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• Mulch is always required for seeding. Mulch can be applied on top of <br />the seed or simultaneously by hydroseeding. <br />On steep slopes, Bonded Fiber Matrix (BFM) or Mechanically Bonded <br />Fiber Matrix (MBFM) products should be used. BFMlMBFM <br />products are applied at a minimum rate of 3,000 pounds per acre of <br />mulch with approximately 10 percent tackifier. Application is made <br />so that a minimum of 95 percent soil coverage is achieved. Numerous <br />products are available commercially and should be installed per <br />manufacturer's instructions. Most products require 24-36 hours to <br />cure before a rainfall and cannot be installed on wet or saturated soils. <br />Generally, these products come in 40-50 pound bags and include all <br />necessary ingredients except for seed and fertilizer. <br />BFMs and MBFMs have some advantages over blankets: <br />• No surface preparation required; <br />• Can be installed via helicopter in remote areas; <br />• On slopes steeper than 2.5:1, blanket installers may need to be roped <br />and harnessed for safety; <br />• They are at least $1,000 per acre cheaper installed. <br />In most cases, the shear strength of blankets is not a factor when used on <br />slopes, only when used in channels. BFMs and MBFMs are good <br />alternatives to blankets in most situations where vegetation establishment <br />is the goal. <br />• When installing seed via hydroseeding operations, only about 1/3 of <br />the seed actually ends up in contact with the soil surface. This reduces <br />the ability to establish a good stand of grass quickly. One way to <br />overcome this is to increase seed quantities by up to 50 percent. <br />• Vegetation establishment can also be enhanced by dividing the <br />hydromulch operation into two phases: <br />l. Phase 1- Install all seed and fertilizer with 25-30 percent mulch <br />and tackifier onto soil in the first lift; <br />2. Phase 2- Install the rest of the mulch and tackifier over the first lift. <br />An alternative is to install the mulch, seed, fertilizer, and tackifier in one <br />lift. Then, spread or blow straw over the top of the hydromulch at a rate of <br />about 800-1000 pounds per acre. Hold straw in place with a standard <br />tackifier. Both of these approaches will increase cost moderately but will <br />greatly improve and enhance vegetative establishment. The increased cost <br />may be offset by the reduced need for: <br />1. Irrigation <br />2. Reapplication of mulch <br />3. Repair of failed slope surfaces <br />February 2005 Volume ll — Construction Stormwater Pollution Prevention 4-95 <br />