Best Minimal Expanding Foam?

For those self-installers
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Why not to use a gunnable sealant to air seal

#16 Post by foam expert » Tue May 02, 2006 3:19 pm


A fillet bead is good to use as an interior asthetic seal? However, long term in the ROG (rough opening gap) the backer rod and sealant detail is weak to the interior side of the ROG. The continuity of the back side of the flange is where you want the air seal except if you are using a pan flashing. Applying this seal with a gunnable sealant at the ROG cannot be done well with a gunnable sealant. Access is the problem. Using a low pressure AAMA 812 test PU foam will ensure a proper air seal. Dispenser Extensions down to 9mm are available for access issues on replacement jobs. ROG that are larger are easier to work with. Gunnable sealants and backer rod fail over time and are not as durable as PU foam and Gunnable sealants need more installation expetise . The whole back dam and pan flashing is a whole discussion in and of itself. Dont forget the adhesion compatibilty if sealing onto a Polyethelene film with a gunnable sealant. Most gunnable sealants dont stick to the film (PE) that is used on the top layers of SAF (Self adhering Flashing). This is what the Mfct dont tell you.

Happy Installing

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#17 Post by foam expert » Tue May 02, 2006 3:28 pm

HI Fenex

Dow cannot provide a foam with as low as a pressure build as the Hilti CF 812. Dow does not have dispensers near the quality of the DS-1. Sometimes quality over price is the choice consumers are wiling to pay for. When it comes to accessories and product inquries, you can talk to Customer support at Hilti and even have a cool box for the job site. Not sure if Dow offers this support. Hilti also provides a cold weather foam for those of us up in Wisconsin.

All the best

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#18 Post by FenEx » Wed May 03, 2006 3:55 pm

Hello Foam Expert

It's fun exchanging thoughts.

You stated, "The continuity of the back side of the flange is where you want the air seal except if you are using a pan flashing."

I would disagree with this to an extent. The airseal is always more beneficial when it's closest to the conditioned space. Air is the primary carrier of heat and moisture in most homes and whenever possible should be stopped before entering the building structural cavities. I recommend an interior and an exterior airseal around windows to create a dead air space for insulation purposes as wood framing and jambs are pretty poor insulators at about an R-1 per inch. Allowing air to circulate around wood members and back into the home is not beneficial and in fact decreases energy efficiency.

As for Hilti, I am a fan and have used their tools for many years. As for your other comments, consumers are not willing to pay for better dispensers as they are used by their hired professional installers. How many homeowners out there own a foam dispensing gun? I use the Pageris guns for the Dow and they work great... my crews love them. DOW also has the softest foam on the market allowing for house movement without cracking. Foam guns are not exactly high-tech computers... if they work well.... it's good enough for me and most. They are afterall cousins to the caulk gun... and BTW, I got mine free from DOW as I use alot of their products. I'd call that pretty good customer service.

The reason DOW is considerably less expensive than Hilti is because they are a manufacturer, not because it's an inferior product. Hilti owns their formulation but they outsource the production and manufacturing over in Europe. At 30% less money, I'll do without the cool toolbox. You may wish to look into the cold-weather formulas as I have been told that they have not yet concluded testing for durability and performance. As I understand it, they become somewhat brittle upon curing and temperature change much like the foams used at flower shops to support arrangements.

As for pressure build and expansion, you want some of both. With no expansion, you greatly reduce the effectiveness of the foam to do it's job and reach all cracks and crevices. Without pressure build, you don't get the best airseal. Too much pressure is bad... too little reduces the effectiveness. The proper pressure and expansion, combined with the cured ability to give way and adapt is in my opinion, the best all around.

Just an added note of potential interest to someone. The straw cans of foams sold in retail stores will not produce the same expansion rates as the same formulas used through professional guns. Due to pressure drop via the dispensing, the cans with straws will produce considerably more expansion.

Nice chattin' and hope you will keep sharing.

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Air Barriers, with foam sealant

#19 Post by foam expert » Sat May 06, 2006 8:22 am


I dont disagree with your first paragraph. However the air seal to the exterior of the wall *On the back side of the flange with new construction windows gives the installation a belt and suspenders approach, assuming there is a gunnable sealant used behind the flange and a flashing tape over the exterior of the flange. The foam then acts as a fail safe if the gunnable selant or flashing tape fails. The foam will then provide an air and water seal. My comments were geared towards how and what material are used in the ROG rather than a one or two bead approach. The concept of the air seal to the back side of the flange then ties into the drainage plain as a secondary seal. A two bead approach I also support, but the reality is, access is the problem half of the time. Thats why extensions and tappered barrels are helpful.

I would challange your comments that low pressure foams dont provide the best air seal. Is there data available that you can provide to support this claim?

In regard to customers purchasing habbits, gun foams vs straw foams I am not sure that I mentioned anything about homeowners vs. professionals on the dispensers. I think that ther eis a distinct difference in dispensers. Have you tried the Hilti DS-1?

I am curious on the cold weather information that you could share. I have been trying to buy CF 511 and cant find it anywhere. What durabilty and performance is Hilti testing? Can you elaborate on the cold weather issue. Which foams become brittle and in which conditions?

Thanks for your feedback


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#20 Post by FenEx » Mon May 08, 2006 12:10 pm

Foam Expert

As I said previously, I am a big fan of Hilti tools, but the DOW guns I use are made by Pageris and work extremely well. They also have a line that uses different application extension tips too. Easy to use, very controlable beads, long storage times, etc. These are so simple, I really don't see a need to spend 30% more money for guns and product. It's pointless.

"I would challange your comments that low pressure foams dont provide the best air seal. Is there data available that you can provide to support this claim?"

No data readily available, just common sense. The pressure and expansion is a primary reason these foams work much better than alternatives. They reach all cracks and crevices and air-sealing is achieved by contact pressure and consistant adhesion to the adjoining surfaces.

"In regard to customers purchasing habbits, gun foams vs straw foams I am not sure that I mentioned anything about homeowners vs. professionals on the dispensers."

Most homeowners would go to a chain location and buy a straw can off the shelf. I think very few would opt for a gun due to expense and availability. They might however expect an installer that is working for them to have better equipment.

I received the testing reports from a gentleman that is a department head in the Research and Development at DOW. We both serve on a technical advisory committee for BPI. I cannot provide the full reports here as they are secured documents. The DOW Pro-Series Window and Door with the gun has a pressure build of 0.0784 psi and the straw version of the same formula has 0.2310 psi. The AAMA 812.04 requires a 0.5 psi or less. Obviously both greatly exceed this requirement. What has Hilti's formula tested at? The gun grade easily passed air infiltration (ASTM E283) and water testing (ASTM E331 & E547) with less than 0.01 cfm/sqft for air at 6.24 psf (300 pascals or 50 mph winds) and NO water penetration at 12.0 psf (the highest test used).

The info I provided earlier for the low-temp products are from DOW R&D as well. They will not release their products until they are fully tested. Perhaps the reason you can't get the Hilti line is for similar reasons. The AAMA reports are available for purchase through them.

Good luck with Hilti... I'll stick with DOW. Both exceptional products.

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Dow Chemical

#21 Post by foam expert » Mon May 08, 2006 3:31 pm


I didnt realize that Dow is launching a winter foam. When do you think this will hit the market?

What do you think of the fireblocker vs firestop issue?


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#22 Post by joe123 » Sat Jul 15, 2006 11:48 pm

The Great Stuff for Vinyl windows worked jus fine for me and it is made just for this purpse.

Here is what it says:

Marietta, Ga. (August 12, 2001) – The Dow Chemical Company's Polyurethane Systems Business, makers of the leading polyurethane foam sealant, GREAT STUFF, has introduced GREAT STUFF Window and Door Foam Sealant, designed exclusively for filling the rough opening gap around windows and doors without distorting the frame.

Website info:

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Re: Reply

#23 Post by bungalo » Wed Oct 25, 2006 1:12 pm

FenEx wrote:The Dow Pro series have the same gun-applicated, low pressure products available at about 30% cheaper than Hilti. Identical performance, easier to get and a third less money as it's manufactured by a company considerably larger than Hilti. The pricing difference mentioned is contractor cost but probably carries over to consumer cost as well.
I think Dow is the company behind "Great Stuff", dunno if Pro is different than their regular Great Stuff door/window foam (except the applicator).

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Re: Best Minimal Expanding Foam?

#24 Post by speldog » Tue Aug 26, 2008 11:45 am

Thank you very much everyone. Great information.

This will help me with my Jeld-wen zap paks that I am installing. Contrary to what most are saying these are great windows for the long as you don't follow their instructions.

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Re: Best Minimal Expanding Foam?

#25 Post by N0F3AR » Wed Jan 19, 2011 10:40 am

Ok guys it seems like I have found the Mecca of Windows Geeks--so I hope you will have an answer for me.

I moved into a home that has windows apparently designed to be window-like screens---that is, they keep little of the cold and wind out even though the rest of the home looks like a million bucks. Since replacing them is costly, we have tried sealing them with a heavy mil plastic and a tape designed to seal between the windowframe and plastic. Believe it or not, it works GREAT--except the plastic blows up like a sail on a ship because of the airflow going on. So I am looking for a foam sealant that (1) isn't yellow llike great stuff since the windows are white (2) might actually be removable in the spring in case my fiance decides she wants the screen-window effect for summer and (3) won't damage the function of the windows if we spray seal the corners of these windows in an effort to keep airflow from outside to a minimum.

I have read this thread and it sounds like you guys know your sealants and windows--any suggestions? Oh, one more caveat--the ASSociation (caps intentional) we pay a monthly ransom to does NOT allow external plastic any longer on windows. Last year I used the same heavy plastic and a clear peelable exterior caulk, but the ASSociation didn't like it, so it is no longer an option.

Can someone please suggest a solution? I appreciate any suggestion that seems viable.

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Re: Best Minimal Expanding Foam?

#26 Post by Delaware Mike » Sat Apr 14, 2012 6:28 am

Wamper, I don't understand by what you meant by stating "what if you have to replace a mainframe?" Are you saying that foam creates a seal that is so super strong that whole wall is now ruined because of the bond from the window frame to the RO?

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Re: Best Minimal Expanding Foam?

#27 Post by Windows on Washington » Sat Apr 14, 2012 6:31 am

See the responses to your questions and assertions below.
wamperkanuper wrote:Foam, even minimal expanding/closed cell is a terrible idea. First, what do you do if you have to replace a mainframe?

Very simple cut the window foam away from the home. This is not difficult or something that is really of concern because of the relative scarcity of this incidence.

Second, foam does NOT clean off surfaces when wet (or dry).

I am not sure how or why that is and issue if the installer is familiar with the use of the product. Some sealants don't clean off either and we aren't pulling them off the shelves. For the record, foam, when uncured, can be cleaned with acetone type cleaners. When cured, it can be scraped off.

Third, the product boasts stopping both air and water infiltration. This is bad. If your window is leaking from outside your foam barrier, you won't be able to find the leak until it's too late. The water will have shed to another opening (usually down the knee wall).

Stopping air and water are a bad thing? Interesting.

Nothing about window construction calls for venting between the main frame and rough opening.

While it is true that the closed cell foam used in window and door applications will not allow water to pass through, this is a good thing. Any water leaking to the interior of the wall will show to either side of the plane of the foam and in most cases, this will me an interior wall manifestation. Window and door headers also prevent water from leaking straight through in its normal pathway but I don't see a necessity to take the structure out of the wall either.

If you're using foam, you obviously don't know how to seal a window beyond your outside fenestration. If you can't properly flash or coil a window so it doesn't leak into the house at some point, you shouldn't be installing windows.

While there are other ways to seal a window, the foam in this application is being used in large part for pocket or insert windows. In these applications, we are not applying flashing tapes, sill pans, etc.

Coil work and wrapping of the window exterior is standard for most folks but wrapping does not address the copious amounts of air that will move in the interstitial wall cavity and ultimately the home.

Foam is used predominantly as and air sealing tool and not a band-aid for proper trim work and water management.

While there are other methods to seal the window to the rough opening or pocket (an absolute must and not really a point of debate) foam is widely accepted as a suitable tool and is probably the more comprehensive option as compared to backer rod and sealant.

Using fiberglass, or worse yet...nothing, is not proper application.

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Re: Best Minimal Expanding Foam?

#28 Post by TheWindowNerd » Sat Apr 14, 2012 7:11 am

PLEASE READ THE FORUM RULES - Dropping company web site links is cause for deletion of your account.


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Re: Best Minimal Expanding Foam?

#29 Post by Delaware Mike » Sat Apr 14, 2012 7:30 am

I've had a single Hilti foam gun for like 3 years now. I rarely clean it and the thing is close to being indestructible. The key is to be the only guy using it and not lend it out. I've had, and still have other guns and the Hilti is the best by far. Pricing is brutal. You can usually get a free gun if you catch the Hilti rep running one of their specials if you purchase an entire case of their foam, which runs almost twice that of the OSI TeQ Foam.

I've found that Hilti to be the "Rolex" of tools. I'm drooling over their new brushless impact driver.

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