Q&A for How to Add Concrete to Existing Concrete

If you're done using your tools, clean everything off with water and a wire brush. Put your excess concrete in a contractor grade trash bag and then dispose of it. Make sure you clean everything immediately when you're done with it so the concrete doesn't dry.

Wear safety goggles, a protective mask, and long jeans when mixing and pouring concrete. The small particles can harm you if you don't protect your eyes, nose, and mouth.

It sounds like the existing porch had an unstable footing for the soil movement (freeze/thaw) and/or was attached to a home with a lot of movement. If the slab underneath continues to move, the upper layer also eventually will move.

It depends on how much you are adding to the top of it. The cement acts like an anchor for the wood post, so that it is not easily pulled up. You may want to put screws in the wood posts halfway in, so they protrude an inch or two. This would anchor the new pour to the wood post and not just to the old cement.

You could, but it would be better to find out why your slab is not level and correct the underlying problem, lest your shed tilt in the future. It may be better to "slabjack" the slab level (inject a product under the slab that will float it level) than to add a thin layer to the top that is prone to adhesion issues.

The objective of proper preparation is for the existing concrete not to be a "base," but to "combine" or "be part of" the new. However, several variables may prevent 100% success, even if all steps are followed accurately. The maximum thickness isn't an issue, but the minimum is. Areas too thin are prone to peel. For best results, use an application over 1" (I also follow these steps and add scoring before step #2). With that in mind, this method is intended for cosmetic purposes ONLY. I am a building contractor with 25+ years.

You can break it with a heavy sledge hammer, or drill a line of holes in it and split it, use a saw and cut it into squares, etc.

I have done this with an existing patio. The key to success was: 1) cleaning the existing surface to ensure good adhesion, 2) installing adequate steel reinforcement to the slab, 3) wetting the existing concrete surface before pouring, and 4) wetting the new concrete periodically after it sets so the concrete cures to the highest strength possible.

If your building and safety office will allow it, consider "bushing" the top of the wall: drill 1/2" holes in the top and epoxy rebar "pins" into the holes. Then, install forms and continue building your wall as you normally would.

There are a few factors. The most important is how the old porch looks. Is the old floor badly cracked or otherwise damaged? If it isn't level or easy to work with, you may need to redo it before you can expand it.

Using an edging tool can help you spread the concrete around corners. Set up wood braces to contain the concrete in a corner.

You should remove the vinyl siding. Depending on what's behind the vinyl, consider mounting 2x6 or 2x8 (depending on thickness of your slab), direct bury rated/pressure-treated lumber against the house and down to grade (ground level). Then, pour the concrete up against the 2x6 or 2x8.

No. The surface of the leftover concrete will cure enough overnight that it won't bond to the new concrete the next day.

You usually can level out a large slab as long as it is stable. If it doesn't have massive cracks or show signs of sinking into the ground, it's worth a try. Otherwise, you can always break the existing slab and replace it.

If you have to do multiple pours, wait only about 30 minutes to 2 hours. There is no exact time frame for this, since concrete's drying speed depends on the weather in your area. However, concrete will begin to harden as soon as your pour it. It should be somewhat solidified but not completely cured by the time you do the second pour.

Yes, using screed is often possible and a cheaper option than concrete. Make sure the concrete level doesn't differ by more than 1/4 an inch or else it may not work. It should work fine otherwise, especially on smaller patios.

If the repair work needed is very large and extensive, you may need to replace the wall. For many damaged spots, you can build a mold and pour concrete in or do some masonry work with bricks and cement.

It can be done. You usually need to create a mold, such as out of wood braces, first. Then pour a strong concrete into the mold as usual and let it cure.

Generally yes, you should pour it all at the same time to get a consistent slab that doesn't leak. It's important to get the concrete footing in place. As you start covering the floor with concrete, spray the walls. You will likely need to add a couple of layers on the walls and floor to get them even.

Resurfacing is often necessary before adding tile. It gives you a chance to level out the floor and provide a new, clean bonding surface for the tile.

Smooth the old mortar out with a floor grinder before adding the new mortar over it. It may not stick well if it isn't smooth.

You usually press the stones flat when adding them to the concrete, but you can try smoothing them out with a concrete grinder or similar tool.

Try to watch and see where the water is coming from. You might have a leak in the area. Patch those up first. Also make sure the area is waterproofed and the concrete slopes properly to let water out. Adding a rubber weatherproofing strip to the door can help, but not if the concrete isn't doing its part.

Usually anything less than 30 degrees Fahrenheit or 0 degrees Celsius. Basically, if the temperature reaches below the freezing point, your concrete can freeze, crack, or otherwise weaken. Take nighttime temperatures into account.

You will need to dig a trench, add a layer of gravel to the bottom, then fill the trench with gravel, dirt, and sod. For indoor work, cut a hole with a concrete saw, add the gravel layer, install the pipe, then fill the hole with concrete.

You can! Mud-jacking involves drilling into the concrete, then pumping the cement mixture underneath the slab to raise it. Level it out with new concrete and it should be just as strong and lasting as normal.

Tearing out the steps first is usually the best bet so you can pour a consistent, smooth slab. Getting the steps covered and level might be a problem right away and weaken the concrete later.

Concrete parking lots need a thickness of about 6 inches or more. Making it a little shallower than this may still be safe thanks to the underlying layer.

You should be able to chip off the tile with a chisel, although you can get a jackhammer if you want to destroy it. If you want the concrete to pour neatly into a small area to reach that exact height, create a mold out of wood or other materials. You can also pour the concrete directly and smooth it out.

Your best bet is patching concrete. Push the concrete down into the crack to fill it, then even it out. If the crack is very deep, you may have a hard time filling it in completely. This could be due to an improper pour or a problematic surface underneath it.