How to Cap a Rock Wall
The capstones form the top layer of a rock wall. If you choose them carefully, the wall will not only have a neatly finished top, it'll be stronger throughout. In a dry-laid wall that's created without mortar, gravity alone holds the stones, and the weight of the capstones spanning the joints keeps the wall from separating. If the wall includes mortar, the mortar helps strengthen it, but well-laid capstones can hold the wall even if the mortar fails. Does this Spark an idea?
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Instructions
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Sort through the stones you'll be using for the wall, laying aside any that are fairly flat and as wide as the top of the wall or up to 6 inches wider. Lay these stones beside the wall and estimate if you have enough to equal the length of the wall when they're fitted side by side.
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Split more stones the thickness of the other capstones, if you need more. Splitting is easiest if you're using layered stone with horizontal seams, such as sandstone, slate or shale. Insert a cold chisel or wedge into a natural crack in the rock and pound it farther with a hammer, then place another wedge at another location as the crack widens. Pound the wedges alternately until the stone separates. If you need more capstones and the stone doesn't split easily, select additional ones that aren't as wide as the wall and plan to alternate them among the full-width ones.
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Build up the rest of the wall so the thickness of the capstones will complete the finished height. Arrange the last layer of stones so they're fairly level, but the highest points are toward the outsides of the wall.
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If you're using mortar, spread it with a trowel on top of the last layer of stones for 3 or 4 feet along the wall. Choose a capstone that spans the full width of the wall or hangs over slightly and is either shorter or longer than the first stones, so it doesn't end above a seam. Lay it in place. If you've made the outer parts of the stones the highest points, it should sit firmly without rocking.
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Lay the next capstones beside it, choosing ones that are short or long enough to span the joints of the stones below. Trim off any rough edges with a chisel and hammer, so the capstones fit together. If you use some stones that aren't the full width of the wall, place them so their joint doesn't line up with a joint immediately below.
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Spread more mortar and add more capstones until you reach the end of the wall. Finish the mortar in the joints to match the rest of the wall. If you're building a dry-laid wall, check each capstone to see if it wobbles. If it does, shift the underlying stones to bring their highest points to the outside, or use a hammer and chisel to knock off any unusual bumps, until the capstones lie firmly in place
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Tips & Warnings
Choose capstones to match the appearance of the wall. Slightly uneven stones suit a rustic, field-stone wall, while nicely dressed, perfectly flat stones look better on a wall where all the stones are rectangular.
An alternate way of capping a wall, common in some areas, is to build up both ends of the wall to full height, then lay the capstones between them vertically, leaning against each other like books between bookends.
References
- Photo Credit Stone Wall image by cheungs7 from Fotolia.com
