MM STEP REPAIR MORTAR

MM STEP REPAIR MORTAR – Repair of Worn or Defective Steps.

Step repairs in the context of this document, are carried out to the existing or original plane, line and level, not over-coating, that would create a difference in the height of the risers. Steps, going and risers should be consistent, except on a winding staircase where the going will be wider at the outside of the radius than at the centre point, the risers will however still all be the same height.

Both the going width and the riser height on all straight flights should be consistent, if not the steps become a trip hazard. As little as 3mm of variation in the height of a riser in mid flight can cause any one to lose balance and fall.

There are exceptions – not planned, but that have over time created a change in height mostly as a function of pavement levels.  Often altered by local authorities and services contractors, the bottom step to a pavement may well change significantly over time, it is not how steps heights are calculated at the outset, but this often means that the altered height of the bottom step just has to be maintained.

The height of risers between landings must not be altered – over coating all steps can be acceptable as long as this is followed through the entire stair. (Where a full tread repair is required, and the thickness of the repair is at least 15mm a full tread may be carried out but with the first layer (10mm minimum) fully bonded with fibres and the finish applied at not less than 5mm wet on wet. –(Always seek advice on this type of repair as there may be structural implications)

 

Step repairs are required when the goings (treads) and risers, become worn through foot traffic, accidental damage and the like.

In areas of foot traffic, the surface repair materials must reach at least 20MPa before a reasonable degree of wear capability is achieved, less than 20MPa will result in wear from common foot traffic.

Step repairs must be carried out in a logical sensible manner, must achieve a sound bond, be consistent in thickness, applied in layers where required, to achieve even curing and drying. Repairs must finish flush with the surrounding going or riser or both and should be finished such that the line and plane of the repairs leave safe navigable passage without deviation in going (tread) dimension or riser height.

The drawings provided, 1, 2, 3 and SK1a show three typical steps from a pavement rising to a landing, commonly supported on support walls in basement areas of tenement buildings. These are probably the most common locations for step repairs subjected to external weathering. Drawing SK1a shows step ends affected by movement of, or corrosion of imbedded metal and refers to the issues associated with pen check staircases.

From the design stage, the masonry used in the majority of cases is amongst the densest, strongest stone available – seldom if ever are steps wrought from stone of less than 90 – 100 MPa in compression and generally 10 MPa or more flexural strength There are very few repair mortars that can achieve these strengths.

The vapour permeability of these types of stone is often very low, but not always. Many sandstones that are used for steps and slabs are tightly grained, free stones and generally low in overall porosity, adding to their durability. The more permeable a stone is, the less likely it will wear well when used as a slab or a step.

Drawing 1

Drawing 1 shows the general configuration with the 6 most common defects and the necessary reference points for ensuring the repairs that are carried out are accurate and properly sized.

Drawing 1          

1.Typical leading-edge damage to going and riser, deepest in the centre of the stairway where maximum foot traffic occurs, tapering out towards the less frequently trafficked edges. The centre areas are almost always where heavy items are bumped up, where prams and other wheeled items are pulled up, hence the riser damage is often on a similar scale to that of the going.

2.General wear, usually very old steps. Recent improvement in shoe design and manufacture, the use of trainers and light foot wear has had a major impact in improving foot health and because of the generally softer more forgiving man-made materials, wear characteristics have changed significantly. Historically Skegs, nails and tackety boots had a major impact on goings in particular, the re-soling of boots and shoes was common for the major part of the previous two hundred years, additionally rubber wheels replaced iron rims and therefore these forms of wear will be far less common in the future, and consequently require repair materials to handle the far less demanding conditions than that of even 30 years ago.

3.Significant cracking, boss, spalled or detached areas of stone can occur where there is rusting of metal railings imbedded either in lead or mortar or epoxy resins.  (See drawing SK1a – Step ends)

4.Generally, rusting imbedded railings causes this form of expansive damage. One should expect to see natural faults such as dries or flaws at the ends of steps. The builders might have stretched their standards when a natural fault was close to the end of the step, rather than having to discard the entire step. (See drawing SK1a – Step ends)

5.General erosion / wear that is greater than 3mm can often be left untouched on a staircase that is being carpeted where a fixed runner is being used to centre the carpet on the staircase. The repairs, completed within the tread covered by the stair carpet, are to the original level and plane. The areas of the step to the far left & right, may remain untouched.

6.Landings – ¼, ½ and full, can be subject to more wear and tear as these are traditional resting areas for heavy loads and manoeuvring of goods & materials before being lifted and carried up a flight of stairs. The principles of repair remain the same for landings, as they do for goings or risers.

The basics of step repair require the steps to be reinstated to their original line, level and plane, not always apparent or easy when the surface of the step is worn, but actually more often than not, very simple in practice.

Finding reference points for setting line, level and plane.

If all the steps are to be repaired, the problem of determining line, level and plane requires no more than simple arithmetic. Where possible damage from previous step repairs have obliterated all the actual evidence of original line, level and plane, the top landing and bottom landing provide the height of the steps divided by the number of risers, gives the riser dimension. In some instances, the bottom step will have altered as a result of level changes, particularly prevalent where pavements have been re-laid. In these instances, a calculation – or best guess as to the likely height of the bottom step means the remaining risers will be accurate for safe access and egress.

The distance from the top riser face to the bottom riser face, divided by the number of goings (treads) gives the correct going dimensions.

Drawing 1 shows typical areas of failure 1-6.  A, B, C and D indicate reference points that will be closest to the original sizes, when the repairs are either isolated or as a function of normal tread wear or corrosion issues.

Position A is usually best to determine the riser height, but it is not always possible to access these areas because of built-in or later alteration, where risers are clearly all different sizes at all the most common reference points, calculation remains the safest option.

Position B is often the best location for determining the plane, line and level of the going, as there is almost never any abrasive wear at these locations. Rusting can cause expansion and bulging so “sounding” the areas before measuring to determine that the stone is solid is important. Again, if all reference points provide conflicting information, calculation should be used to determine the going level, line and plane.

Position C and D  – There are two ends on each step, one may be worn, the other perfectly OK or one element from one end can be used in conjunction with another element for the other end.

Drawing 2

To ensure the best result for repairs, they should be cut out to form neat, accurate mortises, irrespective of the original shape of the decay. The very least that is required is to remove all loose, friable and deleterious materials from the repair area.

Positions 1 and 2 Shows the irregular repair areas properly cut back in various levels in neat accurate straight lines and where practicable, level sections ready for filling with the repair mortar.

Repair mortar in this instance is MM STEP REPAIR  

Drawing 3

Reinforcing will be required where the repairs converge at the junction of the riser and going. This is a leading-edge repair and may often be the deepest repair required on the step. Reinforcing should consist of dowels. These need not be more than 2mm stainless wire, fixed in 4mm oversized holes with Rapid set, High Bond Crack-fill mortar and should be placed at the lowest level first, at 100mm centres along the leading-edge angle, as shown. Lacer wires, 3mm-4mm in diameter, are in blue (horizontals).

Dowels can be readily bent back over themselves to tie into other dowels to form a basic reinforcing cage. Horizontal members must be fixed at the leading edge of a tread repair and in any areas where there is more than 40mm in the depth of the repair.

All reinforcing should have at least 10mm cover. Mesh alone is not a suitable means of reinforcing step repairs.

Reinforcing is fixed by drilling close to or on the inside angle of an internal corner, shown in red. The drill should be angled such that the it enters at an angle of approximately 45 degrees from horizontal. Low level percussion or non-percussion drills may be required with certain masonry units. Dowels from 1.5mm – 3mm from stainless wire should be left long enough to tie in the centre of the reinforcing area.

The shape of the reinforcing is important. It should, where possible be brought out to a line and level consistent with the line of the leading edges of the repair area, such that when the horizontals are fixed in place, they run parallel to the leading edge of the repair. They need to be at a consistent height have a minimum 10mm cover and can be secured sufficiently with fine wire ties without compromising the 10mm cover rule.

Fill deep repairs more than 40mm in two or three passes, keep horizontal reinforcing out of the repair area until the final application to prevent restricting the working space.

For larger flatter areas such as those shown above at location 2 in Drawing 2, it is necessary to carefully scutch or tool the stone to as near as flat as possible to avoid significant differential thickness of repairs. Repairs of this type require fully bonded repairs; this means the use of a bonding bridge, SBR applied neat to the surface of the step, with the repair mortar being laid wet on wet.

All surface repairs should be filled to a level and line above the original or desired level. The final repair is then cut back as the mortar stiffens and hardens up. Surface finishing can be by scratch or needle float, pairing tools such as wood cutting chisels, trowel edges or by Carborundum sanding when the materials gain some strength. This would usually be done not more than 24 hours after application but will depend on personal choice and timing. However, finishing can be left for weeks if needed. In these circumstances, the use of conventional Masons tools and or mechanical buffing & shaping will be required.

Drawing SK1a

Step ends – Open stringers with handrails, expanding corroding or mechanical damage from imbedded metal in steps.

Damage around imbedded railings and handrails – often only detected by resonance testing (sounding)  where initial expansion of the metal work has generated a very fine crack line – all step ends with imbedded metal should be checked by resonance testing before determining the full extent of repairs.

Where A – B is the finished line of materials cut out from the body of the tread – this may be dictated by the radial fractures caused by expansion of the imbedded metal work of the bannister, or where the masonry has split & spalled as a function of weaknesses in the natural bedding plane or both.

Cut out with diamond discs in a series of parallel lines running from the face of the riser to the back of the step. Where pencheck’s are worked to a diminishing waist – narrow to the back of the step as shown. Seek advice if cutting out will reduce the working thickness of the waist of the pencheck by more than ¼.

C –  is a twisted wire dowel drilled into the body of the tread on the horizontal and vertical faces.

Drill holes should be angled into the thickest sections of masonry and never drilled towards thinning masonry or towards an outside face or edge. Holes should be not more than 6mm in diameter and not less than 3.5mm diameter and at least 30mm deep but must not exceed 50% of the masonry thickness. 1 strand of 16 Gauge stainless or copper wire twisted around a 3mm diameter dowel to form an eyelet as shown, should be used for all areas where the repair does not compromise the structural integrity of the masonry. For deeper repairs, the wire may be doubled up and be twisted with eyelets at 20mm diameter. Wire dowels should be fixed in place with high bond fast setting mortar (Rapid set, High Bond Crack-fill mortar)

D  – is the corroded, expanded palling (The vertical component in a banister) that caused the step to fracture in the first place. Wire brushed all around to check the integrity of the metal – after descaling and cleaning, retain the imbedded section only if at least 2/3rds of the metal is sound and corrosion free – otherwise cut and weld a new section of similar material or replace entirely. Treat retained cleaned imbedded metal with an anti-corrosion mortar suitable for marine environment (MMACC) ensuring nothing contaminates the freshly exposed, cut back masonry.

Reform the step using MM STEP REPAIR mortar, over fill the repair and shape back as the mortar stiffens and hardens (Not less than 6-12 hours after application, depending on temperature).  Form work can often allow the repair to be filled in a single pass. An open stringer allows the use of carpenters clamps to support simple form work. Individual railings should be properly spaced, tied and clamped together to keep them stable and movement free when the mortar is placed, and for at least 48 hours after final curing and finishing. However, a run of railings, need to be kept secure for at least 7 days. If the work is to be built up, allow at least 1 hour but not more than 2 hours between layers of mortar, up to 60mm can be placed in a single pass on horizontal surfaces and 40mm on vertical faces.

Total surface covering of stone steps requires different materials and a different approach.

High strength materials are required to effectively cover over steps. The repairs are built up in thin layers to a level and final single application – homogeneously applied over the whole area for a uniform finish.

Temporary suspension of the use of steps is essential during the repair process. One option is to repair half the flight on one side and once fully hardened, repair the other half, in this case access is continuous even though it may be restricted. In all other instances for repairs to be done successfully, the steps have to be decommissioned and where appropriate, alternative access and egress provided. Within certain limits, temporary scaffolding staircases can be usefully employed for most entrance ways.

Masons Mortar Ltd guides are provided to our customers for use with our materials, they are not specifications and are for general guidance only.

All materials inclusive of graphics are under copyright 2009. Any person, company, institution or organisation responsible for unauthorised duplication, replication or copying in any form of this document will be prosecuted.

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