This is how to repair holes and cracks in your boat!

Is your boat damaged and do you want to repair it easily? In this article, we explain step by step how you can repair cracks, scratches or holes in the hull of your boat (below the waterline). In addition to a step-by-step plan, you will also read all about the necessary materials in this article. This way, you get to work with the right materials using an efficient method!

After reading this article, do you have questions about repairs to your boat or do you have doubts about the materials (and the quantity) that are suitable for your application? Please do not hesitate to  one of our specialists for tailored advice!

Step-by-step plan for boat repair (below the waterline)

In the video below, product specialist Arne shows how to easily carry out a polyester repair. Here, he uses the Polyester repair kit. We have written down all the steps so you can read it again later.

Step 1. Map the damage

Before you start boat repair, it is first important to take stock of the damage. Check carefully where and what damage you have. Think of cracks, scratches or holes from removed equipment (such as a log or depth gauge).

After you have inventoried all the repairs, you can calculate how much material you will need to carry out all the repairs.

In this article, we discuss repairing damage to the underwater hull. For repairs to the superstructure, read the article: Repairing the superstructure!

Step 2. Chamfering off holes, cracks and scratches


Chamfer cracks and scratches with an 8:1 bevel. For small repairs, use a sander. For large repairs, an angle grinder with flap disc is indispensable. By beveling the edges, you promote the bonding surface.

Redundant holes should also be chamfered. In many cases, we recommend doing the repair from both the inside and the outside. It is then often chosen to first bevel the outside to about 2/3 of the hull thickness. Once the outside is repaired, you need to grind out and repair the inside.

After grinding, check that the cracks are not deeper than expected. Wet the sanding area and wipe it dry again. In a crack, water will stay longer and become visible again. Grind these cracks even deeper.

Finally, make a plug from, for example, a leftover piece of suture wood covered with tape or cardboard. This way you bridge the gaps of equipment.

Tip: it is also possible to use a fibre disc and adapter. A quick solution without having to invest a lot of money in equipment. 

Step 3. Repairing damage with polyester and glass fabric


Tip: with the Polyester repair kit, you immediately have everything you need to carry out a polyester repair!

In this step, we are going to laminate the holes and cracks with polyester laminating resin combined with glass fibre. Always clean and dust the surface before you start laminating. In addition, make sure you always wear the right protective equipment while working with polyester. Always wear covering clothes, a suitable fume mask and nitrile gloves.

Tip: use the Polyester safety kit with all the necessary protection equipment.

Repairing holes
Add about 2% MEKP hardener to the polyester laminating resin and mix well in a clean mixing cup. While mixing, the polyester resin will slowly change colour.

Once you have mixed the polyester resin well, apply a layer of resin to the surface. Apply enough fibreglass chopped strand mat around the hole. Do this from large to small and vent the surface after each layer with a vent roller. After each layer of fibreglass, apply another layer of polyester resin. Work in this way layer by layer until the fabric is level with the surrounding surface. Now let the polyester resin cure completely.

For holes that are completely through the hull, after curing on the inside, the temporary plug can be removed and on the inside, the spot can also be sanded at an angle and laminated using the above method. The strength is now fully restored.

Repairing cracks
You can easily repair cracks by making a paste of polyester laminating resin and glass fibres. Add about 2% hardener and the glass fibres to the polyester laminating resin base. Mix well to make a splashable paste. Now fill the crack with the paste and spread it well. Then let this cure completely.

Step 4. Follow-up

In the steps above, you have read how to do a polyester repair. Now that you have successfully repaired all cracks and holes, move on to the next step: filling the hull with epoxy putty.

More information about a repair above the waterline?

Do you still have questions about polyester repairs or about refurbishing your boat? Our specialists are ready for you! Feel free to ask all your questions via phone, email or live chat, we will be happy to help you with your project! Check out the other informative articles we have written on boat repair and recovery.

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