Specialist protective coatings are highly complex materials. They are generally a thin film that protects two reactive materials with many factors affecting the success of their application.
Over the past few months CSC Services have seen an increase in enquiries relating to refurbishment of structures where coatings have failed. Failures and defects manifest themselves in many ways. Here, Mick Flounders, CSC Services’ Contracts Director considers some of the key features to look out for and things to avoid, before, during and after application.
Some coatings can fail even before installation. If products are not stored correctly in an airtight container, you may experience skinning or settlement. This is very common when paints and coatings are stored in warm places or are used outside of their shelf life. A contractor should always refer to the product data sheet to ensure correct storage, and never use products that have been partially used or are out of date. Tell tale signs that this has happened include different shades of colour in places and an inconsistent texture to the finished installation.
Look out for drip marks, folds and sagging before a coating has set. This downward movement of a coating, which will be very apparent on vertical surfaces will usually indicate over application, incorrect mixing or just general poor workmanship. A contractor should always be installing products as directed on the data sheet, at the recommended dry-film thickness using correct application techniques.
If you can see clear bubbles on the surface of the coating, the correct environmental conditions recommended for application may not have been adhered to. A high surface temperature can be a common cause for what is often know as solvent popping, when the solvent evaporates from the coating. Film thickness may cause popping if there is too much solvent in the coating.
If the coating has been spray-applied, spraying too close may have also caused problems. This will usually be evident with an orange peel effect on the coating surface. This is usually caused by improper application technique and can also indicate that air pressure was too low.
Once the structure is back in service, an evident sign that the coating has failed is blistering or bubbling. Blisters tend to contain liquid and are generally a dome shape, protruding from the coating. Bubbles are more common with vapour or gas. The reasons bubbling and blistering occur can be complex but are usually linked to surface contamination and highlight the need for correct substrate preparation. Thermal gradient may also have an impact.
If spots of rust start to appear, corrosion has taken place and the protective coating has failed, allowing water and oxygen to penetrate the steel substrate. Rust will often start as individual spots and then rapidly increase in density. This will usually occur due to low film thickness but could also be due to defects in the steel.
Even when a coating has been properly installed, crevice corrosion may attack the edges of nuts and rivet heads, and beneath steel plates, side barings and fasteners. There are now rust mitigating coating systems that can neutralise the acid in crevice corroded joints and stop the corrosion. A reputable contractor would be able to advise on and install such products.
For more information on the range of protective coatings that CSC Services can install call 0191 410 3444 today.
Mick Flounders is NACE certified Coatings Inspector. Follow Mick on Linked In.
