Restoration & Conservation of beautiful period buildings isn't just a job to us, it's been a lifelong passion.

 

Lime mortars, lime plasters, lime renders, lime screeds, limecretes and limewashes provide for good moisture vapour permeability which is always important in period buildings.

 

Non Hydraulic Lime plasters (which we'll now just call Air Lime because when we get onto NHL limes, confusion only worsens) used internally can also provide thermal insulation when mixed with other correct natural elements.

 

Air lime remains flexible and is also 'self healing'; whereas cement based  products simply crack as buildings move, becausevthey are very dense materials which have high compressive strenths, allowing moisture to penetrate.

 

But because Air lime cures through evaporation and carbonation; it actually absorbs atmospheric CO² from. the air?

?as it sets,  (hence Air Lime)  therefore it removes CO² from the atmosphere meaning that if any cracks do appear, those cracks will  absorb more moisture as itbrains, and that moisture will then be re-evaporated again and more CO² will then absorbed again. Meaning Lime is helping the planet!

 

Further to all of this; lime itself posesses natural antibacterial properties that help to combatand reduce the spread of bacteria, germs, and mould/fungal growth within the home.

 

Knowing the correct type of lime to use for a specific task is important and this is where we can help.

 

Today we see a plethora of names used for lime products, including:

 

1 Quick lime

2 Lime kibble

3 Hot lime

4 Fat lime

5 Lime putty

6 Hydrated lime

7 Hydraulic lime

8 NHL 2.0

9 NHL 3.5

19 NHL 5.0

 

So lot's of confusion!

We'll go backwards: NHL stands for Natural Hydraulic Lime, butbfornow we'll just stick with HYDRAULIC 

L lime so to keep it  as easy as possible (NOTE: NHL can easily be confused for both non hydraulic and natural hydraulic limes)

 

We ha  ,, ?ve AIR LIMES ( No.s 1 to 6 above )

&  HYDRAULIC LIMES. ( No.s 7 to 10 above)

 

The HYDRAULIC  (NHL)  limes were introduced in the 1990's in the premixed bags we see today; before that we had to create our own Hydraulic lime mixes by introducing 'pozzolanic'  materials to AIR LIME mixes.

 

The numbers shown on HYDRAULIC LIME bags relate to their final "compressive strength" measured after 28 days of setting time, in the same way as Ordinary Portland Cement (OPC; commonly called 'cement') is measured @28 days.

 

The measurements used are 'Pascals' but as 1 Pascal is equal to 1 Newton per mm² we generally just say 2 Newtons, 3.5 Newtons & 5 Newtons.

We use Newtons in the UK simply becsuse that is a measurement  more commonly used and understood in the UK.Cement)   varies in compressive strength, generally between 30 N/mm² and 53 N/mm² 

 

Whereas HYDRAULIC LIMES obviously also vary in compressive strengths, .

 

l

pbetween 2 & 5 N/mm², however there has always been some "discussion" over whether or  not NHL's continue to 'strengthen' over time due to more moisture/ water contact over time. However we have never seen any evidence to prove this, so.that's just another "old wives tale" in our opinion until proven otherwise. (You'll soon realise that older buildings bring a lot of old wives tales with them and a lot of people today still try to tell a lot of of these old tales).

 

So to quickly finish up: 

 

Air Limes (No's 1 to 6) where moisture permeability & flexibility is required.

 

Hydraulic Limes  (No.s 7 to 10) where strength is required.

 

 

One last point: Hydraulic limes do have some moisture permeability, but much lower than Air Limes because they are  a very much more dense and harder material once set, so it is important to consider this, and consider it intelligently when choosing the correct lime for a particular task.