Spanning the wood storage below the Hearth slab.
(M) This is an exchange between Jim and Marcel which I (Marcel) just pasted here. Btw, some of the Forum Headings overlap so I'm not sure if this should be in the "Newbie Forum"?
(M) 1- I see that either you or James has used angle iron
to span the opening of the block stand below the 4th
course. That span looks to be about 2 1/2 blocks, but
whatever the span ( mine will be only 2 blocks) could I
simply leave off both the angle iron and the
spanning blocks and cast my Hearth Slab directly on top
of the 4th course?_________
(JH) ### Yep, it's 2 1/2 blocks wide. If you're going to
pour your hearth right on top of the block, you'll
need to put a tongue in your form plywood (the piece
that fits inside the block walls) and support it with
some temporary pillars. Make sure you run a double
strip of rebar across the entire front length centered
over the block wall (and gap). I'd also run a couple
of additional pairs of rebar at the 1/3 & 2/3 marks
across the front heading toward the back. Twist tie
the sets of rebar together and then make your pour.
Use high-strength (5000 PSI) concrete and you should
be good (especially with the island hearth design for
the thermal concrete layer).
(M) 2- If you answer "yes" to this, then can I tempt fate
further by also leaving full access to the storage
area; in effect having only 3 blockwalls? ____
(JH) #### What's your finish going to be - igloo or
something more substantial (e.g. heavier)?
(M) We are planning on using faux stones (Owens-Corning) for the hearth stand, and probably for the dome as well. Those "stones" are relatively light. We might make a barrel type enclosure for the igloo and have it look something like an Alan Scott oven. I think I'd build side walls and a top of Durock Cement Board (about 1/2" thick)and just per pourlite or perhaps an even more efficient insulator around and on top of the igloo. Undecided as yet but I doubt it would be "heavy".
(JH) I find the corners helpful as I keep my kindling, a small
hatchet, and some other bits & pieces in there handy to reach but safe from the weather.
(M) If this is structurally sound, it seems I could have
unobstructed access to the wood storage floor which
would make stacking and removing firewood that would
otherwise be stuck behind the front corner,easier.I
would of course bridge that area of the Hearth Slab
above with lots of rebar . It would also facilitate
cantilevering the Hearth Slab for about 6 -8 inches?
(JH) #### If you're thinking of cantilevering, I'd not get
rid of at least one of the blocks on either side.
Typical cantilevering engineering dictates only
cantilevering 1/4 the length of the fully supported
length. That makes the 8" okay if the 4th wall is
there, but dicey if it's entirely unsupported.
(M) I guess I can live with one block around the corner. I hope to use narrow re-bar and mesh to help me shape something of an arch (perhaps Gothic pointed?) of mortar-stucco for the wood storage opening, as well.
(M) Excuse me for not having written to you on the
forum but if you feel you'd like me to copy-paste any
or all of your reply to this question on the Forum, I
will do so. In fact, unless you tell me to
the contrary, I will post your Reply after I get it.
(M) So, friends, that's my story and I'm stuck with it.
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