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Nat
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Definition
A grout joint — the filled gap between adjacent ceramic tiles, stone slabs, or masonry units. In Indonesian tiling practice, nat is filled with cement-based grout (grouting) after the tiles have been bedded and set. The nat width (typically 2–5 mm for keramik and 8–15 mm for batu alam) affects both the aesthetic and the technical performance of the tiled surface, with wider joints accommodating dimensional variation and allowing slight movement.
Example
A common quality defect in Indonesian housing construction is hollow-sounding keramik caused by incomplete mortar coverage beneath the tile — visible cracks propagate from the nat joints when the tile flexes under load, signalling inadequate bed mortar rather than a defect in the tile itself.