Oil base poly over water base poly?

I have a painted table that I put multiple coats of water based poly on. I have since discovered the ease, smoothness and beautiful sheen that oil base poly gives compared to the water based. Can I sand the table lightly and still give it a couple oil based coats? If so, what tool do you recommend using? Sponge or brush?
Thanks.

 

You can do it but it's more complicated than just adding another coat of the same type poly - rough up the surface with steel wool till it's no longer shiny and then use a solvent like alcohol to clean the surface

My answer came from here:
Answers.com - Can you put an oil based polyurethane over the top of water-borne polyurethane

 

One thing to remember is oil poly affects wood differentially than water based poly does. When oil poly hits raw wood, it deepens the colors that are naturally in the wood........ so if you sand thru the existing poly in spots - those spots will look different than the rest of the wood!

You can substitute 220 grit sandpaper for the steel wool if you want. I would think mineral spirits [paint thinner] would also be a decent substitute for the alcohol - just giving you choices

btw - welcome to the forums!

 

MLBecker:

I think that you're treating the symptom, not the disease.

You should be able to get a nice shiny gloss on your table with a water based poly too, and I'm suspecting that you probably just didn't put enough water based poly on to get a nice gloss.

You say it's a painted table, but you also say you put water based poly on it. Can you tell me if the water based poly was put on over the paint, or did you strip the paint and sand before staining and applying the poly? Also, if there's any paint still on that table, what kind of paint is it, latex or oil based? Finally, what water based poly product did you use, and how did you apply each coat?

 

Here's the story. I bought a wooden kitchen table someone painted with milk paint. I wanted a protective surface on it so I gave it multiple coats of MinWax Poly. (so much it turned blue) I sanded it down to get most of the poly off, gave it a coat of water based paint and put two coats of the MinWax on again. In the meanwhile, I accidentally bought an oil based poly for a night stand and was amazed at the difference in application, hardness and finished sheen. I now want that oil finished look on the kitchen table too. Thanks for all the replies.

 

Oil based poly has some yellow to it - do you want that on the table?

Water based poly is clear

 

As Mitch said applying oil base poly over white paint will yellow the paint considerably.... and it will amber more with time. Is there a reason you didn't use an enamel paint to start with?

 

All oil based coatings yellow, but that yellowing is reversible. If you put the table in a room with a lot of indirect sunlight, it won't yellow at all (except perhaps on it's underside which would get much less light. Or, if you let the table yellow, and then every coupla years take it outside for a coupla weeks on days when it's not likely to rain, the yellowing will disappear. This is precisely why yellowing is not an issue for EXTERIOR oil based paints. It's not that the paints are formulated differently in that regard, they aren't. It's just that the much higher energy of the natural sunlight the paint receives outdoors break down the organic compounds that form inside the paint to cause the yellowing in the first place.

Museums will expose their old paintings to indirect sunlight for a few weeks before putting them on display to remove the yellowing that occurs on oil based paints in storage. That way, they show the painting the way it looked when the artist painted it, not the way it looks when it's discoloured by yellowing.

MLBecker:
Well, if you painted the table with latex paint, my guess would be that there were plenty of brush strokes on that table by the time you were finished. And, there's just no way that two coats of Minwax Polycrylic will fill in those brush strokes to leave you with a smooth coat that will reflect light the way a pane of glass or perfectly calm water does (as you see on well finished furniture).

If I were you, I would choose a small area of your table top and sand down the Polycrylic on it a little with fine sandpaper on a sanding block to remove any tiny lumps or bumps cause by the undulating brush strokes underneath. Then, if you have any of that old Polycrylic left, dilute a little of it a good 25 to 30 percent with water and keep that diluted Polycrylic in a sealed bottle that allows you to dispense small amounts of it at a time (like a ketchup bottle or any bottle with a small hole in the cap).

Now, I want you to take a small WHITE cotton rag (six inches square is plenty big enough) and get it soaking wet with water. Squeeze it out so that it's just DAMP (not wet) and apply some diluted Polycrylic to it to get it dampER, but not wet so that it might drip. Now, use that damp rag to wipe on multiple coats of the diluted Polycrylic to the test area. Initially, there will be little Polycrylic in the rag, but as you apply successive coats and keep applying the dilute Polycrylic to keep the rag damp, you should get a nice "bloom" (which is what I call it) of gloss developing after (I'd have to guess here) a dozen coats. (?)

Keep that white rag in a tightly sealed CLEAR plastic bag between coats so that it doesn't dry out. Squeeze the air out of the bag before sealing it. Zip lock bags work well here.

You want to use a WHITE cotton rag and you don't want any printing ink on the clear plastic bag the rag is stored in. That's because all water based coatings that form a film by coalescence will contain a coalescing solvent, and that coalescing solvent will dissolve printing inks on plastic bags and the dyes on coloured fabrics, causing the dilute Polycrylic to become discoloured by those inks and dyes. Let's strive for a nice colourless sheen first before we get fancy.

That "bloom" is really nothing more than the fact that you're establishing a SMOOTH surface on the test area. The reflection of light off of ANY smooth surface will have that "sheen" you're after. By diluting the Polycrylic, we're both reducing the viscosity of the Polycrylic so that it self levels more rapidly AND we're slowing the drying time so that it has more time to self level before evaporation of the water causes it to become too viscous to self level. The combination of the two factors will result in a surface that dries much flatter than you can normally achieve with latex paints using a brush.

Let's try that to see if we can get a beautiful sheen on one small area of your table top. If you can do that, then you can give the whole top a light sanding and get the same result on the whole top.

Now, if you choose an area on a table leg instead of the table top, it's critical that you apply THIN coat of dilute Polycrylic. That's because the lower viscosity and slower drying time will cause the diluted Polycrylic to sag on a vertical surface as it's drying, and the only thing that looks worse than sagging dry paint is sagging dry Polycrylic. If and when you do the table legs, you should probably use a product called "Floetrol" from the Flood Company to dilute the Polycrylic instead of water. (you'll have to experiment with the amount to dilute it using Floetrol) These so called "paint conditioners" are really just thinners that are more viscous than the normal thinner (in this case, water) and so as you thin the Polycrylic with Floetrol, the diluted Polycrylic doesn't loose nearly as much viscosity, and so it doesn't sag on vertical surfaces as it's drying.

Again, when you're sanding with the fine sandpaper wrapped around a sanding block, DON'T try to sand the Polycrylic all off. We're just wanting to sand down the high spots so that we don't need as many coats of Polycrylic to fill in the low spots and thereby establish a smooth flat surface that should give you a glossy "sheen". And, of course, allow each coat to dry completely (maybe let it dry overnight, and possibly longer) before wiping on the next coat.