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Posted by on Dec 10, 2019 in Equipment |

Easy Windsurfing Repairs | Part 5: Soft deck

If you’re reading this, you’re in trouble. Soft deck can have multiple different causes, but it almost always ends the same. Because the owners often realise too late, many boards are diagnosed and repaired way too late. Because a soft deck is a sign of internal damage to the board, its key to act smart and act fast!

Unlike the previous guides in this series, the problems of soft deck boards can vary from board to board. Therefore, it won’t provide a simple step-by-step solution to the problem. Having said that, it should give you a good understanding of when you can try to DIY your way out of a problem and when to call for specialist help.

1. Background

To fully understand why and how decks get soft, we need to fully understand the construction of a modern epoxy-sandwich board.

Cross-section through the epoxy-sandwich board.
Structure of a modern epoxy-sandwich board: deck to core!

As the name suggests, a sandwich board consists of multiple layers creating one solid structure. The inner most layer is the core of the board: usually made of expanded polystyrene, commonly called Styrofoam. The core is covered in the first layer of glass fibre. Following that is the layer of cross-linked PVC foam ( often called Divinycell or Airex). Then comes the final layer of glass fibre laminate that forms the actual structure of the deck.

2. Soft deck on so many layers!

It is important to understand this multi-layer structure, since the source of soft deck can come from any of those. Any two layers that come loose from each other will start to flex and eventually get damaged. However, depending of how deep in the board it sits, soft deck will feel and sound slightly differently. Here’s how to distinguish them!

Core cracking

Core cracking - cause of a soft deck.

The most common early stage soft deck issue stems from a worn-out foam-core of the board. You can see how repeated flexing of the board has crushed the expanded foam whilst leaving the top layers intact. The board will feel soft, but you shouldn’t be able to hear any cracking sounds.

A way to fix this early stage damage might be to inject marine Polyurethane Foam into the board to fill in the gaps. More on that later.

Inner glass – PVC bond

Divinycell/Airex/PVC foam coming away from the laminate - cause of a soft deck.

Another possible way for a deck to become soft is the un-gluing of the PVC foam from the inner glass fibre layer. This time, the soft spot bottoms out distinctly, with a crunchy sound (like a button on a code keypad). This kind of damage is usually a result by abuse and neglect of a board, typically leaving it in a hot car. The temperature decomposes the glue and deforms the PVC foam. In this case, the only repair option would be to reconstruct the top layers of the board from scratch – no injections will do it any good!

Neglected soft deck

This picture is the direct result of neglecting to fix a soft deck resulting from a crushed foam core. Due to extensive flexing, the top layers start to delaminate and crack. The soft area will feel crunchy and dip in significantly. And if left long enough, this will lead to the deck cracking and letting water into the core of the board!
Unfortunately, at this stage the repair won’t be cheap or easy – the board needs reconstruction from the core up, with new lamination and PVC being in order!

Gravely soft deck

Last but not least, is the final form of the soft deck. It’s a combination of all of the problems we’ve mentioned before – but doubled. The core is completely mushed and has fallen apart into distinct layers. The PVC foam and glass laminates have come apart as well! At this point, the board would have likely sipped some water into the core as well, which doesn’t bode well. It might not make financial sense to try to repair this one, as you’d basically be rebuilding it from scratch!

2. Fixes to the soft deck problem

As we’ve seen in the exploration of different modes of failure of soft deck problems, relatively few can be easily fixed. The only damage that can be repaired with relative ease is the worn-out and cracked foam core of the board. All other issues would require a state of the art re-laminating and reconstruction jobs using vacuum bagging.

As for the soft deck being a result of the core failure – polyurethane injection is the answer!

When trying to fix the core of the board, the injected material has to have similar properties to the core itself. That’s why soft and compliant polyurethane foam is a much better choice than epoxy! As seen on the picture, when injected into the core, it can fill out all the crevices of the crack and breathe new life into the board!

So how to do it?

Simple! Drill a series of small (2-3mm) holes about 5cm apart in the soft deck area. Next, prepare a small batch of marine polyurethane foam and load it into a big syringe.

As you move on, temporarily plug the already filled holes with a pencil or a used syringe. This will create pressure that will push the expanding foam deeper into the core. Work fast but methodically to make sure to inject as much as possible, before the urethane finishes expanding.

Once all the holes are filled and the foam has set, you’ll have to seal up the drilled holes. That is a job in itself, but if you’ve followed this guide so far you probably know what you’ve signed yourself up for! If you need a quick remainder, have a look at the lamination part of Part 4 of the repair series.


Unfortunately, many cases of soft deck cannot be easily fixed, as it can be a tell tell sign of a much bigger problem. However, if your board feel soft but doesn’t produce a cracking sound and has not taken on water, urethane injection may be a good way to restore it and make it feel amazing again.
Having said that, this repair takes quite a bit of practice and experience to perform and to know when performing it makes sense. Therefore, I strongly recommend paying for a professional board repairer to do it for you, especially with relatively new and expensive boards.

Pictures and specialist information in this article was taken from the amazing, a great website about advanced board repairs, build technology and renovation. I strongly recommend paying a visit!

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