NBS Source
Seamsil® 400 Fixings Encapsulation


Suitable for use in roof fixings.


A silicone-based remedial treatment formulated specifically to arrest the adverse effects of rust and chemical corrosion, industrial pollution and is particularly effective in marine/ coastal environments. Installed by manufacturer network of Approved Contractors, all project works are inspected and certified to exacting quality standards – consult manufacturer for details.

Features and benefits:

  • Weather and ultraviolet (UV) resistant.
  • Proven corrosion resistance.
  • Encapsulates the damaged area to restrict further deterioration.
  • Water repellent seal.
  • Primer-less adhesion.
  • Remains tough and flexible, and is designed to withstand normal surface movement, ensuring continued optimum performance even in aggressive environments.
  • Long life protection in elasticity and encapsulation.
  • Silicone systems do not degrade by chalking and do not have self-cleaning properties.

System components and installation application:

  • Seamsil sealant: The Seamsil sealant is gun-applied around the base of the fixing, forming a complete bridged seal and tooled off to a neat edge.
  • Seamsil base coat: Whilst the Seamsil sealant is still wet, liberally apply Seamsil base coat by brush to encapsulate and visually obscure the complete fixing detail, taking the coating onto the roof sheet by approximately 25 mm. Allow to cure.

Seamsil sealant:

  • Chemical base: Alkoxy silicone, room temperature vulcanizing.
  • Colour: Grey.
  • Specific gravity 1.39.
  • Shore A Hardness: 20 (approximately).
  • Time to full cure: 10–14 days.
  • Movement accommodation: ±50%.
  • Elongation at break: 700%.
  • Tensile strength: 1.6 N/mm².
  • Application temperature: 3–60°C.
  • Dew point: Surface to be 2°C above the dew point.

Seamsil base coat:

  • Colour: Grey.
  • Chemical base: Silicone coating in a spirit carrier.
  • Specific gravity: 1.22.
  • Shore A Hardness: 20 (approximately).
  • Dry film thickness: Complete system – 350 microns (minimum).
  • Time to full cure: 10–14 days.
  • Solids content: By volume – 80%.
  • Movement accommodation: ±50%.
  • Elongation at break: 750%.
  • Tensile strength: 1.6 N/mm².
  • Application temperature: 3–60°C.
  • Dew point: Surface to be 2°C above the dew point.

General information





Alkoxy silicone.



Liquid applied coating.


One year

  • System material components are fully guaranteed to perform in line with manufacturer specification for the duration of the guarantee. If there is a failure of the system material components, manufacturer will repair or replace as appropriate at no cost.
  • Correct installation/ application methodologies prescribed by the manufacturer are critical to the lifetime performance of the gutter and roof refurbishment systems. The manufacturer Approved Contractor Network receive comprehensive survey and installation training at one of two purpose built training centres. Following review and approval by the manufacturer Technical Team, the Guarantee is issued.


Pr_30_31_76_77 Silicone construction joint sealantsPrimary
Pr_60_55_96_15 Corrosion inhibitor chemicals
Pr_20_31_03_17 Corrosion inhibiting admixtures


G20/670 Anti-corrosion finishes for fasteners

H30/120 Fibre cement

H31/110 Metal

H31/120 Metal

H31/10 Metal

H30/110 Fibre cement

H30/10 Fibre cement

Specification data - Silicone construction joint sealants Enhanced data


Alkoxy silicone.


To suit anticipated moisture and thermal movement.




Seamsil 400 (bolt encapsulation) specification

Seamsil 400 (bolt encapsulation) specification

Seamsil Fixing Grade application

Seamsil Fixing Grade application

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