pulverizing a lava rock--gunny sack, hammer and wail away. When you mix it with your crete treat it as you would the sand or peat. Haven't tried this but it might work. Safety first goggles and gloves.
Paws

Serene in a Z4 it's not likely your planters will last unless you protect them from winter freeze thaw.
As the peat rots it allows more water into the tufa creating winter problems
My concrete experts tell me that the key to longevity is to keep the moisture out of the concrete during the winter.
Lava rock being porious probably won't fair much better than peat in that regard.

Sereneseen, I didn't know that Tufa deteriorates after about 10yrs. Is that only in areas with freeze/thaw cycles?
ie, is the deterioration due to damage from frozen water in the body of the Tufa, or will it start to break down at that age anyway?
Tufaenough..., have your concrete connections ever mentioned the use of concrete admixtures, such as accelerators, silica fume, fly ash, water reducers, (superplasticizers), etc, in hypertufa? Or is that like pouring champagne on Weeties?
Like to know if the benefits apply to Tufa, or if it's a case of overkill,
Thanks,
Slate

Hi Slate
Any thing that helps reduce water makes for stronger tufa.
But as long as we add peat, vermiculite by ther nature they will make our projects porious, fly ash and silica fume won't help much with that.
If water can get in and freeze, the tufa is not going to last.
I'm trying to reduce water damage by making many projects that will remain outside in two layers. A thin stronger water proof layer of concrete on the inside. Then apply the decorative coat on the outside. This works well when forming on the outside of molds.
I don't know if it will make any difference but it's all fun. It's all tufa and it's fun to experiement.:)

I've used black lava. Pulverized in a rock crusher, screened and sorted to various sizes. I would not recommend pulverizing by hand unless you have a lot of time. A large bag of lava rock does not yield very much when reduced to smaller sizes.

Slate1, I read on this forum in the thread "Does peat moss degrade" that objects made of organic substances such as peat moss will eventually degrade. Here is the link to that topic: http://forums2.gardenweb.com/forums/load/hypertufa/msg071628493892.html?5

Serene

Serene,

I have projects I did over 10 years ago and they show no signs of deteriorating. They are still going strong. I just finished carving designs on one and it was still hard as a rock. However we don't have much of a freeze problem here. This could make a huge difference.

Amy

Tufaenough, thanks for the info.
Serene, thanks for pointer to that thread.Interesting.
I guess I'm lucky we don't have freezing problems here.
Slate