Fibreglass sundecks were once a popular feature of new homes in greater Vancouver. But as the trendy decks have aged, thousands of property owners are now in need of fibreglass deck replacement. If your fibreglass deck is cracked, leaking, worn, and in need of repair, this article will bring you up to speed on everything you should know for the repair.

How To Repair A Fibreglass Deck

Properly installed fibreglass decking has a lifespan of 15-30+ years. But even this durable building material will require repair eventually.

Here’s how it’s done:

Materials needed

  • Angle grinder with cutting disc
  • Jigsaw
  • Polyester resin
  • Hardener
  • Gelcoat
  • Acetone
  • 1.5 oz Fibreglass mat roll
  • Scissors
  • Laminating rollers
  • Mixing bucket
  • Paint stirrers
  • Disposable mud knife
  • Disposable putty knives
  • 4” Disposable thin paint roller
  • 12” Disposable thin paint roller
  • Rubber gloves
  • Eye protection
  • Respirator/mask
  • Cover-alls

1. Grind away damaged areas

When a fibreglass deck is cracked, it’s no longer waterproof. If the sundeck is over living space, this can cause very expensive leaks. Even when not in danger of soaking into your home, a damaged fibreglass deck can allow water to permeate the plywood and struts below, leading to rot.

To repair a fibreglass deck, first remove all damaged areas by grinding the fibreglass away with an angle grinder. Grind down to the plywood substrate in a pattern that creates a tapered edge that is about 1-2 inches outside of the crack or damage.  

2. Replace rotten or damaged substrate

If the plywood below is damaged, cut away a square portion and replace. Fill all gaps and nail holes with wood filler. When dried, grind them down to a smooth and flush finish.

If water damage or rot extends beyond the plywood into the supports of the deck, a simple repair may not be feasible. If you expect this level of damage, it’s best to contact your local deck builder to assist in evaluating the best course of action.

3. Apply resin and fibreglass

For the new fibreglass to adhere, the surface must be clean and dry. Make sure any dirt and dust is removed and you haven’t had rain or water on the deck in the last 48 hours. You must also apply fibreglass is moderate temperatures, between 10 and 32 celsius.

Mix the resin with the hardener, per the manufacturer’s specifications, and spread a coat over the area being repaired with a roller. Make sure to overlap the existing fibreglass by at least ½ inch. Allow the resin to dry until it’s tacky.

Cut a piece of fibreglass matting to fit the area being repaired. Feather the edges of the mat by pulling strands out around the edges of the cut section. This will reduce the thickness of the perimeter and create a smooth transition between patch and existing deck. Lay this matting patch over the area to be repaired and apply another layer of resin, mixed with hardener.

Once dried, sand the patch flush with the existing deck to prepare for the gelcoat.

4. Finish with a gelcoat to match

Until this point, the fibreglass patch will be translucent. The coloured component of the fibreglass deck is in the next layer, the gel topcoat.

Once you have applied a layer or two of gel coat, waiting at least 4 hours between applications for drying, you can sand the surface. Sanding with 1000 grit will remove any sharp edges that are tough on feet while maintaining a slightly textured, slip-resistant deck surface.

Unfortunately, matching the existing colour of a deck is difficult. You can apply a gelcoat to the entire deck to avoid unsightly patches and create a continuous, waterproof finish.

Check out more DIY fibreglass tips and tricks.

Fibreglass Decking Benefits

Fibreglass is a building material commonly used in many types of indoor and outdoor structures. Made from a mixture of glass fibres and resin, fibreglass has a few notable benefits as a decking material:


When properly installed over a plywood base, the layers of fibre and resin create an impermeable barrier. This characteristic makes it a popular choice for roof decks.


Fibreglass is much harder than most organic deck materials. It tends to stand up to impact, scratching, extreme temperatures, UV damage, chemicals, and everyday wear and tear very effectively.


Unlike concrete, pavers, and some composites, fibreglass decking is very lightweight. This is important to consider when you’re planning labour costs for transporting and hauling materials. It’s also helpful for roof decks with tight load capacities.


Because of its resilience, maintaining a fibreglass deck is very simple. Seasonal cleaning or pressure washing and hardware inspection is all that’s required.

Fibreglass Decking Alternatives

There are some strong benefits to fibreglass decking, but before you call up your local deck builder, consider some modern decking alternatives:

Liquid deck coating membranes

Liquid deck coatings are waterproof membranes that can be applied to almost any surface. Deck coatings are a smart way to extend the life of your fibreglass deck, or to transform any outdoor space into a low-maintenance, slip-resistant living space.

Vinyl decking

Homeowners looking to repair a fibreglass deck will typically opt to replace their fibreglass with vinyl decking. Because this type of decking is a waterproof, affordable, low-maintenance decking solution, it’s an attractive option. With manufacturers like Duradek providing 10 year warranties or more, choosing a vinyl deck is a financially smart option.

Can I install vinyl Over Fibreglass Decking?

Vinyl decking is a PVC sheet membrane, but it it’s not recommended to install it over anything other than properly prepared plywood or concrete. Applying vinyl over fibreglass decking increases the chance of damaged fibreglass piercing the membrane and compromising its waterproofing capabilities.

While it’s tempting to take a shortcut and apply vinyl directly over fibreglass decking, there is a more laborious proper method of installation. Generally, when installing vinyl decking where a fibreglass deck previously was, the most time and cost effective practice is to remove the fibreglass with the plywood substrate. Then you can replace with new plywood and ensure that the substrate will be able to outlast the new waterproofing membrane.

Need help with your fibreglass deck?

Some DIY projects just aren’t worth the hassle. If you’re looking for some pros to help you out with your Fibreglass deck woes, Citywide Sundecks and Railings is your complete decking contractor. We can replace and repair your fibreglass deck in no time. You can focus on enjoying your downtime on your sundeck.

For a free quote on your fibreglass deck project, fill out this form or call 250-618-2507.