Cem-Rock Extreme x4 1/2” Underlayment is a new-age board, which are specifically engineered to eliminate wet laid gypsum and meet the fire-rating, sound-rating, and dimensional stability requirements of most multifamily and commercial job sites.

Cem-Rock® Extreme x4 (1/2”) is a new age smooth faced multi- purpose magnesium oxide board which is highly durable non- combustible board for use in applications requiring a combination of moisture and thermal resistance as well as superior performance in fire. The board will not rot and can be used as an alternative to fiber cement board, where greater dimensional stability is required

Product Options

Extreme Floor – Square (4’ x 8’ x 3/4″)

Extreme Floor – Tongue and Groove (4’ x 8’ x 3/4″)

Extreme Floor – Ship Lap (4’ x 8’ x 3/4″)

Internal Partitions
Backer Board for the Wet Areas
External Substrate with EIFS
Underlayment Board
SIP Panel Production

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A1 Fire resistant

Water proof

Sound Absorption

Reduced floor deflection

Technical Specifications

Prodcut Name/ Category:

Cem-Rock Extreme MgO Structural SubFlooring Board


3/4” T&G Load-bearing SubFlooring Board


4’ x 8’


3/4” (19mm)


Tounge & Groove (T&G)

Per Sheet Weight:

131 lbs

Pallet Quantity:

22 Sheets

Fire Performance:

ASTM E84: Zero Flame, Zero Smoke

ASTM E136: Passed

Environment Certifications:

UL Green Guard

UL Green Guard Gold