Storage of Materials
Bags of NHL should to be stored in dry conditions. Part used or opened bags should be folded over and used within 3 days, as exposure to moisture in the air will start the setting process.
Aggregates stored outside should also be covered to avoid the smaller particles being washed away by rain.
Which one should I use, NHL2 , NHL 3.5 or NHL 5
Natural Hydraulic Lime is available in 3 different strengths. The number indicates the compressive strength in N/mm2 of the mortar when set.
PLEASE NOTE: Strongest isn’t always the best. You want your mortar to be softer than the masonry. This will absorb any movement in the walls and stop the masonry cracking.
Also keep in mind that when set NHL 5 is the least breathable and NHL 2 is the most breathable.
Typical Uses:
NHL 2
- Internal Lime plaster
- Renovation of soft or crumbling stone
NHL 3.5
- General building mortar.
- External renders and pointing.
NHL 5
- Limecrete Floors
- External render in highly exposed areas
- Chimneys and copings
Mortar / Render / Plaster
Mortars for building, pointing and render base coats 2.5 parts sharp sand to 1 part NHL
Lime plaster finishing coats can be a little richer at 2 parts sand to 1 part NHL and will usually include a finer sand.
Guage the additions accurately. It is important to use a precise measuring vessel such as a bucket or gauging box. A shovel is not an accurate guage for mixing lime mortars.
Spare the Water. Too much water in the mix will leave air gaps when it dries, weakening the structure and leaving external applications prone to water ingress and frost damage.
The lime will act as a plasticiser so it is better to start with a dryer mix. (see the mixing method below)
Mixing lime mortar in a Conventional Drum Mixer.
It is possible to mix lime mortar in a conventional drum Mixer. For larger projects however, it may be advisable to use a Pan mixer
To avoid ‘balling’ of the mortar whilst using a drum mixer, we recommend the following method:
1. To an empty mixer, add half of the required sand amount and switch on.
2. Next add all of the NHL lime and allow to turn over a few times
3. Add the remaining sand
4. Turn over for 5 minutes until fully mixed
5. Slowly add water until the required consistency is almost reached and then switch off the mixer.
6. Leave the mix to stand for 20 Minutes. This is important. During this time the mortar will ‘set up’ and become more ‘fatty’ due to the plastercising effect of the lime.
7. Turn over briefly before use, adding more water if absolutely necessary to adjust the consistency.
Liability Waiver
The information provided in this guide is intended for general use for operators with limited experience of traditional renders. The advice offered here is given for guidance only and will assume that best practice will be used in its execution. No claims for liability can be considered on its intent