Earthman was last seen in his mud shoes trudging toward his garden, muttering about weeds, dogs and goldfish, and defying the skies to open up while he was out. Until he returns, here is an earlier column worthy of perennial interest.
I HAVE BEEN asked to say a few words about concrete in gardens.I
This suits me fine, since (next to lead) concrete is my favorite material. Concrete is not as cheap as it might be or as it used to be, but what is?
First, let us ponder the nature of concrete in lily pools, since pools are almost invariably built of it.
I have said before, and I say again, that concrete is something you should look into pretty well before you just set out on a Saturday afternoon to make something out of it.
Just here let me point out that "concrete mixes" in bags, now widely availably everywhere except at church altars, can vary in their composition, and it is well to know what the composition is before using them for some specific purpose.
If the concrete is to be watertight, certain things are necessary.
I will never comprehend why it is so widely believed that "concrete is concrete" and that any more or less hard mixture of portland cement, sand, gravel and water will do "perfectly well" for water basins.
It is far otherwise.
I cannot in this space give a course in the manufacture of perfect waterproof concrete, but I can very perfectly tell you the most common errors of concrete basins for water, as usually ill constructed in gardens.
Porous walls. These leak slowly. The cause is skimping in the amount of cement put into the mix, usually, and it is important (that means it makes a real difference that even you will notice) to specify a mixture of one part cement, two parts sand, three parts gravel.
Honeycombing. This is a sad situation (not always serious, but usually esthetically revolting) in which the walls are pitted, and there is no cement between blobs of gravel. This is caused by using too much gravel or crushed stone (a thing some workmen are prone to do), or:
Failure to vibrate or tamp the concrete properly when it is set into place in the forms.
Honeycombing is correctable by cutting it out at least an inch deep, and in some cases deeper, and filling up the cavity with new material which, needless to say, presents us with the entire issue of bonding. Some people think, for no good reason at all, that concrete naturally bonds with concrete. It is not so, unless it is done properly. But I do not want to get into bonding just here.
As concrete is placed, I should add, it should be vibrated or spaded so the aggregate is worked in from the surface. The technique of spading is easily learned. I do not know about vibrators.
Leaks where the floor meets the walls. This is extremely common in slapdash construction. It is prevented by using the correct mix of concrete for both floors and walls, and by making the vessel (the pool, the basin, the tank, or whatever it is that is supposed to hold water) all at once.
That is, the floor is placed first (concrete is never pitched with a shovel, since that will undo all the point of mixing it in the first place; it is always placed moderately with a shovel, not wildly flung about) and then the concrete in the walls.
Some people, for reasons best known to themselves, like to finish Wall A, than Wall B, then Wall C, then Wall D in turn. That is wrong.
A six-inch layer of wet concrete is placed all the way around all four walls, and tamped into place while the floor is still good and moist, so that perfect bonding occurs. Otherwise, by the time you get around to the last wall, the floor may have set more than it should, and bonding may not be perfect. Also, the last joint between Wall A and Wall D may not bond properly, for the same reason that Wall A has already set.
All these horrors are avoidable, if you bother to find out how to do something before attempting it.
As I say, do the build-up of the side walls in moderate six-inch increments, tamping properly as you go. That way, by the time you get back to your starting point with the next six-inch layer, the earlier concrete will still be un-set, and bonding will be fine. You will wind up with the great desideratum, a vessel solid as if it had been hewn from one huge monolith.
Some people do not seem to know that it does no particular good for a concrete wall to be enormously strong everywhere except for one stretch of two feet. The weakest part of the wall is, of course, the critical limiting factor. You therefore wish the wall to be uniformly strong, and this is accomplished by using concrete correctly made and correctly placed and correctly tamped and correctly cured.
When the forms are removed, after 24 hours or so (and needless to say they should be constructed of material heavy enough, and sufficiently braced, not to bulge from the wet concrete's weight), you are ready to cure the concrete.
I say nothing of "finishing" concrete, but of course if you want some particular finish, you must be sure what you want before you pour the concrete in the first place. Exposed aggregate, stamped and tool finishes, and so forth, all require special techniques and some of them are simple enough, but the main technique is to know what you want and to know what you are doing before you whip up a couple of pyramids of concrete in the back yard.
It is no time then, while Time's winge d chariot races down upon you, to say, "Let's see, now, what would look nice?" Your world will turn to stone before you can decide. I have often thought the terrible story of Lot's wife in the Bible had something to do with an early experiment with concrete in the garden.
Assuming the finish is all right, the curing requires knowledge rather than skill. Basically, it consists of keeping the concrete from drying out too rapidly.
I will spare you my lecture on hydration and the mystical marriage between cement and water except to say it is perfectly marvelous and ought not be put asunder by any man. In general, wet burlap is set over the concrete and kept moist for a week or 10 days or two weeks, depending on the state of your perfectionism and the surliness of your assistants.
In some cases, concrete can be lightly flooded with water or may be dutifully and repeatedly misted, or may be covered with waterproof paper, or polyethylene sheets, or tarpaulins -- the idea is to keep the concrete moist for a week or so; and you would do well to explore the merits of the various methods before you begin pouring concrete.
Now here is a very critical matter, intimately connected with hydration: It is important (that word means nothing nowadays, I know, but here I mean all hell will break loose if you ignore this) for the correct quantity of water to be used when concrete is mixed.
The ignorant are constantly being surprised by everything in this world and most surprises stemming from ignorance are unpleasant, if I may say so, and few men in this continent have suffered more than I from the shocks of ignorance in my first half-century or so. They are surprised (for example) that the identical concrete mix is gloriously watertight if five gallons of water are used per unit of concrete, yet it will leak badly if seven gallons of water are used.
The ignorant suppose, as I once did, that the excess water will dry out, even if it takes a bit longer. And so it will. But it will do awful things to the mystery of hydration. Using too much water in concrete (the invariable tendency of the innocent) is like dumping a thousand persons on some convenient hill and calling it a government. No, it makes all the difference how the ingredients are mixed and how much liquid is used.
Assuming (as experience teaches us we may safely do) the concrete job has been flawed in various ways, what can be done? Many corrective steps may be taken, such as shutting the barn door after the horse is fled.
Honeycomb can be cut out. Joints can be strengthened by additional concrete. Special bonding preparations may be used to help stick the patches to the general fabric. Silicon and epoxy bandages may be applied to the wounded core.
Just be sure of this: Concrete is not mocked. As a man mixes, so shall he reap, as it were. Cut corners and your corners will leak.
One merit to a rudimentary comprehension of concrete is that when things go wrong, you will know in a flash why they did. Too little cement? Laziness with tamping? Sloppiness with water? Impatience with curing?
Concrete is the ideal material for Puritans. The sins are there, in concrete, forever and forever.