How to Waterproof a Concrete Roof? Steps, and Tools

Written By Adam Paul - Waterproofing Expert

A concrete roof should be waterproof using expert knowledge and guidance, efficient tools and instruments, and recommended products. You can waterproof the old and new concrete roofs and rooftops using these 7 step by step guide. 

7 Steps for Concrete Roof Waterproofing

1. Clean the concrete roof surface
2. Check the cracks and damages on the concrete rooftop
3. Repairing the crack and damage on the concrete roof
4. Seal joints and corners
5. Apply primer on the concrete roof
6. Apply the waterproofing layer on the concrete roof
7. Let the roof waterproofing dry and check for leaks

You can use both liquid waterproofing and sheet waterproofing membranes for concrete roof waterproofing. You should use sealants to fill the cracks and gaps, reinforcing fabrics to reduce cracking and improve the adhesiveness of the sealant, power tools, and hand tools for cleaning and applying the primer and waterproofing on the roof surface. 

A concrete roof can be damaged due to poor construction, bad weather conditions, lack of maintenance, water ponding, subject to heavy loading, exposure to chemical and UV rays, and higher thermal fluctuations.If your concrete roof is damaged, you can see stain marks on the ceiling, paint peeling on the wall and ceiling, wall dampness, water leaking, mold and mildew growth, ponding, cracking, water dripping, and damp odor over the house.

Although you waterproof a concrete roof, it will last between 10 to 25 years. You can waterproof the concrete roof using epoxy without removing the tiles on the rooftop. Not only use concrete roofs, but you should also waterproof metal roofs, tiles roofs and shingle roofs to prevent water damage. 

7 Steps for Concrete Roof Waterproofing

You should follow the below 7 steps to waterproof the concrete roof structure.

1. Clean the Concrete Roof Surface

You should clean the concrete rooftop before you start the waterproofing on the concrete roof. You should clean the concrete rooftop thoroughly using these 7 steps.

7 Steps for Concrete Roof Cleaning for Waterproofing

1. Remove furniture, plant pots, tools, and any other items that might be on the concrete rooftop.
2. Use a broom or a brush to sweep away loose debris such as leaves, dirt, and dust. Pay special attention to concrete roof corners and hidden areas where dirt accumulates.
3. Remove broken and loosening materials on the concrete rooftop.
4. Remove the plaster on the concrete roof if the roof is an old one.
5. Use a pressure washer to wash the solid surface.
6. After pressure washing the concrete rooftop, check for stain marks, oil marks, and molds on the rooftop. You can use a mixture of bleach to clean the surface. You should scrub the stained areas with a stiff brush until the stains are gone on the rooftop
7. Let the cement surface to dry before applying any waterproofing membrane.

After the concrete rooftop cleaning process, you should check the surface for cracks and damage.

2. Check and Repair Cracks and Damages on the Concrete Rooftop

Mark and note the visible cracks, damages, potholes, deteriorated materials, and weakened materials for repairing, filling and fixing.

How to Fix Cracks on the Concrete Roof?

You can fix and seal the cracks on the concrete roof using the below 3 steps

1. Grove along the crack lines if the crack width is more than 2mm. You can use a masonry cutting disc for the grooving. These groove lines help to increase the bonding area to close the crack’s width and increase the adhesive strength between the concrete.
2. Use cement compound sealant to seal the crack width if the crack width is more than 5 mm.
3. Remove all the loosening materials and fill the area with cement and plaster mixture on the concrete roof.

Hairline cracks (width is <2mm) will be sealed by the primer and waterproofing coating when the surface is sealed.

3. Seal Joints and Corners on the Concrete Roof

After roof cracks and damages are fixed, you should seal the structural joints and corners on the concrete roof. You can use a fabric mesh on the joints and corners of the roof to further strengthen and seal them. You can use a paintbrush to apply the mesh with an appropriate sealer.

In particular you should fillet the roof and wall connection edge using waterproof cement. Roof and wall edges have a higher probability of leaking water from the roof. Hence, you should waterproof all the joints, corners, and channels on the roof to remove the water from the roof.

4. Apply Primer on the Concrete Roof

Primer improves the adhesion between the waterproofing layer and substrate. Hence, it should be applied on the concrete surface under the recommended conditions. You can use a roller, paintbrush or spray to apply the primer on the surface uniformly.

You should apply a recommended primer on the concrete roof after fixing and sealing all cracks and spaces. You can apply both liquid and sheet waterproofing membranes on the concrete roof. According to the waterproofing membrane, you should apply the primer on the concrete rooftop. 

You should not expose the primed roof surface once you apply it. You should be allowed to dry the primer layer according to the weather conditions and the product instructions.

5. Apply the Waterproofing Layer on the Concrete Roof

After priming, you should apply the waterproofing layer on the roof. You can apply both liquid and sheet waterproofing methods for the roof waterproofing. 

You can use cementitious waterproofing, polyurethane, acrylic waterproofing as the liquid waterproofing membranes on the concrete roof waterproofing. 

You can use EPDM, PVC, HDPE, TPU, and bituminous membranes (SNS) as sheet waterproofing membranes on the concrete roofs. When you apply liquid waterproofing membrane on the concrete roof, you should apply it uniformly. 

You should apply the first coat on the concrete roof one way continuously. The second coat should be applied perpendicular to the first coat. You can use a brush, roller or spray to apply the liquid waterproofing membrane on the concrete roof.

When you apply the sheet membrane on the concrete roof, you should install them properly with proper joint and sealing lengths and overlapping lengths. These lengths prevent the water from leaking from the seams and joints of the sheet membrane.

You can use a gas torch for the modified bituminous waterproofing membranes. The temperature for the bituminous waterproofing membranes should be 54°C (130°F) – 65°C (150°F). 

You can use a heat gun (550 C°) to install PVC waterproofing. Other sheet waterproofing should be installed on the roof, using a recommended glue or sealant. 

After the waterproofing coat is applied, you should not expose the layer to water untill it is completely dried in the recommended period.

6. Let the Roof Waterproofing Drying and Check for Leak

After the waterproofing is done on the top you should let the layer to dry. Do not expose the layer to water until it is completely dry. You should follow the manufacturer’s guidelines for applying and drying.

After drying the waterproofing membrane, you can check it by ponding 2-3 days before using it.

What are the Concrete Roof Waterproofing Membranes?

Concrete roof waterproofing membranes are mainly two types such as liquid and sheet waterproofing membranes. Liquid waterproofing membranes are highly recommended for stable and new concrete roofs while sheet waterproofing membranes are highly recommended for unstable and old concrete roofs.

1. Sheet waterproofing membrane: You can use sheet waterproofing membranes such as bituminous membranes, SBS, PVC, TPO, EPDM, and HDPE to seal the concrete roof for water. 
2. Liquid waterproof membranes: You can use liquid waterproofing membranes such as acrylic coating, polyurethane, cementitious and epoxy to seal the concrete roof for water.

What Tools and Supplies Need for Concrete Roof Waterproofing?

You should have below tools and supplies for concrete roof sealing project. The tools and supplies depends on the nature of the site and the size of the project.

1. Reinforcing fabrics for concrete roof waterproofing: Polyester fabrics, fiberglass fabrics
2. Application tools for concrete roof waterproofing: Roller, paintbrush, spray equipment, trowel, sponge
3. Cleaning tools for concrete roof waterproofing: Pressure washer, spatula, scraper
4. Safety tools for concrete roof waterproofing: Helmet, safety belt, gloves, goggles, face mask
5. Sealants for concrete roof waterproofing: Concrete roof waterproofing sealants such as silicone sealants, polyurethane sealants, and epoxy sealants can be used to seal the cracks and gaps in the concrete roof.

When You Should Waterproof a Concrete Roof?

When you see the below signs on the concrete roof, you should immediately waterproof the concrete roof.

1. Ceiling stain marks on the concrete roof
2. Pain peeling on the walls
3. Wall dampness after rain and snow melting
4. Water leaking from the slab
5. Mold and mildew growth under the slab
6. Ponding on the rooftop
7. Cracking and concrete loosening on the rooftop
8. Water dripping from the slab
9. White and powdery substance on the ceiling
10. Damp odor the building

How Long Does a Concrete Roof Waterproofing Last?

A roof concrete waterproofing can last between 10 to 25 years if the concrete roof is regularly maintained and repaired. The durability of concrete waterproofing depends on the quality of the material, environmental impact, installation expertise, and human activities. 

How Does Concrete Roof Cracks Are Formed?

A concrete roof cracks can be formed due to these environmental effects and human activities. 

6 Ways to form cracks on concrete roof

1. Poor construction of the concrete roof
2. Bad weather conditions affected the concrete roof 
3. Lack of concrete roof maintenance
4. Water ponding on the concrete roof
5. Concrete roof subjected to heavy loads 
6. Rooftop open to chemical exposure

Can you Seal Concrete Roof Tiles?

Yes, You can seal concrete roof tiles using a waterproof sealant or coating. You should not remove the concrete roof tiles if you use epoxy as the waterproofing membrane on roof.

Should You Waterproof Metal Roof?

Yes, you should waterproof the metal roof to prevent water leaking from the non-sealed screws, joints, and seams and stop the corrosion from the water. You should know how to waterproof a metal roof before you start it DIY. Metal roof waterproofing is easier than concrete waterproofing. But you should follow the proper metal roof waterproofing steps from the beginning.

Can Concrete Roof Waterproofing be Done DIY?

Yes, you can do concrete roof waterproofing DIY. Before you start the DIY project, you should know all about roof waterproofing in order to conduct the project cost effective and time effectively. When you reach Aqvize, one of our experts will help you to conduct your project more efficiently.