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Frequently Asked Questions

Fireproofing is a complex business. The following list of frequently asked questions has been developed to address some of the many issues surrounding fireproofing. For additional help or inquiries, contact your Grace Fire Protection Products Sales Representative.

Click on the question to view response.

What is Monokote® MK-6?

Monokote® MK-6® is a gypsum based cementitious spray-applied fire resistive material for structural steel framed buildings.

What is meant by cementitious?

The term cementitious as defined by ASTM or Underwriters Laboratories Inc. applies to all fireproofing that is wet mixed and then pumped as a slurry. Cementitious does not refer to portland cement content.


Can Monokote® MK-6® be applied by trowel?

Monokote® MK-6® is designed to be spray-applied. All of our testing is done with spray-applied material. Patching and small areas can be troweled. Care must be taken to assure an acceptable installation.

How many inches of Monokote® MK-6® do I need for a 3 hour fire rating?

It does not work this way! Thicknesses for hourly ratings are derived from individual UL fire resistance designs. (We have over 120 designs to choose from). These are classified as:

  • Floor Assemblies
  • Floor or Roof Beam-only Assemblies
  • Roof Assemblies
  • Columns
  • Walls

Within these broad categories thicknesses are dependent on:

  • Steel shape and size
  • Type of concrete (Normal Weight or Light Weight)
  • Thickness of concrete
  • Type of insulation

As you can see, there are no easy answers to this question. Consult your Grace Fire Protections products sales representative for assistance on selecting the appropriate design.


Are Monokote® fireproofing products asbestos free?

Yes, all Monokote® Fireproofing products manufactured by W.R. Grace & Co. - Conn. are asbestos free.

What is Monokote® Accelerator?

Monokote® Accelerator is aluminum sulfate (alum). Monokote® Accelerator reacts with the retarder in the gypsum. (Gypsum is normally retarded to allow for pumping and mixing.) This allows Monokote® MK-6® to set in 10-20 minutes. The use of Monokote® Accelerator with MK-6® results in a lower installed cost.


Is the use of Accelerator necessary?

While not absolutely necessary, Monokote® MK-6®/HY® is designed to be used with Monokote® Accelerator - it is part of the patented High Yield (HY) System. If the accelerator is not used, set time will be longer and the product yield (board feet per bag) will be significantly lower. The fire resistive properties are not affected.

How long does it take Monokote® to dry?

Drying rate is variable and is dependent upon many factors including -

  • Thickness
  • Temperature
  • Relative Humidity
  • Ventilation

The material "sets" within hours but can take many days to fully dry. As with any spray-applied fire-resistive material it is important to follow the manufacturer's recommended ventilation requirements.


Can Monokote® MK-6® be used as a respray after abatement?

No. Monokote® MK-6® is designed for new construction conditions. Post abatement respray is done over post-removal "lockdown agents" and Retro-Guard® is the product recommended for these conditions. Only Retro-Guard® has been fire tested at UL with 12 different UL classified lockdowns. Retro-Guard® is specially formulated for enclosed areas and has a distinctive blue color.

Who is responsible for determining hourly ratings and the correct UL design and ultimately the correct thickness of fireproofing?

Model building codes and numerous state laws mandate that only the "Design Professional" (a registered architect or professional engineer) can make these determinations. W. R. Grace & Co.-Conn. can only recommend the appropriate design and thicknesses. All of our recommendations must be reviewed and approved by the design professional for the particular project through the contractor's normal submittal process and this information must subsequently be reviewed and approved by the building code official having jurisdiction for the specific project.


Can I apply Monokote® over primed steel?

Yes, although we recommend that the best surface is lightly rusted, unprimed steel. The use of primers is governed by Underwriters Laboratories Inc. and must be tested in accordance with ASTM E 736. All spray-applied fire resistive materials require a clean surface that is free of rolling compounds, mill scale and other substances that will impair the proper adhesion of the fireproofing material.

What steel primers are allowed for use with Monokote® MK-6®?

Grace maintains compatibility listings on over 200 commercially available steel primers, more than any other fireproofing manufacturer. Check with your Grace Fire Protection Products Sales Representative for assistance on the compatibility of steel primers.


Can Monokote® be exposed to weather?

Monokote® MK-6® is a gypsum based product and is not intended for long term exposure to weather. However, it's high gypsum binder content does permit the normal amount of exposure that is part of the typical construction process. Our high-density, portland cement based product, Monokote® Z-146, is approved for exterior applications where exposure to wind, rain, and freeze/thaw cycles are anticipated.

Can Monokote® MK-6® products be painted?

Yes, under certain circumstances, Monokote® can be painted. However, the use of paints and sealers is governed by Underwriters Laboratories Inc. The surface flammability and smoke development characteristics of the paint or sealer must be tested in accordance with ASTM E 84. Generally, the paint must demonstrate a flame spread index of less than 200 and smoke developed of less than 450. The paint must be compatible with gypsum based construction materials. The Monokote® MK-6® must be completely dry and the paint application should not saturate the surface.


Do Monokote® products require a sealer in their application?

Absolutely not. The Monokote® family of products does not require, nor do we recommend, surface sealers or water tamping. The hard surface of gypsum-based and cement-based cementitious fireproofing materials delivers excellent in-place performance, including demonstrated resistance to air erosion and abrasion. Monokote® is appropriate for virtually all fireproofing applications including air-handling plenums. Certain types of facilities, clean rooms and hospitals for example, may desire a surface sealer as added protection.


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