Fiberglass Repairs Using RPS

RPS Composites

The RPS Group of Companies designs and manufactures composite corrosion resistant pipe systems and process equipment. From material selection through component design, stress analysis, manufacturing, shipping, installation, and maintenance, PES has the turn key capabilities to ensure you realize the full benefits of your composite installation.

RPS piping systems, process vessels, stacks, duct, hoods, covers, and other miscellaneous equipment; designed with high performance composite materials and built to the highest quality standards; are installed in over 42 countries worldwide. RPS corrosion resistant products are installed in aggressive process applications in diversified industries including: Chemical Processing, Mining & Mineral Processing, Pulp & Paper, (FGD) Flue Gas Desulphurization, Chlor-Alkali, Steel Processing, Marine and Power.

Important Information to Know about Fiberglass Repairs

There are a few principles that, once understood, allow for successful composite repairs. Having a completed successful repair allows you to extend the life of a part or mold, and saves you the cost of replacing your composite part. It is important to consider these three main principles of composite repair:

Repairs Differ from the Original Part

The first principle is that structural repairs are made by a different process than the original piece. A composite part’s resin cures bonding both chemically and physically with the reinforcement fabric resulting in a single unit when it is initially manufactured, regardless of the number or orientation of the plies of fabric. Referred to as the primary structure or bond, it is the strongest type of bond that can exist within a composite part.

All repairs become secondary bonds attached to the original primary structure once a part is damaged. This means all repairs depend upon physical bonding to the surface of the original primary structure. Because of this, fiberglass repairs rely upon the adhesive quality of their resin for their strength — the strength of physical bond to the primary structure. In fact, resins with strong adhesive properties are often times used for repairs.

Increased Surface Area will Increase Strength of Composite Repairs

Increasing the surface area of the bond line will increase the strength and durability of the bond — and by extension the part or repair — since fiberglass repairs depend upon surface adhesion (physical bonding) of the repair to the primary structure.

The method usually employed to increase the surface area is taper·or scarf·sanding. With this type of sanding, the area next to the damage is gradually sanded away, generally resulting in approximately 1/2 – 3/4 of an inch of area per ply of composite laminate. Typically, scarf sanding is done with a high—speed compressed—air power sander. This is a gentle process since most composite structures are fairly thin. Relative to the thickness of the laminate, the size of the taper is expressed as a ratio. Generally, the stronger or more critical the repair needs to be, the larger the ratio. A gentle taper is usually required for structural repairs, with a ratio of 20:1 up to 100:1.

Another method employed to increase surface area is step sanding. The size of the inner repair is defined, then the surrounding materials are removed at a width of 1/2″ per ply of the part, working towards the part surface. A considerable growth of the repair surface occurs as a result, and allows the fiber orientation to be evident in each step.

Each of these methods are acceptable for the majority of the composite repairs, but most consider scarfing to be easier, and it’s generally considered better. Abrupt edges and butt joints in each repaired ply occur as a result of stepping. It is also difficult to step sand without cutting through, potentially damaging the underlying plies.

Match Your Repair to the Original Part

While your composite repair is different than your original part, it is important that the thickness, density, and ply orientation of the original laminate be duplicated when making the repair. This will help with maintaining the functionality of the part. In this case, more is not always better. If your repair is thicker than the original part, it will most likely be stiffer, regardless of the material in use. Unintended stress points can be caused by introducing various strengths with a part, eventually leading to material fatigue or failure.


With these fundamental principles, you have the foundation for understanding the sequencing for repairs. If you have a question about your specific application or if you need your fiberglass repaired, don’t hesitate to contact PES Solutions with the link below!


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