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Glazing Tapes - Correct Use

PREFORMED tape sealants, more commonly referred to as butyl tapes or glazing tapes, offer an economical approach that is neat and easy to install in both high-and low-performance glazing applications - and are the most popular sealant for many applications.Since correct specification and installation are the keys to successful performance, one of the most important steps in any tape-glazed project is to ensure that the correct tape has been selected.

Three kinds of tapes are available for glazing applications: shimmed, unshimmed and hybrid. Hybrid tapes differ from standard shimmed and unshimmed tapes in that they are highly elastic. Hybrid tapes make use of cross-linked rubber technology and are expressly designed for use without the aid of a rubber shim in compression glazing systems.

Compression glazing systems require the use of shimmed or hybrid tape to maintain the designed face clearance while under continuous pressure from a gasket installed at the opposite side of the glass. Tapes in a compression system are designed to be compressed to as little as one-third of their original thickness.

The gasket used to provide compression on the glass must be designed for use with the specific tape being used and in the specific glazing system. If the components of a compression glazing system are not designed to function together, performance may be less than desired or glass breakage may occur.

Non-compression glazing systems typically make use of unshimmed tapes. In these systems, the tape is initially compressed during installation of the glass. This compression can be done by hand or mechanically in factory applications. The tape must completely wet out on the glass and framing surfaces.

In non-compression systems, continuous pressure is not maintained on the glass. On the side of the glass opposite the tape, the glass is held in position by a specially designed removable stop or by a spacer sized to the designed face clearance.

Tapes intended for non-compression glazing systems are easily deformed; therefore, their use is limited to smaller openings subject to less demanding performance conditions. Because tapes have different performance characteristics, manufacturers vary in the limitations they impose on their individual products.

Wind loading and thermally-induced movement are two key influences on the performance of a window. Therefore, the size of the glass panes is the most common factor used to determine when a glazing application needs to be upgraded to a better-performing system. In a non-compression glazing system, it may be necessary to upgrade from an unshimmed tape to a shimmed tape when the glass pane exceeds 0.85m2 . Demands on performance, such as coastal wind exposure, are also reasons to consider upgrading a system.

Choosing the right tape size is as important as choosing the right tape. Glass, gaskets and framing members have specific dimensions and manufacturing tolerances. Preformed tape sealants are supplied in a variety of thicknesses and shim diameters and each is intended for a specific designed face clearance. Just like glass, gaskets and framing, tapes are subject to manufacturing tolerances. Poor performance or even glass breakage can result from failure to select the correct type and size of tape.

There are several basic rules of thumb to determine the correct tape size:

Proper treatment of the joinery is critical to the performance of any glazing application, and the first step in a successful installation is to prepare and seal the joinery in the framing system. Butt, mitre and overlapping joinery conditions need to be sealed. Proper procedures include cleaning and, if necessary, priming the joinery at all corners of the framing. A variety of sealants may be used to seal the joinery, but neutral curing silicone sealants perform especially well in joinery conditions.

The following general guidelines for tape glazing apply regardless of the type of tape or system being glazed:

As with all glazing systems the correct selection of materials to be used and the correct installation will ensure the maximum service life of the complete system. Following the above guidelines should ensure that any tape glazing system will perform satisfactorily for the full extent of its intended service life.