Finishing Walnut Mantel over Woodstove


Sara22

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I have a 9' x 4" thick walnut mantel and a walnut wood storage door.  I have a few questions about how to finish them in consideration of their close proximity to the wood stove.

1) The mantel has been drying for 4 years. The cabinet door was installed a few weeks ago. My cabinet maker made the door and advised to do the same finish on it as I do for the mantel so they match.  Per my cabinet maker, they currently do not match because one is fresh and the other is dried.  He said once I sand the mantel, it will look more like the door. 

Question: Is this true?  Will they look more similar once I sand the mantel? If not, any suggestions on how to prep them so that they look the same after finishing?

2) I have a Quadrafire 7100 wood stove.  It has a fan that blows the heat out when the heat is hot enough, but even without the fan, it really belts out the heat. I want to make sure the mantel stays "moist" to avoid excessive checking from the dry heat. I was thinking pure tung oil may be the best option because it doesn't contain any varnishes that could possibly crack with the intense heat.

The guy I bought the walnut from said that once it has dried, sand it with 220 grit, then rub Watco tung oil on (available at Lowes).  After the first coat dries, sand with 220 grit.  Then put 2 more coats of tung oil (drying between each). Since I don't want a shiny finish, he said to sand only after the first coat.

First of all, I went to Lowes and all they had was "Tung Oil Finishes", which I have read contain little to no Tung oil and Watco Linseed Oil.  I have read many posts stating that Tung oil vs Linseed oil is better on Walnut for seeing the richness of the grain. One post recommended cutting the first coat of pure tung oil 50% with turpentine or naptha to help with penetration. (http://www.woodworkdetails.com/knowledge/finishing/tung-oil).  

My question is, what do you finish experts recommend for the mantel and the door? I don't want a shiny finish - satin is ok, but not high gloss. The mantel area directly above the wood stove will obviously take the brunt of the heat, but the door may get some as well. I want to minimize checking and keep the wood "healthy" and as moist as possible under the circumstances.  There is some checking already from the natural drying process, with the most being on a knot directly above the wood stove, on the underside of the mantel.

Here are some photos.

Thank you in advance for your help.

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Attempting to finish this in place with a linseed or tung oil product is going to stink, literally. Such products take a good while to cure, and most folks don't like the smell.

Personally, I would just use a wiping varnish. General Finishes Arm-R-Seal is a popular product, but I have good luck with the more common Minwax stuff, too.

If using the wood stove really creates wide swings in the humidity of the room, an outdoor varnish, "spar" urathane, will remain more flexible and resist cracking better.

Now, I am no expert, so others may have better advise. The tung oil will certainly work, but I couldn't do it in my house because of the smell. Urathane doesn't stink so bad for so long.

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Beautiful fireplace.

If the door is walnut and the mantel is walnut, and you finish them both with the same process and same finish, they will look very similar when it's done.  It has nothing to do with one being "dried" and one being "fresh," rather, only that they're both the same species and finished with the same finish.

You have a problem with your mantel.  If it has only been air dried (as opposed to kiln dried)...it is not dry...unless you live in the desert and it's been outside for four years.  I'll assume that the moisture content in the middle of that timber could be as high or higher than 20%.  Which means when you take it into your house, and especially when you blast it with the hot dry air from the wood stove beneath it...you are going to get very rapid moisture loss, and therefore, cracking.  That piece of wood really needs to go into a kiln before you put it on the wall, under the circumstances.

No finish will prevent the drying and cracking.

Perhaps you don't mind if the ends of the board develop some cracks?  It is a rustic mantel, after all, and for some people that just adds to the "character."

And since finish doesn't matter in preventing the cracking, you can use whatever you like the looks of.  Whoever told you that "tung oil finish" actually contains little to no tung oil was correct...it's nothing more than extremely diluted varnish.  You can use a straight oil like boiled linseed oil, an oil/varnish mix like Danish oil, or a pure varnish like polyurethane, or any combination thereof to suit your particular aesthetic and protective needs.  Ideally, you would match the finish on the door.

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Can we call a spade a spade? As soon as you said mantel, we moved from woodstove to fireplace. Buried in the wall, there is no stove surface. This is semantic, but key as we consider Google searches down the road. There is a big difference in treatment. When the firebox acts as a true stove, the solution is a simple pan of water left on the stove to evaporate into the air. Fireplaces and buried stoves are so different that a whole new set of rules comes into play. In most coded locations, a wood mantel must be certified by checking the max temp it reaches during a calculated burn. Your mantel looks high. This may have been done to aid in passing such certification. Just know those kind of rulings are out there because dry timbers catch fire more easily. 

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First off, that is a very pretty fireplace wall.  Eric pretty much nailed it. Unless you get the mantle dried in a kiln, it's going to rapidly dry and shrink leading to cracking. Given the overall look, I wouldn't be totally opposed to that. One thing I'll add is that wood drying around large branch knots like you have on the top creates quite a bit of stress. I would personally fill all of those voids with tinted epoxy both to smooth it out and keep it looking as it does now.

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I should also point out that tung and linseed are "drying oils", which do cure to a solid, although more slowly than polyurathane. They do not keep the wood "moist".

If you want a natural looking finish that has no hard film to crack as the wood moves, I suggest mineral oil and wax. Of course, the mantel will resemble a cutting board, but that's the trade-off.

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Wow - thank you for all the advise/responses! I didn't even think of the smell - thank you for that!  The mantel is not going to come out so I need to finish it in place.  I have used spar varnish in a utility closet in the house where my husband put plywood and I didn't like the smell of that, but it was tolerable.  I'll look into a wiping varnishes like Arm-R-Seal.

Glad to know that both the door and mantel will look similar once finished.  As for the drying, it was dried outside for one year before we bought it.  Then three years inside (we weren't told any differently). Since it has been drying inside, should we wait a few years before using the fireplace again to give it more time to dry?

I also didn't know that whatever I put on it would not prevent drying and cracking. We don't mind if it cracks a little - it is a semi-rustic look.  I was more concerned with large horizontal cracks and warping.

shaney..thanks for link to pure tung oil.  I had read it was hard to find so glad to have a lead.  Based on previous posts, the smell may drive me out of the house though!

Shaffer...I wasn't sure whether to call it a fireplace or a wood stove.  Quadrafire calls it a wood stove, but it's true that it is more like a fireplace, only it doesn't suck the heat out of the room.  I did not mention that we bought a rather expensive house humidifier that uses the house ducting.  We planned to run this while we used the fireplace because the entire house has oak floors and we didn't want them to dry out too much.  I also didn't want to be boiling water all the time.  Hopefully this will help.

Based on all your responses, since it really doesn't matter what I use, I will try a few products on some scrap pieces of walnut and see which we like better and which one's smell isn't too bad.  I'll be sure to post photos when done.

Brendon.. Are saying if I fill the gaps with tinted epoxy, it won't crack more?  I don't want it to crack more and was already worried with how much it has cracked.  It is directly above the fireplace and it gets hot.  We used the fireplace early this year to try it out and burn off the gases before we moved in. 

I'm not sure how to measure how hot it gets, but we did place it 6 inches above the recommendation for combustible material by Quadrafire and local building codes. I cannot leave my bare hand on it for very long.

 

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I don't think a timber of that size will do a whole lot of warping at this stage of its drying cycle, but it's probable that it will develop some checks...these are cracks at the ends of the board.  Wood is a very dynamic material and it's difficult to impossible to accurately predict what will happen with any certainty.

Unless you live in the desert, the fact that you've stored it inside is actually much to your advantage, as your basement is going to be a considerably drier environment than the outdoors in most parts of the country.  If the board wasn't so darn thick, I'd say you might get away with it without cracking.  But because of its mass, it's likely that the center of the board will indeed still carry some moisture, which will be driven out fairly quickly when you use the fireplace.

All finishes stink.  Some are more volatile than others.  You may consider a product called Tried and True linseed and beeswax.  It won't offer much protection (which you don't really need anyway), but it's an all-natural product, so while it's not the most pleasant thing in the world to smell, you and your family won't have headaches for a week.

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6 minutes ago, Sara22 said:

 

Brendon.. Are saying if I fill the gaps with tinted epoxy, it won't crack more?  I don't want it to crack more and was already worried with how much it has cracked.  It is directly above the fireplace and it gets hot.  We used the fireplace early this year to try it out and burn off the gases before we moved in. 

 

Knots like that where a branch was growing have a lot going on.  They areally usually a lot more dense so it should move at a different speed.  I can't guarantee it won't move but the  epoxy should penetrate in and  around and lock it in place.  That's the action I would take. 

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Epoxy will stabilize a knot area and help prevent it from becoming more of a problem, but epoxy will not prevent cracking throughout an entire board.  If you fill one crack with epoxy, and the board still wants to crack...it will...only next to the epoxy instead of along it.  The only way to prevent cracking entirely is to use lumber that is seasoned and acclimated perfectly to its environment.  If your board had been kiln dried and then stored in your basement for three years, that would have been absolutely ideal.  It's difficult for a board that thick to ever achieve the 6-10% moisture content with only air drying - even inside your house -  which is typical of kiln dried material and ideal for furnituremaking.

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9 hours ago, Sara22 said:

I'm not sure how to measure how hot it gets, but we did place it 6 inches above the recommendation for combustible material by Quadrafire and local building codes. I cannot leave my bare hand on it for very long.

A digital meat thermometer, the kind that you stick in the meat and get an instantaneous reading will work.  Just touch the probe to the underside of the mantle where you want to measure the temperature. 

From Refrence.com: "More severe burns occur at higher temperatures. An applied heat of 131 degrees Fahrenheit causes second-degree burns on exposed skin. Pain receptors overload and become numb at a temperature of 140 F. At 162 F, human tissue is destroyed on contact. The entire range of burn temperatures, from the first appearance of pain to instant destruction, falls well below 212 F, the boiling point of water."

If you can put your hand on it, it's probably less that about 140 Deg F. 

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Brendon and Eric...thank you for the information about the knot.  I will definitely epoxy the cracks around the knot and then just keep an eye on it. 

Ronn...I didn't think of a meat thermometer.  I will use that just so I know.  I'm glad that it is probably less than 140 since it wasn't painful to touch.  Just hot.

I appreciate all the helpful information.  I will look into all the recommended products, choose something and then send a photo. Thank you!

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Should I get West Systems 105 resin with a 205 slow or a 209 extra slow hardener or something like the Six 10 in the caulk tube?  I have to apply this upside down, so need something thin enough to inject, but not so thin that it runs out. I have syringes & needles, but can also purchase Rockler's dispenser pack if I need the plastic tips.

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44 minutes ago, Sara22 said:

I have to apply this upside down, so need something thin enough to inject, but not so thin that it runs out.

I imagine you'll find this...impossible.

Personally I wouldn't bother with the epoxy.  It's not necessary.  If the board cracks a little...so what...let it crack.  It's rustic.  It's not gonna crumble on you like a stale cookie.  It'll just have some cracks.  Call it character.

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18 minutes ago, Eric. said:

I imagine you'll find this...impossible.

Personally I wouldn't bother with the epoxy.  It's not necessary.  If the board cracks a little...so what...let it crack.  It's rustic.  It's not gonna crumble on you like a stale cookie.  It'll just have some cracks.  Call it character.

I agree.

Plus when you epoxy and it then cracks further it will be unsightly having some cracks filled and others not filled. So then you'll be stripping finish, sanding, applying blue tape, and dripping epoxy all over again. I would just go with the rustic look of checks in the end of the timber.

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Ok, you talked me into it - no epoxy.  :-) It was starting to be rather complicated in determining how to apply it.  I like the concept of locking the knot in place, but the cracks give it character and when/if it cracks someplace else after I epoxy it, those cracks may not be as attractive.  Thanks again for all the advise.

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