Airforms, Water Vapor, and Freeze-Thaw Cycles

[disfrontman]

Okay, thanks. The density is pre-engineered into the product when you receive it.

I'll assume, although I have found very scant info on pricing, that SPF in higher densities is more expensive. I have also read that the R value doesn't really increase much past the 2.0 pcf density, but structural strength and vapor resistance does. The "blister" issue, then, might be another motivator to use heavier density foam, as it is even more resistant to vapor than medium-weight foams.

Is there any other disadvantage to using higher density foam, other than price? Is the application process longer or more difficult? Harder to install rebar anchors? Issues with temperature-related expansion/contraction?

Does anyone out there have a sliding scale of price per board foot of the different densities of SPF?

From what I've read, high density closed cell polyurethane foam is extremely durable so long as it stays out of the sun. For the longevity of the structure, protected and intact SPF should last more or less forever. Doesn't it make some sense to allocate a bit more of the budget to a thicker layer of higher density foam for the long term soundness of the structure?

[Don M]

While I don't remember all the numbers, we used a lot of polyurethane foam in the lab at JPL for insulating cryogenic hardware long ago. Generally speaking it, of course, starts out as a 2 part liquid that chemically reacts quite quickly when mixed together generating a gas that produces the internal bubbles which makes it a "foam" rather then a solid plastic. The hotter the mix (chemically or temperature wise) the greater the volume of gas generated internally and hence the lower the density. So if a certain volume of 2 pound per cubic foot (density) of foam required a gallon of liquid chemicals to produce, one could assume that the same volume of 4 pounds per cubic foot (density) of foam would require 2 gallons of liquid costing twice as much and the foam would weigh twice as much per cubic foot. This cost example would not hold true for finished sheets of foam because they include more than just the cost of the basic chemicals, meaning that one would expect that 2x higher density sheets would cost something less than 2x.

There are other trade offs with density. The lower the density the higher the insulation value (up to some point) and of course the lower the strength. The manufacturer has all that data for their specific products.

Also, duplicate chemical mixes will produce different densities depending on their temperature. The mix quickly produces quite a temperature rise while foaming. Higher temperatures form more and bigger bubbles, that lower the density of the finished foam. The layer of foam in contact with a heat sink, like the wall of a coffee cup, will be kept at a lower temperature and expand less, leaving a very dense layer of foam stuck to the wall of the cup. But, because of the great insulating characteristics of the foam, normal curring temperatures are generated a short distance from the wall of the cup. If the chemical mix starts out at lower than normal room temperature, it takes much longer to foam and never gets as hot resulting in a higher final density. The opposite is true for higher temperature mixes.

As I remember, contrary to ones intuition, polyurathane foam is a much better insulator than polystyrene foam of the same density.

Don M

[silent_Freak18]

This method is feasible and applicable to such extent because they can maximize the use of the machine. Just like the air conditioner that can be used as Basement Dehumidifier but with colder air as a result. This machine is indeed applicable in our home and feasible to avoid moisturizer. They can be done using lots of technique and method but I think this MDI method was better.

[DBS]

To all of you: I really appreciate your interactions with each other. The story is too big to tell for just one of us. And many times you will cover items I have either not thought of a passed over.

A long time ago I had simply a urethane foam company. My book I wrote on foam company is posted on our website. You can purchase it or download it. I posted it to try and help with whose and whats of the foam industry. Obviously some of it is strictly mine and may be disagreed with. Nevertheless it is what we determined to work. For instance you will see I do not like half pound foam unless it is for packing boxes. But there are others who disagree.

For spraying domes I like something about 2 lb, fast, tough foam. There are some 1.8's and 1.9's and 2 lbs. We have used a lot of 4 lb foam for lining potato bulk trucks as it would take a lot of abuse. For a dome I prefer the 2 lb. Why? It is much cheaper than the 2.5 or 2.7 or 3. So why do they spray the heavier densities. It is for roofing. It takes far more abuse. The same would be true on our domes except the abuse it handles better is primarily foot traffic. It will still dent if hit by a ball batt or even the ball. So I would rather spend the extra money on a cover over the Airform that will really take the abuse. There is no foam that will stand up the the abuse like a 2 inch thick layer of concrete -- "chain shell". Look it up in the website. The higher cost of the heavier foams will go a long way towards the application of the "chain shell".

The last posts on this is about water vapor. Boy is that a tough subject. The foam is applied to the underside of the Airform. That interface is the most critical. If we trap free water there we will get blisters. And we have to be sure we do not trap water between the layers of the urethane. So how do we do such. I do not know for every job at every time. We find that at times under the worst conditions we never have a problem and at other times under perfect conditions we will get blisters. But a few ideas.

Never burn anything inside the Airform before, or during the application of the foam. Always cover the floor with plastic sheeting to hold the water under the plastic. You may think the floor is dry. It is not. Cover the floor whether dirt or concrete. The water that migrates up to the Airform will be enough to cause blistering. If you need to heat the inside of the Airform use a ventless system. Always wait for sunshine if possible. Once the urethane foam is in place water does not seem to be much of a problem. Water coming out of the concrete will evaporate to the inside. We have never been able to prove a connection between water in concrete and blisters. (We have had one building which was filled with hot wet fly ash as a storage where we saw blisters that we could correlate.)

My experience is blisters under the Airform fabric simply need to be punctured and left alone. The blisters that will occasionally form between layers of the urethane are probably the result of condensation of water between the layers or water spit out of the foam gun during the application. I have never been able to prove or demonstrate. It seems a bit a luck of the draw.

In all cases the process is worth it. Please look at the "thermographs" on the main website. They show what we know. There is for all practical purposes virtually no heat loss through the Monolithic Dome shell. We get the heat loss through the doors, windows, and vent systems. And as we have to breath we have to have fresh air -- so our best bet is to use ERV's and minimize the heat transfer.

Again thanks to all of you for your help with each other. DBS