Perilite concrete not setting up--normal?

[Rocko Bonaparte]

Re: Perilite concrete not setting up--normal?

I'm going to commit some thread necromancy here because this thread contains a lot of the problems I'm experiencing right now. I made a 4" slab mixing 4 cubic feet of perlite to 2 80lb bags of concrete, and I got something that crumbled apart when I went to lift it up into place. Where I grabbed it in the corners, it simply broke off.

I had mixed it the consistency similar to just-palatable oatmeal and it seemed to pour all right. I had waited 2 weeks since I was building the foundation and walls for it last week. The chunks that broke off showed no moisture. It just had no structure to it at all. The rebar inside didn't help at all either.

So I can see here I needed to use cement . Of course now it's the weekend and it's very difficult to find perlite or vermiculite. I may succeed and pour again tomorrow.

What I am wondering is if anybody has tried to make a slab like this. I leveled out my firebricks under sand to make a base, dropped an old shower curtain liner over it, dropped down a frame over that, and poured the mix into this. The idea was then I could pull a few bricks out of the corners and get four pairs of hands into each corner, lift it up, and drop it onto my cinder block walls with a little mortar waiting to go.

[BarryKeith]

Re: Perilite concrete not setting up--normal?

After tearing out the old I was happy I did. We set the new cement and it looks like everyone described it. It is setting up much better. Thank you all.

[130mountainside]

Re: Perilite concrete not setting up--normal?

I used concrete and it never really set up. I trashed it and used the board for insulation. Good luck

[Neil2]

Re: Perilite concrete not setting up--normal?

"(my dome is on top of my floor, not around it)"

So is mine. For what its worth, I think this a better arraignment when using vermicrete - the weight is transferred a bit more evenly. Also, you don't have to do all the precision cutting of the hearth bricks. The downside is that , although possible, replacing or removing the hearth bricks that go under the wall is more difficult.

[egalecki]

Re: Perilite concrete not setting up--normal?

Also remember that the texture is unlike anything you're used to! It won't ever set up like "real" concrete. The best description is like cork. It's quite strong in compression, but not if you chip at it. I used cove base as my form for the vermicrete under my dome,and then left it in place while I built, so it didn't get nibbled away by accident (my dome is on top of my floor, not around it).

[Neil2]

Re: Perilite concrete not setting up--normal?

"Should I add anything to the vermiculite cement mixture."

No. Remember to hand mix gently to avoid breaking down the vermiculite particles. Once poured,you can start building on it after a couple of days but keep it continually damp for at least a week .

[Raffy]

Re: Perilite concrete not setting up--normal?

Well thank you all for your advise, I am going the safe route and tearing out the old and relaying a new vermiculite to "cement" mixture. Question so I don't have to tear out another one, do I just add 5 parts vermiculite to 1 part cement? Do I add anything else?

Also with the homemade mortar is it 1 part fire clay to 3 parts sand to 1 part lime to 1 part portland cement? It is portland cement and not a mortar mix?.?

I feel dumb asking, but not as dumb as I felt ripping out the old.

Yes all the proportions are correct.

[BarryKeith]

Re: Perilite concrete not setting up--normal?

I agree cuz once it's in it's in, Should I add anything to the vermiculite cement mixture.

[egalecki]

Re: Perilite concrete not setting up--normal?

The homebrew recipe is in the plans online- I can't remember it offhand. And yes, it's portland cement, not a mortar mix.

I'm sorry you had to take it out, but it's best to be right from the ground up, much easier to fix it now than be sorry later....

[BarryKeith]

Re: Perilite concrete not setting up--normal?

Well thank you all for your advise, I am going the safe route and tearing out the old and relaying a new vermiculite to "cement" mixture. Question so I don't have to tear out another one, do I just add 5 parts vermiculite to 1 part cement? Do I add anything else?

Also with the homemade mortar is it 1 part fire clay to 3 parts sand to 1 part lime to 1 part portland cement? It is portland cement and not a mortar mix?.?

I feel dumb asking, but not as dumb as I felt ripping out the old.

[Tscarborough]

Re: Perilite concrete not setting up--normal?

The need and the reason is to get a perfectly level floor. I also do not recommend doing the dry set then wet method, if you are going to use a hydrated cementious mortar, vigorous mixing is required, not optional.

[dmun]

Re: Perilite concrete not setting up--normal?

What is the consistency of the fireclay/sand mixture under the firebrick floor?
Ratio of sand to fireclay?

You can do it one of two ways. The ratio is 50/50 for both. You can mix up the leveling mixture with water to the consistency of quickset, and put it on with a notched trowel, like you were laying floor tile. The notches let you push some bricks lower for floor leveling. Alternately, you can put the mixture down dry, arrange your floor bricks the way you want them, then wet the floor to solidify the leveling mixture. Both ways work fine.

There's no real need to mortar down your floor bricks. It makes it difficult if one is damaged and needs replacement.

[dmun]

Re: Perilite concrete not setting up--normal?

when mixed should it be the same consistency as if I was pouring a sidewalk or patio?

It's nothing like regular concrete, it won't flow, it won't float a smooth surface, and it takes days and days for it to get anything like hard. It never gets much more rigid than cork. You mostly want just enough water so there's not any sitting at the bottom of the mixing tub. The vermiculite/perlite absorbs a LOT of water. Everyone who works with it remarks how weird it is.

[Tscarborough]

Re: Perilite concrete not setting up--normal?

Yes, there is no direct flame to the setting bed and even if it cracks it won't matter. I mortared, some float it.

[Derkp]

Re: Perilite concrete not setting up--normal?

No fireclay in the leveling bed, correct? Just mortar.