Ideas for Concrete Floor Leveling

[bcs001]

Hey Guys. I'm back with a new project in a home I've just moved into. Planning to tile a sun room that was built over an exterior slab porch. This ~200 sqft space is now heated & cooled but about 5"-6" below the finished floor of the house and sloping about 2" in 8 ft away from the original exterior wall.

I'd like to it raise it about 4" at the near side and 6" at the far side to get it flat & level. What is the recommended method for raising a concrete floor that is is excellent condition. No cracks, pits or damage of any kind. Just a little stained from 30 years of being covered with solid bricks as the finished flooring.

Thanks,
Bruce.

[john619]

pour new slab on top

[speed51133]

what will the finished floor material be? Carpet/tile/wood/bare concrete??

A simple mud mix would be the cheapest and easiest. It is essentially a mix of 4-5 parts portland cement and 1 sand. This would work for tile as the finished floor.

https://www.youtube.com/watch?v=_2NOx74qrhY

skim coat it with thinset first to bond it.

Or, if you have access to the area from outside, you can pump in or chute in concrete.

[bcs001]

Will be laying tile on the raised floor. this area is accessible from outside and can get a concrete truck close enough to wheel barrow loads into the room.

Any special preparation needed on the old surface?

Is rebar or lathe needed in the new 4"-6" slab?

[Davy]

If I'm going to bond the deck mud with thinset, I don't use lath.

[jadnashua]

It's easier to get a mud bed perfectly flat than a concrete pour. I'm assuming that this will now be enclosed, otherwise, you should retain the slope.

[cx]

Originally Posted by Bruce

...a sun room that was built over an exterior slab porch. This ~200 sqft space is now heated & cooled...

I took that to mean it was fully enclosed now, Jim.

I'd agree with you that it's easier to get the mud bed flat enough even for very large format tile because it's actually possible to do that, which is not the case with poured concrete. Bring me the guy that can finish a large concrete slab flat to 1/8th-inch in ten feet and I'll see that he's properly worshiped as the god he must be.

[Davy]

The pic I posted above was just that. They wanted the floor leveled first and then the sunroom was built. It was mostly metal and windows. Best I remember I came back and skim coated the mud so it wouldn't erode and walk up. Then once the exterior walls were built, the red door you see was removed and other work was done. Then I put down a membrane and tiled the floor.

After getting the sand and cement on the job, seems like the mud work took about a half day.

[bcs001]

Great info for us amateurs. Thanks much!!!

Now to finish this topic off......can I get an idea about cost. Going the mud bed route for this large an area would be more than I want to do myself so how would hiring this out compare to hiring someone to do a concrete pour and then me coming back with an SLC finish layer to get flat?

Bruce.

[jadnashua]

FWIW, SLC needs some help getting level, and you may end up with it not being any better than your slab unless the guys are good. It's certainly easier to get it nice and flat versus a concrete pour, though. Also, while it would end up more, many SLC products can be used with pea gravel to minimize how much actual product you use. Should you go with concrete, keep in mind that industry standards call for letting it cure for at least 28-days prior to covering with tile. There is an exception that I know of, Schluter allows you to put Ditra over a green slab as soon as it can be walked on, and then tile it. Depending on your schedule, that can be a big thing. The issue with concrete is that as it initially cures, it shrinks, and that movement can compromise the bonds for tile. While it's not fully cured at 28-days, it is pretty much shrunk as much as you can tell without laboratory instruments.

[Davy]

Like Jim said, putting down SLC isn't quite as easy as dumping it out and watching it flow nice and level. If you don't think you can handle mudding the floor with deck mud then I think it's best to find a good concrete man that can pour the concrete fairly flat. Then you can do any fine tuning with floor patch or filler. Many times I've used primer and SLC to fill low areas. I've also used thinset if the thickness is less than 1/4 inch.

[bcs001]

I've done three SLC jobs and know how to work with that material using a metal rake to get it moving once poured. The 30 day cure before tile will be a small inconvenience but not really to big a deal. The added cost of thinset and ditra would be something to consider though. I'll get some pricing for putting down a mud bed vs a concrete pour and go from there.

As always, I appreciate the great info!!

Bruce.

[speed51133]

I never heard of a 30 day cure for SLC????

[bcs001]

The 30 day cure was in reference to Jim's comment if I were to go with an initial concrete pour. Sorry for the confusion.

Bruce.

[JerseyDIYguy]

I'm going to suggest an alternative: Put down tapered sleeper joists topped with plywood and lay your tile over that.

With the area and heights you have you're looking at 4 tons or more of mud bed and SLC material to build it up to level. Definitely not something for the ordinary DIY person.

With sleeper joists you can also insulate which may or may not be important to you depending on how you'll use the room.

I've found that by scribing the joists to the slope of the existing floor you can get a very level and flat subfloor. Scribing the sleepers also provides full contact support from the underlying concrete along the entire length of the sleeper. No worries about stiffness/deflection that way, and it's a relatively straightforward job that a DIY'er can accomplish if they take their time.