Always use the best possible ‘air lime’ and suitable aggregate to ensure the material allows any ingressed moisture to escape. Do not simply chose or allow a ‘sand’ that visually and superficially matches an earlier used mix. At Vivus we choose an aggregate not only for its’ visual match but also for it’s porosity. Porous aggregates work better with lime to ensure humidity is removed to the outside.
If possible use lime wash to coat the exterior. This material is very traditional, has been used for many thousands of years because it not only allows a wall to evaporate its’ humidity but also closes and fills water traps in the surface. The modern term for this process is ‘breathability’ although this term is too simplistic for the process that is actually happening in a traditionally built structure.
Do not ever use modern plastic or other proprietary paint products to coat the external face of walls. These materials are catastrophic for the structure and retain any moisture that may find its’ way into that structure including any attempts the walls may be making to remove internal humidity.
For repainting lime walls, limewash, distempers, and modern breathable paints of good reputable quality can be used.
If internal walls have been papered, the same surface paints [if painted] as above should be employed. Everything is about allowing the walls to work at removing internal air-borne humidity.
If, for instance, paper is pealing it says that the humidity levels have reached a tipping point and that the management/occupation regimes need to be altered as described elsewhere.
To re-adhere the paper simply use paper glue and re-paste back onto the wall.
Never use heavy paper, especially ‘shiny’ printed or strong glues as these will remove any ability the wall has to act as a humidity buffer. This will then negate the use of the lime materials and render the wall impervious.
For plaster repairs, Vivus Solutions has a range of plaster skim and skim repair materials specifically designed to match not only the visible material but the nature and type of material and its performance characteristics in relation to humidity control.
M I X I N G V I V U S L I M E
A conventional cement mixer can be used however, a large paddle-mixer is easier. Lime mortars mixed in drum mixers are prone to balling and/or lining the inside of the mixer, rather than tumbling into itself. The following mixing procedure can go some way to reducing this problem.
1 Always add the water first to the bucket or mixing trough
2 Add the Vivus pre-mixed material to the water and mix with the paddle to achieve the desired consistency
3 Use immediately for best results.
4 Vivus can be remixed, even the following day, if too much has been made but more water will need to be added to achieve the desired consistency. Please be aware however that the speed of setting will be compromised as a result of this. It is however perfectly possible and acceptable.
5 Generally, further water can be added sparingly, until a useable consistency is achieved or to maintain the consistency, if stiffening too fast for the rate of work being carried out.
Storage of Vivus Materials
If bags are allowed to get wet the material may be irreversibly damaged. Also, once opened the exposure to air will start to weaken the set. As a result any part opened bags left at the end of the day should be carefully folded over at the top and put into a dry store or simply left up on pallets and properly covered with a tarpaulin, keeping out any additional moisture. In this state Vivus has been shown to remain useable for many years.
Traditional Lath and Internal plastering
Lath and plaster is a building technique used mainly for interior walls in period buildings. A lath is a narrow strip of wood approximately 2 inches wide which is nailed horizontally to each stud in the frame. Each lath is spaced approximately 1/4inch (thickness of the average little finger) away from the next leaving enough space for the mortar to push through and hook over the lath to form a key laths.
Preparation
The laths must be free from dirt, grease and vegetation. These elements should be removed before damaged laths are repaired.
First Coat
The following is the same process for plastering modern metal lath materials and any other solid surface, internally.
10mm thick, push the plaster into and across th laths at a 45 degree angle to the laths. Rough the surface by scraping back the latent left by the smoothing of the trowel action and leave ‘plucked and level’. This removed material can be put back into the bucket for further reuse. The plaster should be left until setting enough to receive the next coat without deforming. It is not necessary to leave until fully dried before applying the next coat. Infact the opposite is preferred.
Second Coat
The second coat also known as the intermediate or float coat will be applied similar to the first coat and is approximately a 7mm coat. Before scratching up and leaving in preparation of the finish coat again ‘pluck’ the latent surface by scraping back with the edge of the trowel. This encourages a faster drying and therefore the rate of work. Again, put the removed material back into the bucket for reuse. It is acceptable to float this surface to achieve a fine finished line ready for the final coat. This floating can be done at the point that the material will ‘accept’ the process without deforming. Again, leave until stiff/almost hard but not fully dry and then proceed to the next coat.
Finish Coat
Mix and apply Vivus top coat skim in two fine passes for best results, one immediately behind the other. Rule off and leave for a couple of hours. When ready rub up the finish coat using a plastic or wooden trowel to bring back the fat until the required finish has been reached. In the case of any light crazing this can be rubbed up and trowelled out. A steel trowel can also be used and the material can be polished until a mirror finish has been achieved! Continued burnishing will further enhance this polished effect.
Repointing
Protection
Before cutting out of defective mortars, windows, doors, drains, vegetation etc; should be covered and protected. Special care should be given to friable cut masonry and other special features
Cutting out of Defective Mortar
Considerable care must be taken when removing decayed mortar from historic masonry. When the mortar being removed is decayed or crumbly its removal can be carried out using hand tools. Plugging chisels, masonry chisels and old hacksaw blades used in conjunction with a club hammer will easily remove the mortar.
Never use chisels that are wider than the mortar joint as this may result in damage to the adjacent masonry. The removal of cement pointing will require greater care if damage to the adjacent masonry is to be avoided. If wide joints exist, a series of holes may be drilled through the centre of the joint, which will allow the joint to break inward when tapped with a chisel. On finer joints a tap with a sharp masonry chisel on the top and bottom of the joint will help to break the bond to the masonry at the edge of the joint.
The use of power tools or air chisels should only be carried out under strict supervision and by experienced personnel. Remember that the percussion action of these tools may loosen masonry.
Where lime mortar requires a chisel to remove it, it should be questioned whether its removal is necessary.
Depth of Joint
As a general rule joints are cut out to a depth of twice the height of the joint, quite clearly this rule applies to brickwork, but in the case of rubble masonry this could result in overly deep joints, which may de-stabilise sections of masonry. Therefore a minimum depth of 25mm will allow a good body of re-pointing mortar.
Notes should be taken if pinnings are removed in the cutting out process and these should be retained for re-use.
Cleaning the Joint
Once the joints have been cut out, they should be thoroughly cleaned. Brushing out with a small brush will remove loose mortar and dust, once this has been carried out, the joints should be flushed out with water. This must always proceed from the top, working down the building, ensuring all traces of debris are cleaned down. Where there are deep joints or voids, care must be taken not to flood the core of the wall.
Throwing Vivus into the joints with a deft backhand motion from the edge of a bucket trowel can fill the joints in one pass. By throwing, bond will have been achieved, compression will have been achieved, all voids will have been filled fully, all air will have been expelled. A snowball cannot be pasted onto a wall but when thrown……
Immediately cut the surface back with the empty trowel and throw the resultant into the next part of the joint or use it to fully fill the previous throw and cut off again to leave almost to line. DO NOT smooth or flatten the surface unless you then cut off the latent polished surface. Cracking is primarily caused by unequal drying of differing density of material….
Leave alone until the material is stiff enough to brush back with a wire brush to leave in a tidy finished state. This can often be the same day, depending on drying conditions.
DO NOT BEAT WITH A BRUSH. This is a nonsense practice and only began in the late ‘90s. It is madness and I know from where and the reasons the practice began. It will only serve to move the material through percussion which will weaken the bond in the joint. It will also case-harden the surface by increasing density of the surface alone. With a compressed denser surface, the frost can be prone to remove it and begin failure prematurely.
Wire brushing at the right moment will also remove any material that has landed on the faces or anywhere the material is not desired. Equally, at the right moment staining will be avoided – not too immediately, just at the point when the material is nearing drying.
Where there is evidence of stone pinnings/gallets or wide joints, the pinnings (small stone chips) should be packed into the new mortar. These will help to avoid overly large joints, which may result in shrinkage. Pinnings will also support weak areas of masonry.
Finish Style
The style of finish will depend on evidence left of the original work, but take care not to replicate styles from later remedial work. On brickwork, struck, weather struck, penny point, flush finish and tuck, are all common. These finishes can easily be achieved by leaving the material very tidy when wet/still plastic and finished as necessary but again, do not beat with a brush. On rubble masonry, it is unlikely to have been a distinct style, as the remains of the mortar are likely to be nothing more the struck off bedding mortar. Therefore, a joint, which is flush or slightly recessed, will blend with the masonry and is achieved as described above.
