Home » All You Need to Know About Repairing Fiberglass Cracks

All You Need to Know About Repairing Fiberglass Cracks

A fiberglass crack is usually a tiny hole in the surface of the fiberglass that can be caused by things like UV rays, brittle epoxy resin, or when an object scrapes against it. It can also happen when water penetrates small cracks and freezes. These are just some of the many causes for this type of damage to occur. If you want to know how to repair fiberglass cracks on your boat, RV, pool enclosure or any other object read on!

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Repairing Fiberglass Cracks

TotalBoat Polyester Laminating Resin
  • tough resin
  • long-lasting protection
  • easy to use
True Composites Hardener Polymer Resin Fiberglass Repair Kit
  • dries tack-free
  • no need wax
  • cures quickly (4 hours)
Fiberglass Warehouse Polyester Laminating Resin
  • easy to use
  • dries quickly

What is Fiberglass

Fiberglass is composed of glass fibers that are woven together to make cloth. This cloth can be made into anything from a boat hull, to fiberglass insulation for buildings. It is used in the construction industry because it’s lightweight and relatively inexpensive.

What is fiberglass

Fiberglass boats, windows, and roofs have become popular in recent years due to their affordable cost and ease of installation compared with other materials like wood or metal.

The home improvement store sells both resin kits which you mix up yourself using an applicator bottle before applying them with a roller brush onto the crack(es), as well as pre-mixed bottles of gel type glues that come with a caulking gun tip on top (like something you use when installing ceramic tile). Fiberglass cracks are generally caused by a combination of moisture, and lack of proper installation.

What reasons cause fiberglass crack

What reasons cause fiberglass crack

Most people want to know how to repair fiberglas cracks so that the damage is not visible from the outside when they look at their window or door frame. Some also wonder if there’s a way fix it without having to replace the entire unit like in case with wood frames which can be expensive depending on what material you’re using for your house exterior as well as whether you choose contractor services or just DIY . Fortunately, both options don’t need too much time nor money but do require attention and patience especially when choosing between resin vs gel type glues because each has its own advantages (and disadvantages).

So what reasons cause fiberglass crack?

what reasons cause fiberglass cracks

The most common reasons are:

  • Improper installation (note that the gap between the window frame and your wall should be filled with insulation to prevent cold air from getting in)
  • Excessive humidity or moisture due to rain, faulty roofing, leaky pipes etc.
  • Lack of ventilation causing condensation – a difference in pressure inside & outside. For example when you close all windows at night while there’s still warm weather outside which causes warmer indoor temperature than outdoors therefore creating high internal pressure pushing against weak spots like cracks which can lead to breakage fairly quickly especially if they’re only glued instead of using epoxy resin kits for fiberglass crack repair . On another note, it is essential not too use type of chemical cleaners on glass surfaces (like ammonia, acetone etc.) because it can dissolve the adhesive and cause damage to your window frames.
  • Physical impact (hitting them with a moving object or an accidental hit when carrying something).

What should I do?

How to repair fiberglass cracks depends on how badly damaged they are – whether they’re only superficial scratches/nicks that don’t go all the way through or cracks going into deeper layers of glass fibers which may require more than just cosmetic touch ups. It’s recommended not to delay any repairs by trying temporary measures like filling up spaces between glass pieces with caulk as you’ll most likely find yourself having to replace the entire unit sooner rather than later.

Types of materials for repairing fiberglass cracks

Types of materials for repairing fiberglass cracks

Fiber glass can be repaired with either glue or resin; both are equally effective but when applying resin, ensure using only those which are intended specifically for this purpose. Moreover, if your cracked piece contains any metal parts or sharp edges (for example chair legs), then opt for gluing because resins will simply melt these elements away making the entire surface uneven. Once again – always safety equipment such as gloves, mask and glasses.

*Note: when applying resin, you don’t need to sand the area that will be filled in (unless it is necessary). Apply a thin layer of fiberglass repair over your crack or hole and allow drying for at least 12 hours; best results are achieved after 24 hours have passed.

When using glue on any surface make sure to wait until the material gets tacky before actually sticking everything together otherwise all efforts made during gluing process would go down the drain. After making sure that surfaces where crack has occurred meet perfectly – press firmly until you feel like there’s no air between them anymore then let dry completely (in case if you applied some sort of adhesive) leaving enough time for curing. This means that glue has dried up completely and it’s no longer wet.

*Note: let the glue dry overnight for best results.

Afterwards, you can sand down any sharp edges that may have formed during drying process – this way surface will look smooth again. For some people, repairing fiberglass might be a bit complicated because apparently there are so many different methods to do this but in fact with perseverance everything is possible! If done properly – you won’t notice a thing out of place or repaired area; plus your household items wouldn’t need replacing either which means spending hundreds on new stuff and let them eventually gather dust at home. Do not forget about taking proper safety precautions when using chemicals such as resin because they contain harmful substances such as solvents and other chemicals.

How to repair fiberglass crack: step by step instruction

How to repair fiberglass crack

Use a heat gun or blow dryer to warm the area. This makes it easier to remove old paint and glue residue.

Start off by using painters tape, masking tape, or duct tape to protect areas that you don’t want painted during this process.

Use acetone (fingernail polish remover) on your rag/paper towel and wipe away any excess goop from cracks before applying new resin filler.

Once all of the above is complete use sand paper with 220 grit for best results. Gently rub down both sides of crack so they are smooth.

Use epoxy putty in fiberglass color mixed with hardener per instructions on label. Apply mixture into open crack until filled evenly but not too thick.

Let dry per instructions on label.

For small cracks, just use clear fingernail polish to seal the crack until it’s ready for its next adventure in life!

Best Resin for Repairing Fiberglass Cracks

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TotalBoat Polyester Laminating Resin

TotalBoat Polyester Laminating Resin
TotalBoat Polyester Laminating Resin is a durable, easy-to-use and fast resin that won't react in any environment. It's designed to protect and brighten your base coat for Laminating applications and steel structures like car bodies or boat hulls with fiberglass, wood & metal. Pros
tough resin
long-lasting protection
easy to use
a bit expensive

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True Composites Hardener Polymer Resin Fiberglass Repair Kit

True Composites Hardener Polymer Resin Fiberglass Repair Kit
Ever want a project done super-fast? Get started with this Polymer Fiberglass Fabric, Resin and Hardener kit. Within minutes of mixed together you can have a repair cured in just four hours! Formulated with the best resin polymer on the market, it cures fast and dries tack-free without any need for wax or other covering. It's perfect for anyone from an experienced DIYer to large corporations looking for ways to save time and money when repairing boat hulls, building new construction parts out of fiberglass or wood, or working on an auto body.
dries tack-free
no need wax
cures quickly (4 hours)
toxic stuff

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Fiberglass Warehouse Polyester Laminating Resin

Fiberglass Warehouse Polyester Laminating Resin
When boat builders need a strong, tough material that will hold the fiberglass cloth and composite fabrics in place during building or for multiple repairs like a bathtub, automotive fiberglass fabric, surfboards among other projects this resin is perfect. For composites and FRP parts for cars motorboats yachts boats etc use it as the base coat to create either sprays or applying by hand followed up with MEKP catalyst to make sure side stays tacky until next application before adding another layer your project will come out tight.
easy to use
dries quickly
no catalyst included

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Can I repair fiberglass cracks?

In most cases, yes you can.

Will glue work on repairing fiberglass cracks?

It's one option, but it may not be the best choice. If you're working on fiberglass that has dried up or is deteriorating, then glue can definitely help. However, if your crack isn't deep enough to allow for a strong bond between the two pieces of material, then gluing them together will only result in more cracks.

Can I use resin for repairing fiberglass cracks?

Resin can definitely work, but it has its limitations. Resins come in a variety of types and you'll need to choose the right resin for your project. In some cases, using more than one type of resin is necessary since they have different properties that allow them to adhere better with specific materials.


Fiberglass is a strong material but there are times when it does not work so well and cracks. If you have fiberglass around your home, boat or RV then knowing how to fix them can save you money in the long run and keep things looking nice. There’s no reason to let something like that sit broken when all it takes is some simple tools and a little time to fix it.

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