The Art of the Stonemason


Stone building essentials

This book by Ian Cramb is a classic. Straightforward and elegant, everything you need to know about putting one stone on top of another. I’ve been through many tons of stone with only Ian’s stern Scottish advice to guide me. Never looked back.

I don’t remember where I heard it (this book doesn’t cover drywall), but the best short course I’ve seen on dry-stack stonework is this:

1. Gravity always works.
2. If a stone can move, it will.

That sums up pretty much everything you need to know to ensure a wall will still be there for people born after you die.

The most reliable test for stone is to examine an old building nearby that has been built of the same stone. The arrisses (edges where the surfaces meet at an angle) should be firm, fine, and the members of moulds sharp and clean. The lines of stratification should not be prominent. The faces must be hard and solid when struck with a chisel. A loose or spongy appearance would denote decomposition of the chemical constituents.

The following are some specific tests for stone.

Water test -- A few stone chippings are placed in clean water and stirred about. If the water becomes muddy, the stone should be rejected.

Chemical test -- Immerse a stone in a solution of 1 cup sulfuric acid, 1 cup hydrochloric acid, and 1 gallon of water for a few days. When taken out and dried, the grains should be sharp and firm. Loose sand would mean the stone could dissolve in a polluted city atmosphere. NOTE: These acids are very dangerous. Every precaution must be used in handling and disposal.

To detect the presense of lime -- If a few drops of acid are placed on a stone and the drops cause effervescence, carbonate or lime is indicated. Such a stone would not weather well.

Absorption -- A sandstone shell should not absorb more than 10 percent of its weight in water; a limestone not more than 17 percent.



Points to remember

All random rubble is built in courses. This is the traditional method; there is no such thing as uncoursed random rubble.

A hole for every stone, and a stone for every hold. What you lift, you build.

To fit your center key stone, spread mortar on each joint surface of the stone already in position ("h"). Lower the stone into the opening -- do not use a hammer -- until it rests on your sand-lime mix. If joints are too slack, adjust each joint a little to make them all look equal, then flush point the face joints, pressing the mortar in gently. The stones of the arch are now in position, with the face joints pointed. Add a touch of water to your mix, making it into a grout or slurry. Pour this into the back of your arch stones and into any voids in the joints, making sure it does not push out your stones. The lime mix the stones are resting on will prevent the grout from running through. Once your joints are filled up, insert small slivers of stone into each joint, pushing them down gently into the grout, until they are tight. These small stones act as a wedge in each joint.


In grouting stonework, I use a lime-based grout, not a strong cement grout as some recommend. Open up a wall that has been cement-grouted, and you will find little adhesion to the surrounding material. Examine any cement pointing on stone, and you will see hairline cracks between the pointing and the stone, allowing for penetration of water.

09/20/06 -- Matt Thornton