Concrete Bonding

[Paul Denison]

Not boat related exactly ;) . I am going to pour a 4000 psi, high fiber content, concrete slab over an existing interior slab. It will range in thickness from 1 1/2 inches to 3 inches. I will then put tile on it. What products do you recommend for bonding the two slabs? Some recommend a pricey 2 part epoxy and I have seen the quikcrete product at HD and Lowes.

I also have to clean the concrete. How about muratic acid or the quikcrete cleaner (non acidic)?

Yes, this does mean that my attempts to scribe and cut 40 sleeper joists for the existing slab did not turn out well.

[Gresham CA]

Paul,
Why couldn't you spread dry tile mastic down first and then pour your concrete. moisture from the concrete will activate the mastic.

[John Shin]

Years ago I used a product I bought from my local concrete supplier in an outdoor application similar to yours. It looked like Elmer's glue. It is spread on the wetted surface of the old concrete before placing the new layer. This worked well for me. I don't know what this stuff was made of, perhaps latex.

[Rocky]

Tile on concrete is a mistake no matter what you use. Sooner or later the moisture in the crete will loosen them and then it looks like hell. A nicely finished slab, painted or stained, is attractive and easy to clean. If you wanna get fancy put heating coils in the mix! Or lay a rug on it, anything's better than tile.

[ 03-15-2003, 09:53 AM: Message edited by: Rocky ]

[Matt J.]

Paul,
I used to work at the NRMCA / NAA research lab while in college, and for some reason, I recall being told that epoxy is a common bonding agents between layers of concrete.

Don't take my foggy-memory word for it though. Check out the nrmca.org website (or search for it) and call them. Gary Mullings, Colin Lobo both very knowledgeable. Gary will give you the straight forward (short) version or say he doesn't know. Colin will give you a college level lecture on the ramifications and start considering experimentation...

Don't tell them who sent you, or I'll start hearing about using their names on the Net. I haven't spoken with either in 3 years or so.

Good luck
Matt

[WTB]

I wouldn't recommend epoxy as a bonding agent in this case since I assume that this new slab is going down over an existing slab on grade. The epoxy will act as a vapor barrier. It is also difficult to get down evenly and work on top of.

I suggest: Sikalatex (www.sikausa.com) or
Daraweld a WR Grace product. Both should be readily available from a large building supply house. Also a cement slurry works well.

The most important measure you could take to ensure an excellent bond would be to scarify the slab. This would involve breaking the top of the existing finished surface to establish a profile for the new material to mechanically bond to. This can be done with a bushing head on a chipping hammer or there is walk behind equipment available that is manufactured by EDCO. A large rental supply company catering to the construction industry should have this equipment for rent. If this isn't feasible then degreaser and pressure washing with the most powerful pressure washer you can find would be a good move.

A couple of tips: Make sure the existing slab is well moistened but with no standing water before you place the concrete. You don't want to have the dry slab suck the hydration water out of the new plastic concrete. Also the slab will want to curl at the edges and lift as it cures. Install some mechanical fasteners at the perimeter to minimize this. Rawl forming spikes work well and go in quick. Cure the new slab with water and a sprinkler or a spray on curing agent such and L&M Cure. Consider adding super plasticizer to the concrete at the plant. This helps the concrete bond better.

[imported_Steven Bauer]

Paul, I checked the website of my local masonry supply store (big chain actually) A. H. Harris. They have some downloadable manuals on concrete repair and restoration here: concrete repair and restoration (http://www.ahharris.com/Prod/crr.htm)

I always go to where the commercial guys go for these kinds of supplies. Their expertise, product quality and even price will be much better the Home Despot or Lowes.
Good luck

Steven