What are shells used for in construction?

Seashells are the skeletons of molluscs and consist largely of calcium carbonate (CaCO3), in other words lime. In the Netherlands, shells (Dutch: schelpen) are dredged from shell banks in the North Sea, the Wadden Sea and the waters of Zeeland. They are rinsed and washed and supplied as whole shells or as crushed shell.

Application

Shells have a surprising number of uses in and around the home:

• Crawl space: in the Netherlands a layer of shells is commonly spread over the floor of the crawl space under a suspended ground floor. It slows the evaporation of ground moisture and adds a little insulation. Shells do not rot and are not attacked by bacteria.
• Paths and parking areas: loose-laid, compacted shells form a semi-permeable path surface. Mixed with clay, they bind harder and suit footpaths, cycle paths and parking areas.
• Drainage: the gaps between shells let water drain away.
• Shell lime: burnt shells produce lime for lime mortar and lime plaster.
• Garden: crushed shell around plants is used to deter slugs.

Tips for shells in a crawl space:

• Fix the cause first: repair leaking pipes, blocked drains or poor ventilation first. Shells are an addition, not a cure for a leak.
• Full coverage: cover the whole ground surface without gaps, at the layer thickness the supplier recommends.
• Ventilation: keep the air bricks or vents in the outside wall clear.
• Access: keep pipes and the access hatch reachable for inspection.
• Combine: shells can be combined with insulation under the ground floor.

Related Terms

• Crawl space
• Ground cover
• Drainage
• Lime
• Lime mortar

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