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Old 11-29-2015, 11:18 AM
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C-Flex, Sheathing System

The C-Flex Sheathing System was developed to protect the hulls of old and new wooden boats from rot and marine parasites. It is a simple process that covers the hull with a high strength skin of fiberglass that will greatly increase the life and strength of a boat and will dramatically reduce the cost of maintenance.

C-Flex is ideal for the manufacturing of custom boats. The properties of C-Flex allows any form to be built using simple and inexpensive framing procedures instead of costly molding methods.

Each "plank" of C-Flex contains small semi-rigid rods that run lengthwise thoughout the cloth. These rods allow the fiberglass to hold its form while resin is applied. This process eliminates the need for a full mold used in traditional fiberglass construction.

The basic technique involves both chemically bonding and mechanically fastening the C-Flex to the wooden hull. The C-Flex is applied vertically from gunwale to keel so that the rods in the C-Flex run perpendicular to the wooden planking. The mechanical fastening is accomplished with heavy staples, and the chemical is done with an elastomeric adhesive.

The C-Flex is then saturated with resin and covered with chopped strand mat (CSM). A fairing compound is applied to the exterior, and the compound is sanded and painted.


The Adhesive - The adhesive used to bond the C-Flex to the wood is a moisture-cured elastomeric polyurethane which was developed for marine use. It has several characteristics, which make it an excellent material for the bonding agent. First is that it bonds ferociously to both the C-Flex and the wooden planking. Secondly, it will bond to wet wood, treated wood, and virtually all the various types of woods used in marine planking. Add thirdly, being an elastomeric, it will stretch (300%) and compress without breaking its bond. This is essential in preventing the delamination, which might otherwise be caused by the expansion and contraction of the planking and by the “working” of the hull.

C-Flex – C-Flex is a fiberglass planking that was developed for “one-off” fiberglass boatbuilding. It is a high strength (67,000 p.s.i. tensile) material, which contains fiberglass rods and continuous fiberglass rovings.

The C-Flex is applied perpendicularly so that the strength of the C-Flex will directly withstand the expansion and contraction of the planks. The Sheathing is securely fastened to the planking with bronze staples.

Chopped Strand Mat – CSM is a relatively low strength (11,000 p.s.i. tensile) omnidirectional fiberglass material. It is not a woven fabric, but rather a composite of randomly oriented strands of fiberglass. It is used in laminates to assist in bonding between layers of fabric.

CSM is well suited to sheathing because it can be easily applied overhead.

Occasionally multiple layers of CSM are required, depending upon the size, design, use and condition of the vessel.

Fairing Compound – To smooth the exterior surface, a fairing compound composed of polyester resin, industrial talc and glass microspheres is used. This compound is easily applied and dries to a hard, resistant surface. It is sanded to the required smoothness and then painted


The C-Flex Sheathing System may be applied to large wooden boats that cannot be turned over.

Hull Preparation – The hull is sandblasted and/or sanded (24 grit) to remove all paint. Any weak or rotten planks should be replaced, holes should be patched and any necessary fairing work should be done to create a uniform surface.

Applying the Adhesive – The adhesive is a one-part adhesive, which is worked similar to a plaster. It is applied with a notched trowel (1/4” teeth) held at a 45-60 degree angle. The adhesive has a four-hour working time before it begins to cure.

Applying the C-Flex – The C-Flex is applied directly over the uncured adhesive so that the adhesive is squeezed up into the C-Flex. The C-Flex is held in place by small wooded battens that are stapled across the C-Flex using steel staples. These battens hold the rods evenly in place.

The C-Flex is then permanently stapled into the hull with bronze staples. These are applied 12 per sq.ft.

Saturating the C-Flex – Once the adhesive is cured, the battens are removed and the C-Flex is saturated with general purpose laminating resin.

Finishing the Hull – The application of the CSM, fairing compound and paint is similar to the method used on “one-off” boats. The amount of time required for this step depends on the surface finish required.

General Notes on Application Procedure – There are several minor variations on this system which are dependent upon the conditions under which the boat will be sheathed. In general, fiberglass work should be done in a sheltered area. If this in not possible, we have developed techniques for working in the open. Please consult with us at the time of your purchase so that you are property informed of these details.


The technical advantages of the C-Flex Sheathing System are: 1) that it can be easily applied to boats without turning them over, 2) the extremely high strength of C-Flex means that much less material and time is required, 3) the fiberglass is mechanically fastened and chemically bonded to the wood to prevent delamination, 4) the chemical bond is an elastomeric polyurethane which will expand and compress without breaking the bond, thus preventing delamination, and 5) the adhesive will adhere to wet wood, treated wood and virtually every variety of wood used in boat planking.
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