Remedial Works

remedial worksH.A Marks Facades are proficient experts in facades restoration and remedial works, ensuring through diligent workmanship, and using only the highest quality materials and techniques, that problems with facade failures are repaired impeccably and don't reoccur.

Modern facades failures can be caused by a multitude of issues and H.A Marks has the experience and expertise necessary to perform correctional works reliably. Contact us today if you believe you have an issue that warrants our restorative work.

 

Common causes of facade failures are:

1. Cut-edge exposure

The trouble with steel is it corrodes in the presence of oxygen, a process which is accelerated with the addition of water and pollutants. This combination describes most external environments in the UK.

To counter steel corrosion, manufacturers of steel sheets apply a corrosion-protection layer such as hot-dip zinc galvanising or zinc–aluminium alloy. If required, an additional decorative organic coating such as PVC also enhances the corrosion protection.

However, the resulting coils of carefully protected steel sheets, which are hundreds of metres in length, are then cut into manageable lengths, exposing unprotected steel at the cut ends. For an initial period the exposed steel edges are protected by the zinc layer which corrodes “sacrificially” for the steel. In the long term, cut-edge corrosion is unavoidable.

The risk of premature edge corrosion can be reduced by specifying sheeting which is manufactured to minimise edge corrosion risk. For example, sheets with zinc–aluminium alloy have lower rates of sacrificial corrosion, and steel would last longer than those with pure zinc coating.

Painting the cut edges and periodic re-painting where access is possible may provide a solution. If sheets with corroded edges are not repaired or replaced, further damage to the sheet may result, with increased risk of water penetration. Delamination of decorative coating may also be associated with cut-edge corrosion.

 

2. Fixings: corrosion and leaking

Steel cladding sheets need to be secured in place. Through-fixing may appear to be a straightforward fixing method but it creates a hole in the sheet, in effect compromising water and air permeability resistance.

Self-drilling and tapping screws with integral washers are normally used to maintain weather tightness. The best-performing washers are made of EPDM and the thickness and material hardness should be specified for the application.

Fasteners should be selected with durability similar to the expected life of the sheeting. Typically, this means austenitic stainless steel fasteners grade 1.4301 to BS 10088 (UK type 304) for more than 25 year life in urban or polluted environments. Special precautions may be necessary in coastal environments.

Where different metals are in contact, bimetallic corrosion may take place. Leaks may occur if corrosion takes place, the fasteners have been over or under-tightened or fixed crookedly, washers deteriorate, and fixings have insufficient pull-out resistance.

 

3. Condensation: water damage

Condensation can result in moisture accumulation with associated deterioration from corrosion and mould growth, as well as reduced thermal efficiency. The investigation of surface or interstitial condensation to enable successful remedial measures to be designed may take time. Monitoring may be required. The element may need to be opened up to establish the actual construction and processes at work. Investigations should also provide information to enable a remedial solution to be proposed to minimise thermal bridges as well as the risk of surface condensation or interstitial condensation.

The code of practice for condensation control, BS 5250, refers to BS EN ISO 6946 and 13788 for calculation methods to model thermal transmittance and condensation risk. 

Condensation on the underside of sheets may exacerbate cut-edge and fastener corrosion.

 

4. Expansion and contraction

Distortion, warping or buckling of sheets and around fixings may be the result of thermal movement. Dark coloured sheeting above a layer of insulation is most at risk. Cladding surface temperature may increase by 75°C in a 24-hr period, causing nearly 5.5mm expansion for a 6m-long sheet. A surface temperature decrease of 50°C would result in a 6m sheet contracting 3.6mm. Allowance for this scale of expansion and contraction around fixings is critical in avoiding this defect.

 

5. Render failures

  • Cracking

    This is the most common failure in render and may be caused by: thermal, or moisture-induced movement; drying shrinkage; frost damage; differential movement; impact damage and thermal shock in the case of insulated renders.

  • Delamination

    This may be due to poor adhesion with the substrate or where cracks allow water penetrationbetween the render and substrate.

  • Surface Crazing

    This can be caused by differential shrinkage in the thickness of the rendering. It is unlikely to cause water penetration.

  • Impact Damage

    Insulated renders and unmodified cementitious render systems are more prone to impact damage.

  • Chemical Attack

    Polluted urban or industrial environments with concentrations of sulphates and nitrogen oxide in the atmosphere attack the cement content of the render, resulting in crumbling and spalling. Smooth renders are particularly prone to damage.

  • Failure of Insulated Render Systems

    The render on these systems can fail as detailed above. Furthermore, mechanical fixings may fail if they cannot withstand wind forces. Likewise, adhesive-bonded insulated render systems depend on the integrity of the substrate and degree of contact between boards and wall.