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BC W Posted: Mar 18, 2010 11:54 PM	Another Shrinking Foam Question I had the underside of my roof deck sprayed with closed cell soy-based foam a little over a year ago. I haven't made much progress on the project since then, and a few months ago I noticed severe shrinkage with the foam pulling away from the rafters and in 2 cases actually splitting the rafter down the middle! The contractor is willing to come back and fix it, but I'm concerned about when, if ever, the bad foam will stabilize and stop shrinking. I marked the start and end of several cracks last month, and they appear to still be growing slightly. I also scored a couple of bays with a razor blade - initially you couldn't even see the cut, but now they have opened up to about 1/16" which leads me to think the foam is still under tension. Can we get away with just cutting out the bad areas and re-foaming, or does it all need to come out? I know the cracks won't affect the overall heat loss much, but the thing that really drove me to do the foam was the idea of a solid, sealed roof deck - I had the walls done previously and I was really impressed with how much rigidity they added to the structure. Now with my splitting rafters the roof foam is having the opposite effect!
mason Posted: Mar 19, 2010 09:08 AM	I have been hired to provide recommendations on repair to foam that has experienced shrinking similar to what you describe in more than a dozen situations. And yes, the foam can continue to shrink even 6 months after the intitial application. All foam tends to grow or shrink depending on the environment and the density. Because the foam has excellent adhesion to the substrat and the wood rafters, joists, studs or beams, the tendency of the foam to grow or shrink is usually controlled and does not tend to be a problem. But this is dependent on many factors. For example, it is important to use the right foam in the environment you encounter. When using closed cell foam, the higher the density the greater the dimensional stability. For roofing foam you need a 3 lb foam to reduce the potential for movement. In cold storage or colder environments 2.2 to 2.5 lb foam would be required. In mixed or warm climates you can get away with 1.5 to 2.0 lb foam. Other factors can cause shrinkage of the foam beyond the standard formula such as 1. Installing thicker lifts causes the foam to have weaker cells,lower compressive strength and dimensional stability. Stick to lift thickness between 0.5 and 1.5 inches 2. Installing foam lifts too soon on top of each other. This practice does not allow the foam to release the exothermic heat developed during the rise and initial cure of the foam. Best industry practice calls to wait 10-15 minutes between lifts. High exothermic heat (over 250 degrees F) cause the foam to be weaker, have more open cells and cause fissures and cracks in the foam 3. Poor mix due to inadequate pressure. Many folks use a large tip, nozzle, PCD or mixing chamber in order to get greater production when spraying between stud walls or roofline applications. But, this practice can lead to problems if the pressure is insufficient to mix the foam properly. (such as a high percentage of open cells, weak foam and poor dimensional stability. If the pressure and volume is too high and blowing the foam off the wall, go to a smaller tip rather than reducing the pressure. Having described the problem and potential causes now lets go to the repair. You can remove the foam and respray it, if the shrinkage is not caused by the foam being off ratio. But, I have found in all cases that if you remove the foam at the cracked and shrunk areas then respray, that the foam does not continue to shrink after. This would not apply to foam that is obviously off ratio, (A rich, brittle, B rich, soft and gummy). All off ratio foam would need to be replaced. The following is a repair recommendation that I have used in most of these cases. Identify areas of suspect adhesion and poor quality foam by performing test cuts on either side of attic cavities that have observable cracks and/or shrinking foam. Perform random test cuts in other areas (3-5 per area of building) to determine if tension in the foam may contribute to cracking in the future. If the areas crack when the foam is cut, it would require repair. Continue test cuts in the attic cavities until the foam does not crack after it is cut. Remove cracking or shrinking foam by cutting back foam in a 45 degree angle until it reaches foam that exhibits good adhesion and physical properties. (Note V groove cuts should be used when the crack is in the center of the cavity). Prepare substrate as required to accept new SPF. Install new SPF to specified thickness in a picture frame pattern in lift thickness of ½ to 1 for the first lift and no more than 1.5 inches for subsequent lifts. Wait 10-15 minutes between lifts or until the exothermic heat reaction has dissipated (or in accordance with manufacturer’s written instructions). Good luck
BC W Posted: Mar 19, 2010 12:25 PM	Thanks for the very informative response!

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BC W

Posted: Mar 18, 2010 11:54 PM

Another Shrinking Foam Question

I had the underside of my roof deck sprayed with closed cell soy-based foam a little over a year ago. I haven't made much progress on the project since then, and a few months ago I noticed severe shrinkage with the foam pulling away from the rafters and in 2 cases actually splitting the rafter down the middle!

The contractor is willing to come back and fix it, but I'm concerned about when, if ever, the bad foam will stabilize and stop shrinking.

I marked the start and end of several cracks last month, and they appear to still be growing slightly. I also scored a couple of bays with a razor blade - initially you couldn't even see the cut, but now they have opened up to about 1/16" which leads me to think the foam is still under tension.

Can we get away with just cutting out the bad areas and re-foaming, or does it all need to come out? I know the cracks won't affect the overall heat loss much, but the thing that really drove me to do the foam was the idea of a solid, sealed roof deck - I had the walls done previously and I was really impressed with how much rigidity they added to the structure. Now with my splitting rafters the roof foam is having the opposite effect!

mason

Posted: Mar 19, 2010 09:08 AM

I have been hired to provide recommendations on repair to foam that has experienced shrinking similar to what you describe in more than a dozen situations.

And yes, the foam can continue to shrink even 6 months after the intitial application.

All foam tends to grow or shrink depending on the environment and the density. Because the foam has excellent adhesion to the substrat and the wood rafters, joists, studs or beams, the tendency of the foam to grow or shrink is usually controlled and does not tend to be a problem.

But this is dependent on many factors. For example, it is important to use the right foam in the environment you encounter.

When using closed cell foam, the higher the density the greater the dimensional stability.

For roofing foam you need a 3 lb foam to reduce the potential for movement. In cold storage or colder environments 2.2 to 2.5 lb foam would be required. In mixed or warm climates you can get away with 1.5 to 2.0 lb foam.

Other factors can cause shrinkage of the foam beyond the standard formula such as
1. Installing thicker lifts causes the foam to have weaker cells,lower compressive strength and dimensional stability. Stick to lift thickness between 0.5 and 1.5 inches

2. Installing foam lifts too soon on top of each other. This practice does not allow the foam to release the exothermic heat developed during the rise and initial cure of the foam. Best industry practice calls to wait 10-15 minutes between lifts. High exothermic heat (over 250 degrees F) cause the foam to be weaker, have more open cells and cause fissures and cracks in the foam

3. Poor mix due to inadequate pressure. Many folks use a large tip, nozzle, PCD or mixing chamber in order to get greater production when spraying between stud walls or roofline applications. But, this practice can lead to problems if the pressure is insufficient to mix the foam properly. (such as a high percentage of open cells, weak foam and poor dimensional stability.

If the pressure and volume is too high and blowing the foam off the wall, go to a smaller tip rather than reducing the pressure.

Having described the problem and potential causes now lets go to the repair.

You can remove the foam and respray it, if the shrinkage is not caused by the foam being off ratio. But, I have found in all cases that if you remove the foam at the cracked and shrunk areas then respray, that the foam does not continue to shrink after.

This would not apply to foam that is obviously off ratio, (A rich, brittle, B rich, soft and gummy). All off ratio foam would need to be replaced.

The following is a repair recommendation that I have used in most of these cases.

Identify areas of suspect adhesion and poor quality foam by performing test cuts on either side of attic cavities that have observable cracks and/or shrinking foam.

Perform random test cuts in other areas (3-5 per area of building) to determine if tension in the foam may contribute to cracking in the future.
If the areas crack when the foam is cut, it would require repair. Continue test cuts in the attic cavities until the foam does not crack after it is cut.

Remove cracking or shrinking foam by cutting back foam in a 45 degree angle until it reaches foam that exhibits good adhesion and physical properties. (Note V groove cuts should be used when the crack is in the center of the cavity).

Prepare substrate as required to accept new SPF.

Install new SPF to specified thickness in a picture frame pattern in lift thickness of ½ to 1 for the first lift and no more than 1.5 inches for subsequent lifts. Wait 10-15 minutes between lifts or until the exothermic heat reaction has dissipated (or in accordance with manufacturer’s written instructions).

Good luck

BC W

Posted: Mar 19, 2010 12:25 PM

Thanks for the very informative response!

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