Case 2

Peeling of Waterproof Coating

Introduction

The peeling of the waterproof coating on the roof deck is evident on this section of the roof. The peeling of the waterproof coating can be attributed to a number of factors. A few of such factors are using too many layers, improper painting surface preparation, high temperatures, water damage, poor quality of waterproof coating, failure of waterproofing membrane, etc.

The peeling of waterproof coating can be attributed to the following reasons:

Lack of Adhesion
Water Damage
High Temperature
High Exposure to Sunlight and Extreme Dryness
Incompatible Paint Used

Peeling occurs when there is a lack of adhesion between the waterproof coating and the surface it is painted on. A number of factors could have contributed to the loss of adhesion. One such factor would be improper preparation of the surface. For the coating to stick properly, the surface should be prepared adequately. Uneven or unprimed surface will cause any coating applied to it to peel quickly.

Another factor would be water damage. As this section of the building is near to the ground, rising dampness will cause the substrate that the paint is applied on to be constantly wet or damp. Paint does not adhere well to wet or damp surfaces, resulting in the peeling of the paints.

Another factor would be the high temperatures. The waterproof coating on the roof deck is exposed to the external environment daily, causing the substrate to reach high temperatures. When the coating is applied, high temperatures of the substrate will cause it to dry faster, preventing the layers from forming strong bonds with the substrate.

Exposure to intense sunlight makes oil-based paints vulnerable to cracking. Elastic and latex paints tend to contract and expand when exposed to direct sunlight, which weakens their adhesive bonds. As the paint in the image is used on the roof deck, the paint is exposed to sunlight daily. The intense sunlight may lead to extreme dryness of the paint. Extreme dryness of the paint can prevent the formation of strong adhesive bonds that allow the innermost coating of paint to stick to the surface properly. Similarly to painting highly humid surfaces, extreme dryness causes any newly applied coats of paint to peel.

Lastly, the paint used may not have been compatible with the surface. Some surfaces are not compatible with certain types of paints. Some synthetic polymer materials can prevent the paint from having full adhesion, Oil-based paints are affected by galvanized steel and concrete, Wood surfaces can produce natural oils which can prevent paint adhesion. Smooth surfaces are unable to form a mechanical adhesion with some paints, so any layers applied to them could peel off immediately. In this case, the surface might have been smooth which led to poor adhesion with the paint.

Preventive Measures

Design:

Specify the use of a breathable paint system to reduce trapped moisture and to avoid wetness and dampness of basement walls. Fungi resistant paint is also required. Avoid the use of Alkyd based paint on concrete surfaces that may lead to saponification (i.e. the formation of oily patches)

When selecting the paint, consider substrate, environment, application method, the feasibility of surface preparation, over-coating interval, and appearance.

Construction:

Ensure adequate curing of the substrate before paint application to avoid shrinkage cracks. Clean surface and use clean tools. Avoid prolonged storing, inadequate stirring, use of incompatible thinner/solvent, or mixing with leftover paints from previous batches.

Ensure that coatings are always applied in a minimum of two coats. The material should possess some degree of flexibility (i.e. be elastomeric) to reduce the risk of cracking due to thermal/moisture movements.

If the paint is brush-applied, the second coat should be at right angles to the first coat to help eliminate pinholes and avoid chemical attacks.

Corrective Measures

Regular inspection is important to detect or identify the defects immediately so that corrective maintenance could be carried out at the early stages to prevent further complexities. Visual inspection techniques or instrumentation techniques can be used for regular inspections.

Diagnostics of Defects:

Visual Inspection

Inspect at reasonable intervals to identify any peeling of paint.

Use of Moisture Meter

A Moisture meter can be used to measure the reduced resistance between two probes when they are embedded in damp materials. It can be used to trace areas of walls affected by rising dampness or rain penetration. Measurements should be taken at regular intervals to distinguish between surface dampness or dampness within the wall.

Remedial

Inspect at reasonable intervals to identify necessary repairs (depending on the type of coating, degree of exposure to elements, and accessibility, it can range between 3–10 years).

The Remedial Steps are as follows:

First, the loose-defoliated material should be removed. Any repairs that need to be done, must be done before the new waterproofing layer is applied.
Thorough cleaning of the surface from dust and foreign particles
Complete application of the primer on the ceiling
After the primer has dried, a layer of waterproofing sealant is applied along the junction of the roof with vertical elements. While the layer is still fresh, the sealant is reinforced with a strip of polyester fabric or fiberglass
This is followed by a universal coating of the roof with the sealant (in at least two layers) and at the same time reinforcement of the first layer with a strip of polyester fabric or Fiberglass mesh. If there are no suitable slopes on the roof, polyurethane waterproofing should be used after applying the primer.

Standards

Paints:

BS EN 1504-2 Products and systems for the protection and repair of concrete structures. Definitions, requirements, quality control and evaluation of conformity. Surface protection systems for concrete

BS 6150 Painting of buildings. Code of practice

SS 542 Code of practice for painting of buildings

SS 150 Specification for emulsion paint for decorative purposes

SS 554 Code of practice for indoor air quality for air-conditioned buildings

BS EN ISO 12944-4 Paints and varnishes. Corrosion protection of steel structures by protective paint systems. Types of surface and surface preparation

BS EN ISO 1513 Paints and varnishes. Examination and preparation of test samples

ASTM C33/C33M-16e1 Painting of buildings. Code of practice

ASTM E1667-95a Paints and varnishes. Corrosion protection of steel structures by protective paint systems. Types of surface and surface preparation

ASTM E903-12 Paints and varnishes. Examination and preparation of test samples

BS 4873 Code of practice for painting of buildings

Waterproofing:

BS 8102 Code of practice for protection of below ground structures against water from the ground

BS 8217 Reinforced bitumen membranes for roofing. Code of practice

BS 8747 Reinforced bitumen membranes (RBMs) for roofing. Guide to selection and specification

SS 374 Preformed waterproofing membranes for concealed roof

SS 133 Specification for bituminous emulsion for roof waterproofing

BS EN 12730 Flexible sheets for waterproofing. Bitumen, plastic and rubber sheets for roof waterproofing – Determination of resistance to static loading

BS EN 13416 Flexible sheets for waterproofing. Bitumen, plastic and rubber sheets for roof waterproofing. Rules for sampling

BS EN 12039 Flexible sheets for waterproofing. Bitumen sheets for roof waterproofing. Determination of adhesion of granules

BS EN 1108 Flexible sheets for waterproofing. Bitumen sheets for roof waterproofing. Determination of form stability under cyclical temperature changes

BS EN 1107-2 Flexible sheets for waterproofing. Determination of dimensional stability. Plastic and rubber sheets for roof waterproofing

BS 6229 Flat roofs with continuously supported flexible waterproof coverings. Code of practice

SS 637 (formerly CP 82) Code of practice for waterproofing of reinforced concrete buildings

AS 3740 Waterproofing of domestic wet areas

BS 5427 Code of practice for waterproofing of reinforced concrete buildings

Concrete:

BS EN 1992-1-1 Eurocode 2: Design of concrete structures. General rules and rules for buildings

BS EN 1992-3 Eurocode 2. Design of concrete structures. Liquid retaining and containing structures

BS 8204-2 Screeds, bases and in situ floorings. Concrete wearing surfaces. Code of practice

CP 65-1 Code of practice for structural use of concrete – Design and construction

Repair Works:

BS 8221-1 Code of practice for cleaning and surface repair of buildings. Cleaning of natural stone, brick, terracotta and concrete

BS 8221-2 Code of practice for cleaning and surface repair of buildings. Surface repair of natural stones, brick and terracotta

SS 509-1 Code of practice for cleaning and surface repair of buildings – Part 1 : Cleaning of natural stone, brick, terracotta, concrete and rendered finishes

SS 509-2 Code of practice for cleaning and surface repair of buildings – Surface repair of natural stones, brick, terracotta and rendered finishes

BS 8000-0 Workmanship on construction sites. Introduction and general principles

BS 8000-9 Workmanship on building sites. Cementitious levelling screeds and wearing screeds. Code of practice

ASTM C1496-18 Eurocode 2: Design of concrete structures. General rules and rules for buildings

BS 8298-1 Code of practice for the design and installation of natural stone cladding and lining. General

References

[1] PPD Painting. (2019). Why Does Paint Peel – Most Common Reasons. PPD Painting. https://www.ppdpainting.com/blog/why-is-my-commercial-paint-peeling/

[2] Hadjiyiannis. (2022). Peeling of waterproofing layer: Issue & Solution. Hadjiyiannis. https://www.hadjiyiannis.com.cy/peeling-of-waterproofing-layer-issue-solution/

[3] SS652:2019 Singapore Standard Maintainability of Facilities