Hemp Plaster

[TheForge]

I know this has been mentioned often in the past on here but I'm interested in experimenting with hemp lime plaster on the interior of our exterior walls to try and add some insulation/thermal mass. Having removed cement render from the bottom half of these walls we are left with bare stone ready for replastering and wonder if the addition of hemp really does give any benefit over lime and sand alone.

I'm aware of the basic idea involved but wondered if anyone has any practical experience of using it as a plaster?

What lime is best to use, what ratios is the best mix, have you noticed any improvement in thermal efficency, how thickly did you apply it? How many coats?

Also where Is the best value source of hemp? Will the shiv used for horse bedding work for rough work/ base layers? I'm not really interested in pre mixed commercial solutions with additives etc as they are so over priced.

I know there is much hemp cultivated in the Yorkshire area and I've been in touch with a couple of farms already but does anyone have any recommendations?

Ultimately is the cost worth the effort against the benefits?

Any advice, ideas or opinions would be greatly appreciated!

 

[skier-hughes]

Our plasterer added hemp to our first haired coat to add a bit more insulation, but is now not recommending it, as it ca rot in situ.
Our bathroom is not having it.

 

[middi]

Are you sure that the hemp growers you know are not growing it for " SMOKING " purposes. :wink:

Middi

 

[lou]

I am no expert so we had our stone and rubble farmhouse professionally plastered internally with hemp, partly to improve the insulation and partly because the builder had experience of it before. It didn't all go smoothly and I'm not really happy with the finish we got. In fact I have had to hassle the builder into putting another finer lime plaster over the top in the two older rooms (which I felt deserved better). The scratch coat and top coat were VERY thick and I think this has contributed to excessive water retention internally. Some of the walls are still not dry after about 3 months, and though I acknowledge that water ingress from outside had probably been stored in the walls for many years, I think that the inch+ thick hemp plaster was just too thick. Also, the finish reminds me of woodchip so go easy on the amount of hemp in the plaster. If you are prepared to put 5 or 6 coats of limewash on top of the hemp, it will smooth it all down so you don't see the 'bits' but this is time consuming and, in our bedrooms with high ceilings, nearly impossible. I'm sure it can work fine depending on the amount of hemp used, the thickness of the coats and the final finish.

 

[Zebra]

I agree about the woodchip effect. You can use a different top coat on it though. I'm using it as a base coat on laths, with a lime and sand mix over the top. You scratch the hemp coat when its still wet, and apply the second/top coat while it's still green, i.e. a few days later.
No idea about mixing it yourself, I've been buying it ready mixed. And I can't really comment about its thermal effects, as it's an internal ceiling I'm using it on.
Sorry that's not more help.

 

[Feltwell]

If it's a not a daft question, my stripey friend......

Why use hemp plaster on a ceiling? Is it on the first floor and it's fixed directly to the rafters, i.e. not possible to insulate above?

 

[skier-hughes]

Our hemp coat was the first coat, so we went
Hemp/hair/lime plaster
Hair/lime plaster
fine top coat

No woodchip appearance for us.

 

[Zebra]

If it's a not a daft question, my stripey friend......

Why use hemp plaster on a ceiling? Is it on the first floor and it's fixed directly to the rafters, i.e. not possible to insulate above?

Not a daft question, I was going to elaborate in my earlier post, I just didn't know whether anybody'd be interested. But since you ask Feltwell, I did it just because I'd bought a few bags to try and had them hanging about, and I thought it would make a good base coat - I don't need the thermal insulation value, it's a downstairs ceiling, but it's really good strong stuff, seems to hang on the laths really well, is easy to do, seems to be able to take a fair bit of flex when I'm jumping about in the bedroom upstairs and the whole ceiling shakes, and is made from renewable material so is a bit greener too. No reason really!