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Pointing & Harling

Pointing and Wall Rendering

Masonry pointing is the material between the brick or stone in a wall or building structure. It is a bond designed to be sacrificial in the structure, therefore protecting the actual brick or stone with which the structure is built. Pointing of a brick or stone wall is integral to the structural strength of the building. Once the pointing has broken down and become defective the building can start suffering the effects of penetrating damp and in time loose masonry.

Cement Mortar

Not all is the same! In modern houses built with hard high density brick, the bricks are usually bonded with a cement based mortar is a hard substance, but the bricks used in these buildings are even harder, therefore is a suitable material for pointing.

Lime Mortar

Before the introduction of cement in the early 1900's older properties, using softer, less hard wearing brick or stone, lime mortars were used for pointing. This is because lime mortar is a softer substance than the brick and stone used in the structure, therefore remaining sacrificial.

In these cases, replacing the lime mortar with a cement based pointing simply doesn't work. The cement is too strong for the brick or stone and simply delaminates the surface of the softer stone or brick to which it is bonded .

Correct Masonry Pointing

We know how essential it is to specify the correct type of replacement masonry pointing, to achieve a long lasting economical solution. We offer the service of a mortar analysis to identify the original composite of the mortar, to ensure the same type and strength of pointing is used.

It is also imperative that any repointing that is applied is done so to an adequate depth, back pointed if needed and the masonry is correctly prepared. Preparation involves removing the presence of dust and loose material and damping the wall to achieve the correct suction. These are all very important factors to the success, life span and integral strength of the masonry pointing.

Rendering

Traditional rendering methods require the use in a base or scratch coat as shown in the picture left, to provide an adequate key for the top coat to bond to. One of the most important but often neglected ingredients of lime render and cement render is the type, quality and quantity of sand used in each particular type of render. Polymer renders are pre bagged in a powder format so the only thing added is clean water. The use of nylon reinforced basecoats create extremely durable polymer renders. On certain substrates a metal lath system can be used to overcome many problems and achieve greater aesthetic appearances. There are many different finishes that can be achieved with rendering , ranging from a sponged finish which is flat and smooth, a scratched finish which involves scratching back the top coat to leave a rougher finish (see first image), or even a scalloped finish which leaves visible trowel marks. There are also other types of decorative finishes achieved by using spar for pebbledashed finishes. Tyrolean or stucco for a roughcast appearance both of which are particularly useful to conceal uneven walls or alterations to a building.

Lime Rendering

Traditional natural hydraulic lime render (NHL) or Lime Render as it is more commonly referred has been used for hundreds of years across a broad range of substrates. Lime render is by far the most breathable render product available, although relatively soft, lime render expands and contracts with the building which makes it particularly suited to older buildings or wooden framed buildings. Lime renders range in strength from feebly hydraulic lime, moderately hydraulic lime to eminently hydraulic lime each having its own suitable substrate and application benefits.

Chopped hair or fibre can be added to reinforce render base coats and the addition of casein which is a natural extract of cow's milk is particularly useful on difficult substrates as it acts as a plasticizer. As mentioned previously, a new breed of natural hydraulic lime renders are available called monocouche (or one-coat) systems. These are particularly suited to light weight thermalite blocks, concrete blocks and stainless steel mesh. There are also wood fibre insulation boards and insulated render coats available making lime a favourable option for an eco-friendly new build project.

Lime renders should not be confused with hydrated lime products.Hydrated lime products can be found in builders merchants and are used as an additive to cement mixes to extend the properties of the cement but differ vastly from natural hydraulic lime renders.

Natural hydraulic lime render, requires a high level of skill to apply them. Good mixing practices are paramount to the quality of the product. It cannot be stressed enough how important it is to use well graded, washed sharp sand or river sand in lime renders, these are usually only found from specialist high quality suppliers and are far superior to manmade sand which are manufactured by crushing stone such as sand stone. Using low quality sand, contaminated sand or soft sand results in high levels of shrinkage, cracking and spalling of the render system ultimately causing failure of render.

Lime renders were traditionally applied without the use of corner beads or stop beads. Corner beads and stop beads may sometimes be used in restoration projects to rebuild the substrate but can be hidden underneath the finishing coat. Lime render is often applied in a rustic style following the contours of the building and allowing shading of the finish coat to give a traditional and natural appearance.

Lime renders are available as standard renders or through coloured renders in many different colours and shades. The addition of harling or spar can mixed into the finishing coat and either cast by hand the traditional way or spray applied using gravity fed hoppers. Once cured, lime readers require very little maintenance and have a very long life span. Lime renders are Eco-Friendly as they absorb Co2 out of the atmosphere while curing. When fully cured the lime render sets back to lime stone state and provides a very durable finish.

Suitable substrate for Lime Render: Solid stone with rubble filled walls, timber framed buildings, straw bale constructed buildings, new builds using thermalite blocks or breeze block, clay brick built buildings, Accrington engineered brick buildings, insulated fibreboard, metal lath or wooden lath. Other substrates may also be suitable.

Cement Render

Modern cement render is much harder and stronger than lime render. A sealed or painted cement render can benefit a building in certain circumstances by helping prevent penetrating damp. Cement renders are generally mixed using ordinary Portland cement. As these are so rigid they are not suitable to older buildings as they crack and spall in no time at all. Hydrated lime can be added to the cement mix to increase durability and flexibility of the render but it by no means cures all problems associated with cement render.

Cement renders are generally a cheaper alternative to Lime Render or Polymer Renders. They are often applied as they are cheap for the builder to make and relatively easy to apply. Cement render also cures reasonably quickly when additives are used, but caution should be taken when specifying cement renders as they are incredibly rigid and will crack, spall or delaminate if there is any movement in the substrate or levels of moisture build up too high within the render.

Suitable substrate: A cement render would be suited to a modern building, constructed with a double skin wall with wall tiles. The wall will need to be permanently dry and free of defects such as movement around windows and must never be applied below the damp course. Metal lath is suitable other substrate may also be suitable.