Andrew Pace
Fixing screw holes in a fibreglass boat can be done in several ways. One method involves using a two-part epoxy, which is mixed and applied around the hole, left to dry, and then re-drilled. Another method involves using a rivnut, a type of hollow space anchor, which is inserted into the hole and then collapsed using pliers to create a ballooned bulb behind the fibreglass, providing a strong backing for the screw. Yet another approach is to use bolts instead of screws, as they provide a stronger hold. Filling the holes with epoxy thickened with colloidal silica, gel coat, or marine tex, an epoxy paste, are also recommended.
How to fix a screw hole in a fibreglass boat
| Characteristics | Values |
|---|---|
| Hole size | If the hole is huge and beat up, the anchor method won't work. |
| Hole location | If you can't reach behind the hole, you can't use the anchor method. |
| Hole preparation | Drill out the hole to expose clean fibreglass. |
| Hole filling | Fill the hole with epoxy, epoxy thickened with colloidal silica, gelcoat, or fibreglass cloth and epoxy. |
| Hole reinforcement | Use a wood backer, a rivnut, or a bolt. |
| Screw type | Use sheet metal screws, machine screws, or self-tappers. |
| Screw preparation | Dip the screw in epoxy before inserting it into the hole. |
| Screw insertion | Drill a pilot hole before inserting the screw. |
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What You'll Learn
Using bolts instead of screws
When repairing screw holes in a fibreglass boat, it is recommended to use bolts instead of screws. This is because bolts are simpler and more dependable. Screws, especially wood screws, can easily tear out of fibreglass.
If you are able to access the rear of the hole, one method is to use a two-part epoxy to fill the hole. First, tape around the hole, then put some mixed epoxy in the hole, but do not completely fill it. Then, take the screw and put it into the hole so it fits squarely into the fibreglass. The epoxy will harden and hold the screw in place. Once the epoxy is a bit beyond tacky, remove the tape and any excess epoxy on the screw. If you ever need to remove the screw, heat it up with a soldering iron or gun until the epoxy lets go, then pull it out with a pair of pliers.
If you cannot access the rear of the hole, you can use pop rivets to reattach the screw in the same spot. Alternatively, you can fill the hole with epoxy thickened with colloidal silica, let it cure, and then redrill.
When choosing a fastener, it is important to first assess the load that it will need to handle. Bolts or machine screws must be used to secure any component or piece of hardware essential to boat function and/or safety that might experience a load. Hardware of lesser importance or subject to little stress can be fastened with screws.
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Filling the hole with gel coat
If you do not have access to the rear of the hole, you can use a two-part epoxy method. Tape around the hole, then put some mixed epoxy in the hole, but do not fill it up. Then, take the screw and put it into the hole so that it fits squarely on the fibreglass. The epoxy will harden and hold the screw in place. Remove the tape when the epoxy is a bit beyond tacky and remove any excess.
If you want to remove the screw, heat it up with a soldering iron or gun until the epoxy lets go, then pull it out with a pair of pliers. It will not take much heat to release the epoxy.
Another method is to use bolts instead of screws. If you can reach behind the panel, you can also use 1/8" pop rivets with backing washers to reattach the snap without using epoxy or resin.
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Using a rivnut anchor
If you can't reach the area behind the fiberglass, you can use a hollow space anchor called a rivnut. Rivnuts are tubular inserts that are placed into the hole with a special type of plier tool. Once inserted, the pliers are squeezed together, and the cylinder is collapsed, leaving a ballooned bulb behind the fiberglass and a rim around the outside. The tool is then removed, leaving a threaded insert behind which will receive a bolt.
You can pick up a set of rivnuts at any upper-scale hardware store for around $80. When installing the bolt, it is recommended to use locktite on the bolts to ensure a secure hold.
Before installing the rivnut, it is important to clean and prepare the hole. One method is to drill out the holes to create clean, smooth surfaces for the rivnut to grip onto. Additionally, you can fill the holes with a marine sealant, such as Marine-Tex, or epoxy to create an even stronger bond. Allow the sealant or epoxy to cure completely before installing the rivnut.
It is important to note that rivnuts are not suitable for all types of repairs. If the hole is too large or damaged, the rivnut may not hold securely. In such cases, it may be necessary to explore other repair methods or seek professional assistance.
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Filling the hole with epoxy
Firstly, it is important to prepare the area by taping around the hole to avoid making a mess. The two-part epoxy should be mixed and applied to the hole, ensuring it is filled adequately. It is recommended to let the epoxy dry for an extended period, approximately 10 hours, to ensure it cures and hardens completely.
For a more robust repair, consider using a wooden backing. This involves gluing a piece of hardwood behind the hole, allowing the screw to bite into the wood for a stronger grip. Alternatively, some sources suggest using fiberglass cloth, epoxy putty, or "marine tex" (an epoxy paste) to fill the hole, creating a stronger bond.
If you are concerned about the epoxy's strength, consider adding colloidal silica to the mixture. Colloidal silica is a micron-sized silicon dioxide sphere that strengthens and thickens the epoxy. This can be particularly useful if you plan to use self-tapping screws, as they can fracture the epoxy when re-inserted.
Once the epoxy has dried, you can drill and tap the hole for a machine screw or insert a snap/screw to fit square on the fiberglass. The epoxy will hold the screw in place securely.
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Using a wooden backer
If you can't reach the area behind the damaged part of your fiberglass boat, one way to fix an enlarged screw hole is to use a wooden backer. This method involves gluing a piece of hardwood behind the hole so that the wood screw can bite into the backing wood. This will ensure that the fastener holds much better.
Before gluing the hardwood to the back of the hole, you should drill out the hole to expose clean fiberglass. Then, coat the wall of the hole with epoxy or resin, which will help the new screw to bond with the fastener. You can also use a two-part epoxy putty or "marine tex", which is an epoxy paste, to fill the hole. Tape around the hole to avoid a mess, and let the epoxy dry for around 10 hours before re-drilling.
If you want to remove the screw at a later date, heat it up with a soldering iron or gun until the epoxy lets go, then pull it out with a pair of pliers. It won't take much heat to release the epoxy.
You can also use bolts instead of screws, as they are stronger and less likely to tear out of the fiberglass.
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Frequently asked questions
If you have access to the rear of the hole, you can use bolts instead of screws, or rough up the area and add fibreglass and gelcoat. If you don't have access to the rear of the hole, you can use a two-part epoxy and tape around the hole, then put the snap or screw into the hole before the epoxy hardens.
If the hole is large and damaged, the anchor method may not work. If you can access the area behind the fibreglass, you can use a hollow space anchor called a rivnut. If you can't access the area, you can use a two-part epoxy, which will harden and hold the screw in place.
Before filling the hole, use a drill to determine the size of the screw you will use, then drill a pilot hole that is smaller in diameter than the screw. Vacuum any debris out of the hole before installing the new fastening. If you are using self-tapping screws, coat the wall with epoxy before fastening.
