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Working With Two Part Expandable Urethane Foam

Working With Two Part Expandable Urethane Foam

2 part expandable urethane foams are available in several densities from 2 lb per cubic foot insulation foam, which cures with a large amount of air trapped within the cells, through 16 LB density per cubic foot which could be used structurally.

Urethane Pour Foam Overview
  • This two part liquid, expanding rigid urethane foam is a closed cell, pourable foam, which will resist the absorption of water.
  • The densities shown refer to the weight per cubic foot of expanded foam (12" x 12" x 12").
  • Once fully cured this foam can be laminated over with any type of polyester, epoxy or vinyl ester resin without melting.
  • This product can be poured in multiple layers with excellent bonding between layers.
  • All expansion rates and times given are temperature critical. Temperatures below 75 degrees F will lower the expansion rate therefore requiring more foam. Ideal working temperature is 75 to 80 degrees F or above.
  • Accurate measuring of these products is extremely critical.
  • Working time before foaming: approx. 45 seconds
  • Time before full expansion: approx. 5 minutes
  • The lightweight foam is commonly used for filling voids, filling under decks and practically any other flotation or insulation application. Higher densities are used for architectural castings, support applications and has virtually an unlimited number of potential uses.

In the following example, I'm using 2 lb density to insulate one of my livewells...

Before you jump into 2 part expandable foams there are some things that you need to know so that your project goes smoothly and gives you the best results.

First, the expansion rate for 2 lb density foam is about 25:1 - 30:1  One ounce of mixed foam, before it starts expanding has a volume of 1 cubic inch. Fully cured, the volume will be about 25 - 30 cubic inches.  As the density increases, so does the expansion rate.  16 lb density only expands 4 times it's liquid volume.

The next thing you must be aware of is the blinding speed with which the foam starts reacting when the two components are mixed.  You only have about 45 seconds to thoroughly mix & empty the pot.  The mixing ratio is 1:1 & must be completely done within 20 seconds, that only leaves you 25 seconds to pour...

The expansion stage takes about 5 minutes, but the the cure to hard is around 15 minutes. It's best to allow at least 10 minutes before making the next pour. If the temperature is below 80° F, the expansion will be less than complete & the cure to hard will be longer. If you have to work in temperatures less than 75°, use a space heater. Ideal temp is above 80°...

When pouring the foam into a confined space, there must be enough space to contain the entire batch being poured & also enough opening for any excess material to expand out of. Over filling without ample relief openings can severely damage your project. DO NOT pour the foam into any void that is faced with glass. The glass will likely shatter from the pressure...

If the wall thickness of your project is thin and flexible, the expanding foam will distort it. Use some way to keep the shape backed up until all expansion has stopped, (about 10 minutes is safe).

Work with small batches. Stir vigorously to get a complete mix. If mixing more than 1 pint, use a mixing wheel with an electric drill at a medium speed. More small batch pours will be easier to control & keep your waste to a minimum.

Tools & Supplies:
1 gallon mixing pot (for larger projects)
20 oz paper cups, both for mixing & measuring
Drill & mixing wheel
Paper towels
Disposable rubber gloves
Tape, paper, & other masking supplies
Carpenter's hand saw, razor blades, & other tools that may help you level the final surface

Urethane foam sets hard and is very resistive to all solvents.
If the foam gets onto any surface and hardens you will have to sand or scrape it off. It will also stain gelcoat.

Uncured & wet foam can be cleaned with acetone.

Keep things as clean as possible. Wipe the necks and lids of the foam containers. Use a clean paper towel for wiping each container. Thoroughly wipe out the mixing pot after each pour. Wipe mixing tools after each pour. Even trace amounts of the mixed foam will expand.

OK, here we go on the livewell:

The two parts are measured into separate cups. These cups are 20 oz each, so I have about 16 oz in each for a total of about 32 oz & will use the drill to mix in the 1 gallon pot.

The livewell is filled with foam from the bottom. The back has a temporary wall screwed in place and all exposed gelcoated surfaces have been masked out.

The temperature was only 40° F at the time I started the process so I worked in my spray booth with the propane heater keeping the temp at around 85°

I have the livewell tilted over so that I can work one side & will tilt it the other way once the first side is getting close to full. The waxed paper across the base of the tub will keep the foam from prematurely building up on that surface.

The first pour...

Beginning the other side...

I trim excess as I go... The plywood back wall is covered with a waxed paper surface that the cured foam will not stick to.

Now that the walls are full, the bottom will be covered.

With the bottom filled, it is rough surfaced with a flush cut saw.

More detailed smoothing is done with a limb saw blade.

The final surfacing is done with a razor blade, held vertical & used as a scraper. The surface has to be below the fiberglass lavel so that the bottom palste of fiberglass can be inset.

The back wall removed...

US Composites, in West Palm Beach, FL, is who I use for several of my fiberglassing materials & who supplies my urethane foam. I highly recommend them.

Below is the Foam FAQ from their site, along with the links that will take you there. The urethane foam page for US Composites is HERE.

Polyurethane Foam FAQ
Ph. 561-588-1001

Polyurethane Foam FAQ

1. What is urethane foam?

Our urethane foam is a two part, pour in place liquid that when combined will expand into a rigid, closed cell polyurethane foam.

2. What are the differences between the foam densities?

The densities of the foam refer to the weight of the foam when cured per cubic foot (12" x 12" x 12"). Higher densities will result in a heavier foam which is also stronger. We have listed brief examples of hardness and physical properties to help you select the correct density here. Please also be aware that as you increase in density your expansion ratio will decrease, resulting in a higher cost per cubic foot of cured foam.

3. Which density is used for flotation in the bottom of a boat?

Our 2LB foam is generally used for most marine flotation requirements due to its good flotation properties of approx. 60 lbs of buoyancy per cubic foot. For flotation applications requiring some structural elements such as helping to support your deck or strengthening between stringers or bulkheads we would recommend using our 4LB density foam, which is also appropriate for filling around gas tanks.

4. Is there a hazardous fee for shipping?

No. These liquids are not considered hazardous and can ship via UPS Ground or Air shipping methods.

5. What will I need to use the foam?

You will need containers to measure and mix the foam and stir sticks to mix the two parts together. Gloves and eye protection are strongly recommended. This product will out gas carbon dioxide when expanding so for safety you should always work outdoors or in a well ventilated area. You can use a solvent such as acetone, denatured alcohol or lacquer thinner to clean up when the product is still liquid, however urethane foams will stick to virtually everything except slick plastics so you should cover-up anything you do not want the foam to damage.

6. How much time do I have to pour the foam?

After you have combined the two components you have approximately 45 seconds before the foaming process begins. We recommend that you stir the liquids vigorously for 25 seconds, after which time you have another 20 seconds to pour the foam into place. The foam will fully expand in 5 minutes and be fairly hard in about 15 minutes.

7. Can I use multiple pours for large jobs?

Yes, this foam can be poured in layers. For best adhesion you should wait at least 15 to 20 minutes before pouring over a previous batch.

8. How much do I need to order?

You will need to calculate the volume of your cavity by multiplying the length x width x height
Example: 2 Ft x 2 Ft x 4 Ft = 16 CUBIC FEET

If calculating in inches convert all measurements to inches
Example 24 inches x 24 inches x 48 inches = 27,648 CUBIC INCHES. Now to convert to cubic feet you much divide that number by 1,728 which equals 16 CUBIC FEET.

FAQ question 10 to determine volume on a cylindrical type shape such a pontoon.

9. Can I use the foam outdoors?

Yes. Our expansion rate of the foam is based on temperatures of 80 degrees F at moderate humidity. When using this foam in temperatures below 80 F you will see a reduction in expansion. At 50 degrees F you would probably only get half the normal expansion. For using the product during winter months it is ideal to work in a heated garage/shop in which you can get the product temperature and air temperature up to about 80 F.

10. How much foam will I need to fill my pontoon?

First of all, yes you can fill your pontoon with this foam, however it needs to be completely dry and any known holes should be repaired before pouring this foam in. (see question 14 regarding water resistance)

In order to calculate the volume of a cylinder shape you must have the diameter of the pontoon(measurement from side to side) and the total length of the pontoon.

Example: Your pontoon size is 18 inch diameter x 14 feet long
First convert everything to inches. 18 in diam. x 168 inches long.
Since most pontoons are round we need the determine the area of this round part.
Area is radius squared times pi (3.14).
We know that an 18" diameter is a 9" radius.
9" x 9" x 3.14 = 254 square inches
Now we multiple the area by the length.
254 sq. inches x 168 inches long = 42,672 CUBIC INCHES
Lastly we convert that to cubic feet.
42,672 divided by 1,728 = 24.69 cubic feet of total space to fill.

This might not be an exact science since not all pontoons are completely round and usually they taper to each side, but this will give you a good starting point.

11. Do you sell equipment to spray your foams?

No. Our foams are strictly designed for pour-in-place applications.

12. I want to release this foam from a mold what should I do?

Well if your mold is made from something already smooth such as a plastic, metal or fiberglass than you can normally use our mold release called Partall # 2 paste wax found here. This product is applied like a car wax. Multiple coats should be applied to new molds. The more coats you apply and the better you buff the wax between each coat the easier the foam will release.
For porous molds such as wood or plaster these should first be sealed with either a lacquer, polyurethane or shellac in order to create a smooth surface in which to work. Then you can apply the Partall paste wax as described above.
For people that don't want to go through the steps above you can line your mold with a slick soft plastic such as plastic drop cloths or plastic sheeting and this should peel off the foam once cured but it probably will leave some wrinkles

13. Can I use this foam for making decoys?

Sure, the most common foams for making decoys are our 4LB and 8LB densities. The actual density you decide on should be based upon your desire for strength(8LB) versus cost savings(4LB).

14. Is this foam water resistant?

Yes, but with the following caveat. The foams that we sell are considered closed-cell, which means that each cell that makes up the foam structure is completely closed off from surrounding cells which prevents it from acting like a sponge. It is completely safe for this foam to be in contact with water for hours/days/weeks and even months with no adverse effects. However, it should never be submerged in contact with water permanently. Over a period of years the water contact can begin to soften the foam and cause it to lose its closed-cell status. This foam is designed primarily to be used as an insurance policy in case of damage/holes that could cause a vessel to lose buoyancy. Pinhole sized openings would essentially have no effect on the foam since the amount of exposure is so minimal but you should always make repairs as soon as possible to keep the foam effectiveness as good as possible. This will be the case will all after market closed-cell polyurethane foams and even manufacturer installed foams.

15. Can I dissolve this foam once it has fully cured?

No. This foam is designed to be completely solvent resistant once cured. Gasoline and acetone will not cause any destruction of this foam. Please prepare ahead of time by covering any objects/areas that you do not want to come in contact with this highly adhesive product. If you do happen to spill some foam and it cures you will have to either sand or scrape the product away.

16. How can I make sure to get good expansion when working with the foam?

The two things that are most important to achieving good foam expansion are as follows.
1. Temperature. If working below 80 degrees F you will notice a slight reduction in expansion. If trying to work in 40 to 50 degree weather you will be lucky to get half the ideal expansion. Try to work in a heated area, the liquids are not considered flammable so you can use a heater nearby. Also be sure to warm up the product before use to at least 80 degrees, either by storing in a heated room or by submerging the containers in a bucket or warm water. If you're already working in warm conditions these temperature precautions are probably unnecessary.
2. Mixing Quality. The two liquid components should always be stirred together for at least 25 seconds as vigorously as possible before pouring. If working with more than 1 gallon at a time a high speed drill mixer would be a good idea. If you try to mix 2 gallons of liquid together with just a stir stick you will not get a good enough mix resulting in a flawed chemical reaction with reduced expansion. Try working in smaller liquid quantities and pouring the product in layers approximately 15 to 20 minutes in-between.

© 2005 U.S. Composites, Inc.

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