FGCI High Performance Isophthalic Putty

Isophthalic Putty Filler Kit


If you plan on using our Isophthalic Resin, you want to make sure you are using the same quality of putty and filler. This works seamlessly with our other isophthalic products to produce a consistent final product.

Includes MEKP catalyst!

*For Drum Quantities – please contact us via our Contact Us page. 


Water Resistant Isophthalic Putty

Our Isophthalic Putty has exceptional water resistance, which makes this product fantastic to use below the water line on boats and within tank making applications! Effortlessly bonds between substrates and lamination layers.

Isophthalic Putty Benefits:

  1. Extremely high water resistance
  2. Easily sanding for a smooth finished surface
  3. Great for below the waterline on boats
  4. Exactly what you want for tank building
  5. Requires MEK 925 (not included)
Catalyst Concentration Chart - Resins and Gelcoat

Materials Needed

Mix & Measure Bucket

Personal Protective Equipment (PPE)

Measuring Cups or Squeeze Bottles

Mixing Sticks/Power Mixer

Putty Knife or Trowel



Step 1: If the surface contains cured resin or gelcoat, be sure to rough up the surface with sandpaper and clean the surface with Acetone before beginning.


Step 2: Consult the MEK-P Catalyst Chart for proper volumes of 1-1/2%-2% MEK-P by volume. Use a Squeeze Bottle, a medicine cup or other measuring device to ensure an accurate amount of Catalyst is mixed into the putty.

Step 3: Thoroughly mix with a mixer or paddle for 3 minutes, ensuring the Catalyst is mixed throughout.

Step 4: Use a Putty Knife or Trowel and apply the putty over the desired area by pulling the putty over the gap and then change directions by 90 degrees and pull from the other direction, ensuring a uniform flow.


NOTE: Working time will vary depending on temperature and volume. Do not leave product unattended or in the mixing cup for more than a few minutes. 


Step 5: Let the product harden to the touch before sanding. Once hard, sand the product smooth. If there is still an indent or gap to be filled, sand the product and clean the surface before reapplying.


Directions may vary by application. For technical support and assistance with critical applications or large pours, please feel free to contact Customer Service at 1-888-849-0588.

Cleaning Putty:

Use Acetone to clean brushes, rollers or trowels. A small bucket of solvent can be used to clean tools.


PLEASE NOTE: This information is provided in good faith and correct to the best of our knowledge. No warranty, guarantee, or representation is made as to the sufficiency of the information for the safe use of the product, nor to relieve the end user of any Federal, State, or Local regulatory responsibility.


  1. Charlie Norris

    “I love fiberglass coatings. They have great products and excellent advice. I'm trying to open a boat repair shop in St . Mary's, GA and my supply WILL come from fiberglass coatings. When I lived in the Fl. Keys for 36 years and worked for a towing and salvage Co for 15 years all our supplies came from Fiberglass coatings. Great service and never were disappointed. Keep up the great job everyone.”
  2. Brian Lewis

    “The staff are very knowledgeable and friendly Have always gotten the right stuff for the right job. Pat,mark,Colby,Ryan your the best. Pat is the walking encyclopedia of FGCI.”
  3. Justin Lammers

    “Been working on a skiff project and using all FGCI products. They came highly recommended by my friends who are boat builders. It is the highest quality resins, glass, and gelcoat for the money. They made it really easy for a newer person to boat building. The customer service is phenomenal and they are always knowledgeable and ready to help with any questions I had.”