Natural Hydraulic Lime
Whether you are repairing historic building fabric or constructing an environmentally conscious building,Natural Hydraulic Lime Mortar from Roundtower offers many benefits to architects, contractors, quantity surveyors, conservationists and homeowners.
Natural Hydraulic Lime
Available now from Howarth Timber and Building Supplies Natural Hydraulic Lime offers the traditionalist a tried and tested method of renewel , renovation and There are many reasons for specifying and using Roundtower Natural Hydraulic Limes:
Old and New - Roundtower Natural Hydraulic Limes are suitable for building restoration and conservation. Equally, they are well suited for new construction and as mortars, plasters, concrete and grouts.
Choice - Roundtower uniquely has 4 different natural hydraulic limes. An NHL 2, two NHL 3.5s (different colours) and an NHL 5. This gives the user the widest choice of material.
Natural - Roundtower Natural Hydraulic Limes are natural products. They contain no additives and are not blended.
No additives - no need to add pozzolans, cement, plasticizers, water retainers or waterproofers. Roundtower Natural Hydraulic Lime gives consistently high quality results.
Compatibility & Suitability - variety of strengths and colours available to suit existing mortar, whatever age.
Resistance to weather - quick setting means less need for protection from adverse weather conditions compared to fat lime mortars.
Resistance to salts - the absence of gypsum and cement ensures sulphate attack and alkali-silica reactions are impossible. Excellent performance even in marine environment.
Resistance to bacteria & vegetable growth - alkalinity of lime inhibits growth.
Flexibility - Compressive strength is gained gradually, allowing for movement.
Elasticity - no expansion joints, minimal shrinkage and cracking.
Permeability - condensation dispersion, reduces rot, and promotes a healthy living environment.
Insulation - permeability reduces moisture in structure.
Low alumina content - less susceptible to attack by salts.
Excellent workability - Free-lime content gives good workability.
Self-healing - Free-lime content also gives the mortar self-healing properties.
Versatility of use - rendering, plastering, pointing, grouts and other building mortars
Reworking - all Roundtower Natural Hydraulic limes can be re-worked within 24 hours.
Recycling - building materials used with Roundtower Natural Hydraulic Limes can be recovered and re-used.
CO2 Absorption - Natural Hydraulic Lime re-absorbs CO2 during carbonation of the free lime.
Examples - a long list of international reference projects.
Cost Effective - low bulk density means good economy as sold by weight but used by volume.
Customer support - as a customer of Roundtower Natural Hydraulic Lime, you can expect a comprehensive support and advisory service, which is second to none.
Mixing your Mortar
A conventional cement mixer can be used, although for larger projects a roller-pan or paddle-mixer is preferable. Lime mortars mixed in drum mixers are prone to balling. However, the following mixing procedure can reduce this problem. It is vital to ensure that when measuring materials this is done by volume. A gauging box or bucket will be necessary for this task. Measuring by shovel is not acceptable since quantities will be inconsistent:
Start with an empty mixer.
Add 1 part sand
Followed by 1 part lime
Followed by 2 parts sand
Mix dry for at least 5 minutes
After 5 minutes slowly add water until the desired consistency is reached, it is very important not to drown the mix by adding too much water.
Once the desired consistency is reached mix for a further 20 minutes
(The above example is based on a mix ratio of 1:3).
The mix, to begin with, will appear dry but as mixing time increases the mortar will become much ‘fattier'. If too much water is added the risk of shrinkage will increase and the final strength reduced. Do not use any plasticisers.
Water Content
The addition of water should be considered carefully, as it will directly affect the ultimate strength and durability of a mortar. The more water introduced into the mortar mix, the weaker will be the final result. However too little water will prevent the chemical processes taking place and weaken the material. Generally, water should be added sparingly, until a useable consistency is achieved.
The masonry background may also affect mortar strength. Dry backgrounds can quickly ‘suck' moisture from newly applied mortar. This should be controlled by dampening down the background prior to mortar application.
Storage of Lime & Aggregate
Roundtower Natural Hydraulic Limes are supplied in water-resistant paper bags. If the bags are allowed to get wet they may be irreversibly damaged. Also, once opened the exposure to air will start to weaken the hydraulic set. As a result any opened part bags left at the end of the day should be carefully folded over at the top and put into a dry store. In this state the lime will remain useable for a further 2 or 3 days. Thereafter it should be discarded. For larger orders Roundtower Natural Hydraulic Limes are supplied in 1575kg (63 x 25kg bags) plastic wrapped pallets.
Aggregate should also be covered since if left exposed fines can be washed out and the material as a whole can gradually separate.
Hydraulic Lime Mix ratios
Application Roundtower
Typical Mix Approx. Coverage
(Per 25kg Bag)
Internal Plastering Backing Coats (10mm) NHL2 2.5 Sand: 1 Lime 8m2
Finishing Coat (3mm) NHL2 2 Fine Silica sand: 1 Lime 26.5m2
External Rendering Coat (10mm) NHL2 2.5 Sand: 1 Lime 8m2
NHL3.5 2.5 Sand: 1 Lime 8m2
Pointing Rubble Stone NHL2 2.5 Sand: 1 Lime 10m2
NHL3.5 2.5 Sand: 1 Lime 10m2
Pointing Brickwork NHL2 2.5 Sand: 1 Lime 16m2
NHL3.5 2.5 Sand: 1 Lime 16m2
Harling/Wet Dash/Roughcast NHL3.5 2.5 Sand/Aggregate: 1 Lime 7.5m2
Slurry Coats NHL2 2.5 Sand: 1 Lime Refer to supplier
NHL3.5 2.5 Sand: 1 Lime Refer to supplier
Lime Concrete NHL5 1.5 Mixed Aggregate: 1 Lime Refer to supplier
WE ALSO RECOMMEND THE USE OF NHL5 IN AREAS OF HIGH EXPOSURE
(E.G. MARINE CONDITIONS)
Pointing of Historic Buildings
Analysis of Original Mortar
Before carrying out re-pointing work on Historic buildings or structures, determine the type of mortars used in the original building phase. Make sure when removing samples for analysis that they are from an original phase of work, and are not from later remedial works.
The samples should be representative of the bulk of the remaining material. Analysis is needed to determine correct binder, aggregate size, colour and type. Mortar analysis can be carried out by Lochplace Building Conservation. analysis@lochplace.com
Survey
Carefully survey the wall to determine the pointing style and condition of the mortar. Notes should be made of open joints, decayed mortar, vegetation and general extent of re-pointing required.
For further Information on RoundTower Natural Hydraulic Lime click hear of contact Howarth Timber and Building Supplies at Leeds on 0113-200-0100 and ask to speak to RoundTower sales in the building materials department.