traveling through a remote area.

 

Thanks for the answer, Keith. 

Stay safe in those "remote areas".

10 hours ago, Gene Howe said:

Thanks for the answer, Keith. 

Stay safe in those "remote areas".

Driving through the UP of Michigan from SE to NW.   1/3 of land area of the state, 3% of the population.  And once you get past Saginaw, it starts to thin out a lot, too.   I think we missed summer, it was Tuesday last week.

Thanks guys for the helpful replies. The finish is oil based poly varnish. I am forced to change as this oil based finish is not permitted to be sold in California. The first piece I need to refinish is a mahogany exterior door that I had made a number of years ago and has not ever seen wax or silicon of any kind. The existing finish is still good but I do want to refinish it before there is any sign of failure to avoid having to strip the door and all the work that goes with that. However, I know I will have to face this situation at some point on other pieces I have made over the years. 

thanks for clarification.   Can you buy marine varnish for the door?

I'll bet Amazon would ship McCloskys Man O War to CA.

Not familiar with water borne finishes but, I'd guess they'd not offer too much in the way of UV protection.

9 hours ago, JimG said:

The finish is oil based poly varnish. I am forced to change as this oil based finish is not permitted to be sold in California. The first piece I need to refinish is a mahogany exterior door that I had made a number of years ago and has not ever seen wax or silicon of any kind. The existing finish is still good but I do want to refinish it before there is any sign of failure to avoid having to strip the door and all the work that goes with that. However, I know I will have to face this situation at some point on other pieces I have made over the years. 

I refinished my front door with water-poly over oil-poly.  I scuff sanded the original first.  I prefer the water based products for both odor (while applying, and after cure) and clean up.  I like to apply it with a rag (cotton sock to be precise).  Much easier to avoid drips.  Remember that in the case of both oil and water bases, the solvent just conveys the solids. 

3 hours ago, Gene Howe said:

I'll bet Amazon would ship McCloskys Man O War to CA.

Not familiar with water borne finishes but, I'd guess they'd not offer too much in the way of UV protection.

Amazon may be willing to ship it to California, but their shipping could present problems. I had ordered 2 gallons of finish from Amazon and when it didn't arrive by the scheduled shipping date, I  discovered that it was "Damaged in shipping".  Amazon said they would replace the shipment . When it finally arrived, by UPS delivery, I got an oil soaked box with 2 empty gallon cans. Finally got 2 full cans after the third attempt.

8 hours ago, Gene Howe said:

I'll bet Amazon would ship McCloskys Man O War to CA.

Not familiar with water borne finishes but, I'd guess they'd not offer too much in the way of UV protection.

I tried to buy some Waterlox in Ohio a few years ago.   Nobody carried anything but quarts, so I contacted Waterlox (in Cleveland).  I was regularly going to Cleveland, but they could not sell a gallon over the counter nor ship to me.    But I could have a gallon shipped to my friend 12 miles south and across the Ohio River in KY.