Working with concrete a complex, difficult task
over extremely important details.
The mix you order from the concrete plant needs to match the extreme weather conditions you will experience outside your home. You often will see that 4,000 pounds per square inch (PSI) concrete should be used in climates that experience freezing weather. Note this is a minimum standard. You can order stronger concrete, and it might be a good idea to do so.
Water is both the friend and foe of concrete. Add too much at any point in the mixing or installation process and you can ruin the concrete. Allow too much water to evaporate from the concrete after you are washing off your tools, and you can weaken the concrete. New concrete needs to retain water — it’s called curing — so the microcrystals in the concrete can continue to grow for months after the ready-mix truck leaves your home.
Concrete is very strong when squeezed, but it only has one-tenth that strength when subjected to tension. Tension is when concrete gets bent by hollow voids under the new concrete or from frost heaving in cold climates. The addition of reinforcing steel is a must if you want to ensure your new patio doesn't develop wide, ugly offset cracks.
Your new patio will shrink. Concrete tends to shrink inch for every 10 horizontal feet. This shrinkage pulls the concrete apart and can cause ugly random cracking. It is best to put in your own control joints in the wet concrete. These pre-weakened joints must be a minimum of ¼ the thickness of the slab. All too often, contractors make them too shallow.
Lastly, don’t underestimate the enormous amount of work to get the concrete from the truck into the forms. You will need at least six or eight helpers. Pour just before the sun rises to avoid extreme heat. Good luck!
Q: I’m building a new home and visited it during a driving rainstorm. There was water coming into the house. The siding has yet to be installed outdoors, but a self-adhered water barrier is in place. Everything looks fine, and there were no loose pieces of water barrier flapping in the wind. There’s a direct-vent fireplace exhaust hood on the wall above the area that was leaking. What could be wrong?
A: I would bet on faulty installation of the fireplace vent that passes through the wall. My guess is that the installer failed to integrate the metal vent flashing with the self-adhered exterior water barrier.
All too often, contractors and subcontractors rely on caulk to seal penetrations such as this. Caulk is not a substitute for the proper overlapping of waterproof materials on the outside of your new home.
In a perfect world, the fireplace installer would have been working hand in hand with the contractor at the same time the exterior water barrier was being installed.
Tim Carter writes for the Tribune Content Agency. You can visit his website (www.askthebuilder.com) for videos and more information on home projects.