Sloped rough concrete floor to flat level room

[Shropskr]

When we purchased our house it came with a porch fully turned into a sunroom.  Two walls of Windows and a door.   Only problem water damage in the corner.  Turns out the concrete is an outside pad and sloped.  Pulled the cedar planks off and have the water fixed but. Since it's an outside concret pad now indoors. It will always wick. 

The 15 ft room has about a 1 1/2 inch fall.  I think we need a subfloor.  Got a quote $3000.
I've heard this is doable diy.  I've never felt with subfloors and am apprehensive.

Ideas?

[Spork]

It may not be applicable but...

I had a very large living room where the concrete guy was obviously quite drunk when it was poured.  There were numerous idiosyncrasies, but the most notable was that the floor dropped off quite a lot in one corner.  I believe it dropped 3 inches over about 6 feet.  Someone, in their infinite wisdom, had made a mortar ramp from that room into the next, then carpeted over it.  It was a very strange sensation walking from one room to the next.

I wanted a wood-style floor.  In those days the best choice I knew of was a Pergo laminate style floor.  But you need a flat substrate.  I filled the really deep areas with very fine pebbles... then filled the rest with LevelQuick compound.  I believe it was 30-40 bags by the time I was done.  About half the room had some amount of coverage by the time I was done.

I lived there 10 years... and it seemed to hold up well.  There was some serious foundation work... and some of it popped off during that work... but that work also destroyed the flooring, so it only took a minor amount of patching to bring it back to "normal."

[GilbertB]

It's doable but you'll need a cement mixer.
Not for the volume, but to get an uniform mix.

First you need a water barrier, injection is the most common here.
The most time consuming will be making a barrier around the problem area with temporary  ply.
Then fill with a very liquid self levelling concrete; pour a little, spread, pour a little, spread, etc, until you have filled to your mark.
With what I've used, I expect at least 24 hours before removing the barrier and 3 to 5 days till you can do any work on it.

In Belgium, we have additives such as "Conpaktuna" that make the concrete flow better and water proof, you need to check what is available locally.
http://www.compaktuna.be/en/compaktuna-10.htm

I don't get why you need a subfloor for about 3.8cm, pictures would help!

[aerofreaky`]

Clean the surface well and dry... then spray it down with a self leveling floor primer. After that, you'll add a thin layer of self leveling concrete/floor leveler. All of this is available at your big box store. Make sure you frame out a perimeter on the lower side so it doesn't just flow away. You can rent a cement mixer for low $. This shouldn't take more than a few hours of actual work, though on different days for drying.  Lastly, make sure you follow the directions on mixing. Don't add too much water and WEAR A PARTICULATE RESPIRATOR AND SYNTHETIC GLOVES!

[Shropskr]

It's 1 1/2 inches change in depth over the length of the room. 

The contractor talked about building a wooden subfloor over the current poured patio floor.
So as to not water damage current walls.  Is this necessary and how?

[MBot]

It's 1 1/2 inches change in depth over the length of the room. 

The contractor talked about building a wooden subfloor over the current poured patio floor.
So as to not water damage current walls.  Is this necessary and how?

What do they mean not water damaging current walls? You can easily cut out the bottom 3" of the drywall that's hidden by baseboard and still do this levelling process.

You shouldn't need a built subfloor to level it. You also won't be able to perfectly level the floor just by using a subfloor.

You also don't need to just use self levelling concrete - that's very expensive to fill in the entire slope that way.

We fixed a similar slope problem in our basement.

First you use a a laser level to mark "level" on all walls

Then you pour regular concrete at the worst (lowest) part and work up to most of the slope ()say leaving 1/4" inch)

Finally you use self-levelling as the final layer - this gives a smooth and consistent Surface that makes it all work. You don't need a bond or sealer between the different concretes.

For the water issue, if you are having it covered by flooring, I recommend a dimpled plastic subfloor. Get the rolled kind you tape, not tiles. But it can only go on a level slab.  Eg this https://www.lowes.ca/floor-underlayment/delta-fl-3-12-ft-x-30-ft-x-105-sq-ft-roll_g1434328.html

[paddedhat]

It's 1 1/2 inches change in depth over the length of the room. 

The contractor talked about building a wooden subfloor over the current poured patio floor.
So as to not water damage current walls.  Is this necessary and how?

What do they mean not water damaging current walls? You can easily cut out the bottom 3" of the drywall that's hidden by baseboard and still do this levelling process.

You shouldn't need a built subfloor to level it. You also won't be able to perfectly level the floor just by using a subfloor.

You also don't need to just use self levelling concrete - that's very expensive to fill in the entire slope that way.

We fixed a similar slope problem in our basement.

First you use a a laser level to mark "level" on all walls

Then you pour regular concrete at the worst (lowest) part and work up to most of the slope ()say leaving 1/4" inch)

Finally you use self-levelling as the final layer - this gives a smooth and consistent Surface that makes it all work. You don't need a bond or sealer between the different concretes.

For the water issue, if you are having it covered by flooring, I recommend a dimpled plastic subfloor. Get the rolled kind you tape, not tiles. But it can only go on a level slab.  Eg this https://www.lowes.ca/floor-underlayment/delta-fl-3-12-ft-x-30-ft-x-105-sq-ft-roll_g1434328.html

I'm not the only carpenter who has successfully built dead flat sub-floors on sloped, and uneven subfloors. It takes time, skill and patience to scribe and taper floor joists to a sloped floor, but I can assure you that it's done all the time. I wouldn't taper the joists from 1-1/2" to zero BTW.  A minimum of 1-1/2to 2" on the upslope end of the joists would be best to provide a nailing surface for the subfloor and to keep the tapered point from splitting. I have done a job like this that also had a double roofing felt layer as a moisture barrier on the floor  and 1" extruded foam insulation between the joists.

The problem with your technique is that standard, inexpensive concrete mix is not designed to be placed in thin layers. It may of worked fine for you, but it isn't best practice, and you won't find a competent pro. who would do it, and guarantee the work.  Thin slabs have a tendency to develop severe cracks and break up, if the  concrete mix uses standard aggregates and no additional admixtures to the cement powder. Thinset coatings are expensive since they are a lot more than the usual sand, stone and cement mix. Prep work is critical, and a properly cleaned slab treated with a bonding agent is a must to guarantee success.

[Fishindude]

Sounds like someone turned a "covered porch" into an "enclosed sun room". 
Are you in an area that freezes?   Do you know if there is any type of footing or foundation under the outside walls?

 

[Shropskr]

Covered porch to enclosed sunroom is exactly what we think they did.  Now we just get to figure out how to make it work.