Concrete slab build up

[Whoopbass]

I need to level a concrete slab so I can install tiles. The slab in question was a porch so it has a slope to it. It's about 15' long and 8' wide. The slope goes from almost flush (next to an existing slab) and gradually drops about an inch. I plan on using self leveling cement for the topping. What would be the cheapest material that would adhere to the existing slab that I could use for the filler? I would only like to use about 1/4" of SLC for the top.
SLC is close to $35 a bag out the door. Cement patch is about $17 a 40# bag out the door. I need something cheaper if possible. This is inside a house so no cars or anything heavy is going to be on it.

 

[dockwrecker]

Re: Concrete slab build up

So now it's not a porch and inside your house? If it's still a porch, the slope is there for drainage.
The tough thing about most leveling cements is getting adhesion and preventing spalling especially in depths under 1/2". Whatever you are covering needs to be acid washed and free of any coatings, paint etc. A bonding agent should then be applied. Ardex makes a good leveling cement but it ain't cheap. Grout typically sets too quick as well as straight Portland. Make some full width screed boards in advance and install a level fur strip on your low side. Have plenty of help to pull the screeds as well as plenty of mixed material. It needs to go down very wet in one shot with a minimal amount of trowling. If you work it too much, it's gonna break. Ardex also makes a fiber reinforced mix for this which is what we use. Check your local concrete supply house, Home Depot and Lowe's don't sell the right stuff.

 

[Whoopbass]

Re: Concrete slab build up

Thanks for the help Dock,
Yes it was a porch at one time but now its part of the house.
This is what I have:
5 40# bags of Armstrong S-194 patch underlayment / embosser.
5 40# bags of Henry Self Level cement
5 40# bags of Sakrete cement patcher.
I got the Armstrong and Henry stuff fairly cheap so that's why I have all this different material.
I think all the material above says not to pour it any thicker then 1/2" at a time.
I was going to build it up in 2-3 layers with the SLC going on last.
I was hoping that I could poor about 1/2"-3/4" of cheaper concrete like the 5000psi type concrete and then finish it up with the SLC.
I'm more worried about everything bonding then anything else.
The only concrete tools I have is a trowel. I was hoping to throw some concrete down and smooth it out the best I can. Then I was going to poor the SLC over that and smooth it out some and let it do the rest of the leveling on its own. So am I crazy?

 

[Bob_VT]

Re: Concrete slab build up

Be certain that the existing concrete has been prepped for the new coating. You might have to rough it up and also be wet it down (really wet) so the new material sticks. I placed new concrete over old on a garage floor and we wet the old surface down...... it is still lasting after 5 years.

 

[Bondo]

Re: Concrete slab build up

and let it do the rest of the leveling on its own. So am I crazy?

Ayuh,.... Self-leveling is the Name of it, more so than what it does....

The thicker areas can be shimmed with sacrete, at 3.79, an 80lb. bag...

 

[Tim Frank]

Re: Concrete slab build up

You might ask your masonry supply dealer whether there is a compatible additive or adhesive that you can use ...I have used these on patches and surfacing layers with great success.

 

[dockwrecker]

Re: Concrete slab build up

Establish a finish floor elevation around the perimiter of the room first.
Work backwards up your supply list starting with a thorough cleaning of the existing slab. Start with a concrete bonding agent over the entire slab. Use your Sackrete for your deep fill, screed it about 3/8 low from your base elevation. Remember that between the thickness of your tile and your bedding cement, you'll typically need to have the base bed 5/8" lower than your final finish elevation assuming a 3/8 thick tile and 1/4" bed, thus your first pour should be 1" below your finish line. If your tile is thicker you'll need to adjust this accordingly. Your second pour should be your levelling with the Henry's or the Armstrong, they're both fine and will fill the voids of the Sackrete and flow better in your thin areas. Mix em wet and use long screed boards, again, DON"T overwork the material and be prepared for it to go off quickly. Get it as flat as possible and leave it alone. Your setting mortar/mastic will take up the rest of the irregularities.

 

[Whoopbass]

Re: Concrete slab build up

Thanks guys...
I am going to fill in with the cheap stuff (deck mud) and then do everything to a "T" as suggested. I've already etched it and i'm currently working on the perimeter elevation. Thanks for the help and the assurance that i'm not screwing this up.

 

[RandyJ]

Re: Concrete slab build up

IMO, the deck mud is the way to go. Scree it to get everything leveled up. You would be wise to use a membrane if you want to make the investment. The isolation membrane and a good mortar with latex (Ultrabond2 or Flexibond)... several on the market... are the best way to prevent cracking of grout in the future. An excellent site for tile work is johnbridge.com There are some guys there who are extremely knowledgeable and anxious to impart their advice. All very good people!