How to Use Expanding Foam for Boat Flotation

Written by jose leiva
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How to Use Expanding Foam for Boat Flotation
Expanding foam can be used on boats. (boat image by pearlguy from

Expanding foam is used for boat flotation because it is light weight, water resistant and absorbent for long periods of time. Expanding foam---sometimes referred to as "floatation foam"---also works in boats because it forms and shapes itself to the cavity in which it is poured. Because expanding foam can be purchased in three different ways, the best type of foam for using on a boat is a two-part mixture that is simple to mix and cures quickly.

Skill level:

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Things you need

  • Protective clothing
  • Gloves
  • Mixing cup (3)
  • Mixing drill

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  1. 1

    Prep the cavity in your boat that you want to fill with expanding foam, by chiselling out old foam and determining the volume capabilities of the cavity. To determine volume, measure the length, width and height of the cavity and then multiply all the measurements together. Example: a cavity that measures one foot long by one foot high by one foot wide has one cubic foot of volume.

  2. 2

    Change into protective clothing and wear gloves. Long-sleeve shirts with high collars are protective enough to avoid getting any foam on your skin. Expandable foam will not wash out of clothing, so wear clothes you do not mind damaging.

  3. 3

    Pour the first part of the two-part expanding foam mixture into a mixing cup. Note that for every quart expanding foam mixing kit---there is one quart of each part of the mixture---you will get enough expanding foam to fill one cubic foot. If you have to fill a cavity that equals one cubic foot, then you want to use a quart expanding foam mixing kit.

  4. 4

    Pour the second part of the two-part expanding foam mixture into a second mixing cup. Note that the mix ratio is one-to-one so you want to pour the same amount of the second part as you did the first.

  5. 5

    Combine the two parts of the expanding foam mixture into a third, larger mixing cup.

  6. 6

    Mix the expanding foam mixture vigorously for 30 seconds. Use a mixing drill, if available.

  7. 7

    Pour the expanding foam mixture into the cavity of your boat, then wait five minutes for the foam to finish expanding and curing.

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