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cibula11 04-28-2009 08:18 AM

Finish coat for barn wood table
I've just completed the assembly of a barn wood table and I'm ready for the finish coat. I don't know if there is one option better than the other. It will be used for a kitchen table and the wood is doug fir and over 100 yrs old. Should I just poly or use a tung oil of sorts.

handyguys 04-28-2009 12:57 PM

It depends on the look you want. A polyurathane varnish will be durable but may not look right on antique wood. Something like boiled linseed oil (BLO) looks nice but offers little protection without a top varnish. Tung oil is like BLO but has more binders I think and will give a slightly harder finish but still may not be ideal for a table. Shellac looks good but is easily damaged (yet easily repaired). 100 years ago they would have likely painted it. Milk paint looks cool, especially when topped with BLO, but again, not super hard of a finish.

Bottom line - if you want a finish that is easy to keep clean, wipe down with a wet rag, and not something to worry about, then poly is your best bet, several coats. Oil base will impart a bit more color and may be preferable.

Try some different finishes on some scrap and see what you like.

cibula11 04-28-2009 01:26 PM

The wood has been sanded down and has a nice golden color. We'd like to keep it that way, but it is most definitely rustic, so I don't think we would mind nicks and scratches that would only add to the character. That being said, would tung oil be okay. I've thought about using water based poly because I'd rather not darken or yellow the wood too much.

handyguys 04-28-2009 01:41 PM

Water based poly would give you a heard finish with no yellowing. Tung oil will add some color and not be as hard. Tung oil finish is more traditional and easier to repair (just wipe on another coat, maybe light sanding first). Poly, if nicked, will need to be sanded or stripped and re-coated.

Try out both and see what you like. If you have kids and use it as your every day table I would say go poly. If its an occasional use table or no kids I would go tung oil.

Nestor_Kelebay 04-28-2009 03:03 PM

If you wanted to be historically accurate, you'd use a real varnish on the table (with or without staining first). Real varnishes are nothing more than natural plant resins dissolved in drying oils like linseed oil or Tung oil to make these oils dry to a harder film. They're still available, but often from companies that cater to museums which need such materials to be historically accurate for restoration of old furniture:

Linseed Oil Cobalt Varnish - Natural Binders - Kremer Pigmente GmbH & Co. KG

If it were me, I would use a wiping alkyd based polyurethane on it to get the durability you need to provide the best service on a working surface like a table. Also, wiping polyurethane can be brushed on or wiped on with a rag, and it's thin enough to self level very quickly, allowing you to avoid brush strokes.

It's find and dandy to say "We want a rustic look" but the bottom line is that the reason why polyurethane replaced varnish as the clear coat of choice over wood is because it's harder and more durable and you need that on a working surface like a table top to better stand up to wear and tear and stay good looking longer.

Every paint company will use it's hardest paint as a floor paint because you need high hardness to stand up to wear. A harder film will prevent dirt from getting embedded into it underfoot, and that prevents traffic patterns from showing, and that makes the floor look new longer. It's the same with a cupboard shelf or a kitchen table. If you slide something hard and heavy (like a stainless steel or porcelain crock full of stew) across a soft surface, that surface will be scratched. The harder the surface, the less scratching. Simple as that.

You're table will look "rustic" eventually, why hurry the process along by using anything but the hardest coating you can on it. No pioneer would have ever done that. They'd have been HAPPY to have a table made of any wood stay good looking for as long as possible. Not a single one of them would have thought "Hey, let's paint this table with egg tempura paint to make it look like it was made in the 1600's!" They would have used varnish on that table, BECAUSE THAT WAS THE HARDEST AND MOST DURABLE WOOD COATING AVAILABLE TO THEM. If it wuz me, I'd do the same and use the hardest user-friendly coating available to me, too, which would be an alkyd based polyurethane.

Moisture cure, waterborne catalyzed and two component polyurethanes dry harder than:
Alkyd based polyurethanes (which is what traditional hardwood floor finishes are made of)
which dry harder than real varnishes
which dry harder than highly polymerized drying oils like Danish Oil
which dry harder than Tung oil
which dries harder and yellows less than boiled linseed oil
which dries harder than latex paints.

and ALL, except the top one (isocyanate based polyurethanes) and the bottom one (latex paints) transform from a liquid to a solid film through exactly the same chemical process. Post again if you want to know more about that process.

Nestor_Kelebay 04-28-2009 03:18 PM

The "yellowing" of drying oil based coatings like linseed oil, varnishes, alkyd paints and alkyd based polyurethanes warrants a note of explanation.

The yellowing occurs only in locations where there is little to no direct or indirect natural sunlight. So, if you paint a kitchen cupboard shelf and a window sill with the same drying oil, oil based paint or polyurethane, the paint on the cupboard shelf would yellow whereas the window sill wouldn't. That's because when you close the door on your cupboards, the shelves are in the dark and aren't exposed to natural light from the Sun.

Further, this yellowing process is entirely reversible. That is, if you were to remove that painted window sill and put it in that kitchen cupboard, and take the cupboard shelf out and place it where the window sill was, then the window sill paint would yellow and the paint that was on the shelf would return to it's original colour.

And, if you don't believe me, just phone any museum. Museum curators need to expose old oil based paintings to indirect sunlight to remove the yellowing which occurs in their dark storage rooms before putting those paintings on display.

So, if you have a good degree of natural sunlight in your kitchen, then no yellowing will occur. (and you can always take the table outside on an overcast (or even sunny) day (and leave it outside for several days) to eliminate any yellowing. But, that yellowing will start again when the table is taken back indoors.

cibula11 04-28-2009 06:52 PM

Thanks for the info. I had been leaning towards a poly since it will be used daily. Good point on how pioneers wouldn't want a table looking like it came from the 17th century :) I'll let you know how it turns out.

Nestor_Kelebay 04-28-2009 11:20 PM

Wipe-on polyurethanes will still be the same polyurethane as is used on hardwood floors and for furniture "varnish", but you'll notice that wiping polyurethane is much less viscous than polyurethane "varnish", and that low viscosity allows it to self level very quickly. So, avoid overbrushing (which is to continue brushing while the solvents are evaporating from the poly until it's too viscous to self level). Basically, gravity and physics can make a smoother film than you can, so brush the stuff on fairly quick so that it reasonably uniform in thickness and then let gravity and physics take over. You'll get a thicker coat of polyurethane if the stuff you put on is more viscous, but you'll get a smoother coat with wipe-on poly. So, use more coats of wipe-on poly to get the same protection as fewer coats of the more viscous poly. Alternatively, you can use a couple of coats of the more viscous regular poly, allow to dry completely then sand your brush strokes out and apply wiping poly to prove a smooth flat surface over the wood. That way you get a thick layer of protection topped off with wiping poly to provide a smooth flat top coat.

Here's the wipe-on poly I use. The previous owners of my building used cheap latex paint that spattered a lot. I use xylene to remove latex paints spatters from doors, but that leaves the varnish or polyurethane on those doors with a dull appearance. I then wipe on a thin coat of this product just to restore the gloss:

Minwax® Wipe-On Poly - Oil-Based Clear Protective Finishes -

If you want to avoid yellowing completely, but still want a very hard and durable coating on your table, then you might try one of the new water based clear coats that do form a surprisingly hard film. One that I have yet to try was made by Flecto, but is now made by Rustoleum:

Anything that's hard enough to provide good service on a floor will provide good service on a table top.

However, if you do use a water based clear coat, maybe sand the surface of the table down after the first or second coat. Water based coatings tend to raise the grain of the wood so that tiny splinters of wood will stick up from the table top and mess up the reflection of light off it's otherwise smooth surface. Sanding down those glitches after the first coat or two (and removing the sanding dust) will go a long way to getting an attractively smooth finish on your table.

Finally, the solvents in an oil based wood stain will evaporate out through an oil based polyurethane. If you opt for the water based clear coat, and you opt to stain with an oil based stain, I'd talk to some hardwood flooring contractors to see how long they allow the oil based stain to dry before applying the water based clear coat (and any other advice they may have for achieving a successful outcome).

PS: If you use anything but a hard and durable coating over your wood table to protect it and preserve it for as long as possible, then money comes too easy to you. There's absolutely nothing sexy or chic about wasting anything, and allowing something to deteriorate faster than it needs to stands right next to wasting it in my humble opinion. So, if anyone who doesn't know anything asks you why you used a modern coating like polyurethane when you could have gotten a more "rustic" look with boiled linseed oil, please feel free to quote me.

Let us know how the table turns out.

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