148 ENGINEERING ON THE FARM 



so-called regaging cannot restore the setting powers. While 

 being placed into forms the concrete should be frequently 

 puddled or rammed down with a stick or shovel, and a 

 shovel should be forced down into the mixture next to the 

 face of the form to insure a good flow to all parts and a 

 good surface contact between the concrete and the form. 

 This applies especially to such work as walls. Keep the 

 forms wet down ahead of placing, for this insures good 

 contact and easy flow of the concrete. 



Proper curing. Cement work, once placed, must be 

 properly protected from too rapid drying. Surfaces should 

 be wet as frequently as possible, twice a day at least for 

 four days, and protected from the hot sun by a covering of 

 canvas, a shading of building paper, old sacks, or brush, 

 or a covering of a layer of sand. Too rapid drying lowers 

 the ultimate strength and creates shrinkage cracks. With 

 the dry mix especially it is necessary to provide ample 

 protection from the action of the hot sun and to supply 

 moisture for several days in order that the cement 

 may complete its chemical action properly. The longer 

 cement work is kept wet, the greater its ultimate strength 

 will be, even for several months. Keeping work wet thirty 

 days will, in many cases, pay for the trouble by increasing 

 the strength. 



Freezing. Concrete work should not be attempted in 

 freezing weather if it can be done at other times. If con- 

 crete freezes within forty-eight hours after it is mixed, it 

 may lose its setting powers, which will necessitate its being 

 taken out and replaced. If it is necessary to place concrete 

 in freezing weather, it should be protected by a covering 

 of canvas, straw, or manure. In mixing, both the water 

 and the aggregate should be heated, care being taken to 

 see that there are no frozen lumps in the mix and no ice 

 in the forms. If practicable, temporary heat by means of 

 stoves or salamanders should be provided until the danger 

 of freezing is past. Salt is sometimes used to lower the 



