Harded lyme plaster walls

Have a small Cob  building. I've lyme plastered the walls. With 5 or 6 layers. Very pleased with the results. Looks great and an all white finish. But the surface is fragile. Dings extremely easily. Anyone know what I can do to toughen the surface ? Like the white walls. But willing to change the color if a harder surface is achieved.

I find mixing some wood ash with lime plaster helps it cure faster and harder than plain lime on its own. Keeping it damp while it sets up is important, too. If you can cover it with some muslin or old sheets and mist it a couple of times a day you'll get a much better carbonate reaction and that's what provides the hard skin.

Ray,

What lime recipe have you used?
Were you plastering in hot weather/direct sun?
Were you misting the walls st least once per day for few days per one layer?
How thick are the layers?
Why six of them?

The layers have been very thin, Thinner than milk. Conditions were hot, but total shade. I only misted for a short time after apllying the lyme. Sounds like  I need to continue with misting.

So you just white washed the walls with six layers, not plastered with lime/sand plaster. According to your profile info you are in Georgia, so it's rather (too) sunny and (too) hot for any lime operations at this time of the year. I'm assuming you did it outside.

For anything lime related I recommend high calcium lime, it simply reacts better than dolomitic lime.
Preparing lime putty also helps, because it will assure that the lime got fully hydrated and it's ready for receiving carbon dioxide to form calcium carbonate.
The lime wash mix should be very thin, like milk and not a bit more. If it's thicker then it deposits too thick layer of lime and flakes off - even in cooler temperatures (60 F).
I would not lime wash a wall in direct sun and if the wall is warmer than 70 F.
For lime wash no misting is done.

So if it's powdery, or peels off it means that:
-material was not good (not reactive dolomitic lime or too old lime)
-mix was too thick
-temperature was too high

In sunny/warm climates I would wait for a day/nigh temperatures of 45-60, with completely overcast sun. I it's not overcast I would use shading tarp/cloth/etc,
When I lime wash I use two layers applied with a large brush (4x8") and then do touch ups with s small (2") brush. When I'm done with the first layer, it's usually dry and ready for the second one.

So there are 2 thin plaster layers. Then several thin layers of wash ( like milk). Have been misting the walls a few times each day now. I'll have to check which kind of lyme I have. Not sure ... The air temp. has been in the low 90s. Totally in the shade / inside. So if I continue to mist several times a day for several days will that harden the surface ?

The type of lyme I have is "High calcium hydrated lyme" Anything about this type I need to be concerned about ?

Ray, you have high calcium lime, very good. Are you mixing it directly with water or you prepare lime putty first? I remember, long time ago, I have made limewash with dry hydrated dolomitic lime and it dusted off the surface. When I use lime putty it hardens rather quickly and it does not dust. It would be best if you did it when temperature is around 65 F. Misting in your case may help, but you would need to do it several times per day.

I have several rocks coming out of the wall surface. So there's lyme molded around the rocks. So the rocks are exposed from the wall surface. This is why I'm painting a lyme wash around the exposed rocks. Smoothing out the transition from stone to smooth wall surface. There's a lyme plaster (1/2") under everything.