How can you smooth out rough concrete?

What causes concrete to be rough?

Concrete can become rough for a few different reasons:

• Insufficient finishing – If the concrete is not properly finished when it is still wet, this can leave a rough texture behind once it hardens. Proper finishing techniques like troweling are important for achieving a smooth surface.
• Spalling – This occurs when the top layer of concrete breaks off in small chips or flakes, leaving behind a rough and uneven surface. Spalling can be caused by damage from freezing and thawing cycles, mechanical wear, or chemical exposure.
• Scaling – This is when the concrete surface erodes unevenly due to exposure to deicing salts. Scaling creates a rough, sandy texture on the concrete.
• Poor workmanship – Mistakes during installation like insufficient vibration to remove air bubbles or inconsistent mix proportions can lead to weak spots and roughness in the concrete.
• Exposed aggregate – Sometimes concrete is designed to have the aggregate stones exposed for decorative purposes. This type of finish intentionally creates a rough, coarse texture.

Identifying the root cause of the roughness can help determine the best way to smooth it out.

How can you smooth rough concrete?

Here are some methods that can be used to smooth and level out rough concrete surfaces:

Grinding

Grinding uses abrasive discs to sand off the top layer of concrete. This removes bumps and defects, creating a smoother profile. Hand-held grinders are useful for smaller jobs, while floor grinders are powerful for smoothing large horizontal surfaces. The concrete dust created during grinding should be cleaned up immediately.

Sacking

Sacking involves dragging burlap sacks soaked in a cement grout slurry across the surface. The combined friction and cement filling action helps fill small voids and even out the concrete profile. Multiple passes may be needed as the grout mixture fills deeper defects with each pass.

Patching compounds

Using cement-based patching compounds can help resurface damaged or scaled areas of concrete. The patch can be troweled smooth with the surrounding surface. Latex-modified patching compounds offer increased flexibility and adhesion compared to standard concrete mixes.

Overlaying

Applying a fresh layer of topping concrete or mortar can create a new smooth surface over the roughness underneath. This is more labor-intensive but offers a permanent solution. The overlay needs to be at least 1/8 to 1⁄4 inches thick and may require bonding agents or specialty mixes to adhere properly.

Chemical densifiers

Applying chemical densifiers or hardeners can help strengthen and smooth the surface of concrete. These reactive liquids penetrate into the concrete and fill pores to reduce surface defects. The concrete surface becomes more durable and consolidated. Multiple treatments are usually needed.

Polishing

For interior concrete, polishing uses progressively finer grinding pads to create an ultra-smooth surface. This is a multi-step process like granite polishing that removes scratches and exposes the fine aggregate. Polished concrete has a glossy, stone-like appearance when completed.

Tips for preventing rough concrete

It’s always best to take steps to prevent roughness in new concrete:

– Use a concrete mix design with the appropriate aggregate size and proportion. Too much water or too little cement can cause weakness.

– Make sure the forms are sturdy and tightly fitted to avoid leaks and defects.

– Pour concrete carefully into its final position to limit segregation and settling.

– Vibrate the wet concrete to remove air pockets and voids.

– After screeding, let the concrete begin to set before power troweling and edging to smooth the surface. Time the finishing appropriately.

– Avoid over-troweling which can bring excess fines and water to the surface, weakening it.

– Cure the concrete thoroughly after finishing to allow full hydration and hardening of the surface.

– Saw control joints early to help control inevitable cracking.

– Use protective sealers or coatings to prevent surface erosion or damage.

Following good concrete practices goes a long way towards creating durable, smooth concrete surfaces. But when roughness does occur, the repair techniques outlined above can help restore a damaged concrete surface.

Conclusion

Rough concrete is an annoying issue that happens due to a variety of factors. Thankfully, various methods exist for smoothing and leveling out the bumps, defects, and roughness that can develop on both old and new concrete surfaces. Grinding, patching, overlays, chemical densifiers, and polishing are all used in concrete smoothing and repair. The key is assessing the cause and extent of the roughness to select the right solution. With some work, it’s possible to transform a rough, damaged concrete surface into a smooth, polished finish. Taking care during installation is also crucial for preventing problems with surface roughness from arising in the first place.

Frequently Asked Questions

What are the most common causes of rough concrete?

The most common causes of rough concrete are insufficient finishing when the concrete was wet, surface damage from exposure to weathering and wear, weak spots in the concrete from a poor mix design or installation, and intentionally exposed aggregate for decorative purposes.

Can I grind rough concrete myself or do I need to hire a contractor?

Grinding rough concrete yourself is possible with the proper equipment. Handheld grinders can smooth small areas of roughness. However, for large surfaces it’s often advisable to hire a professional concrete grinding contractor who has the heavy equipment and experience to ensure an even, smooth result.

Will patching compounds stick to rough concrete?

Yes, high quality cement-based and latex-modified patching compounds are designed to bond well to concrete surfaces, including rough ones. The key is thoroughly cleaning the concrete first and applying a concrete bonding agent if specified by the patch manufacturer.

What kind of overlay works best on very rough concrete?

For significant roughness or defects, a high-strength polymer-modified cement overlay is often the best solution. These contain polymers that improve adhesion and provide more flexibility and durability than standard cement overlays. A coating of concrete bonding agent should still be applied first.

How soon can I polish newly smoothed concrete?

It’s recommended to allow newly smoothed or overlaid concrete to cure for at least 28 days before polishing it. This allows the concrete to fully hydrate and harden to avoid damaging the surface during the polishing process.

Method	Pros	Cons
Grinding	– Permanently removes defects up to 1/8 inch deep – Provides smooth flat finish – Equipment readily available to rent or contract out	– Generates concrete dust – Can expose large aggregate if ground too deeply – Requires experienced operator
Sacking	– Simple, inexpensive material (burlap, grout) – No special tools needed – Can match existing texture	– Very labor intensive – Not a permanent solution – Multiple passes required
Patching	– Good for small damaged areas – Wide variety of products available – Can match color of existing concrete	– Doesn’t address wider surface issues – May show patch outlines – Surface preparation is key
Overlay	– Resurfaces large areas – Variety of material options – Can improve surface durability	– Surface preparation is crucial – Long curing time before use – Higher material and labor cost
Densifiers	– Simple, low cost application – Penetrates and strengthens surface – Reduces dusting	– Requires multiple applications – Not a permanent roughness solution – Minimal change to appearance
Polishing	– Creates elegant, glossy finish – Makes concrete look like stone – Good for indoor surfaces	– Very labor intensive process – Requires diamond tooling – Not for severely distressed surfaces

Step-by-Step Instructions

Here is a step-by-step overview of the process for smoothing rough concrete:

Step 1 – Assess the concrete

– Identify the areas of roughness. Determine the depth and extent of the defects.

– Consider the overall condition of the concrete. Is there cracking, scaling, or spalling that also needs repair?

– Choose the size of tools and equipment needed based on the coverage area.

Step 2 – Clean and prepare the surface

– Clean the concrete thoroughly to remove dirt, debris, grease, and any unsound concrete.

– Use degreasers or commercial cleaners as needed. Rinse well.

– Check for hollow or delaminated areas and remove any loose material.

– Repair any major cracks or damage. Let patching compounds fully cure.

Step 3 – Grind, fill, or overlay

– Option 1 (Grinding) – Use hand or floor grinder with progressively finer grit discs to smooth and level the surface. Control dust.

– Option 2 (Sacking) – Wet burlap sacks in cement grout. Drag across the surface to fill defects. Let dry between passes.

– Option 3 (Patching) – Apply patching compound to low spots and trowel smooth. Feather edges.

– Option 4 (Overlay) – Apply concrete bonding agent, then spread overlay material. Screed and finish.

Step 4 – Finish and seal

– For grinding, clean up all concrete dust when done. Rinse with water.

– Check for remaining low spots. Repeat filling or overlay steps as needed.

– When surface is smooth, apply a concrete sealer or protective coating.

– For polished concrete, continue with sequential polishing steps.

– Allow new overlays to cure fully before use.

Safety Tips

– Wear proper PPE – Dust mask, gloves, eye and ear protection as needed for the method used.

– With grinding, use dust extraction and containment methods. Wet grinding can help reduce airborne dust.

– Sacking can irritate hands. Wear gloves and rinse burlap in clean water occasionally.

– Practice electrical safety with power tools and extension cords.

– Follow all manufacturer’s instructions for chemicals or overlay products used.

– Work in well-ventilated area and follow exposure limits for materials used.

– Use caution when working on knees for extended periods.

– Properly dispose of concrete dust/debris which may be hazardous.

Cost Comparison

Here is a rough cost estimate per square foot for the different methods of smoothing rough concrete:

Method	Cost per sq. ft.
Grinding (hand held)	$2 – $6
Grinding (floor grinder)	$3 – $8
Sacking	$0.50 – $2
Patching	$1 – $4
Overlay	$4 – $12
Densifiers	$0.50 – $2
Polishing	$4 – $8

– Grinding costs depend on if hand tools or floor grinders are required. Areas under 100 sq ft can be done with hand tools.

– Sacking is very labor intensive but the materials are inexpensive.

– Patching small areas is cost effective but may not address overall roughness.

– Overlays provide a new wear surface but require more materials and labor.

– Densifiers don’t address significant roughness. Multiple treatments add cost.

– Polishing has a wide range based on number of steps involved.

Choosing the Best Method

Choosing the ideal smoothing method depends on several factors:

– Location – Interior or exterior concrete?

– Distress severity – Light roughness or deep damage?

– Surface area – Isolated patches or large areas?

– Access – Can equipment reach the area?

– Budget – What is the project cost range?

– Timeline – How soon does the concrete need to be usable?

– Appearance – Will the concrete be exposed or covered with flooring?

– Use – Is it high traffic flooring or a rarely used warehouse slab?

A professional contractor can assess your specific concrete and recommend the repair approach that will provide the right balance of effectiveness, cost, and performance for your needs.

Consider Maintenance

While the smoothing process can return damaged concrete to an attractive, functional surface, ongoing maintenance helps keep it that way:

– Reseal concrete periodically with a suitable protective coating.

– Address joint deterioration or cracks immediately to prevent spalling.

– Limit heavy vehicular traffic and use wheel pads under steel legs to minimize mechanical wear.

– Remove snow and ice carefully without harsh chemical salts if possible.

– Test and neutralize pH at first sign of scaling damage.

– Clean up oil/chemical spills quickly to avoid etching or pitting.

– Consider recoating garage and basement floors every 2-4 years for longevity.

A little prevention goes a long way! Taking care of your concrete helps retain that smooth, polished appearance.