A clay basin — Dutch kleikom or komgrond — is a limited area forming a kind of valley of clay, usually beside a river. When the river flooded, it dropped the coarser sand right next to its bed, forming the higher natural levees, and washed the finest material further into the hinterland. There it settled as a thick body of heavy clay: the basin, or backswamp.
Basin areas therefore lie lower and wetter than the levees beside them. They were traditionally used almost exclusively as grassland; farms and villages stand on the levees.
Why it matters for building
- Soft ground — a thick clay body, often with peat between the layers, is compressible; settlement and tilting are real risks
- High water table — crawl spaces flood more readily and basements need a watertight construction
- Poor infiltration — rainwater hardly drains away; disposing of roof water into the ground usually does not work here
- Foundation choice — in basin areas piled foundations are almost always used; shallow foundations are rarely justified
Historic meaning: a mould for lead
In stonemasonry a kleikom is something else entirely: a half bowl formed from fat clay, used to cast lead around a dowel. The bowl was pressed against the stone components, in which channels had been cut. Molten lead was poured into the bowl and ran into the recess for the dowel. Once set, the bowl was broken away and the surplus lead cut off and reused.
Practical tips
- Look at the neighbours — tilting and cracking in older buildings nearby say a lot about the ground
- Test the ground first — for new build or an extension on basin clay, a soil investigation is a condition, not a luxury
- Store rather than infiltrate — buffer rainwater (a pond or a swale with an outlet) instead of trying to let it soak away
Related terms
- Clay
- Soil type
- Dowel
- Lead
- Piled foundation
- Terp mound
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