Working with lime mortar. Hot Mix or Cold Mix?& the Gospel according to Lime from a “Born Again Builder”

Phil BrownFriday, 11 October 2019

The largest manufacturer of

lime putty in the UK

Cornish Lime

Premium quality since 1993

Cornish Lime are constantly evolving to meet market needs, while respecting the most important factor of all

That of the buildings themselves !

WHAT IS LIME?Lime is a polysemic word to which our industry adds

many adjectives.

FAT – LEAN - WATER – HYDRATED – HYDRAULIC –DOLOMITIC – AIR

While the above are common terms used we will limit things today to the following

NON HYDRAULIC& HYDRAULIC

Csh

Hydraulic, the ability to set under water

John Smeaton The Eddystone Lighthouse

July 1756 - October 1759

Louis Vicat: French military

engineer classified

hydraulic limes in 1818

Building Limes & Cements a simplified ChronologyFrom John Ashurst’s book “Mortars, Plasters, and Renders In Conservation” (2nd Edition)

5600BC: Red Lime Concrete , YugoslaviaFrom 1AD: Lime based mortar & Plaster. Stone, sand, brick, & kiln ash aggregates. 1756: John Smeaton Eddystone Lighthouse (Aberthaw lime & pozzolana from Civitavecchia 1796: Parkers Cement – produced from septaria later known as “Roman Cement” 1824: Joseph Aspdin a Leeds bricklayer patented Portland Cement.1846: Sawn Lath introduced. 1854: Wilkinson’s patent for a concrete reinforced with iron ropes and rods.1890: Sirapite produced in England.1898: Seaman’s first fully operational rotary kiln process for Portland cement1904: First British Standard (No 12) for Portland Cement.1920-1945 Period of decline in the use of lime mortars and plasters1995 New draft European Standards for lime – BS EN 459-1:2015.

62”

91”

176” ?Crib Goch

41”

78”

43”

32”

Spell as BS 8104:1992 (Airfield indices)

26”23”

25”

Crib Goch is one of the wettest spots in the United Kingdom, with an average of 4,473 millimetres (176.1 in) rainfall a year over the past 30 years.The annual amount of precipitation quoted here is an average of weather data collected from 1981.

37”

49”

BRITISH STANDARD DEFINITIONS OF EXPOSURE BS 5262:1991 CP for External renderingsSHELTEREDAreas of moderately low rainfall in which walls are protected from the weather by overhanging eaves and by the close proximity of buildings of similar or greater heights. Ground and first storeys in towns.

MODERATEWalls are partially protected from the weather by overhanging eaves and by other buildings of similar height in the neighbourhood. Applies to buildings in towns and suburban districts generally.Render thickness not less than 16 mm built up in 2 coats

SEVERE Exposure to the full force of the wind and the rain. Applies to buildings on hill sites and near the coast, and buildings projecting well above surrounding buildings in built up areas.Render thickness not less than 20 mm built up in 3 coats

Non Hydraulic Lime (Lime Putty)

Non Hydraulic Lime, often referred to as air lime, it

hardens over time through carbonation - the

sequestration of atmospheric CO2 in a process that’s

seasonally variable

This is 1 of 21 lime tank/pits on site producing lime putty from Buxton Quicklime.

The lime revival of the last 40 years would have stalled had we relied solely on non hydraulic limes

Set in part by chemical reaction, required to reabsorb CO2 (Carbon dioxide) to form a complete mortar.

Controlled under EN 459-1

v Vary in hydraulic properties

v NHL2 – Weak

v NHL 3.5 – Medium

v NHL 5 – Strong

Variability across the manufacturing spectrum is wide. However, St. Astier is the market leader for good reason

Ca(OH)2 25 % +

Ca(OH)2 50-55 %

Ca(OH)2 20-22 %

Selecting The “Right” BinderExposure level related to

strength

Substrate type and condition related to

strengthNon-hydraulic CL90

(Hot Mix/putty)Low level exposure

& internal work.Non-hydraulic CL90

(Hot Mix/putty)Soft and friable backgrounds

NHL 2 Low level exposure. NHL 2 Soft and friable backgrounds

NHL 3.5 Most weather conditions. NHL 3.5Moderately strong

backgrounds

NHL 5 Severe NHL 5 Dense very strong backgrounds

Selecting the right binderVapour permeability related to strength

Non-hydraulic CL90

(Hot Mix/putty)Very high vapour permeability

NHL 2 Very high vapour permeability

NHL 3.5 High vapour permeability

NHL 5 Moderate vapour permeability

OPC Very poor vapour permeability

Mortar, Thin SectionsPetrographic (thin section) images:scale: Each slide approx. 5mm across

The blue represents voids within the mortar matrix, representing permeability

Above: Natural Hydraulic Lime (NHL 3.5)

Right: Cement (OPC)

Note how the pores are connected for the lime mortars, allowing the transmission of vapour through the mortar

Above: Non Hydraulic Lime (Putty)

Traditional Masonry

Earth mortars account for at least 75% of mortars in Cornwall.Some as just earth, many gauged with quicklime

LIME PUTTY RENDER APPLIED OCTOBER (2009)

LIME PUTTY RENDER APPLIED OCTOBER 2010

Note the extent of the frost damage at low level

Hot mix or cold mix?What does that mean ?

There is no “one size fits all” approach to lime. They are all better than cement

for use on traditional housing stock

Non Hydraulic Lime v NHL’s.Our built heritage is too important to allow

the industry to be caught up in a nonsensicalGood v Evil

A traditional and somewhat “authentic” method for replicating mortars.

Hot-mixed mortars offer a very workable material (with no equal)

Extremely high vapour permeability?

Where’s the problem ?

We have a trade base that struggles to use conventional mortars let alone something that is very hot when made !

HOT MIX

Mixes generally comprised 1 part powdered lime to 2 or 2½ parts aggregate.By the early 21st century alarm bells were ringing in some quartersconcern about excessive strength of NHL mortars might be well-founded ?

The revival for Hot Mix Lime mortars while extremely valid and important is being tainted by scaremongering

“Fake News”

BUT WHERE IS THE EVIDENCE ?We have been supplying St. Astier NHL’s for 22 years and wouldn’t argue they set hard; however, we’ve not seen the evidence to force a change.

Geology & Weathering

Atmospheric pollution e.g. Sulphur dioxide, nitrates,

sulphates etc. all sources of harmful salts into stone

● Moisture movement occurs primarily in mortar and joints

● The performance of mortar is therefore critically important with respect to water penetration

Selleggan Smelting Works

Traditional Mortars?

GUNWALLOW CHURCH (BEFORE)

AFTER – NON HYDRAULIC LIME (PUTTY) WITH LIMEWASH

Hot mix or cold mix?We regard the use of “Hot Mix mortars as extremely appropriate, but with a strong warning as to the expertise of those working with them. That’s not meant to be precious, but reflects our experience and the reality of too many who are all to often clueless?

There is no “one size fits all” approach to lime. They are all better than cement

for use on traditional housing stock

Energy Planning v The heritage values (significance) of

the building

v The construction and condition of the building fabric and building services

v The existing hygrothermal behaviour of the building

v The likely effectiveness and value for money of measures to improve energy performance

v The impact of the measures on significance

v The technical risks associated with the measures

While External Insulation systems may well be the most

efficient.

ARE THEY REALLY, AND DO THEY JUSTIFY

THE OUTLAY ?

Thicker, Quicker and Faster– can be applied as 30mm coats or 50mm green on green, standard drying

(4 to 7 days).

Mineral Based, Highly Vapour Permeable – no organic content (wood, cork) so wont breakdown or rot

under constant moisture.

Highly Insulating – K value = 0.12, at least 50% more insulating than closest lightweight/insulating

render alternative. For 100 bags of Insulating Render, you would need 150 bags of L.G Ultra to achieve

the same insulation value (ultra is the closest alternative, other similar products would be more again).

Cost effective – considerably cheaper than other (I.R £10.95, LG Ultra £14.40)

As a rough rule of thumb every mm will achieve a 1% improvement on U Value (based on RdSAP U

Value of 2.1 for solid walls).

Hygroscopic – actively stores and releases moisture depending on the RH, high moisture buffering

capacity.

Void Structure – whilst no material is salt proof, insulating Render can accommodate some salt deposits

so much better than conventional plasters for remedial works).

Benefits

Cornerstone Insulating Render

• K Value = 0.123• Significantly outperforms similar lightweight

mortars by over 50% (0.17 to 0.23)• Highly vapour permeable – not affected by

moisture, promotes moisture movement.• Non-porous aggregate, accelerates moisture

movement• Non-porous aggregate, reducing cold bridging and

damp spots. • Hardened aggregate – does not breakdown or rot. • Recycled aggregate and high free lime content –

Eco friendly. • NHL2 – suitable for all applications & backgrounds. • Can be applied up to 30mm per coat. • Can be used internally & externally (with finish

coat). • No cement and harmful chemical additives. • Void structure will allow for salt deposits*.• 1mm render = 1% U Value improvement.

ThankYou

www.cornishlime.co.uk @cornish.lime @cornish_lime linkedin.com/in/cornishlime