When restoring period Brickwork & masonry it is so important to do all that can can be done to get the blend of lime and aggregate as close to the original as possible.
Period mortars were often made up to local recipes using the raw materials from the area, so they vary a lot!
SJ SPECIALIST BRICKWORK have a wide range of sources for aggregate ,we will take the time to analyse the original mortar make up by taking samples and then blending our mix to suit.
The right aggregate will produce a mortar that functions as it should and of course looks just right once cured- the colour is critical, so often you will see poorly thought through repairs that stand out simply because the colour is so different.
Consider then, texture and colour, making up a sample, letting it dry and matching this back to the original.Consider also, the other ingredients such as chalk, charcoal and flint, all of which can be found in certain mortars.
The other factor that affects the mortar would be the lime.
Lime comes in two main forms:
Slaked lime ( putty) and Hydraulic lime ( NHL,which comes in different strengths ).
We will use our experience to select the appropriate lime for the job, but will more often than not use lime putty in our work, especially on the listed buildings that we restore.
Lime putty will vary in colour and texture and we will draw upon different suppliers again to achieve as good a match as we can.
When breaking down the original mortar for analysis you will often find lumps of slaked lime putty that have not been mixed into the aggregate-they appear as grey or white lumps in the mortar joint.
It can be difficult to match this, but one excellent slaked lime mortar that can be sourced for this type of finish is from Ty Mawr their course putty is a top class product .
Another supplier of excellent lime is of course Mike Wye and associates . Both companies are very happy to offer free advice on their products.
The putty to aggregate mix will vary, but on the whole around 3: 1 ratio of aggregate to putty is a guide.
Once cured lime putty mixes are very breathable and will certainly help to allow abuilding to function as it should as well as looking good!
Hydrated lime (NHLs)
These come in different strengths and again shades from grey to cream to white.
Unlike putty, NHL (Naturally Hydraulic Lime) will set in water- it is a different product entirely,behaves a bit like a modern cement, but weaker and is a very useful material for specific jobs.
We will use them where there is a definite risk from damp/frost wind damage or where we need a strong mortar to do a specific job, but will always use a putty if we can as this comes closer in our opinion to the original.
NHLs come in roughly 2 ,3.5 and 5 strengths, but will vary within this dependant upon the brand.
Castle ,St Astier, Singleton Birch and Breckweg all have different properties, colours , set times and strengths within the numerical guide range.
NHLs can be stronger than a putty mix, but the other side of the coin is that they can also be less breathable, so it will really depend upon the renovation /restoration project and within that the specific function required as to which one to use- that is where our experience is vital!
Used with selected aggregates it is possible to achieve a match to period brickwork with either lime product, but our first preference will always be putty.
There is a lot of information about lime mortars available on line, some very good indeed, but it can be confusing too, so if in doubt ask either the suppliers or craftsmen .
We are members of the GUILD OF MASTER CRAFTSMEN which is an assurance that our work is monitored, our skills vetted and our reputation excellent.
More on lime matters later……
