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What happens when you pour concrete over an existing slab?

When pouring new concrete over an existing slab, it is important to prepare the surface properly and apply adequate amounts of concrete to create a strong, level surface. The existing surface must be cleaned and any loose material should be broken up and removed.

The surface should then be thoroughly wetted, and the existing slab should be inspected for cracks, holes, and other potential weak spots. Any cracks should be filled in with a patching compound, and any holes should be filled with a material such as grout or mortar.

Once the existing surface has been prepared, it should be marked to ensure that the new concrete is applied in the desired thickness and pattern. Next, a bonding agent should be applied to the existing slab to create a strong bond between the new and old concrete layers.

This should be followed by a layer of damp proofing material to ensure that the new concrete doesn’t become damaged by moisture.

Once the preparing steps have been completed, the new concrete can be applied. Ideally, the concrete should be poured in evenly-sized batches and tamped with a hand or mechanical tamper so that it fully fills in any dips or crevices in the substrate.

Once the top layer of concrete has been poured, it should be floated and finished with a concrete trowel to create a level, flat surface. Finally, the surface should be allowed to cure for at least 24 hours before it is exposed to foot traffic.

How do you add concrete to an existing slab?

Adding concrete to an existing slab can be done in several ways, depending on the circumstances and the result desired. If the existing slab is square and level, the best method is to attach metal reinforcing bars, also known as rebar, to the slab using rebar anchors.

This will help strengthen the concrete and provide support for the new concrete. The existing slab should then be cleaned of any dirt and debris using a pressure washer or other cleaning agent. Finally, the new concrete should be mixed and poured onto the existing slab.

If the slab has holes or cracks, repair them before adding new concrete. Start by chiseling out the damaged concrete and removing any loose pieces. The area should be thoroughly cleaned, including the adjacent surfaces.

An appropriate patch material should be used to fill the holes and smooth the surface. Once cured and dried, the surface should be cleaned. Finally, the new concrete should be mixed and poured onto the slab.

If one wishes to raise the slab, the concrete must be at least four inches thick. Remove any loose concrete and debris from the slab. Install rebar at the desired height and secure it with rebar anchors.

To ensure a good bond between the new topping and the existing concrete, the area should then be lightly wet with a garden hose. The new concrete should be mixed and poured, making sure to keep it an even thickness.

Any cracks or joints in the existing concrete should be filled using an appropriate sealant prior to applying the new topping. After the new topping has been poured, it should be troweled and left to dry, allowing the new and old concrete to bond together.

In some cases, it might be necessary to use an additional bonding agent to create an even stronger bond. Once the new topping has dried and cured, it should be sealed to protect it from water damage.

Will concrete bond to concrete?

Yes, concrete can bond to concrete. This type of connection is called a “cold joint”. A cold joint occurs when two pieces of concrete are joined together without the use of mortar or grout in between them.

Rather, the two pieces must be sealed together with a bonding agent. This bonding agent acts as an adhesive, creating a strong and secure connection between the two pieces of concrete. In order for this bond to be strong and successful, the two pieces of concrete must be “cold”, or free of any harsh chemicals.

Additionally, the surfaces of the concrete should be clean and free of any dust, dirt, or debris before the bonding takes place. Properly installing the bonding agent and allowing it to fully cure and set is also essential to ensure a successful bond between the two pieces of concrete.

With the right preparation and installation, concrete can be very successfully bonded to other surfaces.

How do you pour concrete next to concrete?

When pouring concrete next to an existing concrete surface, the first step is to prepare the area. If the existing concrete is wet or damp, the new concrete needs to be covered with plastic sheeting to prevent evaporation.

The surface should also be cleaned and the joint should be caulked. It is important to place the concrete in such a way that the two parallel surfaces are continuous.

Once the surface has been geared up, the next step is to cut a control joint, or expansion joint, between the surfaces. This will give the concrete room to expand without causing damage. A soft material should be used to create the expansion joint such as foam, thick wood, or plastic.

The depth of the joint should be one-fourth of the slab’s thickness.

When it comes time to mix and pour the concrete, the two parallel surfaces need to be sloped away from each other at a five-degree angle so that water and debris can drain away from the joint. This is the most essential step for ensuring a smooth transition for the two concrete surfaces.

The concrete needs to be mixed to the correct consistency and vibration should be applied to help settle the concrete. It should then be screeded and tamped as needed to make sure that there is no air gap or void between the existing and new concrete surfaces.

The edges of the surfaces should be feathered and the concrete should be given time to cure. Afterwards, the expansion joint should be filled with flexible filler and the area should be sealed.

How do I join old slab to new slab?

Joining an old slab to a new slab can be a tricky yet important part of a larger home renovation project. Generally, the process begins with checking the condition of the existing slab and preparing the grade and drainage for the new slab.

When attaching the two slabs, ensure that you cover the tops of the two slabs with a bonding agent that is applied with a trowel. Once the bonding agent has had its time to set, use a grinder or saw to cut the old slab in a predetermined shape to allow the two slabs to fit together.

Make sure to use a slab saw or grinder to minimize the amount of dust that is created. After the cut is completed, use a wet saw to smooth the edges of the new slab. Once the two pieces are fit together, apply self-leveling compound to fill any remaining gaps and joints, and then smooth it down.

Lastly, use a sealant to seal the seams between the two slabs and protect the compound from settling and cracking. Following these steps should ensure that you are able to join the old slab to the new slab safely and effectively.

How do you join two concrete slabs together?

Joining two concrete slabs together is a process that requires some skill and knowledge of the necessary steps for a successful outcome. Some of the general steps to join two concrete slabs together include:

1. Preparing the Area: The surface of the slab that is being joined should be prepared to accept the concrete by removing any loose material and ensuring the area is dry and free of dust and debris.

2. Applying Concrete Adhesive: Apply the concrete adhesive evenly to both the slabs being joined ensuring equal coverage of the adhesive on the areas that will be coming into contact.

3. Securing the Slabs: Place the slabs together and use a clamp or a machined vice to secure the two slabs until the adhesive has adequately dried.

4. Closing the Joint: After the adhesive has dried, fill in the joint between the two slabs with cement or mortar. Use a trowel or taping knife to ensure the joint area is properly filled and smothered.

Allow the mortar to dry before adding additional layers if necessary and ensure a smooth finish.

5. Sealing and Finishing: The joint between the two slabs should be sealed using a concrete sealer to ensure the joint is protected from the elements and rain water. Finally, apply a finishing coat and finish the surface to the desired level.

Can you pour self-leveling concrete over existing concrete?

Yes, self-leveling concrete can be applied over existing concrete. The existing concrete surface must be relatively sound, clean, and level. The existing surface should also be slightly etched or scarified and saturated with water to ensure a proper bond between the existing slab and the topping.

In addition, products such as Primer 3 or Primer 5 from Level One should be used prior to the topping to ensure proper adhesion. Be sure to also check with the manufacturer of the self-leveling concrete to ensure that their product is compatible with the existing slab.

Once the existing surface is properly primed and prepped, the self-leveling concrete can be applied according to the product’s instructions. The topping should be troweled after installation to ensure good surface finish.

How can we increase the height of concrete?

The height of concrete can be increased by using a combination of approaches which involve both materials and construction techniques.


Using the correct type of concrete can be beneficial in increasing the height of concrete. Using lightweight concrete mix in areas where the load on the structure is not very large can enable the height to be increased without worrying about excess weight.

In cases where load is a factor, continuous reinforcement such as Macro Synthetic Fibres (MSF) might be used to help support higher heights.

Construction Techniques

Certain construction methods can be employed to prevent settling, cracking and other deformations which might arise due to tall concrete structures. Limiting the amount of pouring and the sizes of pours can help the concrete set correctly and evenly, avoiding deformations.

Additionally, post-tension cables, steel trusses and other components can be used to add more strength and stability to the structure, enabling taller heights.

Additionally, some waterproofing measures such as pre-treated base, membranes and coatings can be used on the concrete surface to help improve the overall structure and further increase the height achievable with concrete.

How much does it cost to extend concrete patio?

The cost to extend a concrete patio depends on a few factors including the size of the extension, the complexity of the project, and any additional steps required. The cost also varies depending on if you are hiring a professional contractor to do the work, or if you are doing it yourself.

On average, a professionally installed concrete patio extension can cost anywhere from $4 to $10 per square foot. This includes the cost of the concrete and the labor required for the installation. A complex project that includes other elements such as custom shapes, special finishes, or staining can cost more.

DIYers can often save money on the project, but will also need to purchase tools and supplies in order to complete the patio extension. Depending on the size of the extension, the cost of materials could range from $1 to $3 per square foot.

Overall, the cost to extend a concrete patio can vary greatly and will depend on the scope of the project. A reputable contractor should be able to provide an estimate and advice on the best approach to the project.

What concrete will stick to existing concrete?

Yes, concrete will stick to existing concrete as long as the surface is clean, dry, and free of dirt, debris, and oil. To ensure a strong bond between the existing and new slabs, it is best to use a bonding agent, such as a concrete adhesive or sealer.

Bonding agents can be applied in a variety of ways, including brushing, rolling, troweling, or spraying it onto the surface. Once the bonding agent is applied, the new concrete needs to be mixed with the bonding agent before being poured onto the existing concrete slab.

The concrete should then be spread evenly and carefully over the entire area. After it has been leveled, a trowel should then be used to smooth out any ridges and pock marks.

Once the new concrete is set and dry, it should be sealed with a protective sealant to protect it against wear and tear. This will also help to prevent moisture from getting into the material, prolonging its life and appearance.

The sealant should also be reapplied every few years to keep the new concrete firmly attached to the existing concrete surface.

Can you put a thin layer of concrete over concrete?

Yes, it is possible to put a thin layer of concrete over concrete. This is known as an overlay or resurfacing. It is a great way to give your concrete a brand new look without having to tear out the existing concrete and start from scratch.

Overlaying the surface of concrete can provide a number of benefits. It can be used to resurface pitted, spalled, or cracked concrete. It can also help make the surface of an existing concrete slab smoother, more attractive, and beneficial to foot or vehicle traffic.

Not only can it enhance the aesthetics of the concrete slab, but it can also help to protect the slab from further deterioration or damage.

A concrete overlay can be achieved by either installing a thin layer of self-leveling cement or by using a cement patching mix. For a self-leveling layer, a concrete overlay is typically ¼ to ½ inches thick.

This type of overlay works well on concrete with minor surface damage. For larger cracks and more serious surface damage, a thin layer of cement patching mix is necessary to make repairs.

When adding a thin layer of concrete over concrete, it is important to consider the type of overlay being used. Different overlays will require different levels of preparation and application. Specialty overlays may need primers, bonders, and additives to be added to ensure proper adhesion and longevity of the concrete overlay.

Additionally, be sure to properly prepare the concrete surface to ensure the overlay bonds reliably and evenly to the existing concrete. This involves thoroughly cleaning the concrete and any existing patching material, addressing any underlying repair issues, and following the manufacturer’s instructions of the overlay system used.

What happens to concrete as it dries?

When concrete is initially mixed and poured, it is very fluid and workable. As it begins to dry, the mixture starts to harden and adapt to the shape of whatever it is poured in. The drying process is initiated by the evaporation of the water within the mixture, allowing for minerals to bond together, forming a solid state.

The strength of concrete increases as it dries and its surface becomes more durable. The rate of drying can be influenced by climate conditions and air circulation, the water-cement ratio, and other factors such as aggregate and mineral admixtures, so the process can range from hours to days.

As it dries, the outer layer of concrete turns light grey, due to water evaporating from it. This concrete material should be protected from water and dampness as it continues to dry, or it may experience complications, such as a reduction in strength or an increase in shrinkage.

In general, the strength of the concrete will continue to increase as it dries and, typically, reaches its full strength 28 days after it was poured. After this stage, the concrete will remain stable and durable for decades with proper maintenance and care.

Does mortar stick to concrete?

Yes, mortar can stick to concrete. Mortar is a material that is made of sand, cement, lime, and water. It is used to bond brick, block, and stone together and can also be used to repair concrete. When using mortar to stick to concrete, make sure the concrete is clean and free of dirt, dust, or other debris.

The concrete should also be damp but not wet. Mix the mortar in the proper proportions, spread a thin layer onto the concrete, and press the brick, block, or stone into the mortar. Make sure to let the mortar dry and set for a minimum of 24 hours before applying any additional pressure or weight.

After 24 hours, the mortar should firmly hold onto the concrete.