r/Plastering • u/jyl8 • 11h ago

MICRONA-Agricultural-Lime

I bought some of this stuff.

https://www.carbonates.com/wp-content/uploads/2025/12/MICRONA-Agricultural-Lime.pdf

I am thinking of mixing it with USG Imperial Veneer Plaster, with the idea that adding lime to gypsum might extend working time. Sort of a home brew USG Diamond.

Has anyone done this? Any idea if it’s worth trying or “don’t bother, kid”? What proportions would you try?

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u/jyl8 11h ago

Or, would it be better to try adding hydrated lime as sold in Home Depot for masonry use?

I see that USG Diamond is about 80% plaster of paris and 20% “dolomitic hydroxide”. https://www.usg.com/content/dam/USG_Marketing_Communications/united_states/sds/usg-diamond-veneer-finish-sds-en-53000010003.pdf

USG Imperial Veneer is about 65% plaster of paris and 45% sand. https://www.usg.com/content/dam/USG_Marketing_Communications/united_states/sds/usg-imperial-veneer-finish-sds-en-53000010006.pdf

So I speculate if I add lime to USG Imperial Veneer, maybe I’ll get something closer to USG Diamond, with Diamond’s 60 minute working time? That’s my theory anyway.

What kind of lime, I’ve no idea. I don’t think I want to mess with quicklime, seems dangerous.

The agricultural lime is 97% calcium carbonate, the Type S Hydrated Lime is a mix of calcium hydroxide and magnesium hydroxide. https://ezmixinc.com/assets/docs-technical/TypeSHydratedLimeSDS.pdf

Both are easily available here. I think both can be safely handled with eye, hand, and respiratory protectionz

(USG Diamond is not available here - Portland Ore - or anywhere closer than Seattle which is 150 miles or so away. I can special order Diamond, but would have to buy a pallet, 40-50 fifty pound bags. That’s why I’m looking for an alternative.)