Correct surface preparation is key to successful bonding. In many instances, all that is required, with Sika's Marine Product Line, is a simple cleaning operation, but where there are weak or contaminated surfaces, more extensive preparation is needed to ensure a perfect and long lasting bond. Typical problem areas include dust, dirt, grease, fat, oil, rust, flaking paint, moisture, vapours, etc.
The actual pretreatment selected will depend on the:
Type of substrate (metal, plastic, paint, wood, etc.)
Operating conditions in service
Degree of surface deterioration
Practicalities of any particular installation
Detailed information can be found in our surface preparation table. (The Primer Chart for Sika Marine Applications (see chapter 10) is also available separately from your local Sika Company.)
Some kind of mechanical preparation will be required if:
Corrosion is apparent
The surface layers are weak
Surface degradation is visible (e.g. weathered) but surface coatings are still adhering strongly
An incompatible coating is present
The level of cleaning will be determined by the type of surface and the degree of deterioration. Preparation techniques include any combination in the use of abrasive nylon pads, abrasive paper or fabric, wire brushing, abrasive wheels, and wet or dry grit blasting. Following mechanical treatment, additional cleaning with solvents or vacuum cleaning may be required.
Dust Removal and Degreasing
If compressed air is used to remove dust from surfaces, the air should be filtered to prevent contamination from oil particles. The use of vacuum cleaners is often even better for dust removal. All nonporous surfaces must be cleaned prior to the application of Sikaflex, SikaSil, SikaForce or SikaFast. Only Sika recommended cleaning materials should be used. Solvents, such as white spirits, are not recommended as they contain residues which might hinder subsequent adhesion. Always use clean, lint-free wipes and change them frequently to ensure that the contamination is removed from and not redistributed over the surface. Once clean, the substrates should be left to completely dry before proceeding to the next operation.
||Certain solvents, including Sika Cleaner-226 and Sika Aktivator, are not recommended to be used on absorbent substrates because liquid solvents can affect the curing mechanism of Sikaflex polyurethane based adhesives. Generally, non-evaporated solvents on the surface may impair the cure and the subsequent adhesion of adhesives and sealants, and may result in failure of a joint or bond. Always respect the flash-off times
Certain substrates such as polyethylene (PE), polypropylene (PP) or polyoxymethylene (POM) require a more sophisticated surface preparation such as chemical etching, electrical discharge or plasma treatment to assure proper adhesion. In these instances the local Sika Company should be contacted for advice.