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High Performance Latex Underlayment

SX300 is a two part general purpose smoothing underlayment for interior applications.

SX300 is a two part general purpose smoothing underlayment for
interior applications.SX300 is semi levelling and is specifically designed for the preparation and smoothing of interior subfloors prior to the application of a liquid applied damp proof membrane and receiving a floor covering.

  • Short setting and cure time, facilitating fast track programs and minimising disruption
  • Excellent adhesion to a wide range of common flooring substrates, including: concrete, sand/cement screeds, flooring grade asphalt, TREMCO surface DPM’s, etc.
  • Water resistant: can be used for pre-smoothing Protein free
  • Self priming on most surfaces

Moisture Testing

(in accordance with British Standards 8203)

  • Suitable for application on substrates with <75 % RH.
  • It is recommended that a moisture test is conducted prior to the application of SX300. For further details or to arrange for a moisture test please contact tremco illbruck Technical Services.


  • Ensure all surfaces to be coated are clean, dry, frost free and free from grease, oil, dirt, dust, loose friable material and any other contaminants (coating, laitance, etc.).
  • Any surface hardener or curing compounds should be thoroughly removed prior to the application of SX300. For full details of surface preparation contact tremco illbruck Technical Services.

In some case it may be necessary to prime with CS150 Acrylic Primer for porous substrates or CS100 Epoxy Primer for non-porous substrates. Always check with the tremco illbruck Technical Services.

Gradually add Part A to Part B, continually mixing with a slow speed drill and paddle. Mix the contents for 2 - 3 minutes to obtain uniformity in colour and consistency.


SX300 should be applied directly after mixing by pouring a ribbon of material along the wet edge and then trowelled to form a smooth, even finish. The effective use of spike rolling can reduce visible trowel marks.

For full application information, refer to product data sheet or contact tremco illbruck customer services on 01942 251400

Technical data

CompositionCementitious powder and liquid latex dispersion
Pot Life
(at 20°C)
20 minutes
Tensile Strength28 days 1.4 N/mm²
CoverageThicknesses of 6 mm to feather edge can be applied dependant on surface profile. An average thickness of 3 mm will provide a coverage rate of 5 m² per mix
Thicknesses of 8 mm to 30 mm can be achieved by incorporating an equal volume of 3 mm granite chippings
This will depend on the condition of the substrate and method of preparation (please refer to tremco illbruck Technical Department)
Cure Time
(at 20°C)
Between 2 - 4 hours for foot traffic and 8 - 12 hours
for application of damp proof membrane, floor covering
and loading
StorageStore in dry, shaded conditions between +10°C and +35°C
Shelf Life6 months when stored as recommended in original unopened packaging
High temperatures and humidity will lead to a reduced shelf life

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