Fireplaces, Heating Stoves, Flues and Chimneys - Installing a 400-year-old Cedar Fireplace Mantel

I received a call from a customer. He recently purchased from Washington state a 400-year-old cedar fireplace mantel. It is approximately 5" tall, 11" deep, and 48" long. He spoke to someone about installing it on his existing fireplace and was told to use two 3/4" threaded rods. After applying an epoxy, the rods would be inserted into holes drilled into the back of the mantel and into a mounting board already in position on the fireplace. This method would require extremely precise drilling for exact alignment and orientation of the holes in the mantel and in the mounting board.

Does anyone know how those holes would be drilled so precisely? Or does anyone know how there might be a better way to install this mantel?

Respectfully,

Handy Matt

You could use dowel locators (probably the wrong terminology I have a set but I forget the correct name). They are inserted into one hole and the pointed end is left sticking out a bit. Then lift the mantle into place, tap it with a mallet and the locations will transferred to the mating piece.

Will it be installed on brick, wallboard, rock? Is the surface fairly smooth?
This is the best way to install the mantle so it will be permanent and won't tend to sag. You could use the dowel center pins, or take precise measurements after transferring them to the wall from the mantle. There will have to be a substantial support member for the rods to enter, and they must be cut level and at 90 degrees to the wall face, so a framing square next to the drill is a must. Do likewise to the back of the mantle to the depth of the rod. Dry fit it, pull it down, adjust if necessary. If not, then epoxy the rod into the wall. Before it has time to really harden, inject epoxy into the holes in the mantle, lift it onto the rod, pressing it tightly to the wall, and hold it until it sets. You will have epoxy run out the bottom, so be aware of it and have someone clean it as you go.
400 year old mantle, some guys have all the luck!! What an adventure. Good luck, and measure three times.

Thank you for the replies.

The mantel shelf has been installed successfully. The wall of the fireplace has the 'weeping mortar' finish. I think that's the correct terminology for the mortar oozing out between the bricks. Obviously a very irregular surface. There was a 2" x 4" mounting board laying on its side so the 1-1/2" dimension was visible. I had to find the true horizontal on the board to position the 1/2" all-thread. The mounting board was not true horizontal. I drilled into that board at 3 different locations; the center of the 60" mantel, then 25" left and right of center. The drill I used had a level indicator so I knew I was drilling horizontally. And I used a carpenter's square to make sure I was drilling perpendicular to the surface.

For the mantel shelf I found the center and the 25" left and right of center. The same process was used for drilling into the shelf, except I went in about 6" - 7". I made sure the mantel shelf was on a nice, level surface before I started my drilling. Once the holes were done, the mantel was dry fitted on the 1/2" rod. It fit very nicely. I used Liquid Nails as my adhesive and had to brace just the left corner of the shelf for a true horizontal from back to front. The left / right positioning was right on.

The homeowner removed the brace after 24 hours and all is well. I appreciate your helpful comments.

Respectfully,

Handy Matt