SEMCO Liquid Membrane Roof Waterproofing Membrane

Preparation

If you have an asphalt or tar roof, choose POWER CLEANER. For any other substrate choose NU-LIFT Cleaner.

preparation

Stone Soap will ensure to pH balance your surface and get it ready for waterproofing.

waterproofing

Select the size and color of SEMCO Liquid Membrane needed to waterproof your roof.

Roof waterproofing

Build your roof waterproofing kit

Start by selecting the setup that fits your roof surface and waterproofing needs. Then use the prep and application steps below to complete the job with confidence.

Step by step

How to use SEMCO Liquid Membrane on roofs

Follow these steps for prep, application and cure timing based on the roof surface you are coating. The goal is a clean substrate, even coverage and enough cure time before water exposure.

Prepare your space and Gather your materials

• For bare concrete or water based coatings we recommend our Preparation D in order to remove any mineral deposits or efflorescence from the surface. For this you will need the following cleaners : Nu-Lift Cleaner and Stone Soap
• For asphalt, rubber and EPDM surfaces we recommend Preparation B.For this you will need the following cleaners : Power Cleaner and Stone Soap
Ensure your surfaces are fully cleaned and dried. If you have any rust on your surface, use a water based rust primer first.

Helpful Tip

If you need assistance with which cleaners are needed for the Prep, feel free to use our live chat or call us!

Masking

Mask off areas that are not receiving any coating. Remove masking tape before material has fully cured.

Fabric Reinforcement

We strongly recommend using the Fabric Reinforcement on all the joints.Apply a generous coat of SEMCO Liquid Membrane™ on the joints. 4" on each side of the joint and while product is still wet, put the Fabric Reinforcement over the joint and press it flat. Once Fabric Reinforcement is on, apply another coat of SEMCO Liquid Membrane™ across the Fabric Reinforcement to encapsulate it. Let it dry completely before resuming to next step.

APPLYING COAT

Use a 1/2" nap roller. Allow any pre-treated areas to fully dry. Apply a thin coat (0.015 inch per coat) of SEMCO Liquid Membrane™ with brush or roller over substrate including pre-treated areas. Once you can walk on the surface and not get any residue on your shoe or feet or cannot leave a fingerprint impression it is ready to re-coat. Apply another thin coat of SEMCO Liquid Membrane™ in an alternate direction over the first coat of SEMCO Liquid Membrane™. Let topcoat dry to the touch, approximately 1–2 hours at 70 °F (21 °C) and 50% RH. When last coat has dried to the touch, inspect final surface for pinholes, voids, thin spots or other defects.SEMCO Liquid Membrane™ will dry to a lighter color when it’s dry to touch. Use additional SEMCO Liquid Membrane™ to seal the defects. Required total thickness is 0.03 - 0.04 inches for non submerged applications.

Curing Time

Curing time depends on temperature, humidity and airflow, however typically initial cure is within 6 - 7 days as per specific product recommendations. Avoid contact with water during the curing period.

Additional Information

• For clean up use warm water to clean brush or roller right after use.
• For optimal bonding we highly recommend preparing the surface as mentioned above for best results.
• Stir up the product well before use in order to mix up the color pigments.
• Avoid application in direct sun light in the afternoon or temperatures of over 85F as it might cause the product to dry too fast before it can adhere to the substrate
• It can not be applied to wet substrates or substrates still containing moisture, else it will not cure correctly and stay tacky. Max. rest moisture in substrate can be up to 3%. If you are unsure about the moisture content, have it measured prior to application.
• Application on non porous surfaces such as metal or fiberglass : Apply thin coats as this will allow for the product to cure faster.
• Cure times are displayed in our curing chart. However if coats have been applied too thick, the surface might feel tacky. This is a sign of trapped moisture. If you have left over product, apply a very thin coat over the entire surface. The surface needs to be fully cured and hard before being fully submerged.
• It is always advisable to apply a small test patch in an inconspicuous are to ensure adequate adhesion prior to full application.
• If you have multiple containers of SEMCO Liquid Membrane™, we highly recommend to either mix them together or use one container for the last layer to get color consistency.

SEMCO Liquid Membrane FAQ

Can I use SEMCO Liquid Membrane on my roof, and what roof types does it work on?

Yes — it's widely used as a roof waterproofing and repair coating. Customers apply it to flat and low-slope roofs, torch-down and rubber (EPDM) roofs, metal and tin roofs, asphalt/composition shingle roofs, concrete roofs, RV and camper roofs, sheds, carports, awnings, and patio covers. It rolls or sprays on and cures into a seamless flexible membrane that seals leaks and stands up to sun and weather.

Can I use it on a flat or low-slope roof (torch-down, built-up, or rubber EPDM)?

Yes — flat and low-slope roofs are one of the most common roof uses. Reviewers with torch-down roofs that leaked at the seams sealed them by embedding Fabric Reinforcement over the seams and applying two coats, and owners of old rubber roofs that had started to leak got great results after prepping with the SEMCO cleaners and coating. It creates a solid seamless seal that doesn't crack. For any seams, laps, or transitions, reinforce with fabric reinforcement first.

How do I seal seams, edges, valleys, and roof penetrations like vents and HVAC?

These details are where roofs leak, so reinforce them. Embed SEMCO Fabric Reinforcement into a first wet coat of membrane over seams, laps, roof ridges, valleys, edges, and around penetrations such as vents, skylights, and HVAC curbs, then coat over the fabric with additional coats. The fabric reinforcement spreads stress so those joints don't reopen.

Do I need the Fabric Reinforcement on a roof?

For any seams, joints, cracks wider than 1/4", or transitions — yes, it's strongly recommended, and it's one of the most-praised parts of a roof job. Reviewers use it on flat-roof seams, metal-roof laps, roof ridges, valleys, edges, gutters, and around penetrations, embedded between coats of membrane, and repeatedly credit it for stopping stubborn leaks. On a broad, sound field with no joints you may not need it everywhere, but treat every seam and penetration with fabric.

How many coats do I need on a roof?

Plan on a minimum of 2 coats over the field, with an extra coat and fabric at seams, edges, and penetrations; rough, porous, or foam surfaces can need 4–5 coats. Reviewers who applied two to three coats over prepped roofs report staying leak-free through storms, while thin single-coat jobs are a common reason a roof still leaks. Build it up in thin, well-cured coats rather than one heavy layer, and don't shortcut coverage.

Will it handle ponding or standing water on a low-slope roof?

It creates a fully waterproof, seamless membrane that repels standing water, and it's used successfully on nearly flat roofs. That said, chronic ponding is hard on any roof coating, so for best long-term performance make sure the roof still drains and address any low spots where water sits for days. Build up adequate coats (and reinforce seams/drains with fabric); if a roof holds deep water permanently, correct the drainage as part of the fix.

Is it UV stable — will it survive full sun and heat without fading or peeling?

Yes — it's fully UV-resistant and made for exposed exterior use, so it doesn't need a separate UV topcoat. This is a key reason customers in high-sun climates like Florida, Hawaii, and Mexico choose it for roofs after other product peeled or lost color within a year in the heat.