Lean the slabs vertically against the side of the base - then two people will lift the bottom of the slab until it’s horizontal - and slide the slab into place.
So, I have zero expertise in concrete work, but I’m wondering if it would be feasible to build a frame atop the blocks and pour the concrete slab in place.
What strikes me right away as an obstacle to that solution—even though it sounds attractive—is the “floor” in the form. You’d still have the problem of how to get that out from under nearly 400 pounds of concrete. It wouldn’t be at all difficult if there were two slabs separated by some space. Then you could unbox a slab, wrench off the sides with a demo bar, tip it inward, and slide it toward the center. But, you have three, and you have two 2x6’s adjacent to the center slab.
Add to that the issue of what happens to the void—the empty space formed by the polystyrene pieces. Using the face down casting method, you’d have to find a way to flip each of those slabs while they’re five feet in the air.
You’re casting face down so that you have a perfectly smooth, level bottom surface that lays on top of the blocks. Because your blocks were set in place using a level (right?), your hearth slabs will also be level.
I suppose that you could build a one-piece form out of cement board and 2x6, lay it on the slab, pour your concrete to a precise level, add your void forms, and ensure they are absolutely flush with the top surface. In that case you’d leave the cement board in place when you’re done. But that sounds like much more work than the three-slab, on-the-ground system, and fraught with more problems than it solves. (Also, I have no idea whether it would work!)
In looking through the gallery, and pictures of builds, it appears quite a few folks built the slab in place.
Folks who have some experience with working and forming concrete have done that, Bob. Note the original poster said he had “zero experience” and wanted to know whether someone who is working with concrete for the first time might be successful in building a large reinforced slab with a void balanced on a three sided wall six feet above the ground.
In good conscience it would be hard to say, “Sure, go for it. Piece of cake!”
good point, thanks for replying
I haven’t been able to decipher how folks who built these slabs on the garage floor got them up. The idea of a materials hoist seems like it would work, but how does one get enough space under each slab to even begin lifting it?
I used a hand cart that worked fine for me.
When the casting is being removed from the mold, rest it on a couple of boards. Stack several boards high underneath it until you can get a floor Hoist under it.
I rented a portable engine hoist with bottom legs that extended out for support. ($50 bucks for a weekend) Manually slide the slab onto the legs of the hoist and tie 2 ends with strapping and use the hoist boom to raise it up. Reposition the strapping as necessary to make sure it picks up horizontally instead of diagonally. Raise the hoist all the way up and push the hoist over the Base blocks and lower onto the blocks.
Put the mortar on the blocks where the 1st slab will go and pick up the slab with several friends and place on the mortar. I had 5 people move the slabs once on top of the block walls.
The last Slab I made sure the mortar was already underneath.
The trick is having someone remove the straps while everyone else takes the weight of the slab off the hoist and gently place on the mortar. I filled the gaps between the slabs later. I used duct tape under the slab to keep the mortar from falling out.
Take your time and adjust to make it square. Good luck!
Make sure you put the correct parts on
I downsized mine by 6 inches in length and 1 inch in depth (using more rebar). They are still heavy but we managed at 2 people and a dolly
Welcome to the forum! Another possibility: when I cast my slabs, I put the forms on 2x4s before adding any concrete. I can understand why you were perplexed about the forms being flat on the garage floor. If you found yourself there, it would be possible but not fun to drive some wooden wedges under the form; just enough to get some space for something like a handtruck to slip in.
For that matter, getting the handtruck shelf in position and then driving it under with a hammer would work (on the shelf frame, not the axle!), but you might not want to do that if you’re renting the handtruck.
Good luck with your oven!
I wished I would have put mine on 2x4s also! But thank you for the tip. I wonder if my handtruck (it’s the appliance type) would work with the lip being so small. Will gauge and see if that’s doable. Thanks for the tip!
How did you get the slabs to rest of a couple of boards when removing the casting? Did you use wedges to get underneath the slabs?
Welcome Tom! It sounds like you had plenty of help available, which is great! An engine hoist would be a great machine for this purpose. The materials lift that some of us have used is great for getting the slab up to level, but then you need strong and agile helpers to move it horizontally.
I think this is the part that is perplexing @Tum. His slabs were cast atop a concrete garage floor, which would mean no gaps or clearance to get a purchase on the casting and “get it started.” Was that your situation, Tom? Or did you have some kind of clearance between mold and floor before you added concrete?
I used a large pry bar to lift and slide a wedge under the slab. With the help of my strong son’s we set up to slide two by fours under. Will use a hoist to lift onto place. Would do the lift with five guys but hard to get five together at same time.
The build has been easy so far. Looking forward to that first pizza.
Welcome to the community @tomnsmith!
Pry bar sounds like the ticket. You don’t say it, but I’m guessing you used some kind of block as a fulcrum for the bar. Classic.
Update - I ended up using a crowbar to get enough lift before sticking a combination of dowels + 2x4s underneath each slab. I used an engine hoist to lift it upright enough to get it onto a dolly to transport to my part of the yard where the pizza oven base was. Then I used the same engine hoist to lift the first slab onto the base. Ended up having 4 friends come over and lift the rest by hand.
Did you folks wait for the motor that holds the slabs onto the base (so after step 48) to dry before pouring the insulated cement into the slabs divot? The instructions do not say to do that, but it seems like you should?
In the end, those slabs were no match for you (well, really, the five of you! ).
I don’t think there’s any need. If you are using the Perlite/Vermiculite mixture, you’re not adding a huge load. You might be adding a little more with castable refractory, but I still don’t think that would be enough to disturb it. Your load is distributed pretty evenly across three slabs, and unless you’ve got that stuff at the ready while you’re hoisting your slabs onto the blocks, I think your mortar would already have been compressed and starting to set.
Yes, they were no match for us!
That makes alot of sense about the Perlite/vermiculite mixture not being too huge of a load. I am indeed using that instead of the castable refactory. For the Perlite/vermiculite mix, do you guys fill up a 5 gallon bucket with vermiculite, then mix it with a gallon (i’m just going to eyeball 1/5 of the 5 gallon bucket) into another container?
Yes, sort of. First, I’d consider using Perlite because it’s a little less expensive and more importantly it does not retain water the way Vermiculite does.
For your mix, if you can get one of those cheap black plastic mortar trays from a hardware store (it looks like the dirty dish tray in a restaurant), you’ll find it easier to mix the ingredients. That would be the “other container” you’re describing.
But yeah, you can kinda eyeball this a bit. Or, you can use an empty gallon milk jug, cut off the top, and voila! take five scoops of the Perlite, one scoop of the Portland cement, and you have a proper mix.
That way you don’t risk having too little cement (not enough to hold your mix together), or too much (not enough insulation under your hearth).