Bonsai Study Group Forum

General Category => General Bonsai Discussion => Topic started by: jlushious on October 03, 2014, 11:23 AM

Title: Expanded Shale
Post by: jlushious on October 03, 2014, 11:23 AM
I can't find a good answer on this so I thought I would ask here, is there a difference between expanded shale and pumice? And if there is a difference, is expanded shale a good option for a soil component instead of pumice? Just trying to get clarity!


Title: Re: Expanded Shale
Post by: gaitano on October 03, 2014, 08:45 PM
I use both (not together) for the same component in my mix. The pumice I get is generally smaller in size and the shale is a bigger sized particle, cheaper and easier to find. I use the pumice for the more refined trees and the shale for those that are still in the beginning stages of development. I don't know for sure, I it would venture to guess that pumice would be the better of the two in terms of overall performance.
Title: Re: Expanded Shale
Post by: jlushious on October 04, 2014, 04:18 PM
I am looking to replace my turface with pumice and I just can't get it here, but I found a place with expanded shale in the right size so am wondering if it's an ok replacement for turface.
Title: Re: Expanded Shale
Post by: 0soyoung on October 04, 2014, 08:07 PM
I am looking to replace my turface with pumice and I just can't get it here, but I found a place with expanded shale in the right size so am wondering if it's an ok replacement for turface.

Turface MVP (the brand name stuff) is calcined clay. Pumice is natural calcined clay (calcined by lava/magma). The difference likely is in the grain size. The Turface MVP specification for grain size is around the ideal 2mm, but abut 24% is significantly smaller (maybe you sifted to get rid of the finer stuff, though it has not caused any problems for my trees).
% Retained
6 MESH (3.36 mm) 11.5%
8 MESH (2.38 mm) 35.6%
12 MESH (1.68 mm) 29.0%
20 MESH (.841 mm) 23.1%
30 MESH (.595 mm) 0.6%
40 MESH (.420 mm) 0.1%
Pan 0.1%

IMHO, it doesn't matter a whole lot what the inorganic medium is, as long as it is has about a 2mm particle size - larger holds less water but is more aerobic (watering habits may need to be adjusted). The medium only needs to be hydrophilic. Hydrophobic materials like wax or glass beads is ngf.
Title: Re: Expanded Shale
Post by: Markyscott on October 05, 2014, 09:54 AM
I am looking to replace my turface with pumice and I just can't get it here, but I found a place with expanded shale in the right size so am wondering if it's an ok replacement for turface.

Hi Jodie -

Here in the US, the commonly available expanded shale product is branded Haydite. I prefer it over Turface because Haydite can be obtained here in a more acceptable size fraction.  But be aware that equivalent size fractions of haydite and turface of not have the same moisture retention (haydite holds less water).  I prefer pumice over both of these products if I can get it.

As an aside, here are the differences between pumice, turface, scoria (often called lava rock), and haydite.

Calcination means to heat (a substance) to a high temperature but below the melting point, causing loss of moisture, reduction or oxidation, and the decomposition of carbonates and other compounds.  Calcined clay is processes from mined clay minerals (hydrous silicate minerals arranged in sheets) - usually a kaolin group mineral called montmorillonite - ground and flash heated to a temperature of about 650 deg C.  The products are then ground and sieved to the size fraction needed for the application.

Expanded shale can be processed from clay, shale or slate.  It is crushed and then exposed to high heat (about 2000 deg C) and cooked for a period of time, they expand like popcorn into a very hard rock that is very porous and light weight. So it's kiln fired like a ceramic. There are many names used for these products such as Haydite, Buildex, Expanded shale, etc. depending on the source material and where you live.

Pumice and scoria are naturally occurring volcanic rocks. They form during an eruption when lava is erupted, quenching the molten rock to a glass (no minerals have time to form). As it is rapidly cooled, the tiny air bubbles trapped inside the lava when it turns into glass are preserved, making it quite lightweight with lots of large, internal pores.   Pumice and scoria are differentiated by density alone - pumice is less dense than water and scoria is more dense.  Perlite is a man-made pumice. They start with volcanic glass and flash heat it to high temperatures - trapped water rapidly expands forming the perlite.

Title: Re: Expanded Shale
Post by: jlushious on October 05, 2014, 11:19 AM
Thanks folks, I am in a dry windy climate and so need the extra moisture retention. I had emailed a place about pumice and they got back to me about expanded shale which is why I was so confused. This clears it up!
Title: Re: Expanded Shale
Post by: augustine on October 06, 2014, 09:41 AM
I buy pumice in my local farm supply store under the product name "Dry Stall." It is used to absorb floor moisture in animal stalls. I pay about $19 US for 40 lbs. It is very dusty and needs either screening or squirting with a water hose. (In my exp, the hose works much better.

There is another product called "Stall Dry" which is processed wood chips and not suitable for our purposes.

Best regards,
Title: Re: Expanded Shale
Post by: J.Kent on October 06, 2014, 09:58 AM
I used Dry Stall for a while, but I found it to be too white to look decent in a soil mix.
Title: Re: Expanded Shale
Post by: SHIMA1 on October 06, 2014, 06:38 PM
Pumice is pyroclastic igneous rock, glass. Also available in hydroponic supply stores is Growstone. ( It is also glass. Man made glass. I use it just as I use pumice, mixed with milled sphagnum moss with a layer of moss on the surface. Does not float. Widely available and popular with "growers." ;) Available in different sizes. Great stuff.
Title: Re: Expanded Shale
Post by: Leo in NE Illinois on October 09, 2014, 04:24 PM
I use dry stall brand of pumice, and like it for growing. Good results with it as 100% of the media, or blended into a mix. Sifting is important, often 1/4 or more of the bag is too fine to use. I get it cheap though. from a MBS club member who bought a full semi-truck load 5 years ago).  Color has to be handled for shows, but that is just a matter of removing the top layer and either putting down moss, or a thin layer of crushed purple granite - Cherry Stone Poultry Grit, or other appropriate colored material. At home I just put up with the color of Pumice,

One major use of Haydite - expanded shale is as a light weight aggregate for making light weight concrete. Normal concrete is about 2000 pounds per cubic yard, you can cut the weight in half using light materials like Haydite as a substitute for the stone aggregate. Really only important if you happen to be building a building over 40 stories tall, or perhaps a long bridge span. I recall Colin Lewis and a few others being rather negative on potting mixes that had too much haydite in them. I think with haydite you run into some of the same problems you get with Turface if it is more than 50% of your potting media. As a component, it is just fine, used as the main event, it is not up to the task.

I prefer to use at least 2 or more inorganic components in my media mix. Poultry grit (crushed granite) and Dry Stall, blended are my current main component. I do throw in some Turface, but keep it under 20% of the total mix. Basically using it up.