Tips for Sealing seams on diaper covers, wet/laundry bags, cosmetic pouches, raincoats, tents and tarps.
Seam Tapes: A variety of tapes can be used to seal seams, finding the right one for your application may take a little experimenting. These tapes are available in foam, rubber and TPU in variety of widths, thicknesses and with or without adhesives - 1/4" x 8mil thickness is the thinnest/lightest recommended for diaper covers and wet bags.
Tapes work by gasketing the space between fabrics and and around threads and stitching holes. If an bare tape, like rubber or Lastin, is used, feed the tape into the seam between the fabrics you are sewing together (if that's hard, stitch the tape down to one side material between stitch it to one side of the fabric then adhesive type is used, the adhesive helps hold the tape and fabrics in place while sewing, and some tapes are formulated to make a chemical bon which further reduces seam leaking. Using these tapes is easy, simply insert the tapes between the seams and stitch through the fabrics and tape!
Another technique is lapping adhesive tapes over the finished seam. This can be done after sewing as long as the seam is hidden and protected.
|Lastin Gasketing||PU Tape Gasketing||Tape Lapping|
Chemical Weld: Most waterproofed fabrics are made or coated with polyurethane or PVC so they can be solvent sealed. This type of sealing only works when the plastic/coated sides of the seams are facing each other, it will not work if the textile sides are facing each other.
PVC based products like like ProCare, most vinyls and pleather type materials can be seam welded with PVC glue and light pressure. PVC glue dissolves the surface of the plastic, a small amount of pressure will hold the seam. You can get a good seal by single needle stitching your seam, then daubing PVC glue into the back side of the seam, there is enough pressure at the seam to create a good solvent weld.
PU based products it's a little trickier because the TPU is usually so
thin that solvents dissolve the film/coating entirely -- which ruins the
seam altogether. You can daub liquid polyurethane onto the
backside of stitched seams (available at any hardware store under brand
names like Durathane, Varathane etc).
This takes a little longer but it works. Another tip is to thicken up your polyurethane liquid. You can do this by leaving the can open for a few days, stir once a day then reseal the can when you have thickened it to your liking.
Heat Sealing: Plasticized fabrics like PUL, ProCare, vinyls, and pleathers can be welded using low cost impulse sealers (available fro $20 to $200 off eBay) . In This works best on extrusion and film laminates. For many applications the welded seams are sufficient, no sewing required! Fine fabrics and coated wovens should not be welded as the heat required to fuse the fabrics will melt away their polyurethane coating.
Face the materials together then experiment with the dwell and heat settings. 1/8" flat wire works best for PUL and ProCare. Be sure to inspect and test your welds for strength and melt through -- too little creates a weak seam, too much welding can burn through the barrier or fabric substrate.
PVC glue dissolves the surface of the plastic, a small amount of pressure will hold the seam. You can get a good seal by single needle stitching your seam, then daubing PVC glue into the back side of the seam, there is enough pressure at the seam to create a good solvent weld.
Depending on the solvent you choose, you may need to clamp the seam until the solvent cures.
Bead or Spray (DWR) sealants
Another option for sealing seams is silicone, wax or other pliable caulks. These best applied after stitching. They can be messy and slow in volume production so they tend to be mostly used in repair and low volume production.
Tip: We found a dental irrigating syringe will form a nice bead and make sealing neat and clean.
Another option is spray sealers like Texsport, CampDry etc. These penetrate and gum up seams to prevent leaking. Tip: Borrow a spray nozzle from a can of WD40, place it on top of the spray sealer can to get a directed spray This will minimize waste and keep overspray of your product to a minimum.
Thread - use polyester or nylon. Don't use natural fibers like cotton or rayon, they will wick wetness through the seam.
Ventilation: Solvent and Heat welding gives off fumes, do this in a well ventilated area.
Kids and Pets - chemical adhesives smell interesting to children and pets. Make sure they are used and stored safely.
Catalyzed sealing techniques are not recommended as volumes generally do not warrant the investment into production equipment and material engineering.
Copyright Wazoodle Fabrics, 2002