Fixing Common Glassing Problems on a First Board

Every glasser has a first board they would rather not photograph.

A crater in the resin, a cloudy patch that never fully wets out, or a rail with a cured drip can make a first lamination look rough. These surfboard glassing problems are common when you are learning to control resin, fibreglass, and timing.

The good news is that many glassing faults can be repaired, while others provide a clear lesson for the next board. Understanding what caused the problem is the first step towards fixing it and preventing it from happening again.

Know Your Resin System First

Before you start troubleshooting, make sure you know which resin you are using. The two main types work differently and cannot be swapped. Polyester resin uses MEKP as a catalyst and is usually paired with PU foam. Epoxy is a two-part system and is the right choice for EPS foam.

The most important rule is to match your resin to your foam. Polyester resin has styrene, which will eat away at exposed EPS foam. If you use polyester on an EPS blank, you can ruin the core before you even get the board wet. Always check compatibility before you start working on the finish.

Fisheyes and Craters 

A fisheye is a small, round spot where the resin pulls away from the surface instead of spreading out smoothly. This happens because something on the surface is stopping the resin from sticking properly.

Silicone, wax, oil, polish, dust and even contaminated hands can stop resin from wetting the surface properly. On epoxy builds, there is a second common culprit, amine blush. As epoxy cures, the hardener can react with moisture and carbon dioxide in the air and leave a waxy film on the surface. Humid conditions make it easy to trigger, and coating straight over it invites fisheyes and weak adhesion.

Since fisheyes are caused by something on the surface, adding more resin usually does not help. The new resin will pull away just like before. The real solution is to get rid of the contamination. If it is blush, wash the cured surface with warm water and dry it before sanding. If it is silicone or something else, clean the area well, then re-coat while the resin is still workable or sand and fix it after it cures.

It is better to prevent fisheyes than to fix them. Keep anything with silicone away from your workspace, use clean tools, handle your fibreglass cloth carefully, and get your blank and work area ready before you start mixing.

Pinholes in the Hot Coat

Pinholes are tiny holes that appear in the cured surface of a hot coat. They can become visible over the weave of the laminated cloth and are usually associated with small air bubbles or imperfections in the resin surface.

Air can get trapped in the cloth during lamination or mixed into the resin. With EPS blanks, outgassing is another big cause. When the foam warms up, the air inside expands and pushes through the laminate and hot coat, breaking the surface as it escapes. To help prevent this, laminate and coat when the temperature is steady or dropping, since a cooling blank pulls air in instead of pushing it out.

Small pinholes in a cured hot coat are usually easy to fix. Sand just enough to open up the area without cutting into the laminate, clean off the dust, and add a fill coat if needed. Next time, mix carefully to avoid air bubbles, coat when the temperature is steady or falling, and take your time with the hot coat.

Dry Patches And Starved Cloth

A dry patch is an area where the fibreglass cloth has not been fully saturated with resin. Instead of becoming transparent as it wets out, the affected section remains white or cloudy.

This happens if there is not enough resin to wet the cloth, if the resin is not spread evenly, or if you pull out too much resin with the squeegee. If the resin starts to cure before the cloth is fully wet, it can also make the problem harder to fix.

Dry or starved cloth is not just a cosmetic problem. Fibreglass that is fully soaked with resin is important for the board's strength, so any area that is not properly wetted out may need to be fixed.

If the resin is still workable, fresh resin can sometimes be worked into a dry area and distributed through the cloth. Once the laminate has cured, the affected section may need to be sanded back and reglassed, depending on its size and location.

The best way to prevent dry patches is to manage your resin carefully. Mix a batch size you can handle, make sure the cloth gets enough resin to wet out, and use the squeegee to spread the resin instead of pulling too much out.

The Coat That Will Not Go Off

A common surprise for beginners is a hot coat that stays sticky no matter how long you wait. With polyester resin, the laminating resin does not cure properly when exposed to air, so any surface left open will stay tacky. It is meant to be covered by another layer, not used as the final coat.

To get a hard, sandable finish, you need to add a surfacing agent, usually wax in styrene, to the last coat, or use a special sanding resin. If you skip this step, the surface will never fully cure. This is about choosing the right product, not a problem with the resin itself.

Delamination Around the Tail 

Delamination happens when the glass separates from the foam underneath. On a new board, this is a serious problem and usually starts during glassing. It can be caused by not enough resin in the lap, trapped air, outgassing that lifts the laminate before it cures, or resin applied over dirty or poorly prepared foam. Any of these can create a weak bond that might fail later.

Delamination around the tail is a bigger problem because that area takes a lot of force from your fins when you turn. If the glass around the fin plugs and boxes is weak or dirty, repeated stress in the water can make the glass separate from the foam, even after the board looks finished.

You can sometimes fix small delaminated spots by injecting resin and clamping the area until it cures. If the problem spreads, the repair becomes more complicated. The main lesson is to wet out the tail completely and set fin plugs and boxes into strong laminate, since your fins are only as secure as what holds them in place.

Drips, Runs, and Rail Sags

Resin is a liquid, so gravity always has an effect.

Drips and runs on the rail usually happen when there is too much resin in the laps, or the board is positioned so resin pools as it cures. This is mostly a cosmetic issue, but heavy runs waste resin and make the board heavier.

Keep the laps tight by using steady brush pressure, remove extra resin before it starts to sag, and check the rails a few times as the resin thickens.

Shapers’ Tip

Keep a small piece of foam next to your bench and glass it first with each new batch. This will show you how the resin is behaving that day before you use it on your board.

This is the cheapest way to avoid many of the problems listed here.

Every Fault Is a Lesson 

Fisheyes remind you to keep things clean, pinholes teach you to be patient, dry patches show the importance of working at the right speed, and delamination teaches you to respect the board's structure.

When you look at it this way, surfboard glassing problems are not failures; they are just quick feedback to help you improve.

Using good materials also helps a lot. Clean fibreglass cloth that wets out well, properly mixed resin, and reliable tools take away some of the biggest challenges when building a board.

Shapers Bali has both types of resin, plus squeegees and brushes in their glassing collection. The same materials used by glassers around the island every day.