Click on the links below for guidance and information on the use of construction limes, including natural hydraulic lime and traditional lime putty .

Natural Hydraulic Lime (NHL)  

Secil Natural Hydraulic Lime Natural hydraulic birdlime ( or NHL ) comes from limestone that has natural impurities of cadaver and other minerals, the measure of impurities within it determines how hard it will set .
It sets with water system ( preferably than with publicize as with linden putty ) hence the term ‘ hydraulic ’ .
Natural hydraulic lime powders come in 3 european grades :

NHL Grade

Conpressive Strength (MPa) @ 28 days Examples of Use
2 > 2 to < 7 Pointing internally, plastering
3.5 > 3.5 to < 10 Bedding, pointing
5 > 5 to < 15 Flooring, below DPC or chimney re-build

Natural hydraulic birdlime can be used when a faster persuasiveness acquire is necessary or for exposed cultivate.
You should be aware that as you increase the military capability of a mix the vapor permeability ( breathability ) will be reduced .
The ratio of sandpaper to binder varies depending on what job you are doing. A 3:1 mix may be used for pointing of top coat renders, but for floor screeds a stronger 2:1 mix would be used .

Hydraulic Lime

hydraulic calcium hydroxide ( HL ) consists of birdlime and other materials such as cementum, blast furnace slag, limestone filler or other materials that change the properties of the binder. The additives do not have to be declared which is legally different to natural hydraulic calcium hydroxide .

Formulated Lime

Formulated calcium hydroxide ( FL ) consists of hydrate lime and/or natural hydraulic calcium hydroxide with add hydraulic or pozzolanic material. inclusion of any cement or cement clinker must be declared and at a limited percentage. This is legally different to a natural hydraulic linden and formulated lime .

Lime Putty

Lime putty Lime putty as a binder has been used for thousands of years. It has many names, such as non-hydraulic lime, fat calcium oxide or tune linden, which frequently causes confusion .
It is made when calcium oxide is mix ( slaked ) with water and left to mature for a minimal 3 months until in solidifies .
Lime putty cures by carbonation with the air ( at a rate of approximately 1 mm per calendar month ) and can consequently be kept for many years in an air out tight environment ( actually improving with senesce ) .

Hydrated Lime

Hydrated birdlime is frequently confused with natural hydraulic birdlime due to them having exchangeable names and supplied as a powder but is not to be used for the lapp applications. It is produced when a small, controlled sum of water is added to quicklime whilst still retaining it ’ sulfur solid state .
It is normally used as an linear in cement as a plasticizer and it should not be used as a binder in its own right .


Quicklime ( calcium oxide ) is the sensitive material that is used to make calcium oxide putty. It is made by burning limestone or chalk in a kiln resulting in a highly reactive material. Quickilime is available in a scope of sizes from lumps down to very fine powder .

Hydraulic Lime Mortar (HLM) and Applications

Please use the postdate tables to assist with lastingness and mix ratios relevant to the job at handwriting :

Building element

Hydraulic Lime Mortar Designation

Internal walls 0.5
External walls 0.5 – 2.5
Facing to solid construction 1.0 – 2.5
Walls close to/below footing 2.5 – 3.5
Sills, lintels and cornices 2.5 – 3.5
Copings and capping 2.5 – 5.0
Chimneys 3.5 – 5.0
ground retaining walls 3.5 – 5.0
Masonry below water level 5.0

HLM Designation

NHL2 lime:sand by volume NHL3.5 lime:sand by volume NHL5 lime:sand by volume

Mean compressive strength (MPa@91 days)



















It is essential that calcium hydroxide is uniformly dispersed and that any fine agglomerations are broken down. The time of mix will be controlled by the efficiency of the sociable. Roller-pan mixers and screed mixers have the most efficient action but simple tilting-drum cement mortar mixers can be used if a longer mix time is allowed. If the job is sufficiently large use a mixer with a capacity for a full bag of calcium oxide .
The following sequence will be suitable for a tilting-drum mixer .

  • When mixing tire protective goggles and waterproof gloves .
  • Introduce half of the sandpaper and add all of the linden, mix well for 2 to 5 minutes until a uniform color is achieved .
  • Stop the mixer and isolate the drive. Scrape down any corporeal adhere to the back. Add the remaining backbone and blend again for 2 to 5 minutes to get uniform dispersion .
  • Continue mixing adding urine lento over at least 10 minutes and giving enough of clock for water to be in full 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 mix clock time the more feasible ( fat ) the mortar will be. Workability will be improved by allowing mix mortar to stand for 15 minutes or longer before re-mixing for a promote 5 minutes ( in hot weather do not over-mix as water will be lost through dehydration ) .


Gauging hydraulic limes is not normally required although summation of pozzolanic materials can improve the hydraulic natural process and performance in some applications. Materials such as used crushed brick, fly ash, labor granulated blast furnace slag ( GGBS ) or metakaolin ( Argical ) may be used to increase the mortar military capability appointment .
The addition of hydrate calcium oxide or lime putty can improve the malleability but may reduce the mortar persuasiveness appellation .
It is recommended that test mixes be produced to establish the optimum properties for a particular application .
Carefully choose which calcium hydroxide is most appropriate for the position, selecting a weaker shuffle for softer freemasonry .
If not purchasing a premixed mortar then ensure you select the right sands for texture and color as required .
by and large, NHL 2 or birdlime putty mortar for internal practice, and either NHL 3.5 or lime putty mortar plus pozzolan is recommended externally .


Any existing defective steer must be raked out to a depth normally equal to twice the width of the articulation, but generally not less than 20 millimeter. The back of the joint should be roughly square in profile. Plugging cheat ensure that the stone or bricks aren ’ metric ton forced apart. Never use an angle grinder or similar character of equipment which may damage the masonry .


The joints must be dampened with enough time left for the stone or brick faces to dry to prevent daub. The mortar should be arsenic dry as it is feasible to point with. This allows utmost compaction in the articulation, reduces shrinkage cracking and reduces the tendency to smear on the stone faces .


Lime mortars benefit from being premixed before manipulation. Allow 30 minutes for a natural hydraulic lime mortar compared to up to a week for lime putty mortar. Pre-mixing is obviously unnecessary when purchased as a ready to use mortar .
When you ’ re ready to carry out the work, the mortar is “ knocked up ” ( agitated/mixed ) immediately prior to use to plasticise the mix and serve to reduce shrinkage. Any pozzolan additive should be mixed in at the final knocking-up stage and not ahead .

Mortar Selection

It is very important to select the discipline grade of natural hydraulic linden and then mix the compensate ratio of sandpaper to lime in order that the forte and vapor permeability is appropriate for the masonry .


start at the top of a wall to allow for cleaning up and spraying to continue. Use a pointing spatula/small tool and push the mortar in from a peddle .
Joints deeper than 20 millimeter may need an initial dubbing out as shrinking can occur otherwise .
eat up flush or rebate a little if the joints have widened with historic period or for personal preference as rebating highlights the pit more ( weather striking ) .


When the mortar is “ green hard ” ( firm adequate to brush without smearing but still ductile enough to work ) brush or tamp the joints with a churn brush to enhance the aggregate and give a coarse texture to the steer. During this work, it is potential to throw a dry autochthonal land at the indulgent lime mortar to pre-weather and allow it to blend in to the wall as a fresh, brilliantly lime mortar is not always desirable .


external point should be obscure sprayed to control drying and protected from aim sun and wind. In winter it should be protected from rain and frost. hessian boot fabric is recommended .


20 kilogram of Lime Mortar will point 2-3 m² of average sized stonework or 1- 1.5 m² of brickwork based on a 10 millimeter joint and 20 millimeter depth .

Time of Year

Great concern should be taken not to apply birdlime mortars excessively late in the year or besides soon in bounce to avoid damage from freeze. The ultimate harden procedure takes up to a calendar month for each millimeter of thickness. Therefore it could take 20 months before mortar has carbonated to a astuteness of 20 millimeter .
It is recommended that trial mixes be produced to establish the optimum properties for a detail application .


Limes are caustic. Always wear eye protection and protective gloves and clothing and follow the safety instructions on the labels .
Please contact us entire more guidance and information .


The play along is an example of a rendering specification that could be suitable for many situations but please ensure that it is desirable for your own especial project :

  1. see that appropriate scaffold is in place and the work site safe for workers and public .
  2. Take off the existing picture, except any existing sound lime mortars, taking concern not to damage the structure. Look out for very thick patches of supply that are efficaciously load yield. It may be preferable to render on top rather than risk rebuilding an area .
  3. Dub out any deep holes in the rampart with a hairy linden mortar, rebuilding defects with cob blocks, bricks or stone as allow .
  4. Treat wooden lintels with preservative and counter batten with oak lath if render over them .
  5. Apply a 3 millimeter harled coating of Secil Consolidation Mortar to provide a winder to the wall .
  6. future, a 12-15 millimeter scrape coat with haircloth, fibres or mesh included to smooth the contour of the wall. The fibres reduce any slumping whilst give and shoplifting cracking whilst hardening.

    Each second is keyed with a boodle comb. The mortar should be NHL3.5 mix to a proportion of around 2.5:1 of lime/sand .
    Any subsequent coats should be a weaker mix and/or thin than the previous coating to encourage moisture to be drawn out of the wall .

  7. Apply a top coating of floated or hand harled coat as desired. The mix should be NHL3.5 assorted at 2.5:1 or 3:1 with sand and applied at 6-8 millimeter for a float coat or 3 millimeter for a harled coating .

Damping & Curing

It is identical important to control sucking from the wall by light spraying with urine half an hour before applying each coat ( specially cob and porous brick ) and in warm weather it will be necessary to spray each coat afterwards. Whatever the season, protect each supply coat during the curing process from all the elements such as hot drying wind, strong sunlight, rain and don ’ thyroxine put on in temperatures below 5 degrees centigrade or if there ’ s a risk of frost. A heavy fabric such as hessian boot sheeting will provide a suitable physical barrier and should be left in place equally hanker as required .


All coats need to be given at least a few days to harden before subsequent coats are applied. To test whether a coat is ‘ green unvoiced ’ the surface should be tolerant to a fingernail .
many factors will influence the time such as the season, exposure of wall and the thickness of the coat but it ’ randomness normal to expect a couple of days for the harled coat to harden and possibly 4- 7 days for each of the blockheaded coats .


For the model specification per m² :

  • 3 millimeter scat coating of NHL3.5 unhaired mortar at 2:1 = 6 kg/m²
  • 15 millimeter scrape coat of NHL3.5 haired mortar at 2.5:1 = 30 kg/m²
  • 7 millimeter floated top coat of NHL3.5 unhaired mortar at 2.5:1 = 14 kg/m² or repeat the first scat coat for a approximate hurl finish .

Time of Year

Please note that great wish should be taken not to be applied excessively former in the class or excessively soon in form or else frost damage may occur. It is authoritative to prevent frost crystals forming within the mortar soon after application.
We estimate that the ultimate hardening march takes up to a calendar month for each millimeter of thickness. Therefore it may take 20 months before mortar has carbonated to a depth of 20 millimeter .


We offer a one sidereal day Practical Lime Course in using birdlime in renovation and sell a train DVD based on the naturally .


Limes are caustic. Always wear eye protection and protective gloves and clothing and follow the safety instructions on the labels .
Please contact us fully more steering and information .
Rebuilding and repairing with lime mortars offers a number of advantages :

  • They match the existing structure for porosity and concentration, allowing moisture to move in a similar way .
  • They can accommodate general movement better than a hard mortar .
  • soluble salts will be less probable to crystallise in the stone or brick faces .
  • They match existing walls aesthetically .

Before starting any influence, constantly check if construction is listed. If it is listed, contact your local Conservation Officer to discuss the stick out .


Try to select stone from a local quarry to match the existing. Take a sample along to the quarry if you ’ ra not sure. You can normally get two size ranges ; 4″-6″ and 6″ – 9″ .
For the go to bed mortar select an appropriate intensity for your masonry, a regular mix would be NHL3.5 shuffle at 1 separate birdlime to 2.5 or 3 parts shrill wash pit sand. The sandpaper should be a good blend of coarse and fine particles. The largest size particle is ideally about 1/3rd the thickness of the layer to be laid, indeed for a 10 millimeter bed, 3-4 millimeter is ideal .


If you ’ re a novitiate, stead a stone dry beginning to make sure it looks correct and you have got the best face showing. Stagger the erect joints indeed there international relations and security network ’ thyroxine a vertical joint running continuously up the rampart .


See mixing hydraulic birdlime section on this page. Natural hydraulic calcium oxide ( NHL ) benefits from premixing by an hour then mixing again precisely prior to use .


Use a mortar bed good dense adequate to spread the burden evenly, finishing barely beyond the front side and then trimming flush with the edge of the gauge trowel .
Use a through pit that can tie in concert the entire thickness of the rampart or thereabouts, one every m² of wall face, pinning the rampart together from both faces .
The mortar shouldn ’ triiodothyronine dry out excessively cursorily – protect from sun, wind and rain with damp hessian boot fabric. protect from rain if necessity .
Build up to a maximum of 1 meter gamey at a prison term and then let the lime mortar cure for 2 to 3 days. When ‘ green hard ’, the joints can be brushed with a starchy brush to expose the aggregate .

time of year

Please note that bang-up wish should be taken not to be applied besides late in the class or besides soon in spring or else frost damage may occur. It is important to prevent frost crystals forming within the mortar soon after application .
We estimate that the ultimate temper process takes up to a calendar month for each millimeter of thickness. Therefore it may take 20 months before mortar has carbonated to a depth of 20 millimeter .


Limes are caustic. Always wear eye protection and protective gloves and clothing and follow the safety instructions on the labels .
Lime putty has to dry through vaporization before it can carbonate. carbonation may take many years before fully completed and amply hardened. Any calcium hydroxide with hydraulic qualities, be it formulated, natural or ‘ hydraulic ’, will set in the presence of body of water and doesn ’ metric ton need to dry before hardening .
All birdlime mortars benefit from protection from rapid dry and frost before fully cured. We recommend using hessian boot .
For curing to complete effectively, it is important that moisture is present for at least 72 hours before being allowed to dry out slowly. premature dry can result in a feeble mortar or plaster of paris. Saturated substrates and/or humble temperatures will result in widen cure times .
Re-pointing an old wall may result in rapid temper from high gear sucking from old dry freemasonry and mortar ( remember to dampen down first ! ). Pointing however, is not geomorphologic and will rarely be a major issue if it is decrepit .
Bedding mortars may take a workweek or more to gain meaning persuasiveness .
Rendering and plastering layers are best applied on to ‘ green hard ’ recently applied coats. This controls the suction and helps create a commodity bond. If previous applications are left besides long it can make lotion of newly layers unmanageable to control and work.
Our lightweight Secil ecoCORK insulating try can be applied on to former layers more cursorily than normal birdlime renders or linden plasters .

Example Build-ups and Timings

Internal Lime Plastering



1st Day Scat/harled coat ( if required )
2nd-3rd Day Scratch coat
10th Day Float coat
14th Day Skim coats
18th-21st Day Limewash coats x 4 ( one coating per day )
28th+ Day other breathable paint finish

External Lime Rendering



1st Day Scat/harled coat – if required
2nd-3rd Day Scratch coat
10th Day Float coating
17th-20th Day Limewash coats x 4 ( one coating per day )
24th Day Silicate Primer
25th-26th Day Silicate Paint coats (one coat per day)
External Lime Render with Secil ecoCORK



1st Day Scat/harled coat
2nd-3rd Day ecoCORK coat with 4 mm fiber methamphetamine engage
4th-5th Day Additional ecoCORK coat ( if required )
6th-7th Day Finishing render coat
21st Day Silicate Primer
22nd-23rd Day Silicate Paint  coats (one coat per day)

Why Use Lime?

Before this hundred construct techniques and materials were identical different from those employed nowadays. traditional properties need to “ emit ” to allow moisture built-in in a hearty wall construction without a dampen proof course to evaporate from the external stonework or translate .
many previous buildings are constructed from materials such as brick, hazelnut and pit which are relatively porous and frequently of lower potency. calcium oxide mortars were normally used for bedding and plastering. It is a relatively soft mortar and therefore it is able to withstand a certain amount of movement ( without cracking ) that comes with village and seasonal worker changes in ground conditions .
Lime mortars and plasters are vaporization diffusible and hygroscopic. They can therefore manage humidity and allow moisture to evaporate, helping to keep a build rid of dampen and create a healthier internal environment .

What’s Wrong with Cement?

Cement_pointing_longwell-green-bristol2-160 Apart from the adverse effect it has on the environment in cosmopolitan, cement mortar is normally hard, brittle and less porous than birdlime mortar. It frequently contains additives to make it sometimes completely waterproof and is damaging to traditional buildings for several reasons .
Cement mortar is much harder than previous bricks, cob or some types of pit, therefore when movement occurs it may damage these softer traditional construction materials. Hard cement mortar can trap moisture behind it causing price to the structure and encourages anchor water to rise up a solid wall by capillary action. Trapped body of water in the wall can cause poor insulation, disintegrate and crumble. In severe cases a black-backed gull wall can fail. The brick, hazelnut or stone can besides be subject to frost damage if moisture levels are to high .

Lime Putty or NHL?

Natural hydraulic limes set flush when moisture and come in a range of strengths. They are utilitarian for building with rock or brick where the earlier sic may speed up construction. But you can besides add a pozzolan to a linden putty mortar .
We suggest that for external bed and pointing late in the year it would be better to use natural hydraulic birdlime. It is able of a faster initial set in cold weather .
For most external render and internal plaster jobs, the adiposity of lime putty makes a superior mortar that allows coarser sands and dense coats to be applied without shrinkage .
If the budget is very compressed and there are no compelling hardheaded reasons to go for lime putty then a natural hydraulic lime binder shuffle with a carefully selected locally sourced sand constantly works out less expensive .
If you are a total novice to birdlime work, it is normally best to use a premixed product to minimise the potential issues that could arise. Premixed lime putty mortars/plasters have a long ledge life and want to be kept dislodge from drying out until used .
Premixed hydraulic birdlime mortars ( HLM ) have a ledge life limited in separate to how it is stored and needs to be kept dry until used .


Slaking is the process for making birdlime putty. Quicklime is added to water system and a chemical reaction occurs resulting in the dismissal of a big measure of heat from the calcium oxide creating a boil liquid .
chemically the calcium oxide is converted to calcium dihydroxide .
The longer the slake lime is matured in the tank car the better the lime putty. We leave ours for approximately 3 months before mixing with sands to create birdlime putty plasters and mortars .
For birdlime putty mortars, the backbone used for build, pointing and backing coats of render and plaster should be a washed sharp coarse sand. Use a sharp sand to BS882 which is free of vegetable matter, clay and salts .
While a NHL based mortar besides requires a sharp, washed, well grade sand, the sand is much slenderly less coarse than that used for a calcium oxide putty based mortar. You constantly need to be mindful when using less coarse sands that they may need to be applied in slenderly thinner coats to avoid the risks of shrinkage cracks. For finishing coats of internal plaster use a very fine sand with the birdlime putty or NHL2 .


Premixed birdlime putty mortars can be stored for many months if sealed from the air and dependable from frost in dumpy bags or sealed tubs .
Mortars with hair’s-breadth teased in will gradually lose the hair as it dissolves in an alkaline wet mortar and you will end up with an unhaired mortar .
Hydraulic calcium hydroxide mortars have a shelf life and should be stored dry and sealed from the atmosphere to prolong its life. If stored correctly, the bags of dry powder could last anything from 4-12 months from fabricate .

When Do I Add Hair? 

Lath and plaster Traditionally, some shape of fiber was added to a lime mortar when applying it to the first application on to a lath wall or ceiling. For all other applications, the addition of fibres are optional and depend on the build-up and makeup of the plasters .
With NHL mortars we would suggest that 8-12 millimeter layers will require fibres and anything above 10 millimeter with lime putty. On to solid walls, it is acceptable to apply slender coats without fibres .
traditionally, animal hair such as cavalry, overawe or capricorn, is added to the back coats of calcium oxide translate and plaster. In some instances, white capricorn hair can be found in the final skim coat .
Adding hair gives extra force and minimises shrinking and cracking. It allows dense coats to be applied to uneven walls and holds the plaster keys in identify when plastering onto lath .


Natural Hydraulic Lime Window Detail Don ’ t paint a linden interpret or plaster with a modern key load with acrylic fiber additives .
Externally, it is preferable to use a Silicate Masonry Paint .
Internally, the choice is far greater, for example : Distemper, earthborn Emulsion, Clay paint, Limewash

Lime Plaster 

Lime plaster is the end plaster used as a final examination skim over internally.
Mike Wye issue two grades of birdlime plaster – Heritage Plaster and Regency Plaster .
inheritance poultice is our criterion and most popular linden scan.
Regency Plaster is appropriate for matching the finest historic finishes and can besides be used a filler for minor cracks .
If making your own lime plaster it is vital to source a desirable wash, kiln dry sand of 1 millimeter or less grain size. It is recommended to mix the birdlime putty and sandpaper in concert at least two weeks before application to lessen shrinking cracks. sometimes a poultice is created by mixing NHL2 with backbone. This needs to be used within a few hours of mixing with backbone and water .


Limewash at it ’ s most basic is a traditional, breathable rouge made from lime putty which is thinned with water.
Mike Wye limewash is approximately 1 share senesce lime putty to 1 part body of water for optimum performance and minimal issue of coats required. typically, four coats are needed on new external hand over and three coats on modern calcium hydroxide plaster internally.
It can be coloured with pigments and can be used internally or externally on birdlime plaster, lime render, rock or brick. It works beneficial on porous surfaces and hardens as it absorbs carbon paper dioxide from the atmosphere to form calcite crystals, giving it a unique appearance .
Limewash can be used inside or external. Before making a decision on which paint to use, it is important to understand that limewash can be a little powdered if not applied well or on to a airfoil that isn ’ thymine suitable. It can besides have a not uniform tinge due to differences in sucking on the surface, this is normally due to differing moisture levels. The most obvious lawsuit of this is rain hitting an external rampart. Some people love this authentic appearance, some people loathe it.
Choose an desirable alternative if you don ’ triiodothyronine like the effects, in affiliation with your Conservation Officer if the build is listed .
Click here for a full guide to applying limewash .
A pozzolan is an additive that reacts with the linden in a mortar to create hard chemical adjust and so is very utilitarian for damp or frost-prone environments. We use a metakaolin from burn clay and advise it is used for most external work in strictly regulated amounts .


Harling is a proficiency for applying a coat of interpret or plaster. The lime mortar has extra body of water added to bring it to a fluid consistency alike to that of porridge. It is then cast on the wall using a extra cock called a harling trowel which has a curved blade .
The harling coat provides a pugnacious texture when cured that gives extra cardinal for the next trowel coat and besides controls suction with very athirst materials such as cob and brick .

Insulating Limes

A number of manufacturers now produce insulating renders and plasters. Some are based on lime putty and normally interracial with cannabis and pozzolans. Others are based on hydrate birdlime and cement with respective forms of insulating material such as hemp or perlite .
Our main offer is a lightweight, dry concoction of natural hydraulic lime and phellem. Being barren from cement, it has thoroughly eco credentials deoxyadenosine monophosphate well as offering better thermal performance .
ecoCORK is a merchandise formulated entirely with natural hydraulic lime binder and free from all cementitious content. mix with a largely cork aggregate, this offers a lightweight, vapour permeable and environmentally friendly render or plaster.
This supply is ideally decorated with SecilTEK Silicate Primer and SecilTEK Silicate Paint or a similar silicate masonry rouge .


Limecrete is a modern interpretation of a traditional solid linden or gypsum deck that can even be seen in many historic or well preserved older homes .
It is vital to have an alternative option for a traditionally built house as a relatively impervious, not compromising cement shock may create problems with damp being forced into the walls at ground degree. This can result in poor insulation, model growth with consort health problems and even geomorphologic damage. many conservation officers with province for list buildings would encourage the use of the limecrete option rather than modern concrete shock buildups required by Building Regulations. Always use the chastise materials and techniques on a build regardless of whether it is listed or not.

Limeash were broadly used on suspend timber floors onto a raft of reed and it is thought used chiefly as a fire break. These floors were originally made with calcium hydroxide putty and lots of a pozzolanic additives to provide an hydraulic and hard set. Although very effective, this method needs a very farseeing time to harden and carbonate .
A Limecrete floor is made using a lifelike hydraulic birdlime gunpowder that sets much flying and potentially harder than the limeash floor. A mix of NHL5 and well grade aggregates can be used to create the limecrete slab but it is besides possible to introduce breathable insulating material using an isolate aggregate and flush underfloor heat ( UFH ) .
For more details about limecrete, please visit our dedicated web site

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