# Polyurethane over mineral oil?



## ekallevig (Feb 25, 2012)

I have a butcher block desk top that has so far only been finished with mineral oil. Unfortunately we haven't applied the oil often enough and the desk has some very slight cracks between a few of the boards. I want to fill the cracks, sand away the roughness and finish with a longer lasting sealant (polyurethane). I noticed the underside of the desk top, which has had no wear and tear looks much richer and the grain is darker and nicer looking; the top however looks worn and lighter (I assume the oil has been worn away). I'd like to re-apply some mineral oil to bring out the natural grain and improve the look of the wood before I apply the polyurethane.

Is it ok to put mineral oil underneath a water-based polyurethane? Is there a better way to enhance the natural grain?


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## chemmy (Dec 13, 2011)

ekallevig said:


> I have a butcher block desk top that has so far only been finished with mineral oil. Unfortunately we haven't applied the oil often enough and the desk has some very slight cracks between a few of the boards. I want to fill the cracks, sand away the roughness and finish with a longer lasting sealant (polyurethane). I noticed the underside of the desk top, which has had no wear and tear looks much richer and the grain is darker and nicer looking; the top however looks worn and lighter (I assume the oil has been worn away). I'd like to re-apply some mineral oil to bring out the natural grain and improve the look of the wood before I apply the polyurethane.
> 
> Is it ok to put mineral oil underneath a water-based polyurethane? Is there a better way to enhance the natural grain?


Mineral oil is not a drying oil, fine for butcher blocks that food is being prepared on, not good for a home desk work surface and not necessary. You have a few choices as to "drying" oils to take its place, tung, linseed oil [boiled] are the main two used though BLO darkens with age. Tung darken when applied but once it darkens it does not continue to darken. The other would be dehydrated castor oil which is not generally available to the home owner. there are a few more but with the same unavailability as to ease of local purchase. 

you should not apply poly over a non drying oil. my advice would be to srub the surface with alcohol and then lacquer thinner a few times and then sand smooth and apply one of the two readily available oil, let dry [ a week or more for tung], and then apply your poly.

If for any reason your paper clogs up when sanding, that would be an indication that oil is still present in the wood.


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## ~WoodChuck~ (Jan 17, 2009)

use an oilbased polyurethane . it will enhance the color much better than water based. If the surface is not oily still with the mineral oil there will not be a problem.


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## Steve Neul (Sep 2, 2011)

Mineral Oil is sometimes called parrifin oil so I don't believe any chemical coating can be put over it. You will need to strip it with lacquer thinner or a wax and grease remover, perhaps a paint and varnish remover. I would try to get the top where it doesn't feel like it has wax on it anymore. Since it has soaked into the wood it may take many treatments before it could be finished. When you get it ready I would suggest sealing it with a dewaxed shellac before using the poly. Shellac is often used to seal pine knots for finishing.


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## rrich (Jun 24, 2009)

As all have said, Lacquer Thinner and a lot of it. You will need to "float" any remaining mineral oil out of the surface.

BTW - If you are not in California, Minwax Antique Oil Finish will darken and seal the surface nicely. (It dries a lot quicker than BLO.)


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## cabinetman (Jul 5, 2007)

I agree with the suggestions of removing any oil with lacquer thinner first. If your intent is to try to enhance the grain before topcoating, I would use 25% BLO in VM&P Naptha. Once dry, it can be topcoated with most any film finish.











 







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## ekallevig (Feb 25, 2012)

Thank you all for these tips -- good to know that I'll need to get rid of the mineral oil before sealing with poly. I appreciate the help!


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## djordan (Apr 29, 2017)

Reviving this thread with basically the same question -
Would like to put a polyurethane finish on top of a butcher block - that I'd previously apply mineral oil to.

In my case I'd like to use the water-based Safecoat Polyureseal - and I'd really like to avoid using lacquer thinner or heavy sanding
I'm in a small apartment, and I really won't be able to tolerate the fumes or the mess.

Will simply using lots of alcohol - followed by some modest sanding - be enough to prepare the surface?
Is there any other non-toxic substance I can use to prepare the surface?
Note that I've not applied the mineral oil for a couple of months - and the surface is definitely not oily anymore.
What is the worst that can happen if the surface isn't cleaned properly?

Thanks for the advice!


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## Steve Neul (Sep 2, 2011)

djordan said:


> Reviving this thread with basically the same question -
> Would like to put a polyurethane finish on top of a butcher block - that I'd previously apply mineral oil to.
> 
> In my case I'd like to use the water-based Safecoat Polyureseal - and I'd really like to avoid using lacquer thinner or heavy sanding
> ...


Keep in mind that polyurethane, both the water based and solvent based is one of the worst adhering finishes you can use. If you don't do an overkill stripping the mineral oil off the finish is likely to peal on you. You might also put a coat of Zinsser Sealcoat on the wood before using the Polyureseal. Sealcoat is a dewaxed shellac which adheres as well as any finish and is a universal sealer the Polyureseal will adhere to. I think it's your best chance of getting away with putting a finish over wood that has had mineral oil on it. It never strips off 100%.


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## adamtc (Jun 13, 2017)

Hi Steve,

I'm in a similar position as the OP. I have a walnut butcher block kitchen countertop that we just installed and put two applications of butcher block oil (mineral oil and waxes) on it. My wife decided she wanted a more durable and waterproof finish so after reading this thread we started removing the mineral oil with lacquer thinner. I looked at Sealcoat and I think I want to go ahead and use that. My question is: can I apply some type of drying oil before using the Sealcoat? I liked the color of the countertop with the mineral oil and I'd like to put something on it that will darken/richen the color before sealing.

Thanks


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