Homeowner Forum / Construction / June 2008

Call for an outside salesman at your local readymix supplier.
Tell them you would really like an on site consultation.

If you bond to the existing:
If there are cracks in the existing, they will transfer into the
new
If there is grease and contaminants in the existing they will
interfere with the bond.
If the existing suffers from ups and downs they may well crack the
new.

If you isolate with a layer of sand of similar:
If you plan a finish other than exposed concrete, use a vapor
barrier.  This will force all water of hydration to migrate up,
make sure the finishers understand NO finishing until the bleed
water has come up.  It makes a longer day.
Plan on contraction joints that never allow the concrete to exceed
12 feet in any one direction.  If they are saw joints make sure
they are cut the same day, as soon as the cut does not ravel.
Mesh or hog wire would be appropriate, fiber is considered the
equivalent of mesh.
Plasticizer will make the finishers' lives easier, make sure they
know how to work with it.

Plan to cure the new no matter which method is used.  If you use a
chemical cure, make sure it is compatible with floor covering if
it will be used.
If the floor will be hard troweled, reduce or eliminate air
content in the mix design.

4,000 # concrete may be overkill.  If the topping slab is 4" you
don't need the chip mix, but it will place and finish easier.  The
larger aggregate is stronger.

I always put a layers of sand between the old concrete and the new.
I also use a vapor barrier.....below the sand......This allows for upper
slab movement......
In some ways like shipping glass in a package........
Do you put the 2 together and ship or do you separate them with bubble wrap
and send?
jloomis