Secil Natural Hydraulic Lime

About Natural Hydraulic Lime

Secil Natural Hydraulic Lime is available in three European classifications: NHL 2, NHL 3.5 and NHL 5. These grades relate to the compressive strength of laboratory mortars at 28 days.

Known as ‘feebly hydraulic’, ‘moderately hydraulic’ and ’eminently hydraulic’. However, these descriptions can be misleading as the qualifying strength bands for each classification overlap (see below).

The strength of lime mortar or plaster also varies depending on the manufacturer and origin of the lime. As a result, some NHL can be high in the qualifying band and some can be low. Strength can also vary depending on the ratio of the mix and the type of aggregate used.

Secil Natural Hydraulic Lime is certified to the current version of EN 459-1 and is produced under controlled factory conditions by Secil Martingança SA.

Mixing Secil Natural Hydraulic Lime.

The following guidance applies specifically to Secil NHL products.

It is essential to disperse the lime uniformly and that any fine agglomerations are broken down. The time of mixing will be controlled by the efficiency of the mixer. Roller-pan mixers and screed mixers have the most efficient action, but simple tilting-drum cement mortar mixers can be used if a longer mixing time is allowed.

The following sequence will be suitable for a tilting-drum mixer:

• Wear protective goggles and waterproof gloves.
• Introduce half of the sand and add all of the lime. Mix for 2 to 5 minutes until a uniform colour is achieved.
• Stop the mixer and isolate the drive. Scrape down any material adhering to the back. Add the remaining sand and mix again for 2 to 5 minutes to get uniform dispersion.
• Continue mixing, adding water slowly over at least 10 minutes and giving plenty of time for water to be fully incorporated. The mortar should be more like a dough than a slurry and the less water added to achieve this, the better the mortar performance will be.
• The longer the final mixing time the more workable (fatter) the mortar will be. Allow the mix to stand for 15 minutes or longer for greater workability, before re-mixing for a further 5 minutes (in hot weather do not over-mix as water will be lost through evaporation).

Do not apply lime mortars at temperatures below 5 ºC or above 30 ºC, avoiding application in high sun exposure and/or under strong winds.

Dampen down the substrate with clean water before application to avoid lime mixes drying out and to control suction – therefore minimising the potential for shrinkage and cracking. Renders and mortars may also benefit from dampening down again after application where conditions dictate.

About Secil

Secil is an established European manufacturer of lime products with a strong reputation in the conservation and construction sectors.

Natural hydraulic lime is a unique binder as, although it sets with water, it also carbonates with air, but for a longer period.

Secil NHL offers great quality for those using powdered lime in their work.