Using Slip-Forms to Make Concrete Walls for Small Buildings

Ken Kern responds to a letter from a concerned reader. In articles from MOTHER EARTH NEWS issue 5 and 6, Kern writes about using slip forms to construct walls.

| January/February 1972

  • slip form
    Slip forms can be used to build concrete walls.

  • slip form


There's more than one way to do most projects, but as an architect I think that some of Ken Kern's building methods are probably a little more complicated and less practical than they might be... especially for the inexperienced builder.

Both the stone wall construction and the compost privy were designed to be built with a "curved concrete slip form." Kern recommends this method for the inexperienced builder, but I feel that it's a difficult one for anyone and probably unnecessary in a small building. Slip forming is generaly used on high rise buildings where it's difficult to build regular form work for buildings that are hundreds of feet tall. But why mix and pour three or four inches of concrete everyday for about 60 days (see slip form detail in No. 6) when the same sort of result can be obtained in two days with conventional methods? In fact, why use curved concrete walls that are only three inches thick as shown on the detail drawings. Six or eight inches is minimum because concrete shrinks as it dries causing cracks, and three inches doesn't leave much thickness after steel reinforcing is placed into the wall (concrete needs steel reinforcing not shown in the drawings).

The thing about recommending concrete walls to inexperienced builders is that there's not much room for learning through mistakes. Once the concrete has set up and hardened, there it stays. The only way to correct or start over is to blow the wall up, beat it to death with a sledge hammer or get a bulldozer.

The waterproofing shown on the stone wall detail in MOTHER NO. 5 is not put to its best use. Actually, it's not even needed above grade or in dry climates and, when it is needed, it should be placed between earth and wall, not inside the wall as shown. Once water gets into the wall, the damage is done, so why protect the concrete? Also, fiberglass insulation shown is a soft porous material which can hold moisture and won't give the stone facing the solid backing it needs for anchorage.

I'm not writing just because I want to nit-pick at someone's good ideas, but because I like what MOTHER is doing... and people with the desire to build on their own need sound practical information if they are to succeed.

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