These frames may look simple, but to get the weight down it's been a challenge of materials and skills. I remember learning that most of the weight that goes into a structure is used to make a structure stronger to carry it's own weight. As with a bridge that is built from steel, the combined weight of the steel is so great that two-thirds of the structure is to hold up the steel. A good comparison of modern techniques of bridge building would be the new Oakland Bridge design compared to the old Oakland Bridge design.
The new looking bridge required more elegant design skills and hi-tech materials even though it looks smaller and simpler. This is similar to what I think has gone into the frames that I am building. The new brick facade frames don't look much different than some of my earlier ones, but there has been huge jumps in technique, materials and even design to make the new ones lighter and more useful.
The biggest change has been about whether or not a cement back is required or not for the frames that are made with an epoxy gel coat. I have installed a few of the frames without a cement back and although they are approximately 3 pounds lighter, the cement provides a more stable backing for the epoxy. Earlier models were in the 10-15 pound range and would be difficult to use in a structure without additional external or vertical supports. I don't see any point in getting a 20" X 24" finished frame below the 8 pound level that I am currently although I know I could if I worked with more fiberglass reinforcement and removed the cement, or put some sort of foam backing, however these techniques would also increase the cost.
The rest of this post was moved to a the next post on cave building.
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