View Full Version : How can I level a concrete porch?

08-17-2006, 09:30 AM
Hello, I need some ideas on how to level a concrete porch that was originally sloped for drainage. The porch is being incorporated into our remodel/addition as an entry room. It is 12 x 15 feet and the slope is 2 inches over the 12 foot direction. The 15 foot sides of the concrete porch will interface with wood floors that are 1 1 / 8 plywood over BCI joists. I have already got an OK from the building inspector to build over it as its footings are larger than code requires. Thanks, Bill (Dukes)

08-17-2006, 10:02 AM
You can fir it up w/ tapered 2x4s and put your subfloor over that.


08-17-2006, 02:12 PM
Thanks Jason for the reply, but I need to elaborate. Tapering the 2x4s is not a problem, but the slope starts at a height equal to the original house floor. That means for example if I used 1 1/8 subfloor I would have to taper it from 0 to 1 1/8 inches over a 90 inch span. I don't know how to do that. I could use thinner subfloor and/or break it up into boards rather than 4x8 sheets to reduce the taper per board, but it still looks like a formidable job. The slope of 2 inches over 12 feet is approximately .014 inch per inch. Bill (Dukes)

08-17-2006, 07:51 PM
Well, I kinda foller ya now. I'm actually doing the 2x4 thing. Once upon a time had a balcony over a porch over no foundation. Then they closed in the balcony and it all settled almost 6in over 80 years. Tore off porch, jacked up "balcony" almost all the way up. I was afraid to go up higher. It creaked and cracked and busted up the walls and I was just afraid to go up higher. Bumped out the kitchen below and firred down the ceiling level and now I'm working on the room above. It was a slight step down, so I'm working with 2x4s scribed at a tape from about 1.5" to about 3.625." Busted out the exterior house wall to open the "balcony up," replaced busted out drywall (actually old plaster board), and now relaying doug fur floor that came out of the kitchen. So far working well.

Could reduce the sub floor to 3/4" over the porch on some firring strips. I actually think it's sold 23/32". Then start that where it'll be level w/ the existing subfloor which is about 53" out and then use some SLC to make up the difference over that gap. You could screed it between the existing floor and new subfloor. It'd come out good.

Even if the taper is small, what you can do is place your 2x2 (prolly get away w/ that) on the slope and take a straight edge next to it and level it out. Mark a level line on the 2x2 and then rip that w/ your tablesaw or circular saw.

I'd think using SLC over the whole porch might be too big of an area unless you make some screed bars first and do it in sections.

Can you live w/ the slope? Maybe tilt up the other end of the house to match the slope? :p

08-18-2006, 11:31 AM
Thanks Jason, I had never heard of SLC, so I did a Google search, and found
http://www.levelrock.com/SLC400.asp It sounds like the solution from a feather edge to 5/8 inch thick. From the 5/8 to 2 inch distance I can taper the strips and plywood. I am trying to make this remodel/addition not be obvious that it is not original construction. I think this is the solution, and appreciate your help very much. Bill (Dukes)

08-18-2006, 01:05 PM
Make sure to follow the slc instructions very carefully and don't try to shortcut things and not use the primer. Have some help so you can mix it up in a nearly continous operation...the stuff starts to set up quickly, especially if it is hot out (minutes, not hours). Mix two bags at a time, and don't mix it longer than they say. Ensure you have a 1/2" drill that can handle the load at the prescribed RPM, you'll likely burn out a smaller drill. Buy more than you think...adding a little at the end is much less successful unless you do it all at once.

Some slc's can go up to 2" or more, but the slc is not cheap, so if you can conveniently stop it somewhere, that might be good. If you are going to tile this surface, you will be making it very difficult for yourself with the different materials. You can't install cbu on top of slc, and you need it on the plywood unless you use a membrane over the entire surface, which may be your best bet. The slc isn't designed to be a top layer...you need to cover it, so plan on that fairly quickly...you don't want to be walking across it for weeks before you finish it off with something.

08-18-2006, 01:44 PM
Check out the John Bridge forum for lots of discussion about SLC. I used it in a couple of places and was very happy with the results. For a large area like yours, you might want to rent a mixer or have several people with 1/2" drills, paddles, and 5-gallon buckets working steadily. Things I learned or wish I'd learned during the process:

1) The cheapest SLC you can buy at HD is just as good as the expensive stuff. Shop around. I used LevelQuik or some such; wished it had been called LevelNotQuiteSoQuik.

2) You can mix one bag in a 5-gallon bucket. You can't mix one or 2 bags in a rented mixer -- it doesn't mix thoroughly enough. You probably could mix 4 or 5 bags in a mixer, but I didn't try -- I went directly to the buckets after failing to mix 2 bags nicely. Buckets are also easier to manage for pouring over a large area.

3) Don't mess with it. Pour it and let it do its thing, although it may need some help running up to a knife edge (not your problem). Over a large area, pour it in lots of piles and let the piles merge. I'm not sure how large an area it will adapt to on its own, but it's probably on the order of a 6' diameter circle.

4) It's about the consistency of pancake batter, but runs like water. If you set a form board up at the edge of your patio, for instance, the SLC will run right through the smallest gap between the form and old concrete. After you set your forms, run a bead of cheap caulk along the gap to seal it.

5) As Jim said, follow the directions. If the directions say 6 quarts of water per bag, that's what you use.

6) Also as Jim said, temperature matters. I had a bunch of gallon jugs of water frozen beforehand to use to cool the mixing water to extend the working time.

You won't believe it until you see it work. Very neat stuff.

08-19-2006, 04:43 PM
Thanks guys, for the tips on using SLC. I will put them to good use and report back on completion. My plans are in plan check now. Hopefully I will get the permit next week. Bill (Dukes)

08-21-2006, 05:10 AM
I am trying to make this remodel/addition not be obvious that it is not original construction.

Only the best succede at that! :) Good luck.


09-04-2006, 05:38 AM

From what i read above, sounds like you might be planning to use Self Leveling Cement on half of your surface, or even on the whole slab. I wouldn't do that.

Please check out alternatives.

I think you may want to consider using SLC only as the top most layer after evening out the slope first by using other cement products that have numerous advantages over SLC.

There are many cement products that fill space and are designed to do that. Resurfacing Mix, or Patching Mix, or whatever your locally available brands call it. You trowel them on, spread them out yourself, so you do not get the smooth flat surface that SLC might give you. A layer of SLC on top of it will give you a flat level smooth and even surface.

These other cement products give you a couple hours of open time to work with. They don't crack when drying, they cost little, they are not finicky and difficult.

Using SLC on half is going to create an issue with that crack line.

Using only SLC on the whole surface is almost impossible to do -- too much to mix and pour. You do not want to do several batches of SLC separately, as the SLC manufacturers do not warranty jobs done in batches. Do not create cold joints among plates or sections. Do it all in one pass, and keep SLC thin. So use another cement product designed to go as thick as 2". SLC is not deigned to go as thick as 2".

i may not be saying all this as clearly as someone else could, but i know that SLC is not designed to do the entire "fill job" that you have, and that you are best off with another cement product first, and that you will find out when you call the 1-800-tech support line of the locally available cement product company.

hope this helps you a lot.


09-04-2006, 11:33 AM
There are SLCs that can go as deep as 5" (Custom Building Products Deep Pour for example). It becomes very expensive to do that, and other methods should be sought out first, but it can be done. To minimize materials cost, most suggest using some pea gravel as a filler, but it is not required.

For large areas of slc, it may be necessary to use a mixing pump. These take experience to operate properly and are likely not something you could rent. Lots of friends mixing using several buckets can do a signficant area, but there are limits.

09-07-2006, 12:27 PM

Everything Jim said is true, accurate, precise and valid. And it may be realistic to do too.

What i suggest in general is to use SLC only as the top layer, after filling in most of the volume needed with another easier-to-work-with cement product. Layering cement products is warranteed by the cement manufacturers.

Many people have had bad experiences with SLC. I have read many people's problems described on the Tile-laying discussion forum. So I think here is one area where I prefer to be cautious. Usually I am willing to take calculated risks. Not in this situation. Because alternatives exist that reduce risk without causing any adverse problems.

A thick layer of filler, and a thin layer of SLC. My view on how to proceed.

It's your call.


11-28-2006, 08:49 PM
Thanks guys, Lots of excellent info. I am still some time away from leveling the porch. Currently learning how to do rough plumbing (on this forum, by the way). Had to learn how to drop the shower floor 4 inches for a curbless shower, after I learned how to lay foundation block. I will post photos after I pass inspection. Thanks again, Bill (Dukes)

09-27-2007, 08:18 PM
Hello, I just wanted to give feedback on how our porch leveling project turned out. Using a table saw my son in law cut pressure treated 2x4's from 1 1/4 inch to zero over a 10 1/2 foot length. The 2x4's were placed over roofing paper every 16 inches. 3/4 inch tongue and groove plywood was laid over them. He then drilled for wedge bolts through the plywood and 2x4s and drove the wedge bolt heads into and flush with the plywood. We then used a SLC named Ultraplan Plus 1 manufactured by Mapei he got from a local tile supplier to fill the remaining gap. The gap that had to be filled went from 3/4 inch thick to zero over about a 15 foot length. The results were almost perfect! No troweling necessary, a very smooth finish. We did use a primer recommended on the original concrete. You have to make sure that there are no leaks in the recess being poured, or you will not only waste material, but also form a small sinkhole at the leak spot. The stuff worked wonderful, and my only complaint is that it is expensive. No way we could have afforded to pour the whole 2 inch to zero porch. We have had daily traffic on it for about a month now. This is a good forum. Special thanks to all who contributed. Bill (Dukes)

09-28-2007, 06:40 AM
Make sure to get a finished floor over that slc...it is not designed as a top layer.

09-28-2007, 10:38 AM
Glad to hear things worked out for you. An SLC compound to 2" would have been very expensive. I've ripped sleepers to do a similar job myself and the results were good. For the future and perhpas the cheapest and quickest would be to Dry Pack (Deck Mud) the area. If you are not familiar with Deck Mud, it is a created with clean sand (sharp sand), portland cement and water - Nothing else at about a 5:1 ratio of sand to portland and just enough water to form a meatball. It is very easy to work in this form and has great strength.

09-28-2007, 11:41 AM
Deck mud does work great, but you can't feather it to zero. It could have been used for part of it, then finish the rest, but his solution worked fine, and may have kept him from practicing a new (but not necessarily hard) skill. Mixing up and placing lots of deck mud is a major physical workout. You get to pay for your convenience with slc.

09-28-2007, 01:15 PM
Deck mud does work great, but you can't feather it to zero. It could have been used for part of it, then finish the rest, but his solution worked fine, and may have kept him from practicing a new (but not necessarily hard) skill. Mixing up and placing lots of deck mud is a major physical workout. You get to pay for your convenience with slc.

No - the deck mud in place of the sleepers and plywood and then the SLC. 3/4" deck mud is no problem at all.

10-08-2007, 09:39 AM
Hey, glad it worked out well for you. :)