The first step in achieving a good weld is to wait until the adhesive has properly dried.

For most types of adhesive, the minimum waiting time is overnight.

If you start to weld before the adhesive has dried, the heat from the gun will turn the moisture into water vapour, which will affect the quality of the thermo-fusion (or 'heat' fusion) that takes place.

Secondly, you must select the correct tip - or 'nozzle' - for the type of material being welded.

The size of the foot at the base of the tip controls the amount of air being blown through.

Most solid (or homogeneous) sheets require a 5 mm speed tip.

Layered (or heterogeneous) sheets, on the other hand, generally need a 3 mm tip to reduce 'glossing' on either side of the seam.

Thirdly, you need the right combination of temperature, speed and pressure.

The correct temperature will be specified in the flooring manufacturer's guidelines.

The speed and downward pressure will depend on the materials you're welding and the model and temperature of the welding gun.

Vinyl seams are generally welded at about 2 metres per minute.

Manual welding procedure

The general procedure used to manually groove and heat weld a seam in commercial vinyl is as follows:

1. Groove out the seam to two-thirds of the depth of the material with a hand groover or turbo groover. Make sure that the width of the ribbon that's cut from the edge of each sheet is the same.

2. Turn the welding gun on, and let it reach the set operating temperature. Cut the welding cable to length, and thread it through the nozzle.
   
   
3. Weld the material, starting at the wall and moving away at a steady speed.

4. Complete the weld and trim off the excess material down to about half a millimetre using a sharp spatula and slider.
   
   Do this while the cable is still warm so that it cuts smoothly without gouging. This first cut will also help the cable to cool more quickly.

5. Wait until the material cools, and then trim the cable flush with the floor surface using a spatula angled slightly across the line of the cut.
   
   If the trimming action pulls out the weld, you'll need to remove it and do that part again with fresh welding cable.

Joining a weld

To join a weld where you've left off in the middle of a seam:

1. Trim the loose end with a knife and chamfer down the end of the existing weld with a hand groover where it is to be overlapped.
   
   
2. Start the gun at the end of the existing weld and apply pressure as it travels over the un-welded section. Complete the weld and trim as normal.

Welding PUR coated floors

Most resilient sheet products have a PVC (polyvinyl chloride) coating on top. However, there is an increasing range of PUR (polyurethane) coated products coming onto the market.

These provide the benefit of a harder wearing surface for the client, but present a new headache for the installer who has to weld them.

PUR surfaces tend to plasticise and decompose at lower temperatures than PVC. If they're welded in the same way as for PVC, the surface can be discoloured or destroyed.

There are special welding tips used for PUR floors, designed to heat the inner areas of the groove to the required temperature without destroying the surface.

One example is the 'air knife' nozzle developed by Leister (see the second video clip from the last lesson - 'Welding floor with the Leister Unifloor').