I'd like to build a fireplace mantel that features veneered panels.
Unlike say a cabinet door, the other side of the panel will never be seen.
Is it neccesary to veneer both sides? Does MDF move with moisture?
Brian,
Try this for some info
---------------------------------------- It may not be necessary, but like chicken soup, maybe it has no medicinal value but hadn't ought to hurt.
If it were my project, I'd seal the cut MDF edges with diluted glue (TiteBond) per an earlier thread, then seal all the non veneered surfaces with a couple of coats of 2 pound dewaxed shellac applied with a 2" chip brush.
Quick, low cost and effective.
Lew
I doubt it but the reason folks veneer both sides is to equalize the forces applied to the sub-strate by the veneer. Especially so if you use water base glue as the veneer absorbs that water and shrinks as it dries; that shrinking applies a lot of bending force to the sub-strate.
Have you thought about what the heat rising up to the mantel might to the veneer/glue on the mantel?
Answering your question, MDF absolutely moves with moisture. Not so much with relative humidity but if it gets wet and is not immediately wiped dry it will swell.
Under normal circumstances temperatures being the same it is not necessarily necessary to veneer both sides but it is best. With an extreme temp difference you will be seeing it is probably a must and I would probably want to cover the seams/ edges to hide expansion and contraction with temp changes.
:> I'd like to build a fireplace mantel that features veneered panels. :>
:> Unlike say a cabinet door, the other side of the panel will never be :> seen. :>
:> Is it neccesary to veneer both sides? Does MDF move with moisture? : ---------------------------------------- : It may not be necessary, but like chicken soup, maybe it has no : medicinal value but hadn't ought to hurt.
I agree. However, there's no need to use fancy veneer for the other side -- any cheap veneer (often called "backing veneer") of the same thickness would do. Any veneer merchant will have something that will do.
-- Andy Barss
If the other side of the panel is invisible, you can choose MDF with veneer just one side. MDF is stable with moisture .
Lay a piece on your lawn and see how it looks the next morning.
I have worked with MDF for decades in many environments and MDF is NOT stable with moisture.
I used to frequent a Bob Evans restaurant that had a eating counter. The waitress would always come up, wipe down the counter with a damp cloth, then put down a fresh paper place mat. The thing would curl up like a ribbon, because the paper fibers on one side got damp and expanded. That's the same thing that happens to mdf.
The grass gets all yellowy?
When read the original post I was thinking the same thing. When I built our mantel I used solid 2" Oak and placed it well above the minimum height recommended by the fireplace/stove manufacturer. That dude still gets warm. You might want to check into the durability of MDF when exposed to heat in the 120 to 130 degree range. I don't know if it will degrade; but best to know now.
RonB
I don't understand this business of mantels being exposed to heat. Maybe I'm just old fashioned but to me a mantel is a part of a brick or stone fireplace and if it gets too hot for a cat to sleep on something is badly wrong.
A good part of the mantles being installed today are on insert fireplaces. These are essentially gas heaters or wood-burning stoves that have brick or tile faces surrounded by wood trim and a mantel. Little or no masonry
For example, we installed a Buckmaster high efficiency wood stove in our house which is essentially a souped-up insert with external combustion air ducts, a catalytic combuster and a blower system. The unit builds in like a fireplace with ceramic tile front surrounded by mantel front and shelf. Buck provides specific installation instructions and clearances and our installation clearances exceed recommendations. The internal temperatures in these catalytic fireplaces gets above 1000 degrees and they put out heat. Heat rises from the face and the mantle gets warm. We had two gas fireplaces in our previous house and the mantle above the insert face got warm. The front of the masonry wood-burning fireplace and mantle in the older house we lived in got warm. I cannot imagine the front of a fireplace, that gets used, not getting warm.
I am just a little concerned that fireplace facing is the best place to use MDF. The temperatures involved with our current installation are in the 90 to 120 degree range. Far-far from any combustion concerns but I was suggesting the poster should look at long term effects of heat on his material. Some fireplaces sit unused during much of their lives. Ours is running now and will run muchof the them for the next 4-5 months. Will MDF or Veneered MDF hold up to this?
Also, depends on the cat. Our, now dearly departed, dog would have loved to lay on our warm mantle if he could have hoisted his aging 105 pound butt up there. :^}
RonB
Snip
Actually a wood fire place mantel in many states has to be built to meet code as it is normal for them to get warm to hot and could catch on fire. If a mantel gets hot the fire place tends to be a bit more efficient as more of the heat is actually coming out into the room vs. going up the chimney.
Everything has to be built to meet code if there is a code. I don't see how that changes anything. I can see where it's an issue with some modrin stove that pretends to be a fireplace, but if it's the real firebrick-lined brick and mortar deal there's a lot of brick and mortar between the mantel and the fire and only a slight projecting lip of wood above.
If these things are in the wall and get that hot I'd be more worried about the wall catching fire than the mantel.
If MDF won't take 120F then it's in trouble in Texas.
The front gets plenty warm, but there's a foot or more of brick and mortar between that warm and any wood with a real fireplace, and any heat that gets to the wood has to go through the brick.
The mantel on a real fireplace isn't a shelf that sticks way out in front of it, it sits on top of the masonry and is supported by it.
It was manufactured at around 400F.
My experience is that: It Moves
I had a table top from Subway that I turn into a Router Table top. It was NOT laminated on the "bottom" and had that plastic edging installed (The type that fits in a kerf along the edges). After on year in the basement (cold, not dry) it sagged significantly and I knew it was my failure to seal the bottom surface with laminate or equivalent.
For a one off project, the savings between good plywood and MDF are not worth taking the chance IMHO considering the labor involved ....
Plywood 'curls' just as easily when laminated in an unbalanced way.
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