Solventborne over Waterborne?

Applying an oil-based coating over a water-based coat is likely to create trouble. December 31, 2012

Question
I finished a large built-in (entertainment center, desks and shelves) with a very dark colored oil-based wiping stain and 3-5 thin brushed-on coats of a water-based polyurethane (matte finish). I got really good results except the polyurethane was sometimes hard to deal with because it was drying really fast. Both of these products are by Rust-Oleum. The customer has now decided that he wants a sheen. I like this one particular oil-based spray lacquer (satin finish) by Deft. Will I have problems if I spray 1-2 coats of this over the water-based polyurethane which was applied 4-6 days ago?

Forum Responses
(Finishing Forum)
From contributor W:
Most likely.

---

From contributor M:
The solvents in the lacquer will likely attack the water based coating you applied.

I think your best bet is to top coat the existing water based urethane with a higher quality, waterborne coating. Try something from General Finishes or Target coatings. I think you will find that they are far superior to products like Rustoleum or Minwax.

I would scuff sand first for adhesion, remove dust with a vacuum, and then wipe everything down with a rag dampened with a mix of 50/50 denatured alcohol and water. Make sure to test for compatibility and adhesion first in case you get unexpected results.

I mail order 95% of my finishing materials and supplies. Paint and box stores need to step up their game when it comes to wood finishing products.

---

From the original questioner:
Thank you. If compatibility issues with any product that I use over this polyurethane was going to occur, how long would it take to show the signs? Is it fairly immediate (within a couple of hours) or could it be a few days down the road?

---

From contributor B:
You'll see wrinkling or mottling usually within minutes, but definitely within an hour. I second the comments and schedule for using a WB. My preference is Target.

---

From contributor R:
By far the easiest thing would be to pick up a satin or semi-gloss WB poly and just put it over the top with a lite scuff sanding beforehand.

I've sprayed solvent based (lacquer is solvent, not oil, based - when you think oil, think poly) over WB on several occasions with no problems, but each two finish combinations are unique (including the dry time of the WB and its thickness). So no one here is going to be able to tell you with certainty whether it'll work or not. You'll need to do a test if that's the road you go down.