Install mantle on rock fireplace?
#1

Seems THT always has a wide array of experts, so I’ll throw this out and see if anyone has suggestions. Bought a new house, love the fireplace, would like a mantle. Bought a walnut 72”x4”x7-9 1/2 wide mantle, thought trick would be drill holes (rock or mortar?) install 1” rods, and scribe the wood to fit. Called 3 different contractors, first said he would just grind rocks down and drill rods into the wood frame(?). It’s a fireplace, don’t think they would ever use wood (cbs home) and looks like block with rock front. I asked if we would need to tent, or shield for dust and response is nah, no worries. 2nd contractor says build full tent with plastic, grind rock, mount rods into the rocks. 3rd says build tent, grind rocks, and mount rods into mortar. So, any experts here that can chime in? I am trying to pay, and use a licensed carpenter/contractor, so I’m not being cheap, I just want it right.


#2
Member

Not an expert but redid our fireplace after my house flooded by Harvey. We were able to use real wood beam mounted to the wood studs because the wall was open. Unless you are willing to undergo major surgery on that wall and risk mismatched mortar you are probably going to be limited to a hollow beam. If that is "modern" construction those rocks are only an inch or so thick. Behind it will be wood studs, maybe some sheetrock and lath with the rocks basically glued on with mortar.
#3
Admirals Club




I installed one on ours but it was while we were building it, one of my best friends did the rock work and installed 4 long heavy threaded screws (he said the threads would help hold better ) . We used liquid nails on it
Ours was a actually an old timber from an old barn. Buddy of mine gave me a very nice planed timber that was perfect and this “old POS” timber that you can actually see birdshot in it and even looks like it was hand chopped or shaped when it was cut . I worked for several hours on the “perfect” timber (sanding , staining, sanding, staining, sealing, sanding sealing etc). The Old POS timber I slapped a coat of stating on it and couple coats of sealer.
Guess which one looked “perfect” when it was done
Our fireplace is basically cultured stone over cement board with wire lathe and it was easy since new construction
Is yours solid rock(looks like it ). I would CAREFULLY drill holes and set thread rods in there ( we used 4 for mine) and then use liquid nails and slide the mantle on them.
Ours has been rock solid for 20 yrs
Ours was a actually an old timber from an old barn. Buddy of mine gave me a very nice planed timber that was perfect and this “old POS” timber that you can actually see birdshot in it and even looks like it was hand chopped or shaped when it was cut . I worked for several hours on the “perfect” timber (sanding , staining, sanding, staining, sealing, sanding sealing etc). The Old POS timber I slapped a coat of stating on it and couple coats of sealer.
Guess which one looked “perfect” when it was done
Our fireplace is basically cultured stone over cement board with wire lathe and it was easy since new construction
Is yours solid rock(looks like it ). I would CAREFULLY drill holes and set thread rods in there ( we used 4 for mine) and then use liquid nails and slide the mantle on them.
Ours has been rock solid for 20 yrs
#4
Admirals Club 


I’d go with your plan but build a hollow mantle. Use a scribing tool or a contour gauge to map out the rock and cut out the profile with a coping saw or a grinder. You can inset a 4X4 to the edge of the deepest cut and run the threaded rod into that.


#5
Senior Member


I made and installed this Pecan on our fireplace 2 years ago, ours is just straight brick however I used the brick and hollowed the mantel for support. On yours you need to layout the area that your mantel will fit into and the grind the stone as flat and flush as possible. Your looking at a dusty mess.

Old mantel






Old mantel





#6
Senior Member

The masons are suggesting the grinder route because that's in their skillset. I've done rock work, and I'm a carpenter/furniture builder. From my perspective, I'd drill to install metal rods, and I'd scribe the mantle to the stone. It's only necessary to have the visual edges of the mantle scribed, and undercut the thickness so you don't have to fuss with fitting it.
#7
Senior Member

The masons are suggesting the grinder route because that's in their skillset. I've done rock work, and I'm a carpenter/furniture builder. From my perspective, I'd drill to install metal rods, and I'd scribe the mantle to the stone. It's only necessary to have the visual edges of the mantle scribed, and undercut the thickness so you don't have to fuss with fitting it.
I am sure it is not real stone, but if it is then what I just said x 1000.
#8
Senior Member

The masons are suggesting the grinder route because that's in their skillset. I've done rock work, and I'm a carpenter/furniture builder. From my perspective, I'd drill to install metal rods, and I'd scribe the mantle to the stone. It's only necessary to have the visual edges of the mantle scribed, and undercut the thickness so you don't have to fuss with fitting it.
#10

This is the way to do it. You need a carpenter not a mason.
The masons are suggesting the grinder route because that's in their skillset. I've done rock work, and I'm a carpenter/furniture builder. From my perspective, I'd drill to install metal rods, and I'd scribe the mantle to the stone. It's only necessary to have the visual edges of the mantle scribed, and undercut the thickness so you don't have to fuss with fitting it.
#11

I do rock sculpture work, to grind the rock surface that size, that length to something that is somewhat flat is going to tent plus. The dust you'll create will be equivalent to a fog so thick you can't see the hand in front of your face at arms length. So you'll need large cfm intake to match the large cfm exhaust.
#12
Senior Member

Cut the rock back to the substrate, pad out the cut as necessary, install mantel. Prefab fireplaces are often wood framed, and the stone is glued to the recommended substrate.
#13
Senior Member


Unless you are in love with that rock I'd remove it all and go with real stone or something more colorful and bright. Maybe the picture isn't doing the rock justice?
#14
Admirals Club 


One thing that could be done is to take a flat board the same length and height as the mantle, drill your structural inserts into the framing, etc, behind the stone veneer, place the board face for mounting your mantle at the desired height, use some Tap-cons to mount the loose backboard to the stone, use some washers as spacers to hold the board face parallel to the wall and level. Use modeling clay to seal the bottom and ends of the board to fill any gaps so it's "watertight", fill the gap between the irregular stone and the back of the board with non-shrink grout. After the Grout cures, remove the Tap-cons and board, you will have a flat surface to mount the mantle, plus not lose any mantle depth.
Just a thought I have done this in a few occasions with the mantles we manufacture.
Just a thought I have done this in a few occasions with the mantles we manufacture.
#15
Admirals Club 


We're doing this right now and fortunately the mantle is being installed before the rocks go on. I think it's going to be a mess trying to mount one on that rock.
#16

So, the pic doesn’t do it justice, I’ll retake one tonight. The rocks are real, and the one rock to right side, about what I think is mantle height, is about 8” out from the other pieces. I love the looks of it, and I’m sure it was pricey, I just want it right. Let me retake and see what you all think. If I scribe the wood, I would be down to about 2” of mantle left on the right side with the big, obtrusive rock