Waterproof Cement and Cement Board Guide

Cement-based materials are used in foundations, walls, floors, basements, bathrooms, pools, water tanks, and many other structures exposed to moisture. Because these materials feel hard and solid, many people assume they are naturally waterproof.

However, ordinary cement, concrete, mortar, and cement board are not automatically waterproof.

They may tolerate occasional moisture without immediately falling apart, but water can still move through pores, cracks, joints, fastener holes, seams, and unfinished edges. Over time, this may contribute to leaks, stains, efflorescence, mold-friendly conditions, damaged finishes, and deterioration of surrounding materials.

A successful cement waterproofing system may involve:

• A waterproof cement mix
• A cement waterproofing additive
• A penetrating sealer
• Waterproof cement paint
• A cementitious coating
• A sheet or liquid membrane
• Properly treated joints and penetrations
• Drainage and moisture management

The right method depends on whether the cement-based material is new or existing, vertical or horizontal, above or below grade, and exposed to rain, groundwater, water vapor, or continuous immersion.

Rebotec USA provides mineral-based waterproofing products for concrete and mortar used in residential, commercial, and industrial applications. For help choosing a product for cement walls, floors, foundations, or repairs, call Rebotec USA at +1 469-352-3379.

Is Cement Waterproof?

No. Ordinary cement is not completely waterproof by itself.

Cement is a binding material used to make concrete, mortar, grout, and other cementitious products. When mixed with water, it hardens and bonds aggregates or masonry units together.

Once cured, cement-based materials are strong, but they usually contain:

• Microscopic pores
• Capillary pathways
• Small voids
• Shrinkage cracks
• Construction joints
• Surface imperfections

Water can travel through these pathways, especially when it remains in contact with the material or is pushed by pressure.

The amount of water movement depends on:

• The water-to-cement ratio
• Mix design
• Compaction
• Curing
• Cracking
• Thickness
• Surface condition
• Water pressure
• Waterproofing additives
• Applied coatings or membranes

A dense, well-cured cement product may absorb less water than a poorly mixed or cracked one, but that does not make it completely waterproof.

Is Concrete Waterproof?

Concrete is made with cement, water, sand, and aggregate. Standard concrete is also porous unless it is designed and treated for water resistance.

Water may enter concrete through:

• Capillary pores
• Shrinkage cracks
• Construction joints
• Honeycombing
• Tie holes
• Pipe penetrations
• Damaged surfaces
• Wall-to-floor transitions

Concrete can be made more water resistant through proper mix design, careful placement, consolidation, curing, crack control, joint treatment, integral additives, and surface waterproofing.

What Is Waterproof Cement?

The term waterproof cement may refer to several different things.

It may describe:

• Cement mixed with a waterproofing additive
• Prepackaged waterproof mortar
• Cementitious waterproofing coating
• Hydrophobic cement mix
• Rapid-setting water-plug material
• Concrete made with an integral waterproofing product
• A marketing term for a moisture-resistant cement-based product

There is no single material that should be used for every waterproofing application.

The best waterproof cement depends on whether it is being used for:

• A basement wall
• Foundation
• Floor
• Pool
• Shower
• Water tank
• Retaining wall
• Exterior repair
• Mortar joint
• Active water leak

The product's technical instructions should explain its intended substrate, application thickness, curing requirements, pressure resistance, and exposure limitations.

Cement Waterproofing vs Water Resistance

Water resistance means a material can reduce or slow water absorption.

Waterproofing means the system is designed to prevent water from passing through under the expected conditions.

A cement wall may be relatively water resistant but still leak under:

• Prolonged rain
• Groundwater pressure
• Continuous immersion
• Cracking
• Failed joints
• Poor drainage

A proper waterproofing system must address the entire assembly, including cracks, joints, penetrations, transitions, and drainage.

Main Ways to Waterproof Cement

There are several methods for waterproofing cement walls, floors, and foundations.

Integral Cement Waterproofing Additive

A cement waterproofing additive is mixed into concrete, mortar, grout, or another cement-based material before it is placed.

Depending on the product, an additive may:

• Reduce capillary absorption
• Create hydrophobic properties
• Improve water resistance throughout the mix
• Reduce reliance on surface-only protection
• Support long-term durability
• Protect areas that may be difficult to coat later

Rebotec Admix Powder is a mineral-based product designed to create hydrophobic properties throughout concrete or mortar.

Because it is distributed through the cementitious material, the waterproofing does not depend only on a thin surface film.

Integral waterproofing may be considered for:

• New foundations
• Basement walls
• Basement floors
• Mortar
• Concrete repairs
• Pools
• Water tanks
• Retaining walls
• Commercial structures
• Underground concrete

An integral additive does not eliminate the need for:

• Proper concrete placement
• Joint treatment
• Crack control
• Waterstops
• Drainage
• Correct curing
• Structural design
• Exterior membranes when required

It works best as part of a complete waterproofing plan.

Waterproof Cement Mix

A waterproof cement mix may be a prepackaged product or a site-mixed cementitious material containing a water-resistant additive.

The mix may be used for:

• Patching
• Parging
• Plastering
• Mortar
• Concrete repairs
• Wall coatings
• Floor toppings
• Water-retaining structures

The mix must be prepared according to its specified water ratio. Adding too much water may make the product easier to spread but can increase porosity and reduce strength.

A waterproof cement mix should be evaluated for:

• Interior or exterior use
• Wall or floor application
• Positive- or negative-side pressure
• Continuous immersion
• Potable-water approval, when relevant
• Crack movement
• Application thickness
• Curing conditions

Cementitious Waterproofing Coating

Cementitious waterproofing is a surface-applied coating made from cement, fillers, and selected additives.

It is commonly used on:

• Concrete
• Concrete block
• Brick
• Mortar
• Basement walls
• Foundations
• Water tanks
• Pools
• Elevator pits
• Retaining walls

Cementitious coatings may be:

• Rigid
• Polymer modified
• Flexible
• Brush applied
• Trowel applied
• Spray applied

Potential advantages include:

• Strong compatibility with concrete and masonry
• Application to some damp surfaces
• Mineral-based construction
• Ability to fill surface pores
• Interior or exterior options

Potential limitations include:

• Rigid products may crack with movement
• Preparation is critical
• Active leaks may require separate repairs
• Joints and penetrations need detailing
• Multiple coats may be required

Waterproof Cement Sealer

A waterproof cement sealer is applied to cured concrete, mortar, or cement-based surfaces to reduce water absorption.

It may be:

• Penetrating
• Film forming
• Clear
• Colored
• Water based
• Solvent based
• Mineral based

A penetrating waterproof cement sealer enters the pores of the material. A film-forming product creates a visible layer over the surface.

Sealers may help with:

• Rain exposure
• Surface absorption
• Staining
• Dust
• Light dampness
• Easier cleaning

A general sealer may not stop:

• Active leaks
• Hydrostatic pressure
• Open cracks
• Moving joints
• Groundwater beneath a floor
• Water entering around pipes

Waterproof Cement Paint

Waterproof cement paint is a colored surface coating designed for concrete, masonry, mortar, or cement-based walls.

Depending on the product, it may help:

• Add color
• Improve appearance
• Reduce water absorption
• Fill surface pores
• Make walls easier to clean
• Protect against light moisture
• Resist rain

A cement waterproofing paint should be selected based on:

• Interior or exterior location
• Wall or floor use
• Above- or below-grade exposure
• Positive- or negative-side pressure
• Existing coatings
• Required surface preparation
• Water-pressure rating
• Intended finish

Ordinary decorative paint should not be treated as a waterproofing system.

Waterproofing Membrane

A waterproofing membrane creates a continuous barrier over or beneath cement-based materials.

Membranes may be:

• Liquid applied
• Sheet applied
• Self adhered
• Rubberized
• Cementitious
• Polyurethane based
• Asphalt based
• Thermoplastic

Membranes are frequently used for:

• Foundations
• Showers
• Roof decks
• Balconies
• Pools
• Basements
• Retaining walls
• Below-grade concrete

Seams, corners, drains, fasteners, and penetrations require careful detailing.

How to Waterproof Cement Walls

Waterproofing cement walls involves more than selecting paint.

Step 1: Find the Moisture Source

Determine whether the water comes from:

• Rain
• Groundwater
• Plumbing
• Condensation
• Poor grading
• Cracks
• Mortar joints
• Pipe penetrations
• Roof leaks
• Window openings

The waterproofing method must match the source.

Step 2: Inspect the Wall

Look for:

• Cracks
• Loose material
• Efflorescence
• Mold
• Peeling coatings
• Honeycombing
• Open joints
• Active water
• Structural movement

Bowing walls, widening cracks, or displaced concrete should be evaluated before coating.

Step 3: Remove Failed Materials

Remove:

• Peeling paint
• Loose coatings
• Weak mortar
• Dirt
• Dust
• Oil
• Mold
• Efflorescence
• Construction residue

A new coating cannot bond reliably to a failing surface.

Step 4: Repair Cracks and Openings

Possible repair materials include:

• Cementitious repair mortar
• Hydraulic cement
• Polyurethane sealant
• Epoxy
• Flexible joint material
• Compatible waterproof mortar

The correct repair depends on whether the crack is stable, moving, dry, or actively leaking.

Step 5: Prepare the Surface

Some cementitious coatings are installed on damp surfaces. Other paints and sealers require dry material.

Follow the product instructions for:

• Surface moisture
• Temperature
• Cleaning
• Roughness
• Priming
• Pre-wetting

Step 6: Apply the Waterproofing Product

Apply it at the specified:

• Thickness
• Coverage rate
• Number of coats
• Recoat time
• Temperature
• Application method

Thin areas, pinholes, and missed joints may become leak points.

Step 7: Allow Proper Curing

Protect the wall from:

• Rain
• Freezing
• Rapid drying
• Dust
• Backfilling
• New finishes
• Water exposure

A product may feel dry before it has fully cured.

Waterproofing Cement Walls From the Outside

Exterior waterproofing is often the most complete method for basement and foundation walls because it stops water before it enters the cement-based structure.

A typical exterior system may include:

• Excavation
• Wall cleaning
• Crack repair
• Cementitious or liquid membrane
• Protection board
• Drainage board
• Foundation drain
• Drainage gravel
• Correct grading

A surface coating performs better when drainage reduces the amount of water pressing against the wall.

Waterproof Cement Floor Systems

A waterproof cement floor may refer to a concrete slab made with an integral additive or an existing floor protected with a sealer, coating, or membrane.

Floor waterproofing may be needed in:

• Basements
• Bathrooms
• Mechanical rooms
• Garages
• Balconies
• Pools
• Water tanks
• Commercial kitchens
• Industrial facilities

New Cement or Concrete Floors

A new floor may include:

• Compacted base
• Drainage material
• Vapor barrier
• Integral waterproofing additive
• Correctly designed concrete
• Proper joints
• Careful curing
• Surface coating when required

Existing Cement Floors

An existing floor may need:

• Crack repair
• Joint treatment
• Moisture testing
• Penetrating sealer
• Cementitious coating
• Epoxy or polyurethane coating
• Waterproof membrane
• Drainage

A coating applied over a floor with high moisture vapor may bubble, blister, or peel.

Waterproofing Basement Cement Floors

Basement slabs may face moisture from the soil below.

A surface coating may help with light moisture, but groundwater pressure may require:

• Interior drainage
• Sump pump
• Crack repair
• Cove-joint treatment
• Below-slab drainage
• Exterior water management

A waterproof cement floor coating should be approved for foot traffic and the slab's moisture conditions.

Waterproof Cement Foundations

A waterproof cement foundation requires protection at more than the wall surface.

Important areas include:

• Foundation walls
• Footings
• Construction joints
• Wall-to-floor joints
• Pipe penetrations
• Form-tie holes
• Cracks
• Foundation drains
• Below-slab moisture

New foundations may use integral cement waterproofing additives with exterior membranes and drainage.

Existing foundations may require excavation, repairs, surface-applied waterproofing, protection board, and drainage improvements.

Waterproofing should not be used to hide structural foundation movement.

Is Cement Board Waterproof?

Cement board is generally water resistant, but most cement board is not a complete waterproofing system by itself.

Cement board is commonly used behind tile in:

• Showers
• Bathtubs
• Bathroom walls
• Floors
• Kitchens
• Laundry rooms
• Exterior applications approved by the manufacturer

Unlike standard drywall, cement board does not normally break down quickly from occasional moisture exposure. However, water may still pass through or around it.

Potential water pathways include:

• Board pores
• Panel seams
• Screw holes
• Edges
• Corners
• Plumbing penetrations
• Changes of plane
• Unsealed joints

Cement board should not be treated as a substitute for a required waterproofing membrane.

Is Cement Board Water Resistant?

Yes, cement board is generally more water resistant than ordinary drywall.

However, water resistance means the board can tolerate moisture better. It does not mean the complete wall or floor assembly will prevent water from reaching framing, insulation, or other materials behind it.

Does Cement Board Need Waterproofing?

In wet areas, cement board commonly needs a separate moisture-management or waterproofing system based on the installation and manufacturer requirements.

Options may include:

• Sheet membrane behind the board
• Liquid-applied membrane over the board
• Sheet membrane over the board
• Sealed seams and fasteners
• Waterproof joint tape
• Properly detailed shower pan
• Sealed plumbing penetrations

The selected assembly should follow the membrane, board, tile, and local construction requirements.

Can You Paint Cement Board to Make It Waterproof?

A compatible waterproof coating may be applied to some cement boards, but not every paint creates an approved wet-area waterproofing system.

Before coating cement board, verify:

• Product compatibility
• Interior or exterior approval
• Wet-area approval
• Seam-treatment requirements
• Fastener treatment
• Required thickness
• Cure time
• Tile compatibility

Waterproofing must remain continuous across the entire surface and all transitions.

Cement Board vs Concrete

Cement board and poured concrete are both cement-based, but they are used differently.

Cement Board

Cement board is:

• Manufactured in panels
• Fastened to framing or substrates
• Common beneath tile
• Thin compared with structural concrete
• Joined at seams
• Penetrated by screws

Concrete

Concrete is:

• Poured or placed
• Structural in many applications
• Used for foundations, slabs, walls, and tanks
• Thicker and more massive
• Vulnerable at cracks and joints
• Often reinforced

Both can be water resistant, but neither should automatically be considered waterproof.

Waterproof Cement Paint Price

The price of waterproof cement paint varies based on:

• Product type
• Container size
• Coverage rate
• Number of coats
• Surface porosity
• Wall condition
• Interior or exterior use
• Water-pressure rating
• Required primer
• Labor
• Preparation and repairs

A low-priced product may cover fewer square feet or require additional coats. A more expensive product may provide stronger performance, but price alone does not determine whether it is appropriate.

When comparing waterproof cement paint prices, calculate:

• Cost per square foot
• Required number of coats
• Primer cost
• Repair materials
• Surface-preparation cost
• Labor
• Protection and drainage needs
• Expected service life

The most expensive coating can still fail if applied to dirty, cracked, or water-saturated material.

How to Choose the Best Waterproof Cement Product

The best waterproof cement depends on the project.

Ask the following questions.

Is the Material New or Existing?

New concrete and mortar can use an integral additive. Existing materials usually require repairs, sealers, coatings, or membranes.

Is the Application a Wall or Floor?

Floor products must tolerate traffic and wear. Wall coatings may not be suitable for horizontal surfaces.

Is It Interior or Exterior?

Exterior products must withstand weather and temperature changes. Interior products need to be appropriate for occupied spaces.

Is the Area Above or Below Grade?

Below-grade structures may face groundwater and hydrostatic pressure.

Is the Surface Damp or Actively Leaking?

Some products can be applied to damp cement. Active leaks usually need separate repair.

Will the Material Be Submerged?

Pools and tanks require products designed for continuous immersion and the intended water use.

Is Movement Expected?

Rigid cementitious coatings may crack if the structure moves. Flexible details may be needed at joints and transitions.

Will Tile or Another Finish Be Installed?

The waterproofing system must be compatible with adhesives, mortar, tile, flooring, and other finishes.

Common Cement Waterproofing Mistakes

Avoid these common errors:

• Assuming cement is naturally waterproof
• Using cement board without required waterproofing
• Applying paint over active leaks
• Ignoring cracks and joints
• Adding too much water to the mix
• Applying coatings too thin
• Using wall paint on a floor
• Skipping surface preparation
• Coating over efflorescence
• Ignoring exterior drainage
• Failing to seal penetrations
• Covering structural movement
• Installing tile before the membrane cures
• Combining incompatible products
• Assuming a waterproof label means the product works everywhere

The complete assembly must be considered, not just the main surface.

When to Contact a Waterproofing Professional

Professional evaluation may be needed when there is:

• Repeated flooding
• High groundwater
• Structural cracking
• Bowing walls
• Continuous immersion
• Large commercial areas
• Active running water
• Failed existing membranes
• Water-retaining structures
• Unclear moisture sources
• Significant concrete deterioration

A professional can help determine whether the project needs repairs, integral waterproofing, a surface coating, drainage, a membrane, or a combination of methods.

Get Help Choosing a Cement Waterproofing Product

Choosing between a waterproof cement mix, sealer, paint, integral additive, and surface membrane can be difficult.

Rebotec USA helps contractors, builders, distributors, engineers, and property owners evaluate mineral-based waterproofing products for concrete and mortar.

Call Rebotec USA at +1 469-352-3379 for product information, application guidance, and help selecting a waterproofing solution for cement walls, floors, foundations, concrete repairs, or new construction.

Conclusion

Ordinary cement, concrete, mortar, and cement board are not automatically waterproof.

Cement-based materials contain pores and may develop cracks, joints, and openings that allow water to pass through. Cement board can tolerate moisture better than standard drywall, but seams, fasteners, edges, and penetrations still require a properly designed waterproofing system in wet applications.

Cement waterproofing may involve an integral additive, waterproof cement mix, penetrating sealer, cementitious coating, waterproof paint, or membrane.

For new concrete and mortar, an integral waterproofing additive can provide water resistance throughout the material. For existing cement walls and floors, surface preparation, crack repair, sealers, coatings, membranes, and drainage may be necessary.

The best waterproof cement product depends on the material, location, water pressure, movement, and planned finish. No paint, additive, or membrane should be expected to repair structural problems or replace proper drainage.

For help evaluating a mineral-based waterproofing product for concrete or mortar, call Rebotec USA at +1 469-352-3379.

FAQs About Waterproof Cement and Cement Board

Is cement waterproof?

No. Ordinary cement-based material is porous and can absorb or transmit moisture unless it is specially designed, treated, or protected.

Is concrete waterproof?

Standard concrete is not completely waterproof. Its water resistance can be improved through mix design, curing, integral additives, coatings, membranes, and proper joint treatment.

What is waterproof cement?

Waterproof cement may refer to cementitious material containing a waterproofing additive or a prepackaged coating, mortar, or repair product designed to resist water.

What is cement waterproofing?

Cement waterproofing is the process of protecting cement-based materials using integral additives, sealers, coatings, membranes, crack repairs, and drainage.

How do you waterproof cement?

Clean and repair the surface, address the water source, and apply a compatible sealer, cementitious coating, paint, or membrane. New cement materials may include an integral additive.

What is a waterproof cement mix?

It is a cementitious mixture containing additives or components designed to reduce water absorption or resist water under specified conditions.

What is a cement waterproofing additive?

It is a product added to fresh concrete, mortar, or grout to improve water resistance throughout the cured material.

Can waterproofing additive be added to mortar?

Yes, when the product is designed and dosed for mortar. Follow its mixing and application instructions.

What is waterproof cement sealer?

It is a penetrating or film-forming treatment applied to cured cement, concrete, or mortar to reduce water absorption.

Does waterproof cement paint work?

It can help under the conditions for which it was designed. It may not stop active leaks, structural cracks, or severe hydrostatic pressure.

Can waterproof cement paint be used on floors?

Only when the product is specifically approved for floors and the expected traffic, moisture, and wear.

How much does waterproof cement paint cost?

Pricing varies by product, coverage, number of coats, preparation, labor, repairs, and location. Compare total installed cost rather than container price alone.

What is the best waterproof cement?

The best option depends on the application. A foundation, shower, floor, pool, and repair may each require a different product or system.

Is cement board waterproof?

Most cement board is water resistant but not a complete waterproofing barrier by itself.

Does water pass through cement board?

It can. Water may pass through the board or around seams, fasteners, edges, corners, and penetrations.

Does cement board need a waterproof membrane?

Wet areas often require a membrane or moisture-management layer based on the board, tile, product, and construction requirements.

Can cement board be used in a shower?

Yes, when installed as part of an approved shower assembly with properly treated seams, fasteners, transitions, penetrations, and waterproofing.

Can waterproof paint be applied over cement board?

Some approved liquid membranes or coatings can be applied over compatible cement board. Follow the board and waterproofing product requirements.

Can cement be used to waterproof a foundation?

Cementitious coatings and integral additives may be part of a foundation waterproofing system, but cracks, joints, drainage, and groundwater conditions must also be addressed.

Can you make a cement floor waterproof?

Its water resistance can be improved with a vapor barrier, integral additive, proper concrete, crack treatment, sealer, coating, or membrane. The correct system depends on the water source.

Does waterproof cement crack?

Cementitious waterproofing products can crack if the structure moves, the mix is incorrect, curing is poor, or the product is applied improperly.

Who can help me choose a cement waterproofing product?

Rebotec USA can help you evaluate mineral-based waterproofing products for concrete and mortar. Call +1 469-352-3379 for product and application guidance.