3/4" thick self levelling topping on old conrete slab, without surface preparation

[ajk1]

The flooring contractor on a project last week placed a 400 square foot area of 3/4" thick self-leveling topping, on top of an existing 50 year old slab, without preparing the surface of the old slab. The topping will be overlaid by a glued down vinyl tile. In my opinion, a topping as thin as this should be bonded to the slab, or it will curl and crack extensively. Our structural office for at least the past 40 years has specified that toppings thinner than 3" must be bonded toppings (although I have done unbonded topping as thin as 2" when forced to). To bond properly, we specify surface preparation, usually by shotblast (trade name Blastrak). However the vinyl flooring contractor insists that this is the way he always does it. I believe he does use some sort of a bonding agent.

The self-levelling topping manufacturer's literature, and instructions on his containers, clearly say that the base floor surface should be shotblast.

Questions:

1. Has anyone placed such a thin topping as unbonded?

2. Has anyone placed a bonded topping without surface prep?

3. How concerned should I be about a 3/4" self levelling topping that has ben placed on an old slab without surface prep?

4. Should we ask for it to be removed and redone?

5. Should we leave it be, but put the contractor on notice that he has not conformed to manufacturer's instructions and we will hold him for all future costs arising out of defects that show up in future arising out of this?

6. Should we ask for an extended warranty?

6. Should we just forget it?

 

[Ron]

A2mfk....yes, shot blasting produces a good profile for toppings that is rougher than rotary "sanding". Another thing shot blasting does is open the surface of the concrete so that better drying occurs, thus less chance of inhibiting bond. When shot blasting is used you get the benefits of mechanical and chemical bond. When you don't use good surface prep, you depend almost entirely on chemical bond which can be tenuous, particularly with time.

 

[ajk1]

Ingenuity - yes and no. It bears the Armstrong label, but it is made by Mapei for Armstrong.

Ron - you make some additional very good points.

Happy New Year!

 

[releky]

I read this with interests because I'll also do it. A2mfk, I will re-do the floor by removing all of the old mortar bed. They are just too thick at 2-2.5 inches. I won't do hard screed (paste-like cement mix) for even 1 inch and bonded to slabs, because any deflection of the floor can debond it and tent the screed upward. So I plan to use 1 inch "thick mortar bed" which Wikipedia described as "The thick bed mortar method has been around for hundreds, if not thousands of years. Historically, a sand/cement mixture was mixed with water to a fairly dry consistency and was spread on either a portland cement water paste (neat cement), or over cement powder spread on the surface which is then sprayed with water to create a slurry coat and spread over the surface." This mortar bed not attached to the slabs avoid stress transfer to the tiles. Now my question would be. Can the thick mortar bed be just one inch? Or does it have minimum thickness? In my place we don't have any self leveling grout. We only have sand, cement and adhesive that we use in millions of buildings as mortar bed.

 

[ajk1]

to all who were kind enough to help me, I have some information for you, that I received today from the flooring manufacturer (Armstrong) in reponse to the question that I sent them about how long to wait for the adhesive to cure beofre pushing heavy furniture across the LVT tile. Their response is as follows:

"Do not allow traffic for 24 hours after installation. Tile should not be exposed to rolling load traffic for at least 72 hours after installation to allow setting and drying of the adhesive."