Clay puddle is a mass of clay and sand worked into a plastic condition with water. It is used for filling coffer-dams, for making embankments and reservoirs water-tight, and for protecting masonry against the penetration of water from behind.
Quality of Clay. The clays best suited for puddle are opaque, and not crystallized, should exhibit a dull earthy fracture, exhale when breathed upon a peculiar faint odor termed "argillaceous," should be unctuous to the touch, free from gritty matter, and form a plastic paste with water.
The important properties of clay for making good puddle are its tenacity or cohesion and its power of retaining water. The tenac ity of a clay may be tested by working up a small quantity with water into a thoroughly plastic condition, and forming it by hand into a roll about 1 to 11 inches in diameter by 10 or 12 inches in length. If such a roll is sufficiently cohesive not to break on being suspended by one end while wet the tenacity of the material is ample.
To test its power of retaining water one to two cubic yards should be worked with water to a compact homogeneous plastic condition, and then a hollow should be formed in the center of the mass capable of holding four or five gallons of water. After filling the hollow with water it should be covered over to prevent evaporation and left for about 24 hours, when its capability of holding water will be indicated by the presence or absence of water in the hollow.
The clay should be freed from large stones and vegetable matter, and just sufficient sand and water added to make a homogeneous mass. If there is too little sand the puddle will crack by shrinkage in drying, and if too much it will be permeable.
Puddling. The operation of puddling consists in chopping the clay in layers of about 3 inches thick with spades, aided by the addition of sufficient water to reduce it to a pasty condition. After each chop and before withdrawing the spade it should be given a lunging motion so as to permit the water to pass through.
The spade should pass through the upper layer into the lower layer so as to cause the layers to bond together.
The test for thorough puddling is that the spade will pass through the layer with ease, which it will not do if there are any dry hard lumps.
Sometimes in place of spades, harrows are used, each layer of clay being thoroughly harrowed aided by water and then rolled with a grooved roller to compact it.
The finished puddle should not be exposed to the drying action of the air, but should be covered with a layer of dry clay or sand.