Cork lime plaster experience?

[irishcottagerestoration]

As I sort-of hijacked and resurrected the original thread the first time, I’ll assume this is directed at me and not the OP. The plaster has been great for us, however believe it or not we still haven’t done the finish coat anywhere in the house! The wall temp to the touch is dramatically improved and overall the rooms feel notably warmer where we’ve done this (vs the rooms which we haven’t done yet). Drying time and the hard work mixing the insulating plaster are the biggest drawbacks. Careful using it in places where there is perpetual moisture as the bioaggregates like hemp / cork can start to mold if the wall is too slow to dry.

We had a minor spot of that near the bottom of one wall where a plastic underfloor DPM retrofit laying under a poured-in cement floor keeps the bottom of this wall slightly damp from moisture migrating out from underneath the plastic. Small patches of rusty orange mold appeared after that corner still hadn’t dried out 100% a month after application. So I ran a dehumidifier and small space heater in that corner, finally got it thoroughly dried and the mold has now died and faded and the plaster in that corner is now staying bone dry without any heater or dehumidifier help.

Everywhere else it fully dried out within 2-3 weeks and had zero problem. If I were doing it again, in any areas with some persistent moisture issues I would just swap the cork for perlite.

That's good to hear! did you end up using the quicklime in the end or did you finish it with hydrated? Any difference between the two versions over time?

 

[aockenden]

That's good to hear! did you end up using the quicklime in the end or did you finish it with hydrated? Any difference between the two versions over time?

We make putty from either quicklime or hydrated lime (I’ve still got a bunch of bags to work through, but if I were doing it from scratch I’d stick with hydrated, provided you’re sure it’s fresh stuff, as it’s much safer to work with). And then we mix by volume 2 parts whatever insulating aggregate we are using for the specific use-case (hemp, cork, perlite, charcoal etc), with 1 part lime putty, and some water to make our batch.

 

[mrtomgraham]

I am so pleased to have discovered this thread and have just signed up here off the back of that.

I've just been using some Diathonite (off-the-shelf thermal cork, diatomaceous earth, lime plaster). Really sad to discover it's full of polypropylene fibres. But it got me thinking that a DIY approach might be quite possible. Evidently it is! So happy to discover this.

How thick did you apply in few end? And how thick do you think it would go? Have you ever tried to work out the thermal performance of the wall buildup?

Finally, did you entertain throwing the plaster rather than pressing, to encourage air-entrainment that than compressing?

Thanks so much, Tom

As I sort-of hijacked and resurrected the original thread the first time, I’ll assume this is directed at me and not the OP. The plaster has been great for us, however believe it or not we still haven’t done the finish coat anywhere in the house! The wall temp to the touch is dramatically improved and overall the rooms feel notably warmer where we’ve done this (vs the rooms which we haven’t done yet). Drying time and the hard work mixing the insulating plaster are the biggest drawbacks. Careful using it in places where there is perpetual moisture as the bioaggregates like hemp / cork can start to mold if the wall is too slow to dry.

We had a minor spot of that near the bottom of one wall where a plastic underfloor DPM retrofit laying under a poured-in cement floor keeps the bottom of this wall slightly damp from moisture migrating out from underneath the plastic. Small patches of rusty orange mold appeared after that corner still hadn’t dried out 100% a month after application. So I ran a dehumidifier and small space heater in that corner, finally got it thoroughly dried and the mold has now died and faded and the plaster in that corner is now staying bone dry without any heater or dehumidifier help.

Everywhere else it fully dried out within 2-3 weeks and had zero problem. If I were doing it again, in any areas with some persistent moisture issues I would just swap the cork for perlite.

 

[paulc]

I've just been using some Diathonite (off-the-shelf thermal cork, diatomaceous earth, lime plaster). Really sad to discover it's full of polypropylene fibres. But it got me thinking that a DIY approach might be quite possible. Evidently it is! So happy to discover this.

Polypropylene fibres are just fine in my opinion - Unlike animal hair, fresh lime doesn't break them down, so you can mix a tub of plaster up (using lime putty) and leave for months on end.

 

[aockenden]

I am so pleased to have discovered this thread and have just signed up here off the back of that.

I've just been using some Diathonite (off-the-shelf thermal cork, diatomaceous earth, lime plaster). Really sad to discover it's full of polypropylene fibres. But it got me thinking that a DIY approach might be quite possible. Evidently it is! So happy to discover this.

How thick did you apply in few end? And how thick do you think it would go? Have you ever tried to work out the thermal performance of the wall buildup?

Finally, did you entertain throwing the plaster rather than pressing, to encourage air-entrainment that than compressing?

Thanks so much, Tom

I understand and sympathize with the reluctance to use synthetic fibers for both health and environmental reasons. We add hemp to our cork lime plaster mix as the fibrous material instead.

We applied in 2 coats each of 2 cm. However only the first coat contained granulated cork. This is because the only affordable granulated cork we could find is from Mike Wye and it is of a very large diameter (5 to 10 mm), so it’s too course for the second coat which needs to be floated in preparation for the skim coat. Therefore on the second layer we replace the cork with a finer grained perlite.

I think it’ll go almost as thick as you want it to, provided you do it in 2 cm thick layers at a time and allow each new layer to fully dry before applying the next. Keep in mind, this stuff takes a long time to dry under cold / damp conditions so if you’re having trouble heating and dehumidifying your room then building up a layer thicker than a few cm may take a long time. If you layer the next batch on top before the existing underlying one has dried, you risk exponentially increasing the total drying time and moulding the bio-aggregates (cork, hemp, etc) on the wall.

The only work I’ve done with thermal performance is using a temperature laser gun to measure increases in wall surface temps. We seem to be getting about 2 degrees Celsius of improvement for the total 4 cm of insulating plaster. More dramatic however is the change in the temperature of the wall when you touch it. Bare stone a few feet away from the insulated plastered stone will be extremely frigid to the touch when it’s cold outside, while the insulated plastered sections are basically a comfortable temp. It FEELS like about 5-10 degree difference in temp under your hand.

Throwing should work well, a lot of times I used more of a “hard slap” than a firm press when applying. Either works though, don’t overthink it. Just get it on the wall firmly in contact with the masonry substrate.

 

[mrtomgraham]

Polypropylene fibres are just fine in my opinion - Unlike animal hair, fresh lime doesn't break them down, so you can mix a tub of plaster up (using lime putty) and leave for months on end.

It's that 'forever' quality that troubles me the most. As spillage from the bag there's microplastic pollution in site waste, when cleaning tools there's microplastic pollution heading to watercourses and during any future renovation or removal, there's that microplastic pollution in the waste again. Our insatiable use is the reasons there is plastic in our blood and that of most creatures on earth, from Antarctica to the Norfolk Broads. When nature does fibres so very well, I'm keen to use those!

 

[mrtomgraham]

I understand and sympathize with the reluctance to use synthetic fibers for both health and environmental reasons. We add hemp to our cork lime plaster mix as the fibrous material instead.

We applied in 2 coats each of 2 cm. However only the first coat contained granulated cork. This is because the only affordable granulated cork we could find is from Mike Wye and it is of a very large diameter (5 to 10 mm), so it’s too course for the second coat which needs to be floated in preparation for the skim coat. Therefore on the second layer we replace the cork with a finer grained perlite.

I think it’ll go almost as thick as you want it to, provided you do it in 2 cm thick layers at a time and allow each new layer to fully dry before applying the next. Keep in mind, this stuff takes a long time to dry under cold / damp conditions so if you’re having trouble heating and dehumidifying your room then building up a layer thicker than a few cm may take a long time. If you layer the next batch on top before the existing underlying one has dried, you risk exponentially increasing the total drying time and moulding the bio-aggregates (cork, hemp, etc) on the wall.

The only work I’ve done with thermal performance is using a temperature laser gun to measure increases in wall surface temps. We seem to be getting about 2 degrees Celsius of improvement for the total 4 cm of insulating plaster. More dramatic however is the change in the temperature of the wall when you touch it. Bare stone a few feet away from the insulated plastered stone will be extremely frigid to the touch when it’s cold outside, while the insulated plastered sections are basically a comfortable temp. It FEELS like about 5-10 degree difference in temp under your hand.

Throwing should work well, a lot of times I used more of a “hard slap” than a firm press when applying. Either works though, don’t overthink it. Just get it on the wall firmly in contact with the masonry substrate.

This is fantastically useful and encouraging. I'm going to give it a go! I wonder if there's an easy way of granulating the cork pieces further. Will post any updates here. Thanks.

 

[aockenden]

This is fantastically useful and encouraging. I'm going to give it a go! I wonder if there's an easy way of granulating the cork pieces further. Will post any updates here. Thanks.

Yeah possibly, though it doesn’t crunch so you can’t stomp it. It just squishes / compresses and then rebounds. Maybe a mulching device or grain grinder. It’s a lot of faff though.

You can buy smaller grinds from other cork suppliers but it’s too expensive to be worthwhile really. Good luck with your project.

 

[mrtomgraham]

Yeah possibly, though it doesn’t crunch so you can’t stomp it. It just squishes / compresses and then rebounds. Maybe a mulching device or grain grinder. It’s a lot of faff though.

You can buy smaller grinds from other cork suppliers but it’s too expensive to be worthwhile really. Good luck with your project.

And to be clear, there's nothing wrong with using quicklime produced putty is there, from your point of view, with aggregate added once cool? It seems cheapest and slaking is fun!

On the cork aggregate, I assume one would want the expanded stuff rather than just crumbled, unprocessed stuff? I imagine anywhere that sells cork insulation would have the granules too.

And finally, the hemp, what length of shiv were you using? Thanks for your responses so far. Really useful.

 

[aockenden]

And to be clear, there's nothing wrong with using quicklime produced putty is there, from your point of view, with aggregate added once cool? It seems cheapest and slaking is fun!

On the cork aggregate, I assume one would want the expanded stuff rather than just crumbled, unprocessed stuff? I imagine anywhere that sells cork insulation would have the granules too.

And finally, the hemp, what length of shiv were you using? Thanks for your responses so far. Really useful.

Yes nothing wrong with it, and it will be slightly cheaper than buying hydrated lime. However I do question whether it’s worth the extra risk to health and safety due to quicklime’s extreme reactivity. Slaking is fun, but it’s also a bit dangerous. You’re call though.

I’d have to check if my cork is expanded, but it probably is yes. And yes that expansion processshould make it a better insulator.

The hemp shiv length is probably about 1 cm. I can’t imagine it’s too important tbh though.

 

[a twig]

I wouldn’t go more than 1cm on the hemp as I found it was fairly hard work moving it about on the wall and getting a flat finish at that sort of length and I’d imagine going longer makes it progressively harder / more difficult…

 

[aockenden]

I wouldn’t go more than 1cm on the hemp as I found it was fairly hard work moving it about on the wall and getting a flat finish at that sort of length and I’d imagine going longer makes it progressively harder / more difficult…

Oh you mean length of the hemp fibers, not the thickness of the plaster, right?

 

[a twig]

Sorry wasn’t a very clear post but yep meant length of hemp fibres - the shorter they are the easier the plastering is

 

[mrtomgraham]

All useful stuff! Thanks.