Insulating Hearth Too Big, no room for anchors

[Chris]

I poured the insulating hearth for my Pompeii yesterday. The perlcrete does not seem to be set yet. It's covered in plastic, and still damp. I used about an 8 to 1 mix. I ran out of perlite at the end, so the rear corners are a little shallow. That's ok, since the oven won't cover that part.

I'm thinking I could have blocked out all of the corners, and the landing at the front of the oven, to save on perlite, but I'd have to fill the landing with something in order to get the counter up to the level of the hearth bricks.

My real problem is that I'm concerned that the anchors for my gable house enclosure will not hold in the perlcrete. Even the parts that are starting to harden seem very crumbly. Yet, the plans for the Pompeii and the instructions for the Artigiano (and others?) indicate anchoring directly into the perlite/vermiculite layer.

If I would have read this thread I would have known to bring the forms for the perlite layer closer in, to allow for anchoring the walls.

I might be able to use the grinder or a chisel to knock off some of that perlcrete once it sets up if I can't get the anchors to hold.

-Chris

[DrakeRemoray]

You might be able to drill through the perlcrete and into the structural concrete and put in some kind of expanding bolt.

Drake

[maver]

anchors

I drilled into my structural concrete on the sides with a rotary hammer and used anchors in the side to support a horizontal metal stud (actually used a half stud) that the walls rested on. You can see a bit of this in my attachment. It changed the way I thought I was going to do this, as most steel stud framing I had seen here was with the studs bolted down on the top of the concrete layer.

[Chris]

Good idea, Maver. I'll be going up to the level of the block stand with limestone blocks, then stucco above that, so I'll have plenty of room to work. I might put a countertop on the front and one side, if I can figure out how to fit it in.

[captain]

captain

I just posted similar resuts with my harth I think I am going to drill through the vermiculit into the concrete then apoxy a threaded rod in place with a washer and nut like ancohring a sill plate to a foundation.

[maver]

That should work, but so might conventional plastic concrete anchors, although you may need a longer screw than normal and a metal washer to avoid pulling through the metal stud.

[Chris]

Re: Insulating Hearth Too Big, no room for anchors

An update...

Here's how I anchored the steel frame.

I snapped a chalk line to give me about 5 inches of perlite insulation from the hearth brick to the inside surface of the future wall. Then, I used a wide putty knife and a hammer to cut out blocks of perlcrete. The blocks came out easily, and will come in handy when filling the enclosure with loose perlite.





Having exposed bare concrete, I used a powder-actuated nailer to shoot 1-inch nails through the steel track and into the concrete slab. It was a lot of fun!

[maver]

Re: Insulating Hearth Too Big, no room for anchors

Brilliant! I'll do that on my next oven.