Sika’s How To Bond & Seal Plastic Marine Windows & Hatches Using Sikaflex^®-295 UV

All boat owners want great looking plastic windows, port-lites, and hatches. They are a source of great pride and admiration, but must be waterproof, safe, and long lasting. A properly installed plastic window, port-lite or hatch lens will retain its great looks for many years, with minimal maintenance required.

Plastic windows, port-lites, and hatch lenses are typically acrylic (Plexiglass) or polycarbonate (Lexan). Historically, these materials have been difficult to seal and bond. Ultraviolet Radiation (UV) presents an additional challenge to any window application. For example, automobile windshields have a wide black band around their perimeter to shield the bond-line from UV-light. This same treatment is necessary for your boat window. Improperly installed windows, port-lites and hatch lenses may result in water leaks or failure during severe conditions.

By carefully completing the following steps, your installation or repair will proceed smoothly and your windows, port-lites, and hatch lenses will retain their great looks for many years. Since each step is important, remember to follow all steps.



Important Considerations:
Only use these procedures with flat or pre-stressed (factory bent) plastic window material. Forcing plastic sheets into a curved position causes stress, which can result in cracking. These instructions are for intended for the average repair or installation. For large jobs, or any window larger than 1.5m in any dimension, contact Sika Technical Service.

Due to the large coefficient of expansion, the window must have a gap of at least 10mm between the edge of the window and the frame.

Forming a cured layer of adhesive between the two assembled components is the goal; do not compress the adhesive below 5mm.

The adhesive material must form a bond to both substrates, therefore care must be taken to prepare both surfaces.

Atmospheric temperatures during application or during the curing process should never be above 25°C or below 5°C.

Do not use alcohol or alcohol containing solvents to clean or tool material as the chemical reaction will prevent complete curing of polyurethane-based products.

Allow 4-7 days curing times before full exposure to heavy sea conditions.

Adhesion to the extremely wide range of materials available is not always achievable without consulting Sika’s Surface Preparation Guidelines.


DO NOT PROCEED IF ANY OF THE ABOVE CONDITIONS CANNOT BE STRICTLY ADHERED TO.



Preparation

Before Starting:
Sikaflex^®-295 UV, used in conjunction with SikaPrimer^®-209N is formulated to adhere to plastic materials. It is also formulated to adhere most other common materials used in recreational vessel construction, including fiberglass, gel-coat, marine paints, wood, and aluminum. If you have further questions please contact Sika Technical Service.

Addition information, MSDS’s or Surface Preparation Guidelines are available through www.sika.ca. Adhesion tests are always recommended. Apply materials as directed below to a small area, allow full-cure, then pull with pliers to test adhesion.


Removing Existing Caulk:
All existing material must be removed from the surface of all components under consideration for bonding. The Sikaflex^®-295 UV must achieve long lasting adhesion to both of the surfaces. Any residue has the potential to de-bond in the future, causing release of the newly applied material. There are no specific or recommended tools available for this operation.


Marking Window, Port-Lite, and/or Hatch Lens Location:
Place the plastic material into exact position. Using an erasable marker (test to ensure ability wipe-off) mark the line on the plastic material where the vessel or frame will overlap. It is also advisable the mark the location where any interior trim is positioned. Lay the plastic window aside.


Vessel or Frame Preparation:
It is imperative to remove any trace amounts of wax, mould release products, loose paint etc. Use abrasive pad or 80-100 grit sandpaper lightly scruff to entire bonding area. Remove all dust using a dry cloth.


Cleaning/Priming:
An alcohol wipe will remove trace amounts of dust, oil, and other contaminants. The Sika primer specified next will create a superior surface appropriate for tenacious adhesion for the adhesive.

Fiberglass or Unpainted Metal - Wipe the entire bonding area with Sika Cleaner^®-205 or alcohol. Allow 10 minutes for the alcohol to completely evaporate. One coat of SikaPrimer^®-209N is to applied with a dauber or brush to the entire bonding area. Allow 30 minutes for the SikaPrimer^®-209N to fully dry.

Painted Metal or Painted Wood – Extreme care must be taken to ensure no loose paint or splintering wood exists. Wipe the entire bonding area with Sika Cleaner^®-205 or alcohol. Allow 10 minutes for the alcohol to completely evaporate.

Unpainted Wood – It is highly recommended to paint and/or stain wood which is to be used as the sole landing area for bonded windows. Then, follow the above instructions. Or, brush apply one coat of SikaPrimer^®-290 DC (available through your retailer in 250ml).


Plastic Material Surface Preparation:
It is necessary to take steps to prevent ultraviolet light from destroying the integrity of the polyurethane adhesive. UV passing through the plastic material can cause the adhesive to release exactly at the point of contact with the plastic material. Applying the SikaPrimer^®-209N will largely prevent this. There are two options to consider:

(1) whether to paint the SikaPrimer^®-209N only on the area of the bond line; or,

(2) whether to paint the bondline area as well as extending the area to cover any interior trim as also outlined earlier. After one of the options is decided, add 6mm and using the erasable marker, clearly outline the area to be painted.


Masking the Plastic Panel
Using a high quality masking tape, mask the outline marked on the plastic panel.


Abrading:
Use abrasive pad or 80-100 grit sandpaper scuff outside the marked area. If plastic material has a scratch resistant coating, it must be completely removed by abrading to a depth of 0.5mm. Remember that adhesion must be achieved, so be sure to evenly abrade the entire area.


Cleaning/Priming:
Using Sika Cleaner^®-205, wipe the entire abraded area. Rotate towel at regular intervals to avoid re-contamination. Allow a minimum of 10 minutes for the alcohol to completely evaporate. One coat of SikaPrimer^®-209N is to be brush or dauber applied to the entire abraded area. Allow 30 minutes for the SikaPrimer^®-209N to fully dry.


Application Procedure:
Using a high quality tape, mask the area immediately surrounding the expected location of the adhesive squeeze-out.

It is imperative that care is exercised to prevent the entrapment of air during the application of the adhesive. Cut the supplied nozzle to the desired bead size. Apply an ample amount of adhesive.


Positioning Components:
Using light pressure lay the two components into place being sure to align any fastener holes, if used. Insert any screws or bolts. Do not fully tighten at this time. Lightly tighten hardware into place leaving approx 5mm of adhesive material between the frame and plastic material after compression. If the minimum thickness cannot be maintained, evaluate whether enough sufficient adhesive is available to maintain waterproof seal. The maximum recommended adhesive thickness is 19mm.


Filling Expansion Joint:
After 4 hours curing time, fill the expansion gap area with Sikaflex^®-295 UV.


Clean-up:
Before the Sikaflex^®-295 UV begins the curing process, use Sika^® Tooling Agent N to remove excess material. A mixture of dishing washing liquid mixed with water will also give good quality clean-up results. If masking tape was used, remove it before the adhesive forms a skin. Pull the tape at an angle, which ensures a clean removal of the excess material applied.


Cosmetic Touch-up:
If required, use Sika^® Tooling Agent N or a soap and water mixture to perform cosmetic adjustments to the shape of exposed adhesive material. All cosmetic adjustments must be attempted prior to Sikaflex^®-295 UV beginning the curing reaction.


Curing:
Allow the Sikaflex^®-295 UV to fully cure. During the curing process, the adhesive will chemically bond to both components and form a permanent waterproof joint capable of withstanding high force shocks, dampen vibration, and reduce noise-transfer. Equally important, the cured material will compensate for any extreme thermal expansion and contraction of the window within the frame.


Tighten Fasteners:
After the Sikaflex^®-295 UV adhesive has fully cured, tighten any fasteners if used.


Final Touch-up:
Minor bubbles, gaps or imperfections may be noticed after final cure. These can be filled with a skim coating of Sikaflex^®-295 UV. No special preparation is needed however the touch-up should occur immediately upon discovery.


Future Removal:
The cured Sikaflex^®-295 UV can be removed using these special instructions. Remove any fasteners or retaining components. Using a long blade box knife, cut the adhesive near the center of the exposed bead. Using light pressure, force the two components apart to allow exposure of greater area of the adhesive. Continue cutting the adhesive with long bladed box knife. Information regarding other tools available for removal may be obtained by contacting our Sika Technical Service.