Foundation Sealer and Foundation Sealant Guide

A building's foundation is constantly exposed to moisture. Rainwater, wet soil, groundwater, irrigation, poor grading, and damaged drainage systems can all place water against concrete or block foundation walls.

Concrete may look solid, but untreated concrete is porous. Water can enter through microscopic pores, cracks, construction joints, mortar joints, tie holes, and utility penetrations. Once moisture reaches the foundation, it may contribute to basement leaks, musty odors, mold-friendly conditions, peeling coatings, concrete deterioration, and corrosion of reinforcing steel.

A foundation sealer or foundation sealant can help protect the structure, but these products do not all serve the same purpose.

A concrete foundation sealer may penetrate the surface and reduce water absorption. A foundation sealant may be used to close cracks, joints, and gaps. A liquid rubber foundation sealant may create a flexible surface membrane. A basement foundation sealer may be applied from inside, while an exterior foundation sealer is installed on the soil-facing side of the wall.

Choosing the best foundation sealer depends on the foundation material, moisture source, direction of water pressure, condition of the wall, and whether the product will be installed inside or outside.

Rebotec USA provides mineral-based waterproofing products for concrete and mortar used in residential, commercial, and industrial construction. For product guidance, call Rebotec USA at +1 469-352-3379.

What Is a Foundation Sealer?

A foundation sealer is a product used to reduce the amount of water absorbed by concrete, concrete block, brick, mortar, or another foundation material.

Depending on the product, a foundation sealer may:

• Penetrate into the concrete
• Form a protective surface film
• Reduce water absorption
• Help limit moisture movement
• Protect against soil moisture
• Reduce staining and efflorescence
• Improve resistance to weather
• Prepare a wall for additional coatings

Foundation sealers may be clear, colored, cementitious, mineral-based, acrylic, rubberized, or made from other materials.

A sealer may be used as part of a larger foundation waterproofing system, but it should not automatically be expected to stop every leak. Heavy groundwater, hydrostatic pressure, open cracks, failed joints, and poor drainage may require additional repairs and water-management systems.

What Is Foundation Sealant?

Foundation sealant commonly refers to a flexible or rigid material used to seal a specific crack, gap, seam, joint, or penetration.

It may be used around:

• Foundation cracks
• Pipe penetrations
• Form-tie holes
• Wall-to-footing transitions
• Construction joints
• Window wells
• Utility openings
• Concrete block joints
• The wall-to-floor connection

A concrete foundation sealant may be:

• Polyurethane
• Silicone
• Acrylic
• Epoxy
• Cementitious
• Rubberized
• Asphalt based
• Mineral based
• Another specialized construction material

The word "sealant" is also sometimes used broadly for a coating applied over an entire wall. That is why the product's instructions are more important than the name on the container.

Foundation Sealer vs Foundation Sealant

The terms are often used interchangeably, but they can describe different products.

Foundation Sealer

A foundation sealer generally treats a larger surface. It may penetrate the foundation wall or form a coating over it.

It is commonly used to:

• Reduce surface absorption
• Protect porous concrete
• Seal masonry
• Add water repellency
• Create a protective wall coating

Foundation Sealant

A foundation sealant is often used on a concentrated opening or joint.

It is commonly used to:

• Fill gaps
• Seal cracks
• Close pipe openings
• Treat joints
• Protect transitions
• Accommodate limited movement

A complete foundation system may need both. The wall may receive a foundation sealer or membrane, while cracks and penetrations receive a compatible sealant.

Why Foundations Need Sealing

Foundation walls are often below grade, which means they remain in direct contact with soil.

When the soil becomes wet, water may press against the wall and enter through:

• Concrete pores
• Shrinkage cracks
• Structural cracks
• Mortar joints
• Hollow block cells
• Construction joints
• Form-tie holes
• Pipe penetrations
• Honeycombed concrete
• Damaged coatings

Sealing concrete foundation surfaces can help reduce moisture absorption, but water pressure and concentrated leak points must also be addressed.

Signs that a foundation may need sealing or waterproofing include:

• Damp basement walls
• Water entering after rain
• White mineral deposits
• Peeling interior paint
• Musty odors
• Mold or mildew
• Wet crawl spaces
• Leaking wall cracks
• Water around utility penetrations
• Damp wall-to-floor joints
• Repeated coating failures
• High indoor humidity

White mineral deposits are often efflorescence. They form when water travels through concrete or masonry, carries salts to the surface, and evaporates.

Interior vs Exterior Foundation Sealing

Foundation sealers may be applied from the interior or exterior. The location changes how the product interacts with water.

Exterior Foundation Sealer

An exterior foundation sealer is installed on the soil-facing side of the wall. This is considered positive-side protection because the product is placed where water first reaches the structure.

Exterior sealing may help:

• Stop water before it enters the concrete
• Protect the foundation wall
• Reduce moisture within the wall
• Cover repaired cracks
• Work with exterior drainage
• Protect below-grade concrete or block

Exterior products may include:

• Liquid membranes
• Sheet membranes
• Cementitious coatings
• Rubberized coatings
• Mineral-based coatings
• Penetrating water repellents
• Asphalt-based products

An exterior foundation sealant may also be used around joints, cracks, and penetrations before the full wall coating is applied.

Interior Foundation Sealer

An interior foundation sealer is applied from inside a basement, crawl space, or lower-level room.

Interior sealing may be useful when:

• Exterior excavation is difficult
• The wall has light dampness
• The surface needs protection
• The basement is being renovated
• The product is rated for negative-side moisture
• An interior drainage system is also present

The limitation is that water may still enter the foundation from outside. Pressure behind an unsuitable coating may cause peeling, blistering, bubbling, or loss of adhesion.

A foundation sealer interior product should be selected specifically for the substrate and water conditions.

Sealing Concrete Foundation Outside

Sealing concrete foundation outside is often more effective than applying a basic coating from inside because the exterior product stops water before it enters the wall.

A typical outside foundation sealing project may include:

1. Excavating around the foundation
2. Cleaning the concrete
3. Removing weak or loose material
4. Repairing cracks and voids
5. Sealing joints and penetrations
6. Applying an exterior foundation sealer or membrane
7. Installing protection board
8. Adding drainage board
9. Inspecting the foundation drain
10. Backfilling carefully
11. Restoring proper soil grading

Every step matters. Applying a coating without repairing cracks or addressing drainage may leave the foundation vulnerable.

Exterior Foundation Sealing vs Waterproofing

Foundation sealing, dampproofing, and waterproofing are not always the same.

Foundation Sealing

Sealing generally reduces water absorption through porous concrete or masonry.

Dampproofing

Dampproofing helps resist soil moisture under ordinary conditions. Traditional black asphalt coatings are often used for this purpose.

Waterproofing

Waterproofing is designed to provide stronger protection against liquid water and, depending on the system, hydrostatic pressure.

A black exterior coating is not automatically a complete waterproofing system. Before choosing a product, confirm whether it is designed for:

• Below-grade use
• Soil contact
• Liquid water
• Hydrostatic pressure
• Crack bridging
• Concrete or block
• Long-term exterior exposure
• Protection-board installation

The best exterior foundation sealer is the product that matches the real exposure, not simply the product with the thickest appearance.

Types of Foundation Sealers and Sealants

Different products protect foundations in different ways.

Penetrating Concrete Foundation Sealer

A penetrating concrete foundation sealer enters the pores of the concrete rather than leaving a thick film on the surface.

Potential benefits include:

• Reduced water absorption
• Natural appearance
• Less risk of surface peeling
• Protection within the treated surface
• Possible vapor movement
• Easier use on exposed concrete

Penetrating products may be appropriate for above-grade walls or light moisture exposure.

They may not stop:

• Active leaks
• Open cracks
• Severe hydrostatic pressure
• Water moving through joints
• Major foundation damage

Film-Forming Foundation Sealer

A film-forming sealer creates a protective layer over the wall.

These products may include:

• Acrylic coatings
• Polyurethane coatings
• Rubberized coatings
• Epoxy coatings
• Elastomeric coatings
• Mineral-based coatings

Film-forming products can provide stronger surface coverage than penetrating sealers, but they depend on good adhesion.

Moisture, contamination, weak concrete, and pressure from behind the coating can cause failure.

Cementitious Foundation Sealer

Cementitious waterproofing products contain cement-based materials and selected additives. They generally bond well to concrete, concrete block, brick, and mortar.

They may be applied by:

• Brush
• Roller
• Sprayer
• Trowel

Cementitious products may be used on interior or exterior foundation walls, depending on their design.

Some are rigid. Others include polymers that provide additional flexibility. Rigid products may crack when the foundation moves.

Mineral-Based Foundation Products

Mineral-based products are designed for compatibility with concrete and mortar.

Rebotec Admix Powder is mixed directly into new concrete or mortar to help create hydrophobic properties throughout the material.

Rebotec Paint provides a mineral-based surface-applied waterproofing option for compatible concrete applications.

These products may be considered for:

• New concrete foundations
• Basement walls
• Foundation repairs
• Concrete block mortar
• Commercial foundations
• Crawl-space walls
• Other water-exposed concrete

The right product depends on whether the concrete is new or existing and how much water exposure the foundation faces.

Liquid Rubber Foundation Sealant

A liquid rubber foundation sealant is applied as a liquid and cures into a flexible surface layer.

It may be brushed, rolled, sprayed, or troweled onto a properly prepared wall.

Potential benefits include:

• Flexible surface protection
• Coverage over irregular areas
• Fewer seams than sheet membranes
• Limited crack bridging
• Use on below-grade walls
• Ability to surround penetrations

A liquid rubber foundation sealant/basement coating may be useful for certain exterior and interior applications, but products vary.

Before selecting one, confirm:

• Whether it is intended for interior or exterior use
• Whether it can handle below-grade soil contact
• Whether it resists hydrostatic pressure
• Whether it requires a primer
• The required thickness
• How long it must cure
• Whether it needs protection board
• Whether it is compatible with insulation and drainage materials

The word "rubber" does not automatically mean the product is suitable for every foundation.

Rubber Foundation Sealant

A rubber foundation sealant may refer to a flexible crack sealant or a full-wall rubberized coating.

Flexible sealants are useful where limited movement is expected, such as around:

• Pipe penetrations
• Construction joints
• Changes in materials
• Small nonstructural cracks
• Wall transitions

They should not be expected to stabilize a structural crack or bowing wall.

Asphalt-Based Foundation Coatings

Asphalt-based products are commonly used as exterior foundation coatings.

Some provide basic dampproofing. Others are modified to offer stronger waterproofing performance.

Before using one, review whether it is rated for:

• Hydrostatic pressure
• Crack bridging
• Continuous wet conditions
• Exterior below-grade application
• Concrete or block
• Required thickness
• Protection during backfilling

Block Foundation Sealer

Concrete block and cinder block foundations require special attention because they contain hollow cells and many mortar joints.

Water may enter one part of the wall and travel internally before appearing somewhere else.

A block foundation sealer may be used with:

• Mortar-joint repairs
• Parging
• Exterior membrane
• Drainage board
• Foundation drain
• Interior drainage
• Sump pump
• Crack treatment

The wall's texture and joints must be fully covered. Thin areas around mortar joints can become leak points.

House Foundation Sealer

A house foundation sealer should be selected according to the home's foundation and site conditions.

Important factors include:

• Poured concrete or block
• Basement or crawl space
• Interior or exterior use
• Groundwater
• Soil drainage
• Existing cracks
• Previous coatings
• Structural movement
• Planned finishes
• Local climate

A product that works for an exposed above-grade foundation may not be suitable for a deep basement wall under water pressure.

Basement Foundation Sealer

A basement foundation sealer may be applied inside or outside the basement wall.

Interior products may help with:

• Surface dampness
• Porous concrete
• Efflorescence reduction
• Minor moisture movement
• Preparing walls for finishing

Exterior products may provide stronger protection by stopping water before it reaches the wall.

A foundation sealant basement coating should be rated for the side where it is applied and the pressure it will face.

Outdoor Foundation Sealant

An outdoor foundation sealant may be used on above-grade cracks, wall penetrations, exposed foundation joints, or other exterior openings.

Outdoor products should tolerate:

• Sunlight
• Rain
• Temperature changes
• Freeze-thaw cycles
• Soil contact, when applicable
• Movement
• Exterior cleaning

A sealant intended for above-grade use may not be suitable below ground.

How to Seal a Concrete Foundation

The correct process depends on the chosen product, but most foundation sealing projects include the following steps.

Step 1: Identify the Water Source

Determine whether the moisture comes from:

• Rainwater
• Groundwater
• Poor grading
• Gutters or downspouts
• Plumbing
• Condensation
• A foundation crack
• The wall-to-floor joint
• A pipe penetration

A coating will not correct every source.

Step 2: Inspect the Foundation

Look for:

• Cracks
• Bowing
• Spalling
• Honeycombing
• Mortar damage
• Efflorescence
• Failed coatings
• Active leaks
• Open joints
• Structural movement

Large, horizontal, widening, or displaced cracks should be evaluated before sealing.

Step 3: Prepare the Surface

Remove:

• Soil
• Dust
• Mud
• Oil
• Loose concrete
• Failed paint
• Old incompatible coatings
• Mold
• Efflorescence
• Construction residue

The sealer needs a clean, stable, and compatible surface.

Step 4: Repair Cracks and Penetrations

Repair materials may include:

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

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

Step 5: Address Drainage

Improve obvious water problems by:

• Cleaning gutters
• Extending downspouts
• Correcting grading
• Repairing window wells
• Inspecting foundation drains
• Redirecting irrigation
• Maintaining sump pumps

Reducing water pressure helps the sealing system perform better.

Step 6: Apply Primer if Required

Some liquid rubber, asphalt, polyurethane, and sheet systems require a compatible primer.

Use only products approved as part of the selected system.

Step 7: Apply the Foundation Sealer

Apply the product at the specified:

• Coverage rate
• Thickness
• Number of coats
• Temperature
• Surface-moisture condition
• Recoat window
• Curing time

Do not spread the product thinner than recommended to increase coverage.

Step 8: Protect the Exterior System

Exterior coatings may need protection or drainage board before backfilling.

This helps prevent damage from:

• Rocks
• Tools
• Soil
• Equipment
• Construction debris
• Sharp backfill

Step 9: Inspect Before Covering

Check for:

• Gaps
• Thin areas
• Pinholes
• Unsealed joints
• Open penetrations
• Poor terminations
• Punctures
• Incomplete coverage

Repairs are easier before the foundation is buried or covered by interior finishes.

Best Foundation Sealer: What to Look For

There is no single best foundation sealer for every project.

Evaluate the following:

Foundation Material

Is the wall poured concrete, concrete block, cinder block, brick, or stone?

Interior or Exterior Use

An exterior-only product may have odor or chemical limitations indoors. An interior sealer may not survive soil contact or backfilling.

Direction of Water Pressure

Positive-side products are installed where water reaches the wall first. Negative-side products must resist water pushing through the wall from behind.

Water Exposure

Does the foundation face light soil moisture, occasional rain, groundwater, or hydrostatic pressure?

Foundation Movement

A rigid coating may crack when the wall moves. Flexible products tolerate limited movement but do not replace structural repair.

Existing Coatings

Old paint, tar, epoxy, or unidentified coatings may interfere with adhesion.

Drainage

Even the best foundation sealant may struggle when water continually builds pressure against the wall.

Product Compatibility

Primers, repair mortars, sealants, coatings, insulation, drainage boards, and membranes should be compatible.

Common Foundation Sealing Mistakes

Avoid these frequent errors:

• Applying sealer over dirt or loose concrete
• Painting over an active leak
• Ignoring structural cracks
• Using an interior coating outside
• Using an exterior-only product indoors
• Applying penetrating sealer over existing paint
• Failing to seal penetrations
• Spreading a liquid coating too thin
• Skipping primer
• Backfilling without protecting the membrane
• Ignoring the perimeter drain
• Allowing downspouts to discharge beside the wall
• Sealing damp concrete with a dry-surface-only product
• Combining incompatible materials
• Covering the work before inspection

A foundation seal is only as reliable as its weakest crack, joint, seam, or penetration.

When a Foundation Sealer Is Not Enough

A foundation sealer may not solve the problem when there is:

• Standing water
• Repeated flooding
• Severe hydrostatic pressure
• Bowing foundation walls
• Major structural cracks
• Water beneath the basement slab
• Failed foundation drainage
• Multiple active leaks
• Sewer or plumbing problems
• Significant concrete deterioration

Additional work may include:

• Exterior excavation
• Full waterproofing membrane
• Interior perimeter drain
• Sump pump
• Structural foundation repair
• Crack injection
• Drainage-board installation
• Foundation-drain replacement
• Integral waterproofing in new concrete

A qualified contractor or structural professional may need to inspect serious conditions.

Get Help Choosing a Foundation Waterproofing Product

Choosing among a penetrating foundation sealer, concrete foundation sealant, mineral-based coating, liquid rubber system, exterior membrane, and integral additive 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 choosing a waterproofing solution for a new or existing foundation.

Conclusion

Foundation sealers and foundation sealants protect concrete and masonry in different ways.

A foundation sealer typically treats a larger surface and helps reduce water absorption. A foundation sealant is often used to close cracks, gaps, joints, and penetrations. Liquid rubber foundation sealants create flexible surface barriers, while penetrating sealers work within the treated concrete.

Exterior foundation sealing generally provides better protection against groundwater because it stops water before it enters the wall. Interior foundation sealers may help with light dampness and existing basements when exterior access is limited.

The best foundation sealer depends on the wall material, water pressure, location, drainage, structural condition, and existing coatings.

Proper preparation is essential. The wall should be inspected, cleaned, repaired, and prepared before the sealer is applied. Drainage, gutters, grading, cracks, and foundation drains should also be addressed.

For new foundations, an integral waterproofing additive can create hydrophobic properties throughout the concrete or mortar. Existing walls may need surface sealers, membranes, crack sealants, drainage, or multiple methods working together.

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

FAQs About Foundation Sealers and Sealants

What is a foundation sealer?

A foundation sealer is a penetrating or surface-applied product that helps reduce water absorption through concrete, concrete block, mortar, or masonry.

What is foundation sealant?

Foundation sealant is commonly used to close cracks, gaps, joints, and penetrations. The term may also describe some full-wall waterproofing coatings.

What is the difference between foundation sealer and foundation sealant?

A sealer usually treats a larger wall surface, while sealant is commonly used on specific cracks, joints, or openings.

What is the best foundation sealer?

The best product depends on the foundation material, water pressure, interior or exterior location, movement, and drainage conditions.

What is the best exterior foundation sealer?

Choose an exterior product rated for below-grade use, soil contact, the expected water pressure, and the specific concrete or masonry surface.

What is the best foundation sealant for cracks?

The correct product depends on whether the crack is stable, moving, structural, or actively leaking. Possible materials include polyurethane, epoxy, flexible sealant, and cementitious repair products.

Does liquid rubber foundation sealant work?

It can create an effective flexible barrier when applied to a properly prepared surface at the correct thickness. It must be rated for the project's location and water exposure.

Is liquid rubber foundation sealant the same as basement coating?

Some products are marketed as liquid rubber foundation sealant/basement coating, but they may have different approved uses. Confirm whether the product is intended for interior, exterior, positive-side, or negative-side use.

Can I seal a concrete foundation from outside?

Yes. The wall can be excavated, cleaned, repaired, coated or covered with a membrane, protected, drained, and backfilled.

Is an exterior foundation sealer better than an interior sealer?

Exterior sealing often provides more complete protection because it stops water before it enters the concrete. Interior sealing may be more accessible for an existing basement.

Can a concrete foundation sealer stop active leaks?

A general sealer may not stop active water. Leaking cracks, joints, and penetrations may need specialized repairs before the wall is sealed.

Can concrete block foundations be sealed?

Yes. Block foundation sealing may include mortar repair, parging, an exterior coating or membrane, drainage board, foundation drainage, and interior water management.

What is an outdoor foundation sealant?

It is a sealant designed for exterior cracks, joints, penetrations, or wall surfaces. It should be rated for weather and, when applicable, below-grade exposure.

Can an interior foundation sealer stop groundwater?

Some products resist negative-side moisture, but significant groundwater pressure may require exterior waterproofing, interior drainage, or a sump pump.

Can foundation sealer be applied over paint?

A penetrating sealer usually cannot enter concrete through paint. Film-forming products may be applied over existing coatings only when the surfaces and materials are compatible.

How many coats of foundation sealer are needed?

The required number depends on the product. Liquid coatings often require multiple coats or a specific total thickness.

Does a foundation sealer need primer?

Some systems require primer, while others do not. Follow the instructions for the exact product and substrate.

How long does foundation sealer take to dry?

Drying and curing times vary based on the product, temperature, humidity, surface moisture, and application thickness. Some products require several days before full water exposure.

Can foundation sealant repair structural cracks?

No. Structural cracks should be evaluated and repaired appropriately. A surface sealant may stop moisture but will not stabilize a moving foundation.

Who can help me choose a foundation sealer?

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