Any structural engineers or mason's in the house? New mantle install

[stejus]

Hi all

I finally had my HI300 installed this weekend and I needed to replace the wood mantle with a non combustible stone mantle.

The mantle is brown stone and cut at 65”(L)X10”(W)x2”(H). I have no idea of the weight but it takes two to pick up and lift. It’s resting on the brick without bolts or a bond at this point and will not budge very easily. I’m not sure I really need to secure the mantle but will wait for comments.

My biggest concern is the load on these bricks that extend out. Some of the weight is spread along the back side of the mantle but there’s a lot on the front side as well. Am I putting too much of a load for these support bricks?

The first picture is the original mantle.

Thanks in advance for your help!

 

[LLigetfa]

Your concerns are warranted. I would do some exploration of what structure there is in the wall just above the bricks. You can drill a series of small holes to see what wood is back there.

I would drill holes in the back of the stone mantel to accept steel pins and drill corresponding holes in the wood structure. Drill them at a slight angle so that the weight of the mantel bends them level. When you're happy with the result, get some epoxy that goes in a caulking gun and mixes right in the spout and put epoxy in both ends of the holes.

 

[LLigetfa]

BTW, I'm not a structural engineer nor do I play one on TV and I have never stayed at a Holiday Inn Express, but I did work constuction and designed/built my own house.

 

[wellbuilt home]

The pin idea would make a great safety to stop some one from pulling the stone down . If the stone will sit up there with out falling off You could just lay a bed of Portland cement and sand and stick it on . Use additive in the cement. Let it dry for a few days before you lite up . Fill the holes on the corbels (Funny bricks) with a Portland sand mix. You could use thinset tile mortar also Get it at HD We lay window sills and FP mantle on all the time with cement mix ,it wont be a problem . John

 

[karl]

I would pin it like was already said. Then liquid nails it to the wall.

 

[edthedawg]

I'm gonna go with "just barely". Looks like the two corbeled brick assemblies should be able to hold it fine, but I do worry about cracking - lot of weight cantilevered out there. If it was an inch narrower, i wouldn't worry as much... Mortar and liquid nails are only going to do so much... I wouldn't bother with liquid nails at all - it will be useless if a stone this large decides to move. that and it bonds poorly to stone anyways - you'd be better off bonding stone to brick using mortar.

i wonder if you could fasten a couple small L-brackets to the top, against the wall. If you could align them w/ the wall framing, and carefully drill down into the stone w/ a tiny masonry bit, and sock them down... something to prevent the back edge going up is almost as good as keeping the front edge from going down.

 

[stejus]

I'm gonna go with "just barely". Looks like the two corbeled brick assemblies should be able to hold it fine, but I do worry about cracking - lot of weight cantilevered out there. If it was an inch narrower, i wouldn't worry as much... Mortar and liquid nails are only going to do so much... I wouldn't bother with liquid nails at all - it will be useless if a stone this large decides to move. that and it bonds poorly to stone anyways - you'd be better off bonding stone to brick using mortar.

i wonder if you could fasten a couple small L-brackets to the top, against the wall. If you could align them w/ the wall framing, and carefully drill down into the stone w/ a tiny masonry bit, and sock them down... something to prevent the back edge going up is almost as good as keeping the front edge from going down.

Would adding another corbel brick assembly as shown give more support to make me feel better that this rock won't come tumbling down? I'm sure a mason could pop out these bricks and put them back in without too much effort?

 

[burntime]

I second the corbel brick, AND pinning it. It will look really nice!

 

[LLigetfa]

I don't think adding another corbel in the middle is the way to go. It would be hard to find brick to match as would matching the mortar. It wouldn't look right either.

You could also notch out the drywall behind it and slide it into the pocket you create. That would mechanically hold down the back edge with a little less overhang. Mortar it all in place as suggested with latex modified mortar and you could embed steel screws above it.

My concern is that a child (or two) might decide to do chin-ups on the mantel bringing it down.

 

[Highbeam]

It's too wide, it's too heavy, it'll fall onto you or your stove. Do something different. Yes I'm an engineer, and that tight there is hokey as heck. Take it off.

 

[wellbuilt home]

Guys I'm a builder, an if you use a Portland cement & sand mixed with a latex additive you would have to bang the stone off with a sledge hammed to remove it . A stone 10" by 65" only weights about 125lbs and 4" of it is sitting on the brick 50lbs. The corbels are holding 50 lbs and there is about 25lbs of over hang . I think the F P would look better with a smaller stone. You could just rip 1" off the edge of the stone or cut it into the wall 1/2" You could put a piece of trim behind it to stop it from flipping off . If it was a outside stair tread It would have a 11/2" over hang and be lay-ed in a P/S mix and people will roll refrigerators on it. I do stone work all the time and cement is strong stuff . You could do chin up on it all day,I think the corner of the stone will break off before the stone pops off the brick (check to see if the brick is still tight on the wall , the mortar could be louses ) You could use brick ties under the stone and nailed to the wall to hold it up. It will stay put . John

 

[edthedawg]

I agree with two prior ideas:

1 - scribe the wall, make a pocket, and recess the stone slab into it.

2 - don't bother adding / making more corbels. you're talking about the moment center / C.O.G. of that massive stone slab vs. the combined shear and tensile strength of the mortar (it's poor in both). Big Stone Slab wins. You, and more specifically, anyone or anyTHING in front of it when it decides to WIN, will most decidedly LOSE.

 

[stejus]

Ok, I did some measurements and the brick extends out 7" from the wall at the furthest point and 3 1/2" along the back side. I found some bricks with missing mortar (not a perfect flush mortor joint) here and there. All bricks are solid and not moving with me tugging on them.

I prefer trimming the stone over cutting into the wall. Will 2" off the depth (8" with 1" overhang) make this that much safer?

 

[LLigetfa]

I prefer trimming the stone over cutting into the wall.

You've got to be joking. Cut solid stone versus a bit of drywall?

I give up.

 

[stejus]

I prefer trimming the stone over cutting into the wall.

You've got to be joking. Cut solid stone versus a bit of drywall?

I give up.

I'm not sure if it's just dry wall. There seams to be a mix of sand/concrete behind the mantle. Is this standard blueboard or some other type of drywall? Does it cut as easy as regular drywall? Any cutting tips?

 

[Summertime]

I prefer trimming the stone over cutting into the wall.

You've got to be joking. Cut solid stone versus a bit of drywall?

I give up.

I'm not sure if it's just dry wall. There seams to be a mix of sand/concrete behind the mantle. Is this standard blueboard or some other type of drywall? Does it cut as easy as regular drywall? Any cutting tips?

Sounds like plaster to me,Scribe the area to be cut and use a drywall saw.

 

[edthedawg]

I can see the wall being a bit of a PITA to cut into - looks like something funky going on there - not old-house plaster/lath. some metal edging in there perhaps? or they finished around the brickwork with Dura Bond or something...

but unless you have some real easy way to slice the stone, i'd always pick wall over stone to cut. You should be able to just scribe your line around the stone, then use a utility knife, chisel, and MAYBE a power tool bigger than a dremel (tho a dremel itself sounds like a good idea too) to core out the wall. then re-finish around the cuts using some drywall mud or something...

 

[wellbuilt home]

How old is your house . If it was made before WW2 You should have plaster and wood lath. This material is hard to cut neatly the plaster just cracks off the wood . If it was made from in the late 40s it could be plaster and rock lath .rock lath is a sheet rock with holes in it with plaster over the top , you could use a 1/4 screw driver to cut the plaster out by taping it with a hammer . around 1965 we started using sheet rock . You could cut it with a razor knife. Break a hole with a screw driver behind the 2" slab and check it out . I don't think it matters if the stone hang over the brick 1" or 3" no one is walking on it, it will just lay there one way or the other . I like the way the stone looks with a 1" overhang . I would also just cut the stone . Of course i have cut over 1000 foot of stone this year and it would be faster for me to trim it vs cutting the plaster out cleaning up the junk, making the stone fit perfect , laying a bed of mud and leveling it wile not letting the slab drop away from the plaster and leaving a space . You will need to put a small wood trim on top of the stone anyway, It impossible to Spackle or even caulk the stone to the dry wall the heat will make it expand and re crack . You could just take the stone back to the mason yard and have them cut it .You could cut it your self with a 40 dollar saw blade on a regular circular saw . cut 1/2" deep at a time make 4 or 5 passes . Use a soda bottle full of water with a hole in the side to keep the blade wet . don't get shocked . don't breath the dust , watch your fingers . To cement the stone on, just wet the stone with water/additive mix ,rub Portland power on the stone and make a past . mix Portland cement and sand 1 part Portland and 2 parts sand . mix with water/additive mix . lay a bed of splugee on the brick , place the stone on top, let it sit for 30 seconds then adjust it by rubbing the stone from left to right until its level . leave a 1/2 space in the back for cement . If your wife is worried have her hold the stone til it drys , a day or two should be OK Don'T heat it up for a few days. Make sure you clean the cement off early.
It harder to get the stones to stay on the ceiling . John

 

[ansehnlich1]

this stone has already caused you too much worry. take the thing off there, sell it on e-bay or craigslist, and get one that ain't so dang big.

ain't no consensus here, some say it's an accident waiting to happen, some want to rip into the wall, some want to add mortar, cement, retaining rods, and anti-flip lip at the rear, sheesh,

get RID of it and get the proper size stone for on there, problem solved.

 

[pybyr]

Look up some stuff using Google called "fireslate" it is a manufactured stone, entirely heat resistant, and available in various thicknesses. I have a big slab of the 3/4 thick inch stuff under my wood cookstove- cost less than any natural stone, and has worked well for me

 

[stejus]

How old is your house . If it was made before WW2 You should have plaster and wood lath. This material is hard to cut neatly the plaster just cracks off the wood . If it was made from in the late 40s it could be plaster and rock lath .rock lath is a sheet rock with holes in it with plaster over the top , you could use a 1/4 screw driver to cut the plaster out by taping it with a hammer . around 1965 we started using sheet rock . You could cut it with a razor knife. Break a hole with a screw driver behind the 2" slab and check it out . I don't think it matters if the stone hang over the brick 1" or 3" no one is walking on it, it will just lay there one way or the other . I like the way the stone looks with a 1" overhang . I would also just cut the stone . Of course i have cut over 1000 foot of stone this year and it would be faster for me to trim it vs cutting the plaster out cleaning up the junk, making the stone fit perfect , laying a bed of mud and leveling it wile not letting the slab drop away from the plaster and leaving a space . You will need to put a small wood trim on top of the stone anyway, It impossible to Spackle or even caulk the stone to the dry wall the heat will make it expand and re crack . You could just take the stone back to the mason yard and have them cut it .You could cut it your self with a 40 dollar saw blade on a regular circular saw . cut 1/2" deep at a time make 4 or 5 passes . Use a soda bottle full of water with a hole in the side to keep the blade wet . don't get shocked . don't breath the dust , watch your fingers . To cement the stone on, just wet the stone with water/additive mix ,rub Portland power on the stone and make a past . mix Portland cement and sand 1 part Portland and 2 parts sand . mix with water/additive mix . lay a bed of splugee on the brick , place the stone on top, let it sit for 30 seconds then adjust it by rubbing the stone from left to right until its level . leave a 1/2 space in the back for cement . If your wife is worried have her hold the stone til it drys , a day or two should be OK Don'T heat it up for a few days. Make sure you clean the cement off early.
It harder to get the stones to stay on the ceiling . John

Hey John

House was built in 1991 and its blue board with thin layer of plaster. I wasn't sure if the wall behind the fireplace was different for code reasons. I can easily take the stone to the stone dealer where i bought it and have it cut onsite. The stone cost $130 cut to size with a rock cut (rough edge) on three sides. I can't imagine it costing much more than $30.00 to trim. If i cut to 2" off it will overhang about an 1" to 1 1/2" due to the rough edge. I hope this makes it safer because wifey doesn't want to give up the rock!

 

[meathead]

I haven't done a whole lot of interior masonry work - but have built plenty of stone and paver walls, patios, walks, seating walls, etc. Personally, I always ere on the side of overkill, especially if I have the opportunity to make it look good anyway. You will have a difficult time matching the brick. If it were in my house and I was worried about it, the first solution that comes to mind is pillars of stone that match your mantel run from the hearth right on up tied back in to the brick and pointed all the way around.

Bare minimum dead man the thing back to the wall if possible and mix up some portland cement with silpro c-21 to mortar it to the brick surface. Any sane man would stop worrieing after they got the thing cemented down. I'd have some kind of pillars...just in case I ever wanted to jump up and down on it.

 

[PeteD]

Guys I'm a builder, an if you use a Portland cement & sand mixed with a latex additive you would have to bang the stone off with a sledge hammed to remove it . A stone 10" by 65" only weights about 125lbs and 4" of it is sitting on the brick 50lbs. The corbels are holding 50 lbs and there is about 25lbs of over hang . I think the F P would look better with a smaller stone. You could just rip 1" off the edge of the stone or cut it into the wall 1/2" You could put a piece of trim behind it to stop it from flipping off . If it was a outside stair tread It would have a 11/2" over hang and be lay-ed in a P/S mix and people will roll refrigerators on it. I do stone work all the time and cement is strong stuff . You could do chin up on it all day,I think the corner of the stone will break off before the stone pops off the brick (check to see if the brick is still tight on the wall , the mortar could be louses ) You could use brick ties under the stone and nailed to the wall to hold it up. It will stay put . John

Actually, the brick and the corbels must be holding all 125lbs, or else it would be falling. Sorry, couldn't resist and I realize what you meant. I think you are likely right about it not going anywhere with mortar (but why take chances), but I also agree it is slightly over-sized (aesthetically from the angle provided). I would cut it down, or rework the bricks at the top to make the underlying support wider.

Pete