Cheap lime plaster basecoat

[James34347]

I’m not totally sure since some areas are pretty flat and only need a minimum coat, which I think is about 10mm. Some areas are going to need up to 30mm of filling to get 80% contact with a 1m^2 board.

Once I’ve got the first coat on, maybe I can just build up the areas that need it, without further coats over the whole wall.

 

[aockenden]

Thats really interesting. What ratio of clay to sand did you use? How did you mix it?

Use typical cob ratios which are like 1 part pure clay to 2 or 3 parts sand plus 1 or 2 parts straw. My clay plaster work has been slightly more experimental. I have a thread on it in the project section (clay charcoal plaster). We mixed it by foot-stomping all the raw ingredients together on a large tarp laid on the ground. This method is typical in modern cob-building circles.

 

[James34347]

Will this--- Blue circle hydrated lime mixed with sharp sand do instead of NHL?

Blue Circle Hydrated lime, 25kg Bag | DIY at B&Q

Blue Circle Hydralime is a hydrated lime used for increased plasticity & cohesiveness in cement, mortars & renders

www.diy.com

In terms of NHL 2 vs NHL 3 which would be the preferred option.
It appears NHL 2 is more flexible and breathabl than NH3 but less stronger and takes longer to set and strength is less compared with NHL 2.

In terms of mixing NHL with sharp sand can this achieved using the traditional method of mixing plaster-electrical plaster mixer hand held machine?

Thanks

My understanding is that the hydrated lime that builder’s merchants sell is not able to set when just mixed with sand, you need Portland cement to cause it to set.

I might be wrong though, I’m not an expert, and I don’t understand the chemistry involved.

 

[aockenden]

My understanding is that the hydrated lime that builder’s merchants sell is not able to set when just mixed with sand, you need Portland cement to cause it to set.

I might be wrong though, I’m not an expert, and I don’t understand the chemistry involved.

Nahhhh, idk why that idea has taken hold. Probably because the bags themselves tell people not to use it except for a plasticizer additive to Portland mortars.

As long as it’s a fresh bag and hasn’t carbonated in the bag as powder by being left in a high humidity place for too long then it should carbonate / set just fine.

 

[James34347]

Nahhhh, idk why that idea has taken hold. Probably because the bags themselves tell people not to use it except for a plasticizer additive to Portland mortars.

As long as it’s a fresh bag and hasn’t carbonated in the bag as powder by being left in a high humidity place for too long then it should carbonate / set just fine.

Hmm, so could I just use a hydrated lime mix, 3/1, for a base coat, instead of NHL. I guess hydrated would be non-hydraulic?
Would there be any performance advantage/disadvantage over an NHL 2?
Thanks

 

[a twig]

More likely to die of boredom waiting for the hydrated lime to go off?

Hydrated lime will have a slight improvement in breathability and will be a bit more flexible so able to cope with movement.

NHL “sets” quicker so allows you to blat on through the work, personally I’ve always got better looking results with NHL but that’s probably down to my “informal” education to plastering

 

[aockenden]

Hmm, so could I just use a hydrated lime mix, 3/1, for a base coat, instead of NHL. I guess hydrated would be non-hydraulic?
Would there be any performance advantage/disadvantage over an NHL 2?
Thanks

Yes that should work fine. Might consider adding some fiber into the mix. Hemp works, horse hair, goat hair, sheepswool, or synthetic poly stuff. As Twig said, it won’t set as quick as the NHL but it’ll be a touch more breathable and flexible than NHL.

 

[Lacan07]

This may have already been discussed further back in the thread but hydrated lime needs to be made up into lime putty before use, mixing it in powdered form is generally not a good idea. In this regard NHL might be considered easier.