We have a project where we have to fireproof the metal roof deck in various structures, including exterior eyebrows. Any recommendations for products that are moisture resistant? The eyebrows are enclosed with metal panels, sheathing and an air barrier, so in theory there will be no water. Its also in a dry climate (under 9 inches per year. Climate Zone 3). Nevertheless, in the spirit of belt and suspenders and staples I am looking for something that is moisture resistant.
Is there an advantage to portland cement versus gypsum cement?
You definately do not want to use a gypsum-based fireproofing on the exterior.
Portland cement is better, but still subject to moisture issues in exterior applications.
I would look into the intumescent fireproofings. Thet offer a greater degree of moisture resistance over the Portland cement based products. Look at the Carboline products.
thin-film intumescents are comparatively very expensive. unless clearance for application access or thickness are specific project issues (other than pure aesthetics), you might want to consider medium or high(er) density portland cement products, e.g., Grace Monokote Z-106 or Z-146 (or Carboline Pyrocrete series).
Grace Monokote Z-106 and Z-146 are not intended for exterior use. Grace does have a Z-156/Z-156T which is available for exterior use.
Carboline 7HD @ 40pcf, has the highest density, but I still lean towards the intumescents. Although they are generally more expensive than the cementitious type, they have a much better in-service performance in exterior environments.
Carboline’s Nullifire S605 or Albi 800 would both be appropriate for your application.
I was involved with one of the first applications of an Albi product in an exterior application about 40 years ago.