Primer Chart

Below is an itemized list of the most commonly used substrates in elastic bonding and sealing applications with more specific surface preparation recommendations. This Primer Chart can serve as a general guideline only, given the variety of possible materials and substrates. For more specific guidance on a particular application it will be necessary to contact the Technical Service Department.

Key:
226 = Sika ®-Cleaner 226
206 G+P = Sika ® -Primer 206 G+P
209 = Sika ® -Primer 209
210T = Sika ® -Primer 210T
215 = Sika ® -Primer 215
Akt = Sika ® -Aktivator
SB = Abrade lightly with Scotchbrite®
80 = Grind with 80 grit sandpaper (disk or belt sander)

Comments

1. Aluminum
Aluminum and its alloys are produced in the form of sheet, plate, profiles and castings. The information given here on preparation and priming relates to this group of products. In the case of aluminum that has undergone surface treatment (chromated or coated), cleaning with Sika ® -Cleaner 226 is often the only preparation that is required.

2. Anodized Aluminum
Aluminum is a very reactive material. It protects itself by forming an oxide layer when exposed to air. This resistant layer may be produced in a very consistent thickness by electrochemical or chemical oxidation. Such treated surface may be easy to color. To increase chemical resistance of the oxide layer or to protect the color, additional translucent varnishes with different chemical composition are often applied. Therefore, such substrates require previous adhesion tsting.

3. Steel
Steel is subject to corrosion according the environmental conditions. Sika ® -Primers are applied in a very thin layer and may not be used as a corrosion protection system. In these cases, we recommend to use a corrosion protective 2-C epoxy, polyurethane or polyaminoamide-based paint/primer system.

4. Stainless Steel
Stainless steel is a group of products with different chemical compositions and surface aspects. In most cases, a simple treatment with Sika ® -Cleaner 226 or Sika ® -Aktivator gives good adhesion strength of Sikaflex ®. Rough surfaces may need an additional primer.

5. Galvanized Steel
Zinc coatings are applied by one of three methods:

• a) Sendzimir process
• b) Electroplating or electrogalvanizing
• c) Hot-dip galvanizing

In the case of a) and b) the substrate is defined and documented and the surface film structure remains more or less constant. In the case of hot-dip galvanized components, however, the surface structure is not consistent, which means that its adhesive properties must be periodically checked. Oiled types should be degreased before use.

6. Fiberglass
These plastics are generally thermosetting resins derived from unsaturated polyesters, or less frequently from epoxy resins or polyurethane. Newly manufactured components sometimes contain an unreacted part of styrene monomer. These components are still undergoing an internal chemical reaction, and as such are subject to further shrinkage. Adhesive bonding should therefore be restricted to fiberglass components that are fully aged, weather or tempered.

The smooth face side (gel coat side) may be contaminated with traces of mold release agents, which will adversely affect adhesive bonding. The rough reverse side, which is exposed to air during manufacturing usually contains paraffin, added to assist air drying.

For bonding applications it is necessary to abrade the surface thoroughly before cleaning with Sika ® -Cleaner 226 and priming with Sika ® - Primer 206 G+P or Sika ® -Primer 210T or Sika ® -Primer 215. For sealing applica-tions, a wipe of Sika ® -Cleaner 226 in most cases is sufficient. Pre-testing is recommended on these substrates.

Translucent or transparent varieties require UV shielding as specified in comment 9.

7. Plastics
Some plastics require specialized physical or chemical preparation before they can be successfully bonded (e.g. flame treatment, plasma). Polypropylene and polyethylene are two common examples.

Adhesion testing is necessary in the case of many plastic compounds or blends. It is impossible to give guidance owing to the large number of chemical constituents and release agents, both external and internal, which they contain.

8. Polycarbonate/ Polystyrene and Acrylic (PMMA)
Always seek the manufacturer’s advice and/or Sika’s Technical Service Department prior to bonding thermoplastics like polycarbonate and acrylic that are prone to stress cracking. If there is a scratch/abrasion resistant coating on the polycarbonate or acrylic, it must be removed (i.e. Margard coating on Lexan). Abrade the scratch resistant coating with sandpaper (80x-120x), removing a layer of 0.5-mm thickness. Sikaflex ® -295 UV is the only Sikaflex ® adhesive suitable for bonding polycarbonate, acrylic, and polystyrene.

9. Transparent or Translucent Substrates
In the case of transparent substrates where the bonding surface is exposed to direct sunlight through the transparent layer, some form of UV shielding is required. This may consist of:

• a) An opaque masking strip or exterior paint or cover plate of plastic or metal.
• b) A ceramic edging strip (on glass) with good light-excluding properties. Light transmission at a 280-630 nm should be < 0.1% on tempered glass and < 0.2% on laminated glass.
• c) A black primer, although the use of a black primer as a sole form of UV protection is not recommended for applications that will be continuously exposed to sunlight for an extended period of time.

10. Painted substrates and Surface Coatings
Paint additives designed to modify film formation, such as conditioners and spreading agents, silicones, anti-silicones, as well as roughness of the finish, may affect the adhesion properties. The method of application affects the adhesion properties as well. Therefore, adhesion testing is always necessary in the case of painted substrates and surface coatings. The following may be taken as a guide:

• Reactive coating systems that cure thermally (cataphoretic powder coatings) or by additional polymerization (epoxy or polyurethane paint systems) can be bonded with Sikaflex ® products. Paint systems based on alkyd resins that dry by oxidation are unsuitable for bonding.
• Systems based on polyvinyl butyral or epoxy resin esters that dry by physical action are generally compatible with sealants only, i.e. not adhesives.

Note: Sika ® -Primer 209 can be used with acrylic, alkyds/melamines, baked enamels, and powder coatings. Preliminary testing is always necessary

11. Plywood and Timber
Sikaflex ® develops high bond strength to clean, dry untreated wood surfaces without use of primer. Lower viscosity Sikaflex ® products generally develop stronger bonds to untreated wood than high viscosity Sikaflex ® products. Bonding strength on this substrate can be significantly increased by using Sika ® -Primer 215. Wood surfaces to be bonded with Sikaflex ® should never be wiped with solvents containing alcohol, including Sika ® -Cleaner 226 and Sika ® -Aktivator.

12. Painting over Sikaflex ®
Sikaflex ® products can be painted over with most conventional paint system. The best results are obtained if the sealant is allowed to cure fully first. Trials must be carried out to determine compatibility of the paint system. Note that non-flexible paint systems applied over Sikaflex ® will impede joint movement, which may lead to cracking of the finish.