Is it advisable to apply water-based polyurethane over oil-based stain?
[OP]
Contributor
Water-based polyurethane over oil stain?
Is it advisable to apply water-based polyurethane over oil-based stain?
Member
It depends on the data for the products you are using. Look up the tech data sheets for each product and they will tell you what types of product are suitable i.e. the stain will recommend what kind of top coat and the polyurethane will tell you what kind of stain. Using this approach is the most reliable way to find out. It is good research that can be done before purchasing to ensure your money buys what you want. Cheers
Every construction obeys the laws of physics. Whether we like or understand the result is of no interest to the universe.
Contributor
Is it advisable? No. But in general it works as long as the stain in really dry, typically 72 hours or more. I often spray a light coat of Sealcoat shellac over the stain as a sealer, before spraying my WB topcoats. But Wayne is right, check the TDS for the products you want to use to see if they are compatible. Many times the stain won't say much about what can go on top, but most WB finish TDS's will address it, especially if it's a no-go.
John
[OP]
Contributor
Thanks, guys.
Member
I have successfully sprayed WB topcoat over oil-based stain several times. I was using General Finishes products for both and their recommendation was, as John mentioned above, to let it dry for at least 72 hours. I waited even longer and kept some additional heat going in my basement shop. I sprayed the topcoat directly over the stain with no barrier coat between and it turned out great. (Just for the record, GF discourages spraying their products over shellac. I've done it successfully, but they don't recommend it.)
Scott
Contributor
Originally Posted by Scott Brader
Scott, just a follow up on your correct comment that GF discourages applying their WB products over shellac. They do, now, but at one time they said it was fine to use many of their topcoats over a single coat of dewaxed shellac. Some folks probably thought shellac is shellac and used shellac that was not dewaxed, ran into problems, and then complained to GF. It could be that GF decided to promote their own sealer, too. In any case, I've sprayed EnduroVar, High Performance Poly, and Enduro Clear Poly over Sealcoat shellac w/o issues for more than 5 years. I did have some micro crazing twice, to which I later concluded was due to not waiting long enough for the shellac to completely outgas, or applying the first coat of finish too thick in the case of EnduroVar, which I brushed on. Now, as long as I wait at least 8 hours after the Sealcoat has been sprayed, and as long as I apply the first coat of clearcoat thin I haven't had any problems. This is a sample size of over 50+ gallons of their products.
John
Member
John,
Good point, I should have clarified that I have successfully used dewaxed shellac (Sealcoat) under GF topcoats.
Scott
Contributor
In full disclosure, I've used wax with wax in it, too, w/o issue, but I'm not recommending it as safe practice. What I will say is do your own testing, see what's compatible and what isn't, and choose what to use based on those tests.
John
Member
I don't recommend using shellac as a seal coat. I am aware that many would disagree with this, but I have to agree with the manufacturers. John's cases of minor crazing are one of the risks you take whenever shellac is used to bond dissimilar coatings. It works a lot of the time but not always which is why coatings manufacturers don't recommend it and why I never recommend it. If you are doing stuff for yourself maybe it doesn't matter too much. Customers however pay me to do a job I can guarantee so it is a no-brainer to eliminate procedures that aren't reliable and use procedures that paint manufacturers will back me with. Cheers
Every construction obeys the laws of physics. Whether we like or understand the result is of no interest to the universe.
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