Toby Newell
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But yes, the gelling might help the bonding, or it might reduce the air spaces within the fibres. Great building material though.
- Thread starter joelpriley
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Once we’ve got a full wall plastered with 40 mm of the hemp + cork and a putty skim layer ontop, I’m going to buy one of those laser thermometer things and see how the surface temp of the insulated plastered wall compares to our walls which are still thickly coated with cement and also how it compares to our bare stone walls. I’d certainly be happy with a 2-3 degree increase in surface temp on the hemp+corked wall.
Toby Newell
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As some have said and I have commented too, the real advantage of limcrete is not the increased breathability, it's the insulative effect of the system increasing internal surface temperature and reducing condensation. Hempcrete works in the same way. It matters not if your material is 100% breathable, you have a DPC and your drains are perfect, if your surfaces are cold you will pull water from the air. 3C would be great, keep us posted.
Does depend on how damp the existing wall is, ie how much moisture needs to escape for the wall to reach equilibrium, it’s not just a function of the moisture in the plaster.
At my place when we did the dampest walls on the ground floor (semi underground) we repointed the outside and re plastered inside, our rule of thumb was 1 month per inch of wall thickness to dry out, although I think others on here have found 2 weeks per inch more accurate for them.
We didn’t attempt to use dehumidifiers or anything though
At my place when we did the dampest walls on the ground floor (semi underground) we repointed the outside and re plastered inside, our rule of thumb was 1 month per inch of wall thickness to dry out, although I think others on here have found 2 weeks per inch more accurate for them.
We didn’t attempt to use dehumidifiers or anything though
Fortunately my walls have already mostly dried out, having been repointed outside in lime 18 months ago. I’m hoping this quicklime goes off in a week or two so I can get on with the next coat… if not I might look at adding a pozzolan to my mix to get it setting quicker.
Sorry, I misunderstood your previous point, between layers then two weeks should be plenty as each layer doesn’t need to be fully dry before the next, just solid enough so that it doesn’t fall off the wall when you add the weight of the next coat.
I thought we were talking about the whole lot drying so that you are getting maximum insulating effect from the hemp.
I thought we were talking about the whole lot drying so that you are getting maximum insulating effect from the hemp.
Ideally it's at least knuckle hard rather than needing to be nail hard before the next coat (you can't dent it easily with your knuckle, but still scratch it with your nail). The more the underlying coat has finished shrinking, the less chance of cracking in subsequent coats though...
And the final insulation gain only comes when the entire wall is fully dry, which is the slow bit once all the plastering is finished. Hemp and cork will both hold onto water longer than a sand aggregate but make the plaster partially self-tending while it carbonates.
And the final insulation gain only comes when the entire wall is fully dry, which is the slow bit once all the plastering is finished. Hemp and cork will both hold onto water longer than a sand aggregate but make the plaster partially self-tending while it carbonates.
Tonight’s progress. Second and third batches of hot mixed hemp lime and cork definitely came out better (less sloppy, much easier to work on the wall), although I think the second batch got too hot and might have actually combusted the hemp? If that’s even possible? I swear some of the clumps of hemp were coated in a grey fine ash-like dust! And it smelled a little smokey as well. I think the hemp all stuck to the bottom and got burned from the lime slaking intensely above it.
Toby Newell
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Boiling alkali will destroy wood as I said, but it usually takes over an hour at 120C under pressure to destroy all the lignin, that's how they make paper. I don't understand why they say to mix the hemp with the hot lime as it will start to dissolve it which will reduce the porosity and thus the insulative properties. Slaked lime can reach 300C that certainly can toast the hemp if it gets stuck in an air pocket.
Ok well tomorrow’s mix I’m going to try pre-mixing the water + hemp + cork together first and then add my quicklime, so hopefully the bio-aggregates stay cooler. If that’s still giving me problems I guess I’ll just slake the lime by itself first then add in all the hemp and cork after it’s cooked, but at that point it seems like I might as well just use an aged putty instead?
Toby Newell
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I have no idea about the real world mechanics, as I said, in hot slaked lime the hemp wood will start to decompose, I am not sure whether this would be bad, or desirable, maybe the gelled exterior of the chivs forms a better bond with the lime matrix. Someone out there should know, someone must have conducted tests. I would of thought the insulative properties might suffer, but I could be totally wrong. Must be fun to mix! Like a large chemistry set.
Lacan07
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Looking good! That stone is lovely but plastering is obviously for the best.
Yes it is somewhat fun but it would be more fun if it weren’t so backbreaking mixing it with a Hoe in a big metal bin…
Yeah it’s always bitter sweet to cover it up, as it does look gorgeous when carefully flush-pointed and brushed back. But having a warmer, more energy efficient building has to take precedence for us.