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Use the following Resin Chart as a guideline to determine resin coverage. Resin to glass usage for polyester and epoxy are very similar.

1 Gallon of Resin Wets Out

Materials Sq. Ft.
.75oz Mat 64 SF
1.50oz Mat 32 SF
3.50oz Cloth 150 SF
6.00oz Cloth 90 SF
10.00oz Cloth 60 SF
13.00oz Unidirectional 26 SF
1708 Biaxial 27 SF
18.00oz Worven Roving 40 SF
1808 Biaxial 26 SF
24.00oz Worven Roving 32 SF
2415 Bi-Ply 16 SF

(50″ wide material = approx.. 12 square foot per linear yard)

Example for figuring amount of fiberglass needed

Mr. Smith wants to put an epoxy and glass covering of 1 layer of 10 oz cloth and 1101/2102 epoxy. The cabin top is 9 feet wide by 10 feet long (9×10=90 square feet). The total area to be glassed is 90 square feet.

The cabin top width is 108 inches. Using 38 inch wide cloth, Mr. Smith needs three 10 ft. pieces. (108 in . ÷ 38 in. cloth = 2.84 or 3 pieces).

Always consider the width of the cloth plus an overlap allowance at the seams. (We recommend overlapping all seams 1 to 4 inches.)

Since Mr. Smith will be using 90 square feet. (3-10 ft. x 38 in. pieces) of material, he should refer to the resin chart to determine the amount of resin he will need. In this example, Mr. Smith will need one and one half (1-1/2) gallons of resin to cover the cabin top of his boat.

This Post Has 8 Comments
  1. Hello lad, Im quite loving the articles on your blog. They are created well, easy to read and understand, in spite of English being my third language. Greetings.

    1. Thank You! If you ever have any questions regarding a repair or about any of our guides, please feel free to contact us!

  2. I have a floor to repair on a 17′ cobia. floor length from stern to bow about 14′ and 4.5′ at widest point chine to chine.
    Is there something other than plywood to use?
    Is 1.5 oz mat better or .75 oz ?
    Either way, to encapsulate whatever substrate I use by glassing both sides., assuming just under 50 sq ft for top and same for bottom,
    .75 oz os about 2 gallons
    1.5 oz is 3

    How much gel coat for the top side?

    1. Yes, you can use structural honeycomb core or Divinycell core if you wanted to move away from wood. The heaviness of the mat depends on how thick you want to build the laminate. Generally cloth/biaxial/wovens are used for strength and mat is used for bulk.
      One gallon of resin will wet out 64 Sq Ft .75oz mat or 32 Sq Ft 1.5oz mat.
      One gallon of gelcoat will cover 100 Sq Ft Brushed/Rolled OR 80 Sq Ft if Sprayed.

  3. Hi- I’m not building a boat, but I’m making fiberglass planters. The planters will be 48″ L x 40″ h x 24″ d. Basically, I plan to make boxes out of 3/4″ plywood, then cover in fiberglass. If I might ask a couple of questions-

    I’m assuming I only need a single layer inside the box to waterproof.

    On the outside, probably only need a couple of layers and a gel coat final (with some fine sand and color mixed in, so that it resembles concrete) What weight fabric would you suggest for this type of application?


    1. First you should resin saturate the plywood BEFORE putting the cloth over it. You can find the full guide in the tech pages. If you’re just doing a skim coat to seal the wood, I would suggest a light cloth – 3 to 4 oz. If you’d like a little thicker, then 6 oz cloth would be good.

  4. I am building a truck camper and want to use fiberglass. Don’t know how many coats I will need. Going over lain plywood. I figure about 500 sq ft but don’t know how many coats I will need. All help would be appreciated. Thank Ken

    1. Since you are using plywood you’ll have a nice sturdy structure. I would suggest between 2-3 layers of fiberglass. One layer of 1.5oz mat and one layer of some sort of cloth-you could use 1708 biaxial, 18oz Woven roving or cloth(6oz or 10oz). If you want a little more rigidity on the camper your 3rd layer would be 1.5oz mat.

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