Forms made of closed-cell foam

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Q. Are you familiar with something called ICFs (insulated concrete forms, made of closed-cell Styrofoam)? We’re hoping to build a cottage house with a basement on a hillside upstate, and we want it to be very “energy-wise.” What I’m concerned about is that Styrofoam seems like it won’t be very strong to build a house on and could open up when concrete is poured into it. Can you explain how this kind of concrete forming works and whether it’s a good idea? It seems to cost more, and we’re not sure it’s worth it.

A. Yes, ICFs definitely cost more, mostly because, as formwork, they cost more to produce, and not enough contractors use them. Is it a good idea? No, it’s a great idea. They only get transported one way, to the job site, saving labor on handling and fuel. They have more reinforcement per inch than removable wood forms, have no protruding steel rods to rust away and leave gaps for water to get through the wall, creating a continuous insulation and waterproofing barrier around the foundation wall exteriors. And since concrete is formed by pouring cement into the entire core, they’re strong enough to support your home.

As the idea slowly caught on, first in Canada, consumers began to notice that their homes were warmer, saved energy and money and were more comfortable. If they’re installed by an inexperienced team, you can eliminate the learning curve and mistakes, like any other process. Over the years there were many problems, and the forms did open up because of cement that had too much water in it and the stone in the mix was too jagged. Just by reducing water in the mix (which reduced weight and the force of hydrostatic pressure), but adding engineered plasticizer additives to get the cement to move into every void, using a vibrating probe to work the mix in, and using smooth stones (which cost more), the problems have been reduced or eliminated.

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