Chemical Welding Guide

Chemical Welds

Chemical welds are the most adaptive type of welding available in geomembranes. Many complex arrangements can be performed with Chemical Welds.

Certain liner materials can be welded through the use of chemical fusion. This is not a glue, but an actual weld prepared with chemicals. This tech note describes Chemical Welding.

Chemical Welding Guide
Liner Material Solvent Comments
Flexible PVC THF Excellent Welds
Supported PVC THF Excellent Welds
Fish Grade PVC THF Excellent Welds
Arctic Liner THF No Bodied Solvents
OR PVC THF Excellent Welds
Hypalon Xylene Very Good Welds
Urethane Xylene or THF Certain Styles Only

 


 

Our experience has shown that a glue will normally last only 7 to 8 years in service. A glue is actually a different plastic than the liner material and forms a distinct layer between the two liner sheets. These "other" plastics, such as epoxy and acrylic, are heavily modified in order to make them stick and to make them easy to apply. The problem is that the plastic in glues is so heavily modified that long term life is often sacrificed. While there are a few 30 year plus applications of glues, the extreme conditions that a liner is subject to often limits the expected glue service life.

A more permanent bonding method is the Chemical Weld. A Chemical weld occurs when you dissolve together the two faces of each liner surface to be joined (in a controlled fashion) with a welding chemical. The welding chemical is a volatile solvent that is blended to control the speed at which it dissolves the surface of the liner material and to control its rate of evaporation. The welding chemical is brushed, poured, or squirted onto the liner surfaces before they are pressed together. By carefully pressing the semi-dissolved liner surfaces together a bond is formed that is very similar to the bond we would get if we heated the surfaces using thermal welding. The solvent "flashes off" or evaporates, and after about 24 hours you have a homogeneous weld with no foreign material between the two liner surfaces.

Chemical Welding is a permanent process and produces bonds that will last as long as the liner material.

Chemical Welding is also one of the most versatile welding processes. In liner installations it is easier to perform detail work with a chemical weld than with most heat welding processes. Chemical Welding is suitable to small and large projects and has a low initial skill level; laborers can be trained to make effective welds quickly and reliably.

Chemical Welding is also suitable for repairs. Simple repair kits are available from Layfield Plastics that allow the user/owner of a facility to make quick, permanent repairs without downtime or scheduling delays.

One common variation on chemical welding is to use a "bodied solvent" instead of straight solvent. A bodied solvent is the Chemical Welding solvent that has between 5 and 25% of the material that is being welded dissolved in solution. This additional "body" allows the solvent to be placed on vertical surfaces, helps to fill in uneven surfaces, and slows down the cure time in very hot welding conditions.

There are a number of liner materials that can be chemically welded. Each material has a specific chemical that can be used for welding. In the application chart are listed materials that can be chemically welded with their corresponding solvent.

THF is chemical called Tetrahydrofuran. It is a volatile solvent with a "ether-like" odour. THF works very well on most PVC products but is usually limited to temperatures above +10°C (45°F). Below this temperature heat must be applied to facilitate the evaporation of the solvent. THF evaporates completely after the weld has set and residue is undetectable. THF is the most common solvent in use on PVC liner materials. Safety information is shipped with every container of THF supplied.

Xylene is used primarily for Hypalon, but has been used for some PVC work. Hypalon cures over time and becomes progressively more difficult to weld as it ages. A wipe with Xylene can reactivate the surface of aged Hypalon in most cases so that thermal welding can be accomplished. Chemical Welding of aged Hypalon is dependant on the material condition.

Please contact your Layfield representative if you have any questions regarding Chemical Welding.

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