What is Quick lime?
The process of making lime, starts with the burning of Limestone (Calcium Carbonate) in a Kiln. The material produced from this process is Calcium Carbonate which is also known as Quicklime. Historically quicklime was mixed with and aggregate (sand / clay / Ash) to make a mortar for building. Quicklime powder will double in volume when slaked so this need to be taken into account when measuring mix ratios. A 3:1 mix will become 1.5:1 mix after slaking.
Quicklime is available from Celtic Sustainables in powder form (see Calbux 90)
This method of making lime mortar generates a lot of heat which can burn, so great care needs to be taken when using this product. A safer option is to use a lime that has already been slaked.
What is meant by slaking Lime?
Slaking is the process of adding water to quicklime. This action triggers an aggressive chemical reaction producing Calcium Hydroxide (aka hydrated lime). Depending on how much water is added at the slaking stage you will be left with either a Hydrated lime powder or a lime putty.
The putty is a better quality product for creating hydrated lime mortars as it goes through a maturation process of at least 4 months which ensures complete slaking of a the quicklime.
WARNING: Slaking quicklime triggers an aggressive chemical reaction which produces a huge amount of heat capable of melting plastic buckets. We recommend that this process is only carried out by experienced professionals.
How do you use lime putty?
Lime putty can be mixed with sand to create lime mortars and plasters. Use a well graded sharp sand for building mortars and base render coats. A finer sand can be used for thinner finishing coats.
It can also be mixed with water to create limewash. Start with a mix ratio of 50:50 and mix well. The limewash should have a thin consistency similar to that of full fat milk. A thicker consistency will result in a coating that will crack as it dries.
What’s the difference between Hydrated Lime and Hydraulic Lime?
Hydrated lime is the lime binder produced using pure limestone as the raw material. Hydrated lime is a slow drying, flexible mortar, suitable for most interior and exterior applications. It requires oxygen to cure so does not perform very well in wet conditions. Hydrated lime takes time to fully cure. Approximately 28 days for every 15mm.
Natural Hydraulic Lime (NHL) is a lime binder created from a limestone which contains a small amount of impurities. The impurities burn in the kiln alongside the lime and create a product that reacts with water to trigger an initial set in the mortar. The remaining ‘pure lime’ in the mix continues to cure over time. Because NHL sets in the presence of water it is suitable for use in wet conditions. NHL is harder than Hydrated lime but this benefit comes at the expense of being less flexible and less breathable.
What is the difference between NHL 2, 3.5 and 5?
The numbers 2, 3.5 and 5 are representative of the compressive strength of the Lime when dry. 2 being the least hard and most flexible up to 5 which is the hardest and least flexible. The NHL 3.5 is a good general purpose lime, suitable for most building purposes. NHL 5 is great for floors chimneys and areas around water. NHL 2 is great for soft stone such as shale or old bricks where it is important to ensure the mortar is weaker than the masonry. Please note that although NHL 2 is the most breathable NHL option, it is still not as breathable as Hydrated lime.
Why is horse hair / synthetic fibre added to lime mortar?
Animal hair or synthetic fibres are often mixed into render base coats to help reduce shrinkage and increase the tensile strength of the mortar. This is particularly important when rendering onto wooden lath.
Why should you use a render mesh over boards before rendering?
Similar to hair and synthetic fibres, a render mesh will help to strengthen lime render. Boards that are fixed to a timber frame are particularly susceptible to movement and cracking will occur over the joints if the render is not reinforced. The render mesh should be trowelled into the base coat while it is still wet.
What is a Pozzolan?
Pozzolans are added to hydrated lime (putty lime) mortars to trigger an ‘early set’, causing them to act like a Hydraulic lime. The Pozzolans react with water and the lime, causing the mortar to go hard quicker. The remaining hydrated lime in the mortar continues to cure as normal. Brick dust pozzolan can also be used as a colourant making the finished mortar a pinkish/red colour.
What is Hemp Shiv?
Hemp Shiv is the woody core of the hemp plant, a bi-product of the hemp fibre, hemp seed and hemp oil industry that would otherwise be thrown away. In the construction industry it is what is known as a bio aggregate which can be used instead of sand for making hemp mortars and hempcretes. Hemp mortar provides additional insulating properties to walls and ceilings. Hempcrete which is made with a courser hemp Shiv can be cast between formers to create solid walls. These type of walls are not load-bearing so are usually cast around timber frames.
What is Adaptavate Breathaplasta
Breathaplasta is a ready mixed lime mortar which uses hemp bio aggregate instead of sand. Just add water to the breathplasta and mix, to create a mortar which is suitable for plastering many types of surfaces. Hemp is a quick growing sustainable crop that crops annually and doesn’t require pesticides to grow.
What is Eco-cork render
Similar to Breathaplasta eco-cork is a plaster that uses cork as the Bio-aggregate which has similar insulating properties to hemp. Eco cork is part of a 3 coat system and requires a base coat (Secil Consolidation Mortar Consolidação) and a protective plaster coat (Secil Finishing Plaster - Acabamento)