Adding water to concrete or masonry will definitely make it flow better and make it easier to work with, which is why just about everybody does it. At the same time you have all heard that this will weaken the final product and increase shrinkage, but just about everybody does it anyway. If the driver accepts to add water, he is not delivering the concrete at the specified strength. If he refuses to add water, the workmen will probably find someone who will. Why pay extra for a super plasticiser, when water is free? Why work harder when all you have to do is add water?
I know you're not going to do it, so I sat down with the Canadian Portland Cement Association's Engineering Bulletin to try and get some real world answers to this question. Here are a few sort of "out of context notes" that might mean something to your workmen the next time they think about using water as a tool for pouring concrete.
SHRINKAGE
For each 1 per cent increase in mixing water, concrete shrinkage increases about 2 per cent.
COMPRESSIVE STRENGTH
One chart showed that changing the water/cement ratio of a particular mix from 0.5 to 0.6 made a difference in 28-day strength from 25Mpa (code minimum) to 18Mpa -- a 28 per cent loss of strength.
ABRASION RESISTANCE
Surface abrasion resistance is closely related to compressive strength, hence more water, less resistance -- although hardness of the aggregate and trowelling technique may be more important here.
AIR RETAINMENT
The air voids become coarser at higher water/cement ratios, thereby reducing concrete freeze/thaw durability.
WATER & PERMEABILITY
Cured concrete is more permeable (less water resistant) when the initial water/cement ratios are higher. This aspect is even more pronounced for concrete cured one day moist, 90 days in air than for concrete cured seven days moist, 90 days in air.
It appears to me that the single greatest improvement we can make to the quality of concrete is to turn the water off while pouring it. Order it right and use it the way it comes in the truck. Then turn the water on and keep it moist as long as you can. But don't use water as a tool for placing concrete.
WATER AS AN ABRASIVE
Power washing is actually using water as an abrasive. One catch is that with too little pressure it doesn't clean, with too much pressure or the wrong head angle, you destroy your surface. Always "tune up" where it won't show.
Not only can the water itself do damage, but also it carries soap to places where soap should never go. If we shoot up under shingles, or into the vent holes of siding, we will wet the building or roofing paper. If there is soap with that water, and that soap then dries onto or into the building paper (construction paper or house wrap) the soap will do what soap does: reduce the surface tension of any water that eventually hits that paper. That means that the building paper is suddenly no longer a water shedding membrane, and the wall is now susceptible to future moisture problems. Apparently this changing of the characteristics of the house wrap is permanent, or at least very long term.
WATER AS A FILTER
Drywall sanding in a furnished house is problematic, and although a few true drywall dust vacuums exist (like the trigger actuated vac from Porter Cable), water can do the job. The Water Vac from Orbit Tools simply passes the exhaust through a water bucket on the way to your old shop vac. The drywall guys tell me that it actually works.
WATER AS A CURING AGENT
In a very dry atmosphere, some caulking and some adhesives have a problem curing. That is because they do not cure by evaporating solvents, but rather by chemical reaction using H2O. The most common examples are all true silicone caulking, polyurethane caulking and polyurethane adhesives like PL Premium. If they won't skin or set fast enough, simply mist them with water. If you are using them outdoors on a dusty site, hose them down gently right after application. That will keep the dust off and accelerate skinning. And since the water only acts like a catalyst, the curing process will then proceed through the whole bead.
**Originally published as an article by Jon Eakes in Home Builder Magazine, the magazine of the Canadian Home Builder's Association.