Tips for leveling out cracked concrete

[CCCA]

I have a concrete slab after removing an old shed that has cracked and settled in some places. It's about 15 x 30'.

I am trying to figure out if putting a layer on top to cover the cracks and making it level and flat is possible as a DIY.  There are some 'steps' between sections that may be 1-2 inch different and sections that are a few inches lower than others.  I was thinking of using concrete floor leveler or more concrete to do this.

Is this a bad idea to try to DIY this? I'm wondering if anyone has any thoughts or suggestions on how to best approach this. The cost of removing and pouring new concrete seems like it would be fairly high.

thanks

[thedigitalone]

I don't have the answer for you, but I do know that if you pour a new layer on top of the old one the cracks will propagate through the new layer in short order.  It is a well known problem in roadwork and applies to asphalt and concrete alike, but that may be due to the moving weight load?

[lthenderson]

There is really no way to "cure" what you have other than to have it torn out and redone properly. Keep in mind that all concrete cracks, especially pads poured that size. But there are things you can do to prevent that from looking bad and becoming a tripping hazard. The first thing is when having it repoured, to make sure there is a good compacted fill underneath it so it doesn't settle which is what happened here. From virgin soil, I like to add fine gravel that can be compacted (if you have a lot of fill required) or sand. Either will compact easily and won't settle after the concrete has been poured. The second thing is to use rebar throughout the pad. It should be placed about a third of the thickness of the concrete up from the ground. This prevents one section of concrete from heaving relative to the other section of concrete and creating an unsightly tripping hazard. Finally, all concrete cracks so instead of waiting for it to crack where ever it likes, dictate where it cracks. We do this by cutting up the concrete into square pads at little at 5 feet by 5 feet and no bigger than 10 feet by 10 feet sections. Use a concrete saw the day after the pour while the concrete is green and cut grooves in it about half the depth of the concrete slab and not through your rebar. This creates a weak spot where the concrete will crack but because the lines are all nice and straight and you used rebar to prevent heaving between sections and you prepared a proper base so it didn't settle, you won't see the cracks and your concrete pad will still look beautiful as the day you poured it. Some people like to fill the man made cracks up with caulking and such but I just fill it up with leftover concrete dust from the concrete saw. I've seen pads where the caulking will fail and water gets in but can't evaporate and then becomes a problem when it freezes and expands. I've never had any problems with just using the concrete dust and letting it evaporate in the sun. You may have to spray it once or twice a year after weeds get a root in there. I poured my driveway about ten years ago now and I have to spray weeds twice a year in late spring and again late summer but only about twenty or so along the entire 40 feet driveway. Once the weeds die, it still looks like the day I poured it with its nice symmetric man made cracks I cut into it.

[Goldielocks]

Mud jacking -- they drill holes and inject material below the sunken portion to raise it up.  Mud or expoxy or more concrete, depending on what is needed.   Then you just crack fill the concrete as usual.

This is the solution for driveways and sidewalks.

[lthenderson]

Mud jacking -- they drill holes and inject material below the sunken portion to raise it up.  Mud or expoxy or more concrete, depending on what is needed.   Then you just crack fill the concrete as usual.

This is the solution for driveways and sidewalks.

Except for the drawbacks that rarely get mentioned.

1. The materials that they use for mudjacking is not waterproof and is susceptible to breakdown and erosion especially in northern climates with freeze thaw cycles.
2. Mudjacking is extremely heavy material. The OP has a slab that has settled due to a poor base and adding lots of additional weight will likely cause it to settle even more.
3. For a slab that size, large unsightly holes needs to be drilled at regular intervals to get the mud in the proper spots. Is seeing lots of holes in addition to all the cracking that will still be there post mudjacking worth having an even slab for a year or two until the water and weight cause it to settle again? I guess that is up to the OP.

Using polyurethane foam is a much better option because it is waterproof and is lightweight so not contributing to the settling issue but it can still leave unsightly holes and the original cracks behind.

[Goldielocks]

Mud jacking -- they drill holes and inject material below the sunken portion to raise it up.  Mud or expoxy or more concrete, depending on what is needed.   Then you just crack fill the concrete as usual.

This is the solution for driveways and sidewalks.

Except for the drawbacks that rarely get mentioned.

1. The materials that they use for mudjacking is not waterproof and is susceptible to breakdown and erosion especially in northern climates with freeze thaw cycles.
2. Mudjacking is extremely heavy material. The OP has a slab that has settled due to a poor base and adding lots of additional weight will likely cause it to settle even more.
3. For a slab that size, large unsightly holes needs to be drilled at regular intervals to get the mud in the proper spots. Is seeing lots of holes in addition to all the cracking that will still be there post mudjacking worth having an even slab for a year or two until the water and weight cause it to settle again? I guess that is up to the OP.

Using polyurethane foam is a much better option because it is waterproof and is lightweight so not contributing to the settling issue but it can still leave unsightly holes and the original cracks behind.

Yes, using the mud alternatives is generally preferred, unless it is a low-cost / low risk area where it is ok if it breaksdown a bit.  Drive areas are usually better off with the alternatives, but a patio can be fine.

I had major cracks, up to 1/2" along the final foot edge of my patio... it was not enough to need jacking, but I did crackfill it with normal material, that is grey and blends in a lot better visually than I expected.  Something that looks "repaired / maintained' but still obvious actually looks pretty good.   The large cracks looked horrible in comparison.

[Fishindude]

The only permanent fix is to jackhammer it out, grade and compact the base, then form, pour and finish a new slab.   
You will need adequate, correctly spaced control joints sawed or tooled in the slab to prevent random cracking.

[CCCA]

thanks everyone for your answers, even if it's not exactly what I wanted to hear. Sounds like the best solution is to remove the concrete.  Will have to think on it for a bit. 


thanks again

[alcon835]

@CCCA I am in the same situation. This thread has been extremely helpful! Like with you, it looks like I'll need to fully remove and replace my concrete patio if I want to fix the massive cracking. Not ideal, but I'm glad I know and can budget for it when I'm ready.

[sonofsven]

There's a saying I adhere to, it's kind of a joke, but it rings true quite often : "when in doubt, rip it out".
In my experience that means to get back to original conditions and then proceed according to established construction practice for the best results. You can spend hours/days/weeks scheming a way to accomplish your goal in an alternative manner, or you can rent a jackhammer and start busting up the slab
Of course, I am approaching this as a professional and so substandard results are not acceptable (no offense diy'ers!).
Another way of looking at it when you get bogged down in a construction project, what is the Critical Path?
Remove slab, form new slab, pour new slab, finish new slab
This would be a two day job for my concrete sub.

[Tempname23]

Years ago, I had a concrete drive that was cracked 6 of 7 feet before it entered the garage and it sank at the garage. This created a bump entering the garage. I used a jack, chain and some hooks I bent from flat iron. I levered the large piece up enough to get the hooks under and jacked it up high enough to through gravel underneath. It took two tries to get it level, but I was lucky and came out very good.
PS. it was a lot of work. I was young back then.