Training Manual                                                             

Specific Techniques
Minor Seam Failure Repair


SCOPE:        
Identify the nature of a seam failure and describe how to repair.

PURPOSE:        
Repair a leaking seam

EQUIPMENT:        
Stanley Knife/Scissors
Sandpaper
Glue pot & 1” brush
Adhesive & hardener
Roller
Watch or 15 minute timer
Screwdriver or blunt object

INTRODUCTION
1.  Assuming a leak is identified (by soap testing etc).
2.  Avoid the temptation to stop the leak by coating the area with adhesive “Glue filling” or simple placing a patch over the suspect area.  This may get you out of a crisis situation but for 99% of the time it will complicate correct repair methods.  Coating with other fillers like silicone rubber, or epoxy MUST NEVER BE ATTEMPTED.
3.  Most leaks are caused by small volumes of air passing through “hair line channels” in a seam that can be regarded as structurally sound.  When opening such a seam the bond in the adjacent area will be so strong that the coating will be split (torn apart) as the seam is opened.  In this situation it is critical to confine the leak is a hairline failure and not caused by a bonding failure in the surrounding area.  See procedure in 1 - 3 below.

4.  If the leak is more serious than a hairline failure, when opening the seam (bond) the seam is likely to peel apart along the glue line.  The failure causes virtually no damage to the coated fabric, and the seam opens up with relatively little pressure.   (5 to 7 kg force for a 25mm wide seam).   See procedure in 4 - 10 below.

Where this failure occurs it can be helpful to determine if the failure is caused by an “adhesive failure” where the glue does not adhere to the rubber.  (Characterised by all the glue peeling off one surface leaving the rubber clean).  or a “cohesive failure” where the glue will not adhere to itself.  (Characterised by glue being left on both surfaces).  In both situations it can be assumed that the structural strength is SUSPECT and the seam should be peeled back until it is felt that there is ADEQUATE structural strength.  This is largely subjective and can only be determined by experience, but the most significant sign to watch for is the amount of coating being damaged as the seam is opened.

REPAIR PROCEDURE:
1.  Identify the source of the leak.  Soap test.
2.  Use a blunt object to START to open up the seam for say 5mm (1/4”).   Re soap test to confirm the location of the leak.  Where possible use a hot gun to warm the bond and soften the adhesive.  Slow warm heat that penetrates is better than a blast of hot air that scorches the surface.  Hot to touch but never hot enough to scorch or smoke.
Open up about 3/4 of the width of the seam.  This provides an adequate area to rebond, while leaving sufficient “original” strength in the seam.  

IMPORTANT.  Avoid opening the last 5mm (1/4”) of the seam as this protects the strength, and keeps both surfaces aligned correctly etc.

As the seam is being opened, carefully observe where the seam is breaking apart.  If the coating is being damaged only open enough to enable a repair to be performed.  Ideally open up a wedge shaped section as this is easier to reclose.



4.  If the seam has little strength and the failure is along the glue line (adhesive or cohesive) open up a larger area until the seam strength is obvious (shows coating damage, e.g. glue plucks off some of the coating, etc).   If necessary open up a large area also depending on the strength it may be advisable to open up the full width of the seam.  

5.  During the opening operation it is likely that the surface of the coating will be damaged.  This could be anything from a thin skim of coating to large chunks of coating.  It is also possible for the coating to tear off leaving bare nylon.  The latter should be avoided by applying a little more heat or by only opening up about 5mm of seam.

6.  Where the coating has become damaged it is essential that it be smoothed by buffing.  If the torn surface could be likened to a hills and valleys with sharp edges of the cliff face should be smoothed or rounded off.




7.  Proceed to bond opened surface.  Preglue and allow to dry.  During the drying process do not allow the surfaces to accidentally close.  If necessary prop open with a toothpick or similar object.   If raw textile has been exposed, apply several thin layers of adhesive to compensate for missing coating.

8. Apply bonding coat.  Avoid any excess of glue building up along the edge of the seam.   Roll very heavily.

9.  If a large seam has been opened for a major repair.  It may be desirable to match mark both surfaces to ensure a correct alignment of both surfaces.

10.  If you are unsure about performing this repair.  Do not hesitate to call Lancer Industries Ltd.