How To Add A Concrete Slab To An Existing Slab

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No thing how strong a slab of concrete seems, information technology will wear out over fourth dimension. Imperfections form when concrete hardens or sinks into the basis. Adding fresh concrete is a common mode to level out old slabs and patch damage. If you plan on pouring a lot of concrete, build a forest and mesh barrier get-go to ensure your new slab is potent. Stop the work past priming the surface and pouring a mix over it, giving your concrete foundation a fresh, new coat.

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Sweep clay and debris off the concrete. The old concrete needs to be completely clean or else anything you pour over it won't bond to it. The start society of business is to remove gravel, leaves, sand, and dirt. Go as much of it off the physical as you lot can. Push the droppings off the concrete surface or collect it in a bag to throw away.
- Utilise a strong-bristled broom to knock as much debris out of cracks equally possible.
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Use a pressure level washer to clean out the remaining debris. Y'all won't get all of the subconscious debris at first, so you will demand to requite the physical a more thorough cleaning. Use a fan tip on the pressure washer with a PSI of about 3,000 and hold information technology about 6 in (15 cm) above the physical. Sweep the nozzle slowly over the concrete, making sure you striking every surface area.^[1]
- If you don't ain a pressure washer, check dwelling comeback stores in your area. You may be able to rent a washer from them.
- You tin add a liquid detergent or degreaser to the h2o to ensure y'all get all stubborn spots, including those from mildew and algae.
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Scrub difficult spots with chemical products. Purchase a commercial cleaner formulated for use on concrete. Pour it onto tough stains you can't otherwise remove, then piece of work the cleaner in with a stiff-bristled scrub brush. When you're washed, rinse the area with a hose. This can assist remove stains from oil and sap, which are very difficult to get rid of once they set in.^[two]
- Most home comeback stores sell these cleaners. Look for ones that are effective against oil.
- Another option is to utilize trisodium phosphate (TSP). Follow the manufacturer'due south instructions to mix the TSP pulverisation with water into a paste. Try mixing almost one fl oz (30 mL) per .125 fl oz (3.7 mL) of water.
- If commercial cleaners and TSP don't work, you may need to get hydrochloric acid. The acrid is strong, so dilute it first, mixing 1 office acid in 3 parts water. Vesture protective gear, including a respirator mask.
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Saturate the existing surface with h2o. Correct before you become to work mixing and pouring new physical, spray the onetime surface with a hose. Get the old concrete slab completely wet, making sure any cleaning chemicals you used get rinsed off in the process. Keep spraying it until the moisture runs off the sides instead of beingness captivated. Dry out up whatsoever water pooled over the concrete before standing.^[3]
- Concrete is porous, so it tin can absorb liquid. If it absorbs moisture from the new concrete, you will get a dry out top slab that didn't bail well with the onetime concrete.

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Mensurate the infinite yous wish to fill up with physical. Taking measurements is necessary if you plan on filling a large space. Apply measuring tape to effigy out the length and width your new slab needs to exist. Write your measurements downwardly so you know what supplies to go to pour a smooth, consequent slab later.^[4]
- If you are only going to pour a thin slab or patch up existing physical, make a general estimate of the surface area's size and how much physical you need for it. You can usually mix and cascade a small batch without setting up a perimeter.
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Marking the pinnacle y'all want the concrete to reach. Slab thickness is important and depends on your plans for your home. If y'all want the slab to accomplish upwardly to your doorstep, for instance, yous need to measure from the existing slab to the bottom of the doorstep. Use chalk to mark the height the slab should accomplish.^[5]
- Take your time measuring. The ground beneath the existing physical may not be level, so mensurate on all sides.
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Utilise the measurements to calculate how much concrete you volition need. Measure out the length, width, and depth of the area you wish to make full. Multiply these numbers together to get a general estimate of the amount of concrete you lot need. Add an extra 10% onto your total estimate to business relationship for spillage.^[6]
- The calculation can be an imperfect gauge, especially for areas that aren't perfect squares or rectangles. Always get more concrete than you demand to ensure you accept enough.
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Install braces around where you will pour the physical. Using your measurements, cut some boards to help hold the liquid physical in identify. You can get forest boards that will reach the depth marks y'all made in chalk earlier. Ready the braces up around the perimeter of your erstwhile concrete slab.^[vii]
- These braces serve every bit a mold. When you cascade the physical into it, you no longer accept to worry almost it spilling off the old slab and making a mess. It gives you lot a meliorate hazard at creating a stiff, level slab.
- You can cut the wood yourself with a round saw. Article of clothing protective gear, including a dust mask and eye protection, if you lot exercise this. Alternatively, become the wood cut at a dwelling house comeback store.
5
Prop up the braces with wooden stakes. Dig out the soil around the braces, then stand up the stakes in them. You can employ 2 in × 4 in (5.1 cm × ten.2 cm) forest for most projects. Identify the stakes approximately every 12 in (30 cm), then drill them to the braces with 3 in (7.six cm) forest screws.^[viii]
- Brand sure the stakes are planted firmly in the dirt so the braces don't fall every bit you work.
- If your slab won't be very high, you may be able to lay the wood braces on the basis and spiral them together without using stakes.
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Test the evenness of the boards by laying a chimera level on top of them. The braces should be even before yous begin pouring the concrete. Set up the level on top of each lath ane at a time. Spotter the liquid in the center of the level to make sure the bubble stays in the center. If the bubble moves to 1 side, that side is lower than the other side and needs to exist adapted.
- Another way to examination the boards is to run string backside them. The string should be the aforementioned altitude from the board at all times. If one finish is closer to the string than another finish, the brace isn't straight and should be adjusted.
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Lay wire mesh between the braces. Wire mesh provides actress strength to thick concrete slabs. It can also prevent cracking and settling.^[ix] You lot can purchase a gyre of welded wire mesh at a home improvement shop, and so simply spread it out in a single layer over the old concrete. Press it downwards so it is flat and level before you add the new concrete.^[ten]
- The new concrete you pour binds to the mesh. Although it makes the concrete stronger, it won't foreclose it from cracking.
- Another selection is to go rebar and lay it out in a filigree pattern similar to the mesh. Place rebar chairs underneath the rebar to concur them in identify.

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Purchase physical with a fine aggregate for minor repairs. Aggregates are additives that make upwardly about of a concrete mix. Fine aggregates are typically sand or crushed stone. This type of mix is best for pouring a very thin coat of concrete, such as when topping off or leveling out an existing slab.^[11]
- The aggregate in a physical mix is listed on the label. You can also meet information technology when you open up the bag. Fine physical looks polish or has very small stones.
- Physical is mostly a mixture of cement, sand, gravel, and h2o.^[12]
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Choose a coarse aggregate concrete when pouring thicker slabs. Coarse concrete has gravel or larger stones as an condiment. This blazon of concrete is stronger but less dense, then you lot can safely pour a large slab onto existing physical. It is a good selection if you lot need to fill a large area with something thick that will concluding a long time.^[13]
- Larger aggregates cannot be used to make thin coats, then make sure you get the type of concrete mix all-time suited for your projection.
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Habiliment safety equipment to protect yourself while mixing concrete. Concrete tin can splash up every bit yous mix and pour it, and that isn't anything you want in your eyes or on your pare. Wear protective goggles or safety glasses, a safety mask with ventilation, and long jeans.^[xiv] Likewise consider wearing work gloves to protect your skin from concrete splatter.^[15]
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Mix up a scratch coat consisting of concrete and water. The scratch coat is a layer of wet concrete mixed to a liquid consistency similar to paint. You will need a big plastic mixing bucket. Combine the physical in a ratio of virtually 1 part water to 7 parts physical, then mix it with a wooden mixing stick or electric paddle mixer until it reaches a uniform liquid consistency.^[16]
- Utilise the same physical yous program on using for the final layer. Have the area estimate available for the space yous wish to cover, then follow the manufacturer's instructions for an guess on how much to mix.
- Less is ordinarily more with the scratch coat. Think that is liquid, so it volition spread out over the existing slab.
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Spread the liquid mix over the existing concrete. Dump it all out onto the existing concrete, then begin spreading it effectually using a paw trowel or paver. Press downwardly hard on the physical to work the liquid mix into any cracks every bit you smooth out the scratch glaze layer. The layer of moisture concrete doesn't need to exist thick. A layer virtually ^one⁄₈ in (0.32 cm) thick, about the thickness of a credit card, is enough.^[17]
- You can besides use a rag or a gloved hand to spread the scratch coat. This can work well when priming pocket-sized areas.
- The moisture mix is there to aid the new physical bond to the erstwhile physical, so you don't demand a lot of it.

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Mix a batch of concrete according to the manufacturer's instructions. Read the concrete packaging to detect out how to mix information technology. The ratio is ordinarily about 1 part water to 3 parts concrete. Add the h2o and concrete to a mixing container, then use a wooden stirrer or electrical paddle mixer to combine them into a thick liquid.^[18]
- The mixing ratio may vary depending on what product you own, then check the manufacturer's recommendations to become the physical to the proper consistency.
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Add a bonding adhesive if you are using regular concrete. If yous got a bag of concrete and mixed information technology normally, you should use a concrete bonding adhesive to ensure the layers of concrete stick to one some other. The agglutinative is a liquid that comes in a plastic jug and you pour information technology directly into the concrete mixture. Check the manufacturer's instructions to add the product at the recommended ratio.
- You can get the additive online or at near home improvement stores.
- If yous are using a physical patching product, you most likely do not need the agglutinative. It is frequently included as part of the patching mix. Bank check the production's characterization to brand certain.
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Use the new concrete over the primer. Pour concrete onto the existing slab until it is around where you want the final level to be. Make sure y'all have enough concrete to fill up the entire area to the depth you desire. Add all of the concrete right away so none of the mixture has a chance to dry.^[19]
- Y'all practice not need to await for the scratch coat layer to dry completely. It will have dried enough while you mixed this batch of concrete.
- You can effort to fill up in a slab with multiple pours of concrete, but this usually isn't advisable. You lot won't get a single, uniform slab, which tin can atomic number 82 to bonding issues in the layers.
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Use a trowel to smooth out the physical. The concrete needs to be leveled out before information technology solidifies. You lot can use a trowel to shine over small areas or a screed board and bull float for large areas. Piece of work back and forth, passing over a petty more of the rough concrete each time. Make multiple passes over the entire surface to ensure it is shine.^[20]
- On hot days, the concrete can dry out very chop-chop, so don't waste whatsoever fourth dimension subsequently pouring it.
- Brand sure there are no marks left in the concrete when yous are done smoothing it.
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Protect your work by spraying the concrete with a curing compound. A good curing compound is the best mode to preserve moisture concrete. Mix the curing compound according to the manufacturer's instructions, add it to a garden sprayer, then spray information technology directly onto the concrete. This should exist done right later on y'all finish pouring the physical. Concrete takes virtually 7 days to fully cure.^[21]
- Some other mode to do this is to spray the concrete thoroughly with water from a garden hose, then lay a polyethylene canvas or concrete curing insulation coating over it. Make sure the plastic is apartment against the concrete or else it will cure unevenly, causing discolorations. Remove the sheet to moisten the physical again every day for a week.^[22]
- The longer the concrete is allowed to cure, the stronger it will exist. Make sure no i is able to step on the concrete until it has finished curing.

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Question

How practise I clean up my tools after pouring concrete?

Gerber Ortiz-Vega is a Masonry Specialist and the Founder of GO Masonry LLC, a masonry company based in Northern Virginia. Gerber specializes in providing brick and rock laying services, concrete installations, and masonry repairs. Gerber has over iv years of experience running GO Masonry and over ten years of full general masonry work feel. He earned a BA in Marketing from the University of Mary Washington in 2017.

Masonry Specialist & Founder, GO Masonry LLC

Skillful Answer

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 handbag so dispose of information technology. Make certain you make clean everything immediately when you're washed with it so the concrete doesn't dry.
Question

What PPE should exist worn when pouring concrete?

Gerber Ortiz-Vega is a Masonry Specialist and the Founder of GO Masonry LLC, a masonry company based in Northern Virginia. Gerber specializes in providing brick and stone laying services, concrete installations, and masonry repairs. Gerber has over 4 years of experience running Go Masonry and over x years of general masonry work experience. He earned a BA in Marketing from the University of Mary Washington in 2017.

Masonry Specialist & Founder, GO Masonry LLC

Expert Answer

Wearable prophylactic goggles, a protective mask, and long jeans when mixing and pouring concrete. The small particles tin can harm you lot if you don't protect your eyes, nose, and oral fissure.
Question

Can a concrete slab be poured over an existing half dozen-inch, heavily croaky concrete porch?

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

When setting fence posts, can more concrete exist added over dry physical in the hole?

It depends on how much you are calculation to the top of information technology. The cement acts like an anchor for the wood post, so that it is not easily pulled upward. You may want to put screws in the forest posts halfway in, then they protrude an inch or 2. This would ballast the new cascade to the wood mail and non just to the old cement.
Question

I demand to level slab of concrete for a shed base of operations. Can I skim the concrete with cement to level the concrete

You could, merely it would be better to find out why your slab is non level and correct the underlying problem, lest your shed tilt in the future. It may exist better to "slabjack" the slab level (inject a product under the slab that will float it level) than to add together a sparse layer to the top that is prone to adhesion issues.
Question

What is the maximum thickness I can add together on top of an existing pad?

The objective of proper preparation is for the existing concrete non to exist a "base," but to "combine" or "exist part of" the new. However, several variables may prevent 100% success, fifty-fifty 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, apply an application over 1" (I also follow these steps and add scoring earlier footstep #2). With that in mind, this method is intended for corrective purposes But. I am a building contractor with 25+ years.
Question

How can I remove/excavate existing concrete?

Yous tin can break it with a heavy sledge hammer, or drill a line of holes in it and split it, utilise a saw and cutting it into squares, etc.
Question

If my building has been rezoned and I need a 6-8 inch slab, is information technology possible to add a layer of concrete on top of the existing 4 inch slab or do I need to pour an entirely new slab for it to exist a permanent ready?

I have washed this with an existing patio. The key to success was: 1) cleaning the existing surface to ensure skillful adhesion, 2) installing adequate steel reinforcement to the slab, 3) wetting the existing concrete surface earlier pouring, and 4) wetting the new concrete periodically later it sets then the concrete cures to the highest strength possible.
Question

I poured a concrete wall and it's not high plenty, how practise I get in higher?

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

How do I know if I should go with an extension or a brand new porch?

Brett Gilbert

Top Answerer

At that place 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 piece of work with, you may need to redo it before you can expand it.

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You can always cut out old concrete and replace it. Apply a chisel or jackhammer to remove damaged portions.
If your concrete is badly cracked, it may not be salvageable. Consult a professional to make up one's mind what needs to be done.
Oil and sap must exist removed before new physical can exist poured. If you tin't remove information technology, chisel it out or comprehend it with a sealant.

Things You lot'll Need

Physical mix or physical patching product
Physical bonding condiment
Concrete cleaning chemical product
Wheelbarrow or bucket for mixing
Mixing stick or paddle
Trowel
Curing compound
Hose
Potent scrub brush
Center protection
Long clothing
Wood for large projects
Electrical drill
Wood stakes
Chalk
Wire mesh or rebar
Level

About This Article

Commodity Summary 10

To lay new concrete, sweep and make clean the old physical, and saturate the old concrete with water. Then, build a perimeter, or a wood brace, that is the same height equally y'all want the physical to be. Make sure the braces are level, and lay downward a barrier of wire mesh over the existing concrete within of the barrier. Pour and spread a thin later of scratch coat, and then add a bond layer on top of the coat. Mix and cascade the concrete according to the package instructions, and spread the physical with a trowel before spraying information technology with a curing compound. For tips on which type of physical to utilise and how to build the perimeter, curl down!

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