A dowel hole is the recess — usually a round or square drilled opening — in a stone or substrate, into which a dowel is placed to invisibly connect two elements. The dowel hole is therefore an essential part of a dowel joint in natural stone and heritage construction.
Shape and dimensions
The shape depends on the application:
- Diameter — generally 8 to 25 mm, depending on the load
- Depth — at least 1.5 times the dowel diameter
- Shape — round for drilled holes, square or rectangular for older, hand-cut holes
- Position — central in the bearing surface, not too close to the edge
In old stonework, holes were chiselled by hand; today they are drilled with percussion or diamond bits.
Fill material
The space around the dowel is filled to make the connection effective:
- Molten lead — traditional: poured and caulked so it expands and locks
- Cement mortar — common in less critical work
- Epoxy or polyester resin — for critical restorations, especially with stainless steel dowels
- Sulphur — historically used to fix wrought iron anchors
Applications
Dowel holes appear in almost all natural stone work:
- Capitals on columns — hole on top of the column, hole on the underside of the capital
- Steps and thresholds — to prevent slipping
- Sculpture — arms, hands or wings are dowelled to the body
- Restoration — when refitting detached pieces
Points to consider
- Distance from edges — too close and the stone breaks out under load
- Drying — a damp hole cannot be filled well
- Symmetry — two holes must align perfectly
- Material match — avoid combining iron with porous stone (corrosion risk)
Related terms
- Stone dowel
- Anchor
- Alignment pin
- Natural stone
- Restoration
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