Perilite concrete not setting up--normal?

[BarryKeith]

I have had a great time with this project. My boys are 16 and 17 and talked me into building a smoker and a grill on each side (in firebrick) and setting my pizza oven in the middle. What a great way to spend time with my boys. We went to set my insulating concrete layer and after 3 days it is still soft. Is this normal. We used 5:1 mixture of perilite to concrete and when a peices brake off it is wet on the underside. Do I need to let it set longer? It has been in the 60s to 70s as a high. Was I suppose to add anyting to the mixture? I can't see this being effective for the outer layer of insulation, but I already bought the perilite. ANy help or ideas?

[Neil2]

"5:1 mixture of perilite to concrete "

Perlite to cement. Keep it damp and under cover for a few days and see what happens. It will always be a bit "crumbly" on the surface.

[BarryKeith]

I used sakrete(concrete mix) from home depot, 5 parts Perlite to 1 part sakrete. Is this wrong? Should I have used something else?

[Raffy]

I agree with Neil. Give it time to set but keep it hydrated for it to cure properly. Perlite on the surface has a tendency to chip off. It happened to me too. DOn't worry too much about it. The fireclay mixture will help smoothen the uneven surface of the perlite for you to lay the bricks on.

[BarryKeith]

I have researched the difference between the concrete and cement. I feel like an idiot. Do you think that the perlite and concrete will set up and be useful or should I scrape it off and go again with perlite and cement?

[BarryKeith]

Raffy,
Thanks, I was typing while you responded, Sorry. I feels almost wet to the touch and when I chip a peice off (which is not hard to do) it feels wet. How long should I wait?

[Tscarborough]

The amount of water required to mix perlite and cement is very high in relation to what is required to actually hydrate the cement. I also noticed that it required a long time to dry. It will always be soft and crumbly, but the water will dry out.

[tfasz]

Mine took a while to setup. I think I mixed it too dry, and every day I would spray about a liter of water over it. After about a week or two I could actually stand on it without a problem. I'd wait a bit more and see if it has strength - you just want to make sure it can hold up the weight of the oven.

Even if you do have to redo it, at least it is a really in-expensive mistake to make.

[BarryKeith]

I need to have little patience. My boys are begging me to be able to go out in the dark and take the pick axe to it. I just want to make sure that it is going to work. I would hate to build the oven and have it not work.

[Tscarborough]

The bottom line is that 3 or 4 days will put it at 75% ultimate strength. No need to wait to continue with the build. I placed the perlcrete on Saturday and wet-laid the floor the next day, soaked though the perlcrete was. I did leave the crappy wooden forms for the perlcrete on so I wouldn't destroy the edges, though.