NHL 5 for masonry...
of high density.
Granite, basalt, flint, engineering brick, etc.
NHL 5 in conditions...
of extreme exposure to water or weather.
Retaining walls, paving, coping stones, cornice, plinths, balustrades, chimneys, parapets, ridge tiles, eaves.
Marine building and construction.
Bridges, canals, dams, harbours, marinas.
Re-pointing or building by the sea, river, canal.