cure time

[Adrianvip]

How long do I have to wait before I can start laying bricks on top of a 5 to 1 perlite floor? I understand that the cure period is 28 days but can i start before that?
Also perlite floor needs to be spray few times a day during the cure period as the regular concreate?

[david s]

Because the vermicrete or perlcrete layer requires so much water in the mix there is way more than is required for the hydration process. Also as it takes weeks for it to dry naturally there is no need to add any extra water to assist damp curing. If extra water is added it will have to be removed or the insulation properties of the slab will be drastically reduced.Attached is an experiment I did re drying of vermicrete slab.
Vermicrete insulating slab copy.doc.zip

[Adrianvip]

Thank you for the info. So you recommend to wait at less 28 days before I start to build the dome? I'm planing to build a 5X5ft internal barel dome and I'm afraid that the perlcrete may not hold the weight. It feel so soft.

[UtahBeehiver]

5 to 1 is correct ratiuo under the floor. It will harden up and give you the required strength. Don't rush it, one you cover it with fire brick it will be that much harder for the mechanical water to evaporate out. Is there a particular reason you are doing a barrel? Have you read the eplans from Forno Bravo? They talk about radiant heat efficiencies of different shape ovens, dome shape being the most efficient. Barrels are not easier to build and may require buttressing of the side walls depending in size and design of the barrel.

[Adrianvip]

I try to decide between dome and barrel for a few days. The only problem with the dome is that I can't figure out an easy way to keep the bricks in place while I lay them. I was looking at a yoga ball but the bigest I can find is 3ft and is to late now since I already have the floor. Also I would like to use it to roast piglets and bake bread. I understand that barrel it's more recommended and easy to build.

[UtahBeehiver]

You need to download the "FREE" Forno Bravo eplans and study them.