Natural hydraulic lime (NHL) is used to create plasters, renders and mortars. It is far kinder to the existing building fabric than a sand/cement mix. NHL lime has been growing in popularity over recent years, mainly due to it’s ability to set much faster and harder than the more traditional non-hydraulic lime products. Because of this quick set time, they can often be more suited to exterior works (provided non-hydraulic lime isn’t necessary). Natural hydraulic lime is produced from limestone which contains clay and other impurities which give a faster initial set time in wet conditions and will even set under water!