Vermicrete concerns

[franciscocb]

Hi guys, I just poured yesterday the vermiculite cement mix, at 10 vermiculite:2 cement:3 water (5:1), at FIRST, but noticed it was crumbly and maybe needed a little more water, so I added maybe another part of water to the ratio to make it 5:1:2, but it still kinda looked the same consistency, so I ended up pouring the 2.5 in layer. Woke up today, quite sunny and whats on top looks too dry and incredibly crumbly.

On top of the 2.5 in Vermicrete will be a 2 in FB, then a 1.5in refractory concrete to add thermal mass, and then the fire bricks (Allan Scott style inspired oven).

Should I just let it stay that way for a while, or should I mist it with some water? or should i pour a little bit of a new mix of vermicrete with more water on the top?

I feel like I messed up, 1st time doing it.

[SableSprings]

Hi guys, I just poured yesterday the vermiculite cement mix, at 10 vermiculite:2 cement:3 water (5:1), at FIRST, but noticed it was crumbly and maybe needed a little more water, so I added maybe another part of water to the ratio to make it 5:1:2, but it still kinda looked the same consistency, so I ended up pouring the 2.5 in layer. Woke up today, quite sunny and whats on top looks too dry and incredibly crumbly.

On top of the 2.5 in Vermicrete will be a 2 in FB, then a 1.5in refractory concrete to add thermal mass, and then the fire bricks (Allan Scott style inspired oven). Should I just let it stay that way for a while, or should I mist it with some water? or should i pour a little bit of a new mix of vermicrete with more water on the top?

I feel like I messed up, 1st time doing it.

The mix is correct but sometimes overmixing or how the water is added can cause the Portland to "rinse off" the insulating particles of perlite or vermiculite. (Also, I'm assuming you were doing these portions by volume not weight.) You are correct, the picture of the vcrete doesn't look right. there should have been some "sticking" between vermiculite pieces with the Portland Cement component. The good news is that the 2" of CaSil insulation board is adequate for the base of the oven. Vcrete does take much longer to cure than mortar or concrete and is crumbly even when done correctly. It's the compression strength that's important and 5:1 will support the footprint of a WFO. After a week, dig into a corner a little and see if you start seeing a matrix that holds together. If that is the case then I'd mix a little mortar up and put in a perimeter band about 2-3" wide to contain the loose vermiculite. When you set your 2" FB on top, you'll be ready to start planning the dome & cooking floor build steps. Because the vcrete is crumbly, you should be planning on leaving your forms in place until ready to enclose the base layer(s) with your perimeter & cover materials...you don't need to be knocking off corners and edges of the vcrete while you're working on the rest of the oven.

Don't add more water to the existing vcrete, it's tough enough to remove at the recommended hydration level. Also, did you drill any weep holes in your top slab? This would be your last chance to do so if you haven't.

Hope that answers your question(s).