By Bruce Schundler

Perlite and vermiculite aggregates have been used in fire-proofing products for decades.

PLASTERS Among the better known uses of perlite and vermiculite for fire-protection has been in fire-proof plasters. Traditionally "plaster" had been made from a mix of gypsum plaster and sand; and sometimes to strengthen the plaster reinforcing materials like horsehair was added. The problem with sand plaster is that in a fire the sand "explodes" and cracks, and can be easily destroyed.

In contrast, perlite and vermiculite plaster can offer a product which is both lightweight and fire-proof. For many years, these plasters were used primarily in large, urban construction where the combined benefits of weight reduction and fire-proofing were desired. They were especially used to fire-proof steel beams, columns, and floors.

In the U.L. Fire Resistance Directory, for instance, there are many ratings of up to four hours for basic mixes of gypsum plaster and either perlite or vermiculite for use around steel beams and columns, or under metal decks. Here is a sampling of these:

SOME TYPICAL U.L. FIRE RATED SYSTEMS FOR STRUCTURAL COLUMNS	SOME TYPICAL U.L. FIRE RATED SYSTEMS FOR RESTRAINED AND UNRESTRAINED ASSEMBLIES	SOME TYPICAL U.L. FIRE RATED SYSTEMS FOR WALLS AND PARTITIONS
X401 -- 2 HOURS X402 -- 2, 3 & 4 HOURS X403 -- 3 AND 4 HOURS X404 -- 4 HOURS X405 -- 4 HOURS X406 -- 4 HOURS X407 -- 4 HOURS X408 -- 4 HOURS X410 -- 3 HOURS X411 -- 3 HOURS X413 -- 2 HOURS N.B.S./BMS-135 --2, 3 & 4 HOURS	A406 -- 5 HOURS A401 -- 4 HOURS A405 -- 4 HOURS D403 -- 4 HOURS D404 -- 3 AND 4 HOURS D405 -- 4 HOURS D407 -- 2 HOURS D910 -- 11/2, 2, AND 3 HOURS D911 -- 2 HOURS P405 -- 3 HOURS P406 -- 3 HOURS P909 -- 1 HOURS	U-201 -- 4 HOURS U-203 -- 2 HOURS U-316 -- 1 HOURS U-409 -- 1 HOURS U-413 -- 2 HOURS

Some of these ratings are for perlite, and some for vermiculite.
Please check your U.L. Fire Resistance Directory for the most current values
and for designs, listings of manufacturers, etc.

For more information about perlite and vermiculite in plaster, go to www.schundler.com/plaster.htm

Beginning in the 1950's and up to the present, many pre-blended forms of vermiculite and perlite fire-proof plasters have been sold under a number of different brand names---all with their own U.L. listings and benefits. Most of these are well known in the construction industry and among architechs around the world.