DIY Network

We recently hired a contractor to build an outdoor fireplace and finish an existing concrete patio with stone. Based on the quality of the work so far we are skeptical about some of the design assumptions. Here are some of our questions/concerns:
1. The fireplace is constructed over a concrete foundation that is about 10 inches deep. The concrete is re-enforced with re-bar but not attached to anything. Is this adequate to support the fireplace in our area. Approximate dimensions of the fireplace are 5 ft deep by 5 ft wide with a flue that comes up about 8 ft.
2. The fireplace is constructed out of masonry block and not re-enforced with rebar. It is attached to the concrete by mortar, nothing else. The overall structure does not have any re-bar that would "hold it together". Is this an appropriate design for it?
3. The patio, approximately 600 square feet is supposed to have sandstone (New York Blue) laid on top of existing concrete. The concrete is attached to the house, has rebar in it, has the appropriate stress cracks in it and has not moved for several years. We are told that with proper maintenance (applying sealant) this is a lasting design. We would like to validate that statement.
Thank you in advance for your help and guidance!

10" of concrete under it should be more then enough. The only reason I could see to use rebar inside the blocks is if you were just building a wall with no side support.
Even a whole two story house chimmney with a fireplace would not have 10" of concrete under it.
Any house that has a brick and block foundation is just sitting on top of a concrete foundation footing and is only "attached" with morter.

I should have probably clarified, that the fireplace is free-standing. Is the re-bar the right approach for that scenario?

The soil in your area generally is gravel, sand and a little bit of fines. Your soil can support well over 1000# per square foot. So the footing should be able to carry 25,000 pounds if it is fully 5 feet square. As to the method of attaching the structure of the fireplace to the slab, I'll have to know how serious your seismic risk is. I doubt that there is a wind threat big enough to move the fireplace sidways.

In your enavironment I don't think you have much problem with frost heave or water penetrating into the grout under the flagstones. The control joints in the concrete slab may or may not have broken. You said that they haven't broken. There is a small chance that the changed weight of the slab with the stones. Probably very small. It's good that the fireplace isn't attached to the slab in any way. The concentrated weight of the fireplace might cause it to move slightly differently than the patio slab. Since the two aren't joined you shouldn't have any problems. I'd watch out if any irrigation or watering is done near the slab. You don't want moisture to collect on or under the slab. The occasional rain won't make much difference but on=going watering could.

Check out these modular fireplaces. There are a few models that are for outdoor use and then you put whatever facade around them that you want 9brick stucco, ect...). This may be a cheaper alternative to having a mason build a complete fireplace. Look at teh galleries; they are very nice.

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