Bonding and Sealing Basics on Marine Application

Sika’s adhesives and sealants are working materials which show good affinity for other surfaces. Their task is to flow as a liquid onto and into the contours of a surface and then transform themselves into a solid, by developing both a physical and a chemical bond with the substrate. Sika Marine Adhesive and Sealant Systems can range from fluid liquids to heavy thixotropic paste-like systems, able to supply low-to-high-strength values and cure to a highly elastic or rigid bond.

The ability of the adhesive or sealant to “wet” a surface is very critical in the development of a proper bond; solidification (curing) can take place through a physical or a chemical reaction or through both at the same time. Experience has shown that chemically reactive adhesives like Sikaflex have the highest strength, durability and resistance to water.

Preparation

Correct surface preparation is key to successful bonding. Where there are weak or contaminated surfaces, extensive preparation maybe needed to ensure a perfect bond. Typical problems are dust, dirt, grease, oil, rust, flaking paint, etc. The preparation selected will depend on the type of substrate (metal,plastic, paint, wood, etc.), the operating conditions in service, the degree of surface deterioration and the practicalities of any particular installation. See the ‘notes on substrates’ in this manual or contact Sika for details.

Mechanical Cleaning

Mechanical preparation, will be required if, for example, corrosion is apparent, weak surface layers prevail, or surface degradation is showing. The level of cleaning will be determined by the type of surface and the degree of deterioration. Preparation techniques include the use of abrasive nylon pads, abrasive paper/fabric, wire brushing, abrasive wheels, and wet or dry grit blasting. Following mechanical treatment, additional cleaning with solvents
may also be required.

Dedusting, Degreasing

If compressed air is used to remove dust from surfaces, the air should be filtered to remove traces of oil. The use of vacuum cleaners is even better for dust removal. All nonporous surfaces must be cleaned prior to Sikaflex  application. Only Sika recommended cleaning materials should be used. Solvents,such as White Spirits and alcohol based, are not recommended as they can hinder cure or subsequent adhesion. Always use clean, lint free wipes, and change them frequently to ensure that the contamination is removed from and not redistributed onto the surface.Once clean, the substrates should be left to completely dry before proceeding to the next operation.

Note: Certain solvents, including Sika Cleaner 205, are not recommended for use on absorbent substrates as unevaporated solvents can affect the curing mechanism of Sikaflex.

Priming

Priming is a means of transforming a surface, either chemically, physically or both, into an ideal condition for successful bonding, thus ensuring long-term performance. The simplest form of priming is wiping the prepared surface with a conditioner (such as Sika Activator) which reacts with the surface providing improved “wetting” characteristics and more reactive sites. Porous and rough surfaces require a primer with “film-forming” properties to re-profile the surface, producing a denser, more even bond line. Primers must always be allowed to dry thoroughly before application of the Sikaflex adhesive. If left too long, primed areas must be reapplied or reactivated. Minimum and maximum drying times are given in the primer chart in this guide. Primed surfaces should be protected from contamination by dust, dirt, grease, vapours, moisture, etc., until the bond is formed.