Mechanical fastening

Nailed connections

Yes, as long as you’re nailing your composite to a material that provides enough grip to hold the nail in place, e.g. wood. You should never nail a composite to another composite.

Common nails can be driven through composites up to 1.6mm (1/16″) thickness, without pre-drilling. Tempered nails will go through thicker composite material, up to 8mm (5/16″).

For composites thicker than 8mm (5/16″) you must pre-drill holes. The hole must be slightly oversized, to allow for expansion and contraction between the composite and the material to which it is nailed.

Yes, composites of a thickness above 8mm (5/16”) require that you pre-drill slightly oversized holes.

It is also advisable to drill holes before nailing long lengths of lighter composites.

Screw connections

If high-strength fasteners are not required, self-tapping screws work well in many applications. Self-tapping screws are best used in combination with adhesives to cure the connection and add a small amount of mechanical strength.

In corrosive environments, stainless steel or Monel screws should be used, unless a suitable polyester/epoxy coating is applied to exposed screw heads.

Lag screws are not recommended because they do not bite well into the composite.

Bolt connections

You can use standard bolts, nuts, and washers. Since composite materials can fail under high localized stress conditions, the tighter the bolt, the more effective it will be.

Always use flat washers on both sides of the bolt connections.

The strongest joint between composites is created by properly fitted bolts and applying adhesives to the prepared mating surfaces.

We do not recommend using bolts or screws in tapped holes as it creates a weak connection.

For removable cover plates, sheet metal screws can be used. The strength of the connection can be improved by using threaded inserts and bonding them into place with adhesive.

Yes. When removable bolts are required, threaded metal inserts or fasteners should be installed in the composite and preferably bonded in place with a suitable adhesive.

Bear in mind that FRP threads will wear out quickly and may not give sufficient holding strength.

Many types of suitable metal inserts and fasteners are commercially available.

  • Molly nuts
  • Tee nuts
  • Dzus fasteners
  • BF Goodrich
  • Rivnuts
  • Helicoils

Some types must be bonded in place while others can be mechanically fastened. Please refer to manufacturer’s instructions in each case.

A common method for installing removable bolts is to tap your composite product and apply epoxy or polyester adhesive in the hole. Next, cover the threads and shank with a releasing agent and insert the bolt.

After the adhesive has formed and hardened around the threads, the bolt can then be withdrawn.

Note: this method is not recommended when an exceptionally strong connection is required.

When bolts are to be installed permanently, a tight connection can be made by tapping the composite and applying epoxy or polyester adhesive to the hole just before inserting the bolt.

Riveted connections

We recommend Emhart POP® rivets. These are available in various sizes and head styles in aluminum, steel, Monel, copper and stainless steel.

Other rivet types, including drive, rivet gun and ball peen hammer can also be used.

The strength of the connection can be improved with suitable adhesives. Back-up washers are also recommended for distributing load stress. When drilling, make sure you use a drill that makes a hole slightly larger than the diameter of the rivet.