In most cases the answer is YES! If the existing concrete is structurally sound, is not heaving or settling, then you can pour concrete over concrete.
My rule of thumb is this:
- If the new concrete is 3 inches thick or more – you don’t have to bond the new concrete to the old concrete.
- If the new concrete is less than 3 inches thick – you will want to use a bonding agent to bond the new concrete to the old concrete.
- Make sure the old concrete is clean, wash it or vacuum it, don’t pour over any dirt, dust, debris or loose concrete.
My name is Mike Day, I own Day’s Concrete Floors, Inc. I’ve owned my own concrete business for 39 years. I specialize in all aspects of concrete flat work.
In the picture above, we’re pouring a new concrete floor for a garage over the existing concrete floor.
The old concrete floor was very worn on the surface. You could see the aggregate in many places. Some areas had deteriorated up to a half inch deep.
This old concrete floor also had a gradual slope towards the back wall, right where you see us in the picture, so water would puddle back there whenever it rained or when water dripped off the cars.
When the customer called me to ask about what a solution to this problem would be, I recommended pouring a new concrete floor right over the old one.
The only issue was the garage door openings. He would have to move the garage doors up the thickness of the new floor for them to close properly.
The good thing was, he was installing new doors. So this problem was solved easily. If he wasn’t installing new doors, the solution would have been to un-bolt each track (on the sides of the doors) and move them up so the door would close tight on the top.
In the video below, you can watch us pour this new concrete floor right over the existing concrete floor.
What’s the minimum thickness you can pour new concrete over concrete?
In most cases, I don’t like to pour any new concrete less than 2 inches thick over an old, existing concrete floor, slab, patio, or driveway.
Two inches thick (or more) gives you adequate strength for a wear surface, especially if you’re driving over it.
Although it is possible to pour 1.5 inches thick with a pea stone mix, I don’t really recommend pouring that thin. If that’s all the height you can afford to lose, it will work but you may develop more shrinkage cracking than normal because of it being so thin.
A solution for that is to saw cut some extra expansion joints to help minimize any shrinkage cracks if you’re concerned about that.
And remember, if you’re new concrete pour is less than 3 inches thick, you will want to BOND the new concrete to the old concrete using a bonding agent.
How do you bond the new concrete to the old concrete?
The bonding agent I use is called WELD-CRETE.
This stuff is very easy to use and is designed to bond new concrete to old.
You just paint it on, using a roller or a scrub brush, an hour or up to 10 days before your new pour.
When you pour your new concrete over this bonding agent, it activates it and bonds the new concrete to the old concrete.
If you don’t use Weld-Crete, there’s no guarantee the new concrete will stick to the old concrete.
If you want to check out the Weld-Crete data sheet and application instructions CLICK HERE.
When wouldn’t I want to pour new concrete over old concrete.
There are cases when pouring new concrete over old just isn’t a viable solution.
If you’re concrete has large cracks and the slab may still be moving due to freeze and thaw conditions or settling, then a tear out and replace is a better solution.
If tree roots are causing your concrete to crack, then tear out the old concrete, resolve the tree roots problem, and pour new concrete.
If door thresholds or stair risers are an issue, pouring new concrete may cause some other problems you would have to resolve.
What if my old concrete has a lot of cracks in it?
If you’re existing concrete has a lot of cracks, but is structurally sound, isn’t moving, heaving, or settling, then it’s ok to pour new concrete over it.
I recommend installing a bond breaker between the old slab and the new one so the cracks won’t transfer up through the new concrete.
Some of the things we have used as bond breakers are:
- Plastic sheeting
- Typar house wrap
- Roofing felt paper (tar paper)
- Thin layer of sand
- Thin layer of crushed stone
- Thin layer of styrofoam
Using a bond breaker will keep the two slabs of concrete separate and the cracks will not mirror up through the new slab.
You’ll still need to saw cut or groove expansion joints in the new slab to help control shrinkage cracks, just like you would any new concrete pour.
The thinner the new over-pour, the closer the expansion joints should be.
How close should they be?
- For 4″ thick slabs 8′ x 10′ squares
- For 3″ thick slabs 6′ x 8′ squares
- for 2″ thick slabs 4′ x 6″ squares
This is just a general rule of thumb to give you an idea of how close your crack control joints should be to minimize any new cracks from developing.
What’s the procedure for pouring new concrete over old?
After you’ve determined you can pour new concrete over your old concrete, here’s how you prepare your old concrete.
- Clean the old concrete First – pressure wash it, vacuum it, remove any dirt, debris, or loose concrete.
- If you’re new concrete is under 3″ thick, apply Weld-Crete, let it dry at least 1 hour, then you’re ready to pour your new concrete.
- If you’re new concrete is 3 inches thick or more and your old concrete isn’t all cracked up, then you’re ready to pour your new concrete.
- If you’re old concrete is cracked up, install your bond breaker (for really wide cracks I recommend sand or 1/2″ styrofoam), then you’re ready to pour.
- If you’re old concrete is very smooth and you’re using Weld-Crete, you will want to acid-etch the old slab before applying Weld-Crete.
- If you have door openings or open edges, you will have to install wood forms to keep the new concrete from flowing over the edge.
If you watch my video above, you’ll see how we installed forms for the garage door openings to stop the new concrete.
Should I use reinforcement in my new concrete?
YES, you should use some kind of reinforcement in your new concrete pour.
For all my over-pours, I use fiber mesh reinforcement in the concrete. This type of reinforcement is tiny polypropylene fibers that get mixed into the concrete when the concrete is loaded onto the concrete truck.
Also, like in the video, I use wire mesh if the new pour is thick enough to allow for it.
Sometimes I’ll use rebar instead of wire mesh if the new pour is thick enough and a lot of weight is being driven over the new pour.
But the bottom line is YES, use some type of reinforcement in your new concrete over-pour to help control any cracks that may develop and keep them from spreading.
In most cases it’s OK to pour new concrete over existing concrete. Use my above recommendations and work experiences as a guideline to determine if your concrete is a good candidate or not.
I’ve personally poured hundreds of jobs where we poured over existing concrete that was worn out, cracked, pitted or sloped the wrong way.
If you have a question about your project, watch the video on YouTube and leave me a question in the comments section. I’ll try to help you any way I can.
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Why Does Concrete Crack?
One of the biggest hesitations people have when it comes to choosing concrete for their projects is that it cracks over time. While this practical, durable material is one of the strongest goods on the market, the forces of time and nature will eventually cause it to crack–especially if it’s been installed by a non-reputable
One of the biggest hesitations people have when it comes to choosing concrete for their projects is that it cracks over time.
While this practical, durable material is one of the strongest goods on the market, the forces of time and nature will eventually cause it to crack–especially if it’s been installed by a non-reputable company.
But why does concrete crack, and is there anything that will prevent this from happening?
These 5 mistakes are some of the most common causes of concrete cracks.
1. The concrete dried too fast
Faster is not always better. If your concrete mix doesn’t have enough water in it, it will dry too quickly and crack prematurely. Depending on the project, it should take at least a few weeks, maybe even a month, to dry completely.
2. Your contractor put too much water in the mix
Poorly mixed concrete can create a range of problems. Just like having too little water in the mix can cause it to crack, so can having too much water. Water must combine with the concrete at just the right pace so that it can cure and set properly.
3. Control joints weren’t used
Your concrete must be able to properly expand and contract in different temperatures, otherwise it’ll crack. Control joints are made specifically to help your concrete move about without breaking.
If your contractor doesn’t use these joints, there won’t be extra room for the slab to adjust its size with the changing temperatures, and it will end up cracking due to its internalized pressure.
4. It was too cold when your concrete was poured
Just like the amount of water affects concrete’s hydration process, so does cold weather. When the temperature drops too low, concrete won’t be able to cure correctly. In these situations, the pour will either need to be postponed, or the subsurface will need to be warmed before pouring.
5. Your concrete is too thin
Concrete that’s too thin is extremely susceptible to cracking. The proper thickness of your concrete will vary based on its purpose. For example, a driveway that’s meant to support vehicles needs to be thicker than a sidewalk that is not.
Improper concrete thickness is one of the top reasons why DIY concrete projects fail. When taking on a massive project like this on your own, it’s easy to miscalculate the weight your concrete will be expected to bear and the subsequent thickness necessary. Unfortunately, this will result in severe premature cracking.
At Port Aggregates, our contractors have 40 years’ worth of experience built into their pours. Our beautiful concrete has been trusted for decades with good reason. When you hire our professionals, you can say goodbye to premature cracking and rest assured that your slab has been installed properly. Contact us today to request a quote!
Jan 2, How To Form and Pour A Concrete Slab – The #1 Resource on The Web
Learn how to form and pour a concrete slab. My step by step guide will teach you everything you need to know from forming to pouring to finishing.
The tools and materials you need to form and pour a concrete slab
- Ready-mix concrete (yardage will depend on size of slab)
- Wire mesh or Rebar reinforcement
- Anchor bolts
If your concrete slab is smaller, you can use bags of concrete instead or ready-mix.
Find out how many bags of concrete it takes to make a yard. I did all the calculations for you.
On my Tools Page you can find all the tools required to form and pour concrete.
I also have a concrete yardage calculator that shows you how many yards you need and how many bags of concrete you’ll need.
step by step: how to pour a concrete pad
These are the basic steps I use form and pour concrete slabs.
I also have a step by step video course with multiple training videos that teaches you all you need to know about how to install your own concrete slab: My Concrete Slab Course
step 1. prepare the area for concrete
Under your concrete slab there should be a compacted base of gravel. You can also use road base, crushed rock, or sand, as long as it’s well compacted.
You’ll probably have to remove some of the existing soil like in the picture above. We removed about 12 inches of the existing sod & loam and replaced it with 8″ of 3/4″ crushed gravel.
This area had a slight slope, so we had to remove more soil on one side than the other to get a level pad.
After installing the gravel, we raked it level (using my laser level) and ran a vibratory compactor over it to settle it and pack it very hard.
NOTE: You may need a permit to install a slab. Contact your local building code officer to see what they require for building a slab. You may also have to keep it a certain distance away from your property line.
PRO TIP: If you have a lot of soil to remove, you can rent a skid steer to do it much easier or hire an excavation contractor to prep the area for you.
BE SAFE: Some states require you to call Dig Safe (811) to check for any underground wires or utilities before you start digging. It’s state law. It’s a free service so be safe.
step 2. building the forms for a concrete slab
Lay out your forms. It’s better to have forms that are a little longer than the size of your slab.
Set up your leveling device. I’m using a self-leveling laser. You can use a 4′ level or a transit level. All 3 will get the job done.
My slab size is 14′ x 10′.
Starting on one side, measure the length of your slab and mark it on the form. (my mark was at 14′ on this side)
Mark each side the same way. (my next side was 10′)
You’ll use these marks to screw the forms together in the next step.
step 3. screw the forms together and square the slab
Use your marks to screw the forms together.
Align the inside of the form with your pencil mark.
You can use a drill driver and deck screws like we do or you can use a hammer and nails to fasten the forms together.
I personally like to use screws, there’s less movement to the forms because you’re not banging on them with a hammer.
Screws are also easier to take out when you go to remove the forms.
After the forms are fastened together it’s time to square the slab.
I measure diagonally each way and slide the forms a little one way or the other until I get the exact same measurement for both diagonal measurements.
It usually takes a few times going back and forth checking until you get it exact.
When you have the slab square, you’re ready to stake it in place.
step 4. stake the forms and set them to grade
Use wooden stakes (or metal pins like me) to secure the forms in place.
I like to stake each corner, about 8 – 12 inches from the corner, on both sides.
After my 4 corners are staked, I hammer in a stake about every 4′ on all the sides.
To make sure the forms are straight, I use a string line on top of the forms to check them as I stake the forms in place.
After pounding in all the stakes, I use my laser level to set all the forms perfectly level.
The receiver on my grade stick has a solid sounding “beep” when the form is at the pre-determined height. (5″ above my dirt grade)
Screw the form to the stake when it’s at the level you want.
Repeat for all 4 corners, then do the rest of the stakes and your forms will be level.
step 5. add the reinforcement
It’s time to install the reinforcement, I’m using wire mesh for this slab. The best way to cut wire mesh is with a pair of bolt cutters.
I buy the flat sheets of mesh, they measure 5′ x 10′. Some local lumber companies stock the flat wire. If not, they usually have the rolls of mesh (5′ x 150′ get these at HD and Lowe’s also)
Another good reinforcement to use for concrete slabs is 3/8 (#3) rebar or 1/2″ (#4) rebar. Rebar comes in 10′ or 20′ lengths and you cut it to the length you need.
If you use rebar and have to cut it, you can rent a rebar cutter at HD or a local tool rental store. Or you can buy a good rebar cutter / bender on Amazon.
After the wire mesh goes in, you’re ready to pour the concrete. If you’re using ready-mix concrete, choose a nice, dry day and call your local concrete supplier to schedule the pour.
Most likely you’ll have to give them about a weeks notice so don’t wait till the last minute to call.
If you’re using bags of concrete, use my concrete yardage calculator to see how many bags you’ll need.
step 6. how to pour the concrete
When the concrete arrives, ask the mixer driver for for a 6 inch slump. Slump is how dry or wet the concrete is mixed. A 6 slump is a good workable mix to pour with.
Start pulling the concrete around and filling in the forms. Pull up the wire mesh or rebar into the concrete as you pour. (or you can put small pieces of brick under it to hold it up)
Pour out as much as you’re comfortable with (maybe about half on something like this if you’re a beginner) before you screed it level.
If you’re mixing bagged concrete for your slab, it’s the same process. Just slower.
Mix enough concrete until you have enough of the forms filled to screed the concrete.
I like to use ready mix myself. It’s just faster and more convenient for me since we do multiple pours like this in a day. Either way is good. Ready mix will be more expensive on a smaller slab vs bag mix.
See how many bags of concrete come on a pallet and what they cost.
Screed the concrete level using a magnesium screed board like us or a straight 2 x 4. Use short pulling strokes and tip the screed slightly on the back edge.
Put pressure down on the screed as you pull it to make sure it rides on top of the forms. Let your helpers push concrete (to fill low spots) and pull concrete back (if it’s high) as you screed.
The concrete rakes (kumalongs) we use make moving the concrete around a lot easier.
After you screed the concrete, use a bull float to smooth the surface.
A bull float pushes down the aggregate on the surface and brings up some cement paste (creme).
Tip up the front edge and slowly push it from one side to the other. When you reach the opposite side, stop, tip up the back edge and slowly pull it back to you.
It might take multiple passes in the same spot to get it nice and smooth (usually 1 – 3 times).
After you’ve done the entire slab this way, you’re almost done with the pour.
step 7. installing anchor bolts in concrete (optional)
If you’re using anchor bolts, now is the time to put them in the concrete. Measure out where you want them and make a mark in the concrete.
Push the anchor bolt into the concrete to the desired level you want. I usually leave about 2 inches sticking up out of the concrete.
PRO TIP: Once you push it into the concrete a few inches, slightly jiggle it up and down to consolidate the concrete around the bolt as you set it to your finished level.
Now you’re done pouring the concrete.
Learn how to pour and finish concrete in my private training academy The Concrete Underground.
watch and i’ll show you how to pour a concrete slab
If you’re thinking of doing a broom finish, smooth trowel finish, or a textured finish on the concrete, I can show you how to finish the concrete HERE.
Another very important step is to “cure” the concrete. Click on CONCRETE SEALER to learn about this.
You can remove the forms the next day.
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Jan 2, How To Mix Concrete – The Most In Depth Guide On The Internet
Learn how to mix concrete by hand using a wheelbarrow, concrete mixing machine, bucket or a tub. Detailed instructions and a video shows you how mix concrete.
diy how to mix concrete at home
I’ll teach you my method of how to mix concrete: to get the proper firmness, texture, and strength.
tools you need for mixing concrete
Warning: Always wear safety gloves, safety goggles, and a dust mask when working with concrete.
Materials used for mixing concrete
- Concrete bag mix
- Portland cement – sand – gravel – optional if you’re mixing concrete from scratch.
Video: shows you how mix concrete by hand using quikrete
Owner Mike Day of Day’s Concrete Floors shows you how to properly mix concrete to repair a broken section of pool deck.
step by step: how to mix concrete
step 1. set up your mixing area
If you’re mixing multiple bags of concrete it’s a lot easier and faster if you have your mixing area organized.
If you’re only mixing one or two bags (like in the video) then all you need is your bag(s) of concrete, wheelbarrow, water, hoe.
On bigger projects it’s important to get all your bags in order and have plenty of water on hand. Having 2 people mixing and one spreading and smoothing the concrete makes the work go a lot faster.
step 2. measure the proper amount of water
I like to pre-measure the amount of water needed per bag and add it to the wheelbarrow first.
I feel putting the water in first, then adding the dry concrete ingredients, makes the mixing process easier and faster.
The water table below shows you how much water to use per bag.
Depending on the bag size, there’s a range of water you can add for mixing.
For and 80 lb. bag of Quikrete, you can use 6 pints to 9 pints (3 – 4.5 quarts) of water to mix each bag.
I like to add the minimum amount to the wheelbarrow first, then add more water up to the maximum if I feel it needs it to get a good workable mixture.
If you use more water than the maximum amount recommended, then your concrete mix will not be as strong as advertised on the bag.
step 3. add the bag mix to your wheelbarrow (tub, bucket, or mixer)
Add about 1/2 to 2/3’s of the bag mix into the wheelbarrow. Mix that amount with the water until all the dry ingredients are saturated.
Add the rest of the bag and keep mixing. Use this same technique if you’re mixing in a bucket or a tub.
If you’re mixing in an electric concrete mixer machine, then you can add the whole bag at one time.
step 4. mix the concrete to a workable consistency
Add the remainder of the bag and continue to mix the concrete. Move the hoe back and forth completely mixing the dry concrete mix with the water.
Add more water (up to the maximum amount) until you get your desired consistency.
Your concrete mix should look similar to the concrete below when it’s mixed properly.
It took me about 3 minutes to measure and add the water, then mix the 1 bag of concrete to this texture.
Be careful not to get the mix too wet or it’s more likely to crack and won’t be as strong.
If you feel the concrete mix is too runny (wet) just add some more concrete mix from another bag until you feel it looks like the picture below.
PRO TIP: Always have an extra bag of concrete on hand just in case your project takes more concrete than you expected it to.
step 5. place the mixed concrete where you need it
A good thing about mixing concrete in a wheelbarrow is you can wheel the concrete right where you need it.
Dump the concrete out of the wheelbarrow or shovel it out, like I’m doing on this job.
One way you can tell if you mixed the concrete properly is if you can move the concrete in place using a mag float and float it smooth going back and forth over it a few times.
step 6. clean the concrete off your tools as soon as possible
Clean the wheelbarrow, hoe, and shovel with water as soon as you finish. The concrete mix will dry on them very quickly.
PRO TIP: If the concrete mixture dries on your tools, use a margin trowel to scrape it off first, then rinse and scrub with water.
If you have a water hose and a stiff bristle brush nearby, rinse off the bulk of the concrete first, scrub the remaining cement paste, and rinse clean.
Do this in an area you don’t have to clean up the washed off concrete afterwards. Never wash off concrete onto your driveway or garage floor, it could permanently stain it.
how to mix concrete in a bucket
18 gallon bucket in the picture. (best place to buy this is on Amazon)When I mix concrete in a bucket, I like to have an over-sized bucket like this
I also like to use a mixing drill to mix my bags of concrete. A mixing drill like this one makes the mixing process very fast and is really the only way to mix concrete using a bucket.
The mixing process is the same as above: Add your water first, add 1/2 bag and mix, add remainder of bag and mix, add water up to the max. amount if needed.
how to mix concrete in a mixer
If you’re using an electric concrete mixer machine it’ll speed up the mixing process because you can mix 2 – 3 bags of concrete at one time. (depending on the size of your mixer)
The Mixing Process Goes Like This:
- Pre-measure your water and add it to the mixer first.
- Turn on the mixer before you add the first bag of concrete
- Add the first bag and let it mix for a minute (2 minutes if you’re only mixing one bag)
- Add the second bag and continue to mix for 2 – 3 minutes
- If the mix looks too dry add a little water as it’s mixing (only add water up to the max. amount)
When the concrete looks mixed to the right consistency, dump it out of the mixer and into a wheelbarrow.
You can buy a really good portable electric concrete mixer machine on Amazon for $200 to $300 dollars.
what is the ratio for mixing concrete?
How do you mix your own concrete?
If you’re using Portland cement, sand, and gravel to make your own concrete, you can use the 1-2-3 mixing ratio.
This concrete mixing ratio is done by mixing 1 shovel of cement with 2 shovels of sand and 3 shovels of gravel. (or some other accurate way to measure your ingredients)
Add the dry ingredients into a wheelbarrow or the electric mixer before you start adding water.
When you add more dry material to the mix, keep the 1:2:3 ratio of cement to sand to gravel the same for consistency and strength.
The amount of water you add to the mix will be based on how the mix feels while you’re mixing it. Use the wheelbarrow method above to judge how the final mix should look.
For more examples of proper concrete mix proportions check out my concrete mixing ratios for mixing concrete from cement, sand, gravel, and water.
Learn how many bags of concrete it takes to make a cubic yard.
what’s the best type of concrete mix to use for:
1. Best concrete mix for a driveway is:
2. Best concrete mix for concrete countertops
3. Best concrete mix for fence posts
4. Best concrete mix for a patio
5. Best concrete mix for sidewalks
6. Best concrete mix for footings
7. Best concrete mix for slabs
Quikrete 5000 or Quikrete Crack Resistant Mix
Quikrete 5000 (add 2 cups cement)
Quikrete Regular or Fast Setting Mix
Quikrete Crack Resistant Mix
Quikrete Crack Resistant Mix
Quikrete Regular Mix
Quikrete 5000, Crack Resistant, or Regular
This list is my opinion only based off my experience using Quikrete Concrete mixes for my jobs.
Sometimes I’ll mix 1/2 a bag of Quikrete 5000 with one of the other bag mixes because it has a higher ratio of cement in it. This makes the overall mixture a little easier to finish.
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