question about hearth slab framing

[johnnybrewmeister]

Re: question about hearth slab framing

Thanks for all the tips!

Stonecutter, the "legs" are already shimmed to level things out and stabilize, but still it is quite wobbly.

SableSprings/Mike, I've already learned from your past experience, because I was gonna screw some braces to the top to see if that would help - now I won't try this.
I like your idea of the wire...might give that a shot.

NCMan, are you saying you just screwed some of your "legs" to the block stand? I could probably get some tapcon screws (if they aren't too pricey).

Les, I can't honestly picture what you're describing. Got any pics? I know I've been thru your build thread, maybe it is time for a re-visit.

Thanks,
John.

[Les]

Re: question about hearth slab framing

May be too late for you but I placed some plywood inside to block 3 1/2 below the top. Was able to brace the hell out of it from below and simply knocked the braces out when done.

[NCMan]

Re: question about hearth slab framing

I'm not sure if what I did will work in your case, but here's what I did. Keep in mind, I used solid cap blocks on top and they were already nice and level. I simply added some Tapcon screws in a few mortar joints, along w/a shim or two where needed. I just placed the concrete in fairly easily and spread it around as I went, to stabilize the pressure. The forms never budged, even when I tapped on them to get the honeycombs out. It is quite important that you get your slab nice and level at this point. Best of luck to you.

[SableSprings]

Re: question about hearth slab framing

I'm pretty much following the FB plans for my stand and hearth, and am getting ready to pour the slab for the hearth floor. My side forms are 2x4s for a 3.5" slab, and they are resting on & screwed to 2x4 legs to get the right height/level. But my forms are reallly really wobbly with this setup! I would love to nail/screw the form "legs" to the concrete blocks to stabilize things, but that's probably not too practical. Am I the only one who has a wobbly hearth form?
Should I worry? How can I fix it?

Thanks a bunch,
John.

John, it's really important that your slab form is solid. I did a similar thing (wobbly form) for my first slab pour using bits & pieces of wood that were laying around--and it was a nightmare. Never having worked with that amount of concrete, I did not realize how heavy and how much outward pressure that wet mass of a +yard would exert. Make sure you shore up the form...you should not be able to wiggle it when you're ready to pour. And you don't want anything secured to the top of the forms as it will interfere with the pour and the scree work (leveling)...also a mistake I made with my first attempt

Here's a thought if you're having trouble getting the form to "firm up". I did a hearth pour a while back where we had restricted space and couldn't get a solid form setup. We did the best we could, then drilled several small holes along the middle line of the 2x4s forming the perimeter. Next we ran stiff wire back & forth through the holes side to side in the 2x4s to tighten & reinforce the form's vertical strength & integrity. It was important to be fairly close to the middle so the sides of the form didn't get pulled out of vertical. (Of course the wire was separate from the slab rebar.. ... although I'm sure the soon to be embedded wire added something to the slab strength.). After the slab hardened, we cut the wire on the outside and pulled off the forms. The small stubs of wire remaining were easily cut off the concrete slab edges.

[stonecutter]

Re: question about hearth slab framing

Get a couple packs of composite shims and wedge them under the form to stabilize it. Just snap them off if the won't release after the form comes off.

[johnnybrewmeister]

I'm pretty much following the FB plans for my stand and hearth, and am getting ready to pour the slab for the hearth floor. My side forms are 2x4s for a 3.5" slab, and they are resting on & screwed to 2x4 legs to get the right height/level. But my forms are reallly really wobbly with this setup! I would love to nail/screw the form "legs" to the concrete blocks to stabilize things, but that's probably not too practical. Am I the only one who has a wobbly hearth form?
Should I worry? How can I fix it?

Thanks a bunch,
John.