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How to Fiberglass a Boat Floor? – A Boat Owner’s DIY Guide

Written by Anthony Roberts / Fact checked by Jonathan Larson

how to fiberglass a boat floor

Every boat owner wants to have a long-lasting boat floor. Fiberglassing is one of the most effective ways to do it. You can have the manufacturing company do it or from where you purchased your boat.

You can also do it yourself, but how to fiberglass a boat floor properly? The article teaches you the step-by-step guide, including some tips to make the DIY task easier.

Read on to know the details.

Step-by-step Guide to Fiberglassing a Boat


The four basic steps are first, repair or overhaul your old boat flooring. Second, mix the primer coat. Third, lay out the Chopped Strand Mat (CSM). Lastly, apply the first and second layers of gel coat, sealing it off with a polished finish.

Follow these detailed instructions for you to successfully complete the DIY task.

Step 1: Prepare the following tools and equipment:


Fiberglass flooring materials:

  • Chopped Strand Mat (CSM) – made of fiberglass strands and held together by a styrene binder. This creates the thickness you need for the floor. So, multiple layers are advisable. Take note, however, it is incompatible with epoxy resin. If you are using CSM, it is best to use unwaxed resin.
  • Knit Fabric – bundled fiberglass fabric stitched with CSM layer. It doesn’t crimp, given the stitching, and works well with epoxy resin, vinyl ester, and polyester resin.
  • Fiberglass Cloth – there are different types or weights of the cloth: lighter ones act as finishing cloths to create that clear laminate look; mid-weight is for a water-resistant finish; and heavy-duty ones are for those requiring thick laminate.


  • Epoxy Resin – with its superior quality and durability, it is the most expensive type of resin out there. However, it is worth the price, especially if you want your fiberglass floor to hold together for a long time.
  • Vinyl Ester Resin – it resists corrosion and sticks easily to surfaces. However, it can quickly yellow over time. So, if you want your fiberglass to remain clear, you may want to choose another resin or fix it up.
  • Polyester Resin – a general-purpose resin, polyester can cure with a tack. This means you no longer have to sand between layers.

Other Materials:

  • Graduated measuring cups and mixing ticks like paint sticks and tongue depressors for mixing resin and hardener
  • Squeegees and spreaders to ensure the resin is evenly spread. Squeegees are suitable for spreading thickened epoxy putties.
  • Brushes and rollers for applying the resin to the surface. Aluminum is good for flat surfaces, Bristle is suitable for stitched and knitted fabrics, and Radius Aluminum Corner Roller is perfect for spreading on inside corners as it also gets rid of air bubbles.
  • Cleaning supplies for cleaning resin excess and your brushes and cups
  • Safety gear such as goggles, gloves, and respirators

Step 2: Repair the old flooring



Before installing anything new, change or repair the previous floor of the boat. Take note that any holes or damage left untreated on the old floor become a problem once you start installing the fiberglass.

Depending on the damage, repairs can include gluing or nailing broken planks, overhauling entire sections, caulking gaps, and sanding the floor. Make sure to repair soft spots as well.

Here are boat floor repair tips:

When there are gaps between the hull, stringers, and posts, lightly sand the floor to smoothen it before caulking them. Use clear caulk to correct mistakes easily should there be one.

Step 3: Mix the primer coat


When mixing the hardener, always follow what the resin manufacturer recommends. Hardeners can be tough to work with as you also need to consider the environment’s temperature. You should work at 60 degrees and below 90 degrees Fahrenheit.

After mixing, cover the areas you want to exclude from the project with a clean cloth. Then, use an appropriate-sized roller to paint all over the floor–from the top to bottom to the sides. Remember to keep a minimal and even coverage.

The recommended amount is 3 oz of resin per square foot of 1.5 oz of CSM. Another option is to use 4 oz of resin per square foot of 2 oz of CSM.

Step 4: Lay out the Chopped Strand Mat (CSM)


The mat serves as your workspace. Cover all the areas where you want to place the fiberglass in. It is advisable to have an overlap of 1 inch. You can just cut out any excess, as this is easier than having a shortage on the mat.

Once covered, pour the resin mix slowly across the mat. Use a roller to brush the mix. Make sure all areas are covered and are evenly coated.

Leave the resin mix overnight, allowing it to seep onto the mat.

You can also use another layer of CSM. The double layer strengthens your fiberglass and can prevent damage like cracking over time. The recommended thickness of resin is calculated using the formula: 2.5 x CM weight.

Step 5: Apply the first and second layers of the gel coat


Any gel coat on the boat floor is fine to use as long as you use acetone to make it thin first. About 10% of acetone is recommended. After, you must pair it with a hardener (e.g. wax) to create that glossy yet tough finish.

Use a roller to spread the mixture evenly across the CSM (or multiple layers, if you used them). Once done, let it dry for a while to make sure the first layer is all settled.

Afterward, apply the second layer. This serves as the outermost protective layer or barrier of your fiberglass. While it is fine to have one layer only, sealing the floor with another one can firm up your fiberglass.

Benefits of a Fiberglass Floor


While there are many reinforcement systems, fiberglass resin for boat floors is one of the most suitable for long-term use and stability. Here are its advantages in detail:

  • It has a strength-to-weight ratio of 4,000 psi which proves its flexural strength.
  • It is highly durable, minimizing replacement costs for cases of cracking, shrinking, and curling. This is ideal for homes and businesses, especially in high-traffic areas.
  • It is resistant to high temperatures, which makes it unaffected, or it doesn’t chemically or physically change in specific environments. It retains 25% of its original strength even when subject to high heat, like 540 degrees Celsius.
  • It is water resistant, making it easy to clean and less vulnerable to structural damage.

Frequently Asked Questions


Is it necessary to fiberglass on a boat floor?

Fiberglass is a popular choice for boat floors, given its high strength. It is resistant to water, corrosion, and high temperatures, making it ideal for boat floors. Given the unpredictability of weather and ocean conditions, you need highly durable materials for your boat.

Suppose you are wondering about aluminum vs. fiberglass boat floor. In that case, the former is less expensive and weighs less than the latter. However, fiberglass has better seakeeping abilities and can be formed into more complex shapes, ideal for any size or model of boat.

How many layers of fiberglass are needed for the boat floor?

The minimum is two layers. While fiberglass is the best material for boat floor replacement, a single layer may be insufficient to prove its strength.

Take note you need to do some calculations before doing your fiberglass project. First, identify the thickness you want for your fiberglass. Then, divide that by the thickness of the fiberglass sheet you intend to purchase.

Do I have to sand between layers of fiberglass?

Generally, you don’t need to. When using general-purpose resin, it cures with a tack, so it already sticks to the multiple layers. Additionally, sanding may ruin or cut the higher threads of the fiberglass. The last thing you want is to weaken the glass’s strength, and fiberglass boat floor replacement can be expensive.

How much fiberglass do I need?

There are many options, but it depends on the size of the floor of the boat, its weight framework, and the properties or quality of the fiberglass chopped strand mat (CSM) to saturate it with resin.

CSM is measured with ounces per square foot. For instance, 60 oz. of fiberglass cloth needs one gallon of resin to saturate. When you are uncertain, always consult with an expert.


For boat owners who like DIY projects, you may have asked, “How to fiberglass a boat floor?” Fiberglass is the ideal material for boat floors, given its high strength, durability, and resistance to water and corrosion.

You need to repair any damages to your old floor, lay out the CSM, and mix and apply the resin with hardener, making sure to use at least two layers of fiberglass. All this ensures you get the maximum strength fiberglass provides, turning your boat structurally stable.

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