Title: Tape Seam Guide

Tape Seam Guide

Tape Seams are a practical way to join thin film layers or to repair lining materials when welding equipment is not available.

Tape seaming of lining materials has been successfully used for many years. Tape seams provide excellent joints in thin film lining materials, and are especially adapted for repairs in many lining materials. There are two basic types of tape seams as well as two types of overlap seam.

Tape Seam Guide
Material Tape Comments
RPE® RPE Fab Tape Very Good
Enviro Liner® RPE Fab Tape Very Good
PP RPE Fab Tape Very Good
HDPE RPE Fab Tape Temporary Only
EPDM EPDM Tapes  Permanent Seams
VaporFlex VaporFlex Tape Permanent Seams
Tape seams and overlap seams are used on specific materials (such as RPE®, Vaporflex, and EPDM) or when site conditions or weather prevent the preparation of solvent or heat welded seams. Canal linings have successfully used the overlap seam for many years. The amount of water lost from an overlap joint is well below the specification for water loss from most canals. 

Tape seams are also ideal for joining large fabricated panels of material in remote locations, or at other times when expensive welding equipment, or skilled technicians are not available. Other materials, such as Vaporflex and EPDM, use tape seams exclusively. See the sections on Vaporflex and EPDM for specific information on special seam tapes.
Some tapes provide structural seam strength. These are specialized tapes that adhere strongly to the liner materials in use. Layfield utilizes a specialized tape that has very good adhesion to Polyethylene materials to make joints in RPE® and to make repairs in many other lining materials. This special tape material, called Layfield RPE Fab Tape, is a modified rubber resin adhesive, with excellent tack, and good chemical resistance. RPE Fab Tape is placed between the overlapped, clean, surfaces of the liner, and pressed together (using a roller to press on a firm backing provides the best contact). A full bond does not develop until about 24 hours after application and a weight should be applied to the seam area until the tape has had time to cure. RPE Fab Tape is excellent for repairs to RPE® and can provide temporary repairs for Enviro Liner and HDPE liner materials. RPE Fab Tape seams should be backfilled for additional security but can be incorporated into carefully designed exposed liners. RPE Fab Tape seams are also used to repair RPE® tarpaulins and covers. 
The second type of tape seam is a waterproofing seam tape. A water proofing seam tape relies on the weight of backfill to hold the seam together mechanically. The tapes acts as a sealant to prevent the movement of water through the seam. 
Waterproofing seam tapes such as a Butyl Rubber sealant, or a water putty tape, are placed between the overlapped liners and pressed together. Waterproofing seam tapes can be placed at very low temperatures if the tapes and the liner surfaces are kept warm. 
A third method of jointing liners that does not involve a tape is to use an overlap with a bentonite powder. The bentonite powder is placed between the overlap of the fabricated liner panels. Backfill is required for this application to provide the mechanical weight to hold the joint together. An advantage of a bentonite powder seam is that it can be prepared at extremely cold temperatures (as low as -40°C, or -40°F). Bentonite seams provide permanent waterproofing of seams for water containment applications. 

The final type of overlap seam is a simple overlap of lining materials. A 1.5 m (5 ft) overlap of clean liner material is carefully backfilled to provide a seal. This is an especially effective method for joining thin film liners for canal linings. A variation of this method is to dig an anchor trench at the seam location and place both panel edges in the trench and backfill. This method has been used to join two dissimilar lining materials (such as RPE® and PVC). Adding a small amount of bentonite powder to the overlap in the trench provides a better seal. 
Combinations of tapes are often used in difficult seaming situations. Usually one continuous line of RPE Fab Tape is used, however two continuous lines can be used in more critical applications. Occasionally both RPE Fab Tape and Butyl tape are used together, side-by-side. This combination provides better water containment, with the added strength of the RPE Fab Tape. Overlap seams can always incorporate bentonite powders to help make a seal, however bentonite powders will interfere with seaming tapes and they should not be used together. 
Application of seaming tapes is very straightforward. First, position the fabricated liner panels in position. Tape seams should have a minimum 300 mm (1 ft) of overlap. Clean the overlap to be seamed then apply the tape to the bottom surface. The application of heat from a hot air gun can be used in cool weather to make a better seal. Flip the top sheet into position while removing the release paper on the tape. Press the top lining panel onto the tape using a roller or hand pressure. 
When backfilling seams made with tape or overlaps proceed carefully. Ensure that all seams and overlaps are "shingled" in the direction from which the backfill will be pushed.