Priming the boat hull below the waterline with epoxy putty

In this article, we explain how to get your boat's hull below the waterline smooth again after a major repair of holes and cracks. You do this simply by priming the boat! The guide is also applicable if you are not satisfied with shape of the surface or with how smooth it is. Use this guide to prime boats made of polyester, epoxy, wood, steel or aluminium. Before you start, it is important to cleanbare and sand the boat first. Before doing so, read the articles we have written on this subject.

You can smooth the hull of your boat with epoxy putty by following these five steps:

  • Step 1. Marking uneven areas.
  • Step 2. Sanding and degreasing the substrate.
  • Step 3. Application of first coat of epoxy filler.
  • Step 4. Sanding, checking and refilling.
  • Step 5. Follow-up work.

Supplies to prime your boat

To prime a boat, you need the products below. You can easily order all supplies online at If you order before 5:30 PM Dutch time and all products are in stock, we will send your order the same day so you can get started asap. 

Raw materials:

  • Variopox Epoxy Putty


The right amounts depend on the overall size of your boat's hull. In doubt about the quantity you need? Then feel free to contact our specialists for tailor-made advice. 

Step-by-step plan boat puttying

In the video below, product specialist Arne shows how to make the underwater hull smooth again with epoxy putty. Below the video, you can read a more detailed step-by-step plan in which we explain in 5 steps how to putty a boat.

Step 1. Marking uneven areas

Use an old fluorescent tube (without fixture). Grasp it in the middle (2 fingers and thumb) and slide it slowly across the trunk. At high spots you can now clearly feel the TL beam flip over. Mark these high spots (e.g. by scratching with a pencil). Mark all uneven parts in this way.

Step 2. Sanding and degreasing the substrate

Dry sand the marked areas with a sander (P60 grit). Then degrease the substrate with acetone or Double Coat degreaser. This will improve the adhesion between the substrate and the putty.

Step 3. Application of first coat of epoxy filler

Now that the surface has been properly pre-treated, we proceed with applying the first layer of epoxy putty to smooth the boat. We use Variopox Epoxy Filler for this purpose. This two-component epoxy putty is easily sandable and suitable for applications where water resistance is important. So this putty is very suitable as a boat putty and can be applied both above and below the waterline.

Weigh both components according to the mixing ratio 2:1 on a digital scale and mix the components to an even colour. Then apply the putty with a putty knife, flexible spatula or Japanese spatula. Always use nitrile gloves when working with epoxy.

Tip: in addition to ready-made epoxy putty, you can make your own epoxy putty. Mix universal epoxy resin with red microballoons. Add as many microballoons as needed. We recommend adding a little filler each time and mixing the resin until the desired thickness is reached.

Step 4. Sanding, checking and refilling

Make a sanding board from a piece of suture wood and 2 good handles. Glue or pin sandpaper 60 grit (dry) on this and sand the hull with diagonal strokes (left and right). You can now quickly see where filler is still needed. Apply more putty where needed to get the hull tight.

Use the epoxy putty to touch up air bubbles, dimples and streaks that were created during the trimming process. Finally, sand the surface with a fine grit so that the hull is nice and flat and smooth.

Step 5. Follow-up work

Now that you have a nice smooth finish on the hull and underwater ship, move on to the next steps. We have written the following articles about (applying) antifouling:

Buy filler for your boat?

All the products you need to putty boats can be ordered quickly and easily at We supply boat putty at lightning speed from stock so you can get started on your project quickly.

Do you have any questions about putty or boat maintenance? Then feel free to contact our product experts. We will be happy to give you honest advice to make your project a success. Email your questions to or send us a WhatsApp message!

Frequently asked questions about puttying a boat

Our experts receive many questions about tightening boat hulls with putty. Below we answer the 3 most frequently asked questions:

Is it necessary to sand before I apply putty?
Before applying filler, it is important to smooth uneven areas. You do this by sanding. After sanding, use a degreaser for ideal adhesion between the substrate and the putty. It is also important to continue sanding between layers of putty.

How do I remove any unevenness in the putty after curing?
Still not completely satisfied with the result? Sand diagonal lines with 60 grit paper. This way you can quickly see where more putty is needed. Apply more putty where needed to make the hull nice and tight.

How do I determine the right thickness of putty?
The right amounts depend on the total size of your boat's hull and its current condition. In doubt about the quantity you need? Feel free to contact our specialists for personal advice.

Related products:

Do you have a question?

Do you have a specific question? Call one of our specialists for free advice +3185 0220090