Improper use of impact drivers can lead to paint finish damage and failed connections. –
The Metal Construction Association has developed a technical bulletin on “Proper Tools for Fastening Metal Panels.” In particular, it addresses the improper use of impact drivers.
Andrew F. Williams, PE, Director of Codes and Standards for the MCA noted that the increasing popularity of impact drivers motivated the MCA to gather a Task Group to address the topic. “… the use of impact drivers is increasing in the field,” he noted. “With that increase in use, the amount of claims for damaged paint finishes is also increasing. Add to that the importance of correct washer compression to maintain weathertightness and MCA felt guidance would be helpful in the field. This also presented the opportunity to highlight the negative impact of metal chips and drill filings when exposed on the finished surface.”
Williams, who is also Director of Technical Support for the National Frame Building Association, noted that post-frame builders also need to take note. “The same types of issues that affect MCA also effect NFBA in the area of connections,” he said. “The goal is to create a weathertight, structurally sound connection that will perform as required with minimal negative effect on the fastener and the surrounding metal sheathing.”
The number of incidences of paint finish damage to both wall and roof panels are definitely on the increase, according to Williams, who added: “Reports from the field often tie this damage back to the use of impact drivers.”
So what is a builder to do? Here are some major points taken directly from the bulletin.
Selecting the proper tools
The selection of the proper tools for the fastening of metal roofing panels is critical for ease of installation, proper watertight sealing of the building, and the integrity of the connection.
In any type of metal panel fastening application, screw guns with an adjustable clutch and/or a depth sensing nosepiece, and a minimum of 6 amps of power are the recommended tools of choice to maintain integrity of the panel and building. This will assure that fasteners are installed at their optimum level. Often panels can be pre-drilled to prevent “walking” of the drill point across the surface of the panel. One should select a tool with the appropriate RPM for the application as noted in this Technical Bulletin.
Accessories
Drive sockets with a recessed magnet and internal lobular hex design can help to reduce damage to paint on the fastener head, reduce wobble and increase socket life.
Care should be taken to remove metal chips that accumulate in the magnet socket so that the hex of the screw is embedded completely into the socket.
Make sure the head of the fastener is fully encapsulated into the hex drive socket. This will eliminate wobble of the screw, improve drilling performance and minimize damage to the head of the screw.
Also, any drill filings need to be removed from the panels immediately to prevent rust stain.
Installers are encouraged to check the fastener product specifications for additional information on correct tools to use.
Tightening the fasteners
It is critical to install fasteners so that the sealing washer performs at its optimal level to prevent leaks. Care should be taken when tightening the screws for sealing of the EPDM washer.
(The fastener manufacturer should be consulted for recommended tightening guidance).
Tools not recommended
Impact drivers are not recommended for fastening metal panels, or composite panels used for roof and/or wall system installation. These tools can cause damage to the drill points, break screws, chip painted surfaces, and strip threads on Type 300 stainless steel screws. Overdriven screws also damage the EPDM sealing washer and could potentially cause leaks.
Paint damage that can occur from using impact driver guns
High speed screw guns with RPM greater than 2500 should not be used with fasteners used to attach metal panels to framing systems. When the drill point is rotating and cutting the substrate, it creates friction which generates heat. If the heat is high enough it can damage the hard surface of the screw and cause the point to “burn-up”. Slower speed screw guns used with less pressure during drilling will minimize the amount of friction, heat and damage to the drill point. The high RPM tools can also cause over-driving, damaging the fastener head which can lead to premature corrosion.
TOOLS RECOMMENDED AND SCREW GUN SPEEDS
Metal to metal application
When fastening metal panels to metal framing the total thickness of materials being used must be determined. Whether a self-drilling or self-tapping fastener is used, proper selection of the RPM is important. Slower screw gun speeds will improve the drilling performance by reducing the heat that is generated during the drilling of the screw.
The following screw gun speeds are recommended to assure fasteners perform at their optimal level. Use variable speed screw guns for best performance.
(Carbon steel or 410 Stainless Steel)
Steel Thickness Screw Gun RPM
- Less than 1/4-inches 2,500 RPM Maximum
- 1/4- to 1/2-inches 2,000 RPM Maximum
(304 Stainless Steel)
Steel Thickness Screw Gun RPM
- All thicknesses 2,000 RPM (max) for self-drilling
- All thicknesses 1,000 RPM for self-tapping
Metal to wood application
In this application, a screw gun with 0-2500 RPM is recommended for fastening metal panels.
Conclusions
Use of the wrong tool or a driver with excessive RPM can lead to fastener damage and problems. Among these are damage to fastener heads, over-driving, scratches, and damage to paint finishes leading to premature corrosion.
You can download the “Proper Tools for Fastening Metal Panels” technical bulletin from the MCA website (www.MetalConstruction.org) under the Education/Technical Resources tab.