Using high quality masking tape, measure and mask off an area for the perimeter band, 1 ½ to 2â wide. (See. Exhibit 1
Sika’s How to…Series
Guide to Bonding & Sealing Plastic Marine Windows with Sikaflex 295UV Plastic windows are typically acrylic (Plexiglas) or polycarbonate (Lexan). Both have been historically difficult to seal or bond. Sealing is simply what it says; keeping water and dirt out from a window that is mechanically fastened. Bonding occurs when the window is affixed to the structure using only an adhesive. There is usually no frame or mechanical fasteners. The following procedure is used for both sealing as well as bonding. Sikaflex 295UV is a moisture curing polyurethane sealant/adhesive that exhibits outstanding UV resistance. This high strength elastic adhesive is specifically formulated for use with plastic windows. Sikaflex 209N is a black primer that develops tenacious adhesion to acrylic and polycarbonate. Used as a system, Sikaflex 295UV and SikaPrimer 209N provides very durable adhesion to plastic windows. Important Considerations: • Only use with flat or pre-stressed (factory bent) plastic window material. Forcing the sheets around a large curvature may cause stress cracking. • These instructions are for smaller windows and hatches. For large jobs, or any windows longer than 5 ft. in any dimension, always contact our Product Engineering Department for specific guidelines. • Due to the large coefficient of expansion, the window must have a gap of at least 3/8” between the
295UV Instr. 7/2006/SRP
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edge of the window and the frame. (See Exhibit 1) Since the bond will be to both the structure of the boat itself as well as the window it is just as important to prepare both surfaces correctly. These recommendations are to be used as general guidelines only. Refer to Sika’s Surface Preparation Guidelines for further information Pre-testing is always recommended.
As with any elastic bonding project, proper surface preparation is of great importance. Following are general surface preparation instructions for successfully bonding plastic windows. Completely remove any existing sealant. Unpainted Metal or Fiberglass Frame: Lightly sand the bonding surface with Scotchbrite or similar grit sandpaper. Remove dust. Using a clean, lint free cloth wipe the surface with SikaCleaner 226. Wait 10 minutes. Paint on a thin coat of SikaPrimer 209N. Wait 30 minutes. Painted Metal or Painted Wood Frame: Wipe surface with SikaCleaner 226. Wait 10 minutes. Unpainted Wood Frame: Wipe surface with acetone or similar solvent. Paint on a thin coat of SikaPrimer 215. Wait 60 minutes. Do not use SikaCleaner 226 on unpainted wood surfaces. Plastic Window Surface: Ultraviolet Radiation (UV) presents a serious challenge to any window bonding application. It is necessary that all steps be followed exactly. Look at a car windshield. It will have a wide black band around the perimeter of the windshield. That is necessary to prevent UV from destroying the integrity of the polyurethane adhesive that is bonding the windshield. The same
treatment is necessary for a boat window. Using high quality masking tape, measure and mask off an area for the perimeter band, 1 ½ to 2” wide. (See Exhibit 1) After masking off the area, lightly sand the surface using wet/dry 320-400 grit sandpaper or Scotchbrite. If window has a scratch-resistant coating, it must be completely removed by sanding with 100 grit sandpaper to a depth of .5mm. Clean the surface and edges with SikaCleaner 226. Wait ten minutes. Then, using SikaPrimer 209N, paint the perimeter band onto the window. Also paint the edges. Allow to dry for 30 minutes. Cut the nozzle at a 30-45° angle or in a large inverted V, apply a generous bead of Sikaflex 295UV to the bond surface about ¼” away from the edge. Apply soft rubber or plastic spacers every 1012” next to the bead of Sikaflex. These spacers must be at least 3/16” thick. These are to assure that the Sikaflex maintains proper depth and is not compressed too much. Set the glass in place and gently but firmly press the glass in place. Clean up any squeeze out with mineral spirits. Sikaflex can be tooled smooth with a plastic “squeegee”, tongue depressor or a pastry spatula. Applying masking tape to the edge of the frame structure will aid in clean up.
of the bond line plus twice the width of the glass
Plastic Window
SikaPrimer 209N UV Resistant Paint
Sikaflex 295UV Bond Area
3/8” Expansion Joint Sikaflex 295UV
Window Opening
Exhibit 1
Sika warrants its products to be free of manufacturing defects and that they will meet Sika’s current published physical properties when applied in accordance with Sika’s directions and tested in accordance with ASTM and Sika standards. There are no other warranties by Sika of any nature whatsoever expressed or implied, including any warranty of fitness for a particular purpose in connection with this product. Sika Corporation shall not be liable for damages of any sort, including remote or consequential damages, resulting from any claimed breach of any warranty whether expressed or implied, including any warranty of fitness for a particular purpose or from any other cause whatsoever. Sika shall also not be responsible for any use of this product in a manner to infringe on any patent held by others.
After the window has set for a few hours, remove any temporary spacers and backfill the edge gap with Sikaflex 295UV. Sika highly recommends the application of an opaque perimeter band around the exterior window perimeter for long term UV resistance. Use a UV resistant paint that is suitable for use on plastic surfaces. Do not use SikaPrimer 209N. This perimeter band should be the width
295UV Instr. 7/2006/SRP
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