Surface preparation is one of the most important processes when it comes to the (re)coating of a substrate. There are a number of factors which can directly influence a client’s decision on which surface preparation method to use, including: time available, monetary constraints, operational shutdown, environmental and H&S concerns.

Water Jetting

Water jetting is the process by which a stream of pressured water is used to prepare a surface prior to the application of a coating system. There is little set up time required when using water jetting. This method of surface preparation can prepare the surface and remove salt contamination all in the one process. Due to the environmentally friendly aspects of this preparation method, Health & Safety and Fire Precautions are also significantly reduced.
This method is gaining popularity due to their cost-effective and environmentally friendly nature. One consequence of water jetting is the inevitable development of flash rust on the surface; which is problematic for conventional paint systems. However, Chemco have eliminated this problem by developing innovative wet & rust technology where flash rust is acceptable.
These coatings exhibit exceptional adhesion to rusty or poorly prepared and wet surfaces, without compromising on the quality or long-term performance of the coatings.

Abrasive Blasting

Abrasive blasting is the process by which a stream of abrasive material is propelled against a substrate to prepare the surface before a coating system can be applied.
Abrasive blasting to Sa 2½ will always offer the best surface preparation. This is the method traditionally utilised for all conventional paint systems.
Unfortunately abrasive blasting encompasses a lengthy setup, large labour squads and extensive equipment requirements. Abrasive blasting also involves many time consuming processes; containment, collection, removal and disposal of the abrasive. Today it is considered a hazardous and costly process which is not permissible in many projects (e.g. Offshore).

Advantages of Water Jetting

By utilising the unique combination of water jetting and solvent-free coatings the advantages which can be achieved for both applicators and owners are substantial.
The number of surface preparation stages is significantly reduced. As previously stated, water jetting only requires one process to prepare the surface and remove any salt and other contamination.
Abrasive blasting already requires a form of pressure washing before the abrasive blasting itself even takes place.
Abrasive blasting is a hazardous process which carries many Health & Safety and Fire Precautions. Moreover, abrasive blasting will normally cause all other nearby ongoing work to halt due to the H&S and fire issues which are involved in the process. However, due to the environmentally friendly nature of water jetting, the H&S and Fire Precautions are significantly reduced, with applicator safety increased. There is also no disruption to other nearby ongoing work, meaning no operational shutdown is required. This will allow owners to obtain huge cost and time savings.

The Coating System of Choice

Chemco have developed a solvent-free coating system which is tolerant to wet & rusty surfaces. The material properties of this system allow it to be applied directly onto soaking wet surfaces with no adverse effect on the coating’s performance. This means that as soon as the water jetting surface preparation is complete, application of this coating system can begin. This will significantly reduce downtime resulting in huge cost savings being achieved.
In many instances, the adhesion value obtained by applying this system on a water-jet prepared surface actually outweighs the adhesion value obtained from applying conventional paints (solvent- based) on an abrasive blast prepared surface.
The coating system in question comprises of two coats. Firstly, one coat of solvent-free, wet & rust tolerant epoxy primer/finish Epo-chem™ RS 500P is applied. This is then top-coated with one coat of solvent-free, wet tolerant, glassflake epoxy Epo-chem™ RA 500M.
This system has many additional benefits which include:

• Environmentally friendly
• Solvent-free
• Increased applicator safety
• No disruption to other nearby ongoing work (including hot work)
• Significantly reduced downtime
• No recoating limitations (with itself)
• Reduced Health & Safety and Fire Precautions
• Ideal system for confined space applications
• Compatibility with shop primers
• Long-term corrosion protection

These coatings have been extensively used for almost all vessel areas including all tank internals, pipework, decks, superstructures, cofferdams, void spaces and engine rooms.
Source: Chemco International