MORE ON KEN KERN'S SLIP FORM

Dear Mother,

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 (MOTHER NO. 5) and the compost privy (MOTHER NO. 6) 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.

Richard Gergel
Rocky River, Ohio

Reading Richard Gergel's letter (page 122, MOTHER NO. 11) took me back 20 years, when I decided to replace architectural theory as taught in college for the practical experience gained in construction. I remember the exact instance this metamorphosis took place: a design professor told our class about two women in Ohio who had, almost single-handedly, mixed and slip-formed a two-story 30 by 40-foot double-wall concrete school building. Impossible! Ridiculous! Every architect knows that slip-form techniques are reserved for high rise buildings, hundreds of feet tall . . . as Gergel reminds us.