How to Seal a Cable Duct: A Pro’s Guide to Cable Duct Seal Systems

When you're working in industrial settings like electrical substations, utility plants, or basements, you can’t stress enough the importance of getting a cable duct seal right. It’s all about safety, durability, and performance.

In this guide, we’ll walk through how to install a duct sealing system from start to finish — from choosing the right materials to getting the best results. You’ll learn why preventing water and gas ingress is essential when dealing with cables or pipes within ducted networks, how to avoid common pitfalls, and how to choose a sealing solution that matches the environment.

What Is Cable Duct Sealing and Why Does It Matter?

In many installations, you’ve got large bundles of cables or pipes passing through ducts, walls or floors. Those openings can become major risk points: moisture ingress, dust contamination, rodent damage, or even exposure to gases (like hydrogen sulphide) in certain areas.

A reliable duct sealing compound forms a long-term barrier that protects the installation and maintains system integrity.

For example, when cables pass through a substation wall or enclosure, the right sealing material can prevent gas or water transfer from one side to another, manage cable movement, and maintain structural separation.

Our DuctSeal LG, DuctSeal HG and DuctSeal FR systems are fully re-enterable, remain flexible over time, and have been tested for resistance to hydrocarbons, dust and common industrial contaminants — making them well-suited to demanding electrical environments.

How to Seal a Cable Duct — Step by Step

1. Preparation

Identify the duct, pipe, or opening to be sealed. Clean it thoroughly — remove dirt, old mastic, foam or debris. Poor surface preparation is one of the most common causes of seal failure.

In retrofit installations, shaping and positioning are critical. A clean, stable surface gives the sealing material maximum adhesion and reduces long-term movement.

2. Choosing the Right Product

Select a sealing material based on the environment and cable layout, not just the duct size. Consider:

  • Water or gas exposure
  • Chemical contact (e.g. hydrocarbons, ASTM oil)
  • Whether fire resistance is required — always contact us for advice, as requirements vary by project
  • Cable spacing and configuration
  • Whether re-entry is needed in the future
  • Curing speed and practicality on site

Our DuctSeal LG, DuctSeal HG and DuctSeal FR systems are designed for a wide range of duct sizes and applications. Each provides strong adhesion, full re-entry capability and reliable long-term sealing performance.

3. Installing Backing & Supporting the Cables

In both new and retrofit installations, correct positioning is essential to create a stable foundation for the sealing material. Good practice includes:

  • Using suitable backing or support around and between cables/pipes
  • Ensuring the support sits securely against the duct wall to prevent movement
  • Maintaining consistent spacing between cables and the inner duct surface
  • Shaping or trimming backing to fill voids and support uneven cable layouts
  • Leaving space at the front of the duct for the sealing material

Well-supported cables and pipes within the duct ensure the sealing material cures correctly, maintains separation, and delivers long-term integrity.

Ensure compliance with DSEAR (Dangerous Substances and Explosive Atmospheres Regulations) — particularly when separating cables in hazardous or potentially explosive environments.

4. Applying the Sealing Compound

Apply the sealing material directly into the prepared area, working it into all voids and ensuring full contact with cables and duct walls. Shape it neatly to achieve the correct depth and finish.
No mixing is required — simply apply and form into position.

For larger ducts or high-performance requirements, DuctSeal HG and DuctSeal FR offer strong mechanical stability and full re-entry capability.

5. Curing & Inspection

  • Bonds securely to the duct surface
  • Maintains spacing between cables and pipes
  • Can be re-entered and re-applied if required
  • Provides long-term protection against water, gas and contaminants

Correct installation ensures a long-lasting, reliable seal for a range of infrastructure, utility and industrial applications.

Chemical Resistance – Why It Matters for Long-Term Integrity

Industrial environments often expose cable ducts and sealing systems to various chemical agents — from oils and fuels to cleaning solvents and corrosive gases. Over time, exposure can cause softening, cracking, or loss of adhesion in inferior materials — leading to failure.

DuctSeal systems (LG, HG, and FR) are tested to ensure long-term performance under tough site conditions.

  • Resistant to ASTM reference oils, diesel, petrol and common hydrocarbons
  • Maintains strength when exposed to acidic vapours and cleaning agents
  • Tested for resistance to hydrogen sulphide, saltwater and industrial detergents
  • Flexible compounds prevent cracking or shrinkage over time
  • Compliant with DSEAR standards for hazardous areas

💡 For chemical-heavy sites, we recommend DuctSeal FR or HG — both formulated for high resistance to oils, fuels, and aggressive contaminants.

Common Mistakes to Avoid

  • Insufficient cleaning before installation
  • Incorrect or inadequate cable backing
  • Using untested materials in chemical environments
  • Ignoring future maintenance or re-entry needs
  • Assuming all sealants behave the same

FAQs

Will DuctSeal systems damage electrical cables?
No — our compounds are neutral, non-corrosive and safe for cable jackets.

Can these systems be used outdoors?
Yes — just ensure the backing and sealant selection match the environment.

Are they re-enterable?
Yes — DuctSeal LG, HG & FR can be cut, accessed and reinstated when required.

Do I have to mix the material?
No — all systems are supplied ready to use.

Final Thoughts

Sealing cable ducts correctly is essential for safe, reliable installations across industrial, utility and infrastructure projects. With the right approach and the appropriate sealing material, a professionally installed seal can protect an installation for decades.

Need help selecting the right system for your site? Get in touch — we’ll recommend the ideal solution based on duct size, environment and cable configuration.

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