2" Topping on Slab on Grade
2" Topping on Slab on Grade
(OP)
I have small room (15'x12') that requires a 2" concrete topping over a newly placed slab on grade with a vapor barrier.
I am going to use sikacrete 211 as my topping, without a bonding agent, so as to not trap moisture between the barrier and the bottom of my topping.
i am concerned about cracking, and if i use the 24 x thickness rule for unreinforced concrete, my 1" deep sawcut joints would be spaced at 48" o.c. Does this seem reasonable for this application? Am i missing something? Would it be best to use fibers?
I am going to use sikacrete 211 as my topping, without a bonding agent, so as to not trap moisture between the barrier and the bottom of my topping.
i am concerned about cracking, and if i use the 24 x thickness rule for unreinforced concrete, my 1" deep sawcut joints would be spaced at 48" o.c. Does this seem reasonable for this application? Am i missing something? Would it be best to use fibers?






RE: 2" Topping on Slab on Grade
Why would you want an unbonded 2" topping?
It is likely that you have no control joints in your 15x12 slab. If that is the case, I would bond the topping by using a roughened surface on the slab and use a latex bonding agent. I would not worry about moisture entrapment.
If you have joints in the underlying slab, make the joints in the topping correspond to the joints in the substrate. Toppings do not follow the 24x rule of thumb because they have much less water and less shrinkage than conventional concrete.
RE: 2" Topping on Slab on Grade
You should bond the topping to reduce the probability of cracking.
RE: 2" Topping on Slab on Grade
We've also done a number of thin topping slabs, and have asked for a shrinkage reducing admixture in the concrete, but I remember reading in the same ACI 360, that you shouldn't use shrinkage reducing admixtures for topping slabs on fresh slabs on grade.
We've always asked for a bonding agent, but make sure to have a conversation with the contractor that they should be careful not to let the bonding agent set before placing the topping slab.
RE: 2" Topping on Slab on Grade
RE: 2" Topping on Slab on Grade