All,
A customer who has a stone fireplace hearth, wants it covered w/ concerte. I can build a frame, pour the mix, & level it. But there are a few things which I do not understand and would appreciate any help if you know the answers to the following questions:
1) Is there a certain type of concrete that I should consider using?
2) Is there any preparation of the stone needed prior to application of the concrete?
3) What is the minimun thickness that the concerte can be?
4) Are there any chemicals that need to be added to the concrete?
Thanks in advance,
dlb
.
The undisciplined life is not worth examining.
Replies
I have no idea how to do this, but it just struck me as funny -- seems backwards from the common scenario. Also, I can just imagine the customer covering up your concrete in a few years with fake stone.
Mike Hennessy
Pittsburgh, PA
that's the same thing I thought........plus you would have to go pretty thick to keep the stuff from cracking up......no?
Well, the customer has stone from floor to ceiling, covered up from hearth to ceiling w/ a surround. She wants the surrouond finished and in order for the hearth to match the surround it needs to be concretized.
If you know of any links that may help, I am all ears.
Thanks,
dlb
.
The undisciplined life is not worth examining.
Wont the hearth height be rather high in relation to the
floor of the firebox? I agree it wont be much trouble to go over top, but it
could be fairly easy to pop the stone out. Then your height wouldn't increase.
I have poured several Hearths from concrete but never over a stone base.
I use the 5000 lb. premix from Sacrete, nothing to add (Unless you want to color it).
If (and it is a big if ) the stone is solid and on a good footing it shouldn't present any problem.
I would put a slip sheet of some kind between the concrete (Plastic, felt etc.)or paint the stone and face of the firebox where the hearth will butt to it with "bond breaker" so that the new hearth isn't affected by thermal expansion and contraction between the two.
I would think you could get by with as little as 2" on the stone. Mine have all been 3" + but that was determined by the desire to have the hearth raised off the surrounding floor surface not the need for the extra depth for strength.
Slow cure it. That means a spray on cure, sealer or damp covering for at least 1 week.
I will bump this to Waters to has done counters out of concrete.
Bump.
They can't get your Goat if you don't tell them where it is hidden.
I would put a slip sheet of some kind between the concrete (Plastic, felt etc.)or paint the stone and face of the firebox where the hearth will butt to it with "bond breaker" so that the new hearth isn't affected by thermal expansion and contraction between the two.
Why would the stone and the concrete expand at appreciably different rates? This is not like a wood-framed subfloor of ply with ceramic tile over it. She's going concrete on stone; the thermal coefficients of those two substances are very similar.
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
May not be needed. Without going back to my post to check I believe I said "I would " not that "You need to " However I have always isolated the hearths I have poured from the surrounding surfaces because the hearth heats rapidly from the radiant heat while the surrounding areas don't. For me it is a matter of better safe than sorry, and there is no downside to doing it that I can think of. I haven't had any that I poured crack so I will stay with my theory unless I can learn why not to do it.
They can't get your Goat if you don't tell them where it is hidden.
Hey there,
I'll echo what dovetail has to say and add my 2 cents:
From dovetail:
I use the 5000 lb. premix from Sacrete, nothing to add (Unless you want to color it).
This is a great way to go--especially for reduced thickness. This mix already has fiber, air entr. (I think) and water reducer in it. A 16" square paver done 1" thick has proven to be almost impossible to break, short of whanging it across something over your head.
If (and it is a big if ) the stone is solid and on a good footing it shouldn't present any problem. The key is solid base. What's under the stone? If it has adequate footing and won't move, then the cc facade won't break.
I would put a slip sheet of some kind between the concrete (Plastic, felt etc.)or paint the stone and face of the firebox where the hearth will butt to it with "bond breaker" so that the new hearth isn't affected by thermal expansion and contraction between the two. I'd just use 3 mil plastic. A counter I did cast in place (I make molds and cast off site--see "dirtbag backyard concrete counter" method posts) we used 3/4" ply substrate, beefed up cabinets, then layed the plastic over the substrate to separate the two.
I would think you could get by with as little as 2" on the stone. Mine have all been 3" + but that was determined by the desire to have the hearth raised off the surrounding floor surface not the need for the extra depth for strength. The thickness of that poured in place counter was only about 1" in the 'field' and had the appearance of 2.5" thickness due to dropped edge. I would think 1 1/2 to 2" would be more than enough thickness to get some reinforcement in. You don't really need anything but chicken wire, really, to 'net' the thing together. You're only making a facade, not a slab that needs it's own structural integrity.
Slow cure it. That means a spray on cure, sealer or damp covering for at least 1 week. By all means pay attn. to the amount of water in the mix--too much, too much shrinkage, and cure it very slowly so it does not shrink to much.
Sounds like fun!
I will bump this to Waters to has done counters out of concrete.
"Research is what I'm doing when I don't know what I'm doing..."
Thanks for the reply. I had no idea how much was involved which is why I made the initial post.
This is what is great about Breaktime - the sharing of information and the curing of ignorance!
I understand most of what has been posted but this idea of a slip sheet leaves me baffeled. If I understand correctly, it is just a layer of plastic over the stone onto which the concrete is poured. I had intended to apply a concrete bonding agent to the stone first prior to the pour.
The customer quit using her fireplace over 10 years ago when she almost burned down her house so for her the difference between the hearth and firebox is a mute point.
Regarding your chicken wire comment; I assume that it will be layed into the concrete prior to the pour and its intent is similar to rebar.
It seems that I need to pour at least 1" of concrete using the 5000 lb. premix from Sacrete.
I'll have to make a frame to surround the hearth on the 2 sides and front. Any tips on construction of it?
Lastly, the hearth is ~18" in height and is ~6' wide. Can you tell me approximately how long it should take a medium-experienced concerte man (me!) to do this job?
Thanks again for all of your and everyone else's help.
dlb
.
The undisciplined life is not worth examining.
Hey DLB,
I understand most of what has been posted but this idea of a slip sheet leaves me baffeled. If I understand correctly, it is just a layer of plastic over the stone onto which the concrete is poured. I had intended to apply a concrete bonding agent to the stone first prior to the pour. As the concrete and the stone are two dissimilar materials, they'll expand and contract at different rates. The slip sheet is necessary to keep the stone's movement from breaking the concrete. With the slip sheet, it can move as it needs to--and the also the cc--and they won't break each other.
The customer quit using her fireplace over 10 years ago when she almost burned down her house so for her the difference between the hearth and firebox is a mute point. Yow!
Regarding your chicken wire comment; I assume that it will be layed into the concrete prior to the pour and its intent is similar to rebar. Yeah, I don't think you need rebar. Cut the wire to size of form, lay in form, pour, then pull it up into the wet crete a little with a plier, or coathanger with a 'j' bent at the end.
It seems that I need to pour at least 1" of concrete using the 5000 lb. premix from Sacrete. I'll bet you could even go thinner, but I won't advise that and watch your job fail as my experiment. ;-)
I'll have to make a frame to surround the hearth on the 2 sides and front. Any tips on construction of it? You'll need a sturdy, watertight frame, so you'll need something sturdy to screw it to. How much room is there bt the stone and the floor and is it stone all the way down? Post a picture? I'd build some type of little wall to form a ledge under the stone, then form up from that to make the edge. Then caulk with irregular (likely) gap between your form and the stone with silicone to seal it up. You want your form to hold water. Use 100% silicone to seal all gaps and places where the forms are screwed together.
Lastly, the hearth is ~18" in height and is ~6' wide. Can you tell me approximately how long it should take a medium-experienced concerte man (me!) to do this job? Post me a picture maybe and I can offer some insight. Just break it into steps and account for any surprises (there will be!) and cost it out. The materials will be cheap. You know how to get volume of the form right? And there's like .6 a cuft in each 80lb bag of quikcrete 5000 if I remember correctly.. A constr. calculator makes this job easy as pie, measuring in inches, converting to cu ft. I would think you could form it in a day, pour it in 1/2 a day, unform it much later after it's sit in the forms for at least a week. + materials.
Thanks again for all of your and everyone else's help. Hope I'm of help. I certainly have pulled a lot of great info from this site and it's folks also!"Research is what I'm doing when I don't know what I'm doing..."
Here is a picture of the hearth ...
The undisciplined life is not worth examining.
Ah, now that I see it perhaps just setting a piece of
blue stone down might look better.
Here is one I did. Wood framed , not stone beneath it. The wood skirt might work for you .
They can't get your Goat if you don't tell them where it is hidden.
That is beautiful and a neat idea. I may propose a wooded skirt to the H.O. of this project. Thanke for the photos.
dlb
.
The undisciplined life is not worth examining.
How long did this project take?
Thanks,
dlb
.
The undisciplined life is not worth examining.
Concrete hearth alone ?
3 partial days maybe a bit more.
1 part day to form, 1 to pour , 1 part day to finish up trim etc.
They can't get your Goat if you don't tell them where it is hidden.
I'm confused now.
You want to just cap the lower hearth portion?
From the photo it doesn't look 18" high?
If your new cc cap will reach the floor, form right to the floor. You'll have to do some silicone cleanup but that shouldn't be too hard.
Will your cc meet the surround/mantle there at that gap at the bottom?
Was the mantle/surround just added?
What's up with the receptacle to viewer's left, half buried by the surround?
Hmmmnn..."Research is what I'm doing when I don't know what I'm doing..."
I'm confused now.
I don't intend to make you confused but that is just my nature!
You want to just cap the lower hearth portion?
The H.O. wants the entire hearth (top, front, and both sides) covered in concrete to hide the stone.
From the photo it doesn't look 18" high?
Maybe between 12" & 18"
If your new cc cap will reach the floor, form right to the floor. You'll have to do some silicone cleanup but that shouldn't be too hard.
I figured that would need to be done but I think I can handle it.
Will your cc meet the surround/mantle there at that gap at the bottom?
The surround/mantle will be removed first. The cc applied, surround/mantle returned and scribed to fit the 'new' hearth.
Was the mantle/surround just added?
No, it was custom built and installed ~ 20 years ago. I will dismantle it, refinish it, bring it up to code if need be and reinstall it.
What's up with the receptacle to viewer's left, half buried by the surround?
I will reposition the outlet to the left one stud bay while at the home.
Hmmmnn...
Please feel free to ask any more questions. I am looking for any advice on this project. Thanks again,
dlb
.
The undisciplined life is not worth examining.
I gotcha now.
Yes, without the surround in place, I'd form up from the floor, seal all around and go for it.
Level the top of the forms perfectly where you want the new hearth to go and finish in place.
Temporarily attaching the form to the floor is a bit of a pickle. I think I would brad nail ply cleats down, nailing so as not to split floorboards, and fill the inconspicuous holes later.
You'll have the baseboards off the wall too right? Then you can just form right to the wall and then run your bb to the new hearth.
About the bond breaker--slip sheet of plastic--there is also a paint/roll on waterproofing membrane for tiling that's very flexible. TEC product is called 'hydraflex' and then there's a tilelabs (or home depot) product thats red too. I'd probably try that stuff in lieu of plastic because it may be difficult to get the plastic where you want it over the rock, corners and whatnot.
I'll be interested to see your end result."Research is what I'm doing when I don't know what I'm doing..."
Waters covered it. There is no need for the concrete to bond to the stone, and the possibility of problems are increased if it does, so why bond it? Form lumber: I use MDO plywood because it gives me a smooth surface on the concrete side and makes finishing the edges easier. Caulk seams as Waters recommended. Form: I always create an overhang for the concrete hearth. Without some idea of what you have existing in terms of the hearth I can't help beyond that .
Raised hearth now? Flush hearth?
If raised do you want to leave the vertical surface of the stone exposed or cover it with concrete as well? Time will depend on the "setting" time of the mud and that depends on a lot of variables (temp., water content, humidity) . I give myself a full day just to handle the pour but always accomplish a lot of other stuff while the mud is setting up to the point I can get the final finish (Hard steel trowel) on it. Actual time spent working on it for the pour is maybe 3 hours including mixing, pouring and finish.
When I do pour the hearth it is the most important item of the day and takes priority over any thing else I am working on, If I have to sit on my butt and drink coffee all day to get it right that is what I do.
They can't get your Goat if you don't tell them where it is hidden.
Just thinking some more on this.
If you end up raising the hearth more than an inch or so, you might wanna lay some brick or pavers down first as a prototype, start a fire and make sure you don't muck up the draw. Some fireplaces are pretty particular about the opening shapes/sizes.
Mike Hennessy
Pittsburgh, PA
I'd have some reservations about this and would want at least, a disclaimer to do the job.
Sometimes a large cast heart will crack due to a high differential of temperatures - very hot at center at fire and near room temp at the outer ears.
I had to replace a bluestone hearth once for that reason. I had notified the owners when they made the choice of a one piece that they could have a problem because of that.
Alas, when it cracked the first year, they did not remember or their understanding was that I would be willing to replace it free if it did crack.
There was no arguement tho. I ate it and did a lot of other work for them with enough profit built in to satisfy me. Anyways, a slip sheet when pouring this might help if it comes to replacing it later.
The other reservation I have is that when the surface is built up 2-3 inches, that will change the draft profile. Probably not enough to hurt, but draft is a funny thing. So are people and their subjective opinions. If this is marginal now and they don't really notice it, they could suddenly start to complain after you touch it, after they develope the opinion that it is YOUR fault that the chinmny doesn't draw well.
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Not sure but from the looks of it he will be just
below the opening of the doors.
Usually there is an air intake, wouldn't want to block those.
But I don't see any. If not then it won't change opening size, or
effect the draft.
You make a good point about thermal stress tho. That would
worry me. Mostly I don't think concrete will match the look of that trim.
I sent the H.O. the posted photo by dovetail and she stated that it may be a possibility. Peraonally I believe that his idea would look better than a plain cc hearth. We will see what the customer thinks.
Thanks for the postings,
dlb
.
The undisciplined life is not worth examining.