Saturday, June 9, 2012

Montana Slates...

Working with Montana Slates...

A friend of mine and I were talking about the different materials we were using for our projects the other day, and we thought it would be a good topic for our blogs to talk about those materials in depth, as well as look at the results. I chose to talk about our most common choice of material by our customers- Montana Slate

Hand sorted before delivery, sorted again, then walling....
Dry stone retaining wall after completion. 4' tall by 170'

I can't think exactly how much of this material we used in the last 5 years, but 300 plus tons seems a fair number. We have built stairs, dry stone fences & dry stone retaining walls, flat work for beautiful patios, and even thin veneer. It is not a tremendous amount of material by any stretch, but it is enough to have learned a few things about the material that I can share.

One of my favorite things about this material is the color range. It looks great wet and dry.
The Montana Slate we used to build these stairs was  extremely hard, even layers, and we were able to use feathers and wedges to split it nicely.

It varies hugely from quarry to quarry, from one side of the mountain to the other, from what is on the surface to what comes out of the ground below grade. There is an ancient layer, and a younger layer... so a friend has explained to me of the material in the Kalispell area.
Most have a heavy iron content that will 'bleed' out over time and stain  themselves and the surrounding stones. 

This quarry produces a nice consistent 2-3" flatish material.
Same quarry in a dry stone fence I built for a display 4 years ago. The fine detail work looks nice, but takes longer to build! All the edges I shaped are nicely oxidizing now.

I also tend to think of this stone as a masculine material. It tends to have flat hard lines, be angular, and tear rather than cleave nicely like a granite. Most of the patios I do with this material I put into an organic shape like this to soften the material.
For this large patio area and dry stone retaining wall we used 2-5" thick material for the walling and 2-3" thick material for the patio. They came from 2 different quarries near each other, yet one surface had slight wrinkles in it, and the large patio pieces were very flat. The other stone in the image is a local Olivine which was a nice contrast in color and shape.
When we shape the patio material we use a demo saw to minimize our material loss. A hammer and chisel end up under cutting the material as it tears away below. It can be ok on the thin walling stone, but really doesn't produce consistently nice joints with great contact. I like the thin material best for coping......
The coping here for our dry stone fence is all 2-3"patio grade material. You can see how tapered the edges become as you shape it from both directions pulling it back slowly to your shape. This is not a fast process by the way. There are roughly 5-6 pieces of coping per lineal foot.
This wall is 60' long.

Another characteristic I noticed with the material I am using in the wall stone above is the material is heavily cross fractured vertically and horizontally. Quite the challenge when you want to lay a stone length in and the grain runs from top to bottom, and perpendicular as well. Within this quarry the material shifts to a sandstone- to a shaley mud stone- to hard, dense slate.
It has been great blending these two quarries material. One is great for walling, and the other for quoins and treads. these lower treads project about 30", with twice that in the wall. The same equation is true for the other 14 treads as they wrap around the dry stone retaining wall.
For the curious....
On a whole I really like the material. I use a 22 ounce carbide brick hammer to shape the small wall stone, and coping, and 3lb. hammer and chisels for the larger stones. For the big ones we use what is called a 'Bull Set'-10 lb. and a 12 lb. sledge to move more material in a broad stroke. Like any stone we work with you have to choose your material well. 'Well' to me means hand sorting before I purchase to insure we have high quality material we need for where we are in the project. Most of the stone we have in the Pacific North wet is palletized. 

We are lucky here to have access to these Montana Slates.