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Stucco ( EIFS )

So My question is Why is it that carpenters only sheath the corners of a house and the stucco guys sheath the rest of the house with styrofoam boards..??? Is this standard ??? I plan on doing a stucco job and want to know if I can just apply Foam Board  over studs with out any OSB or PLY .. The way I seen them do it was : Stud wall then building paper, then foam board, then mesh wire, then stucco ....

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Posted 2012-09-05T21:54:46+0000  by kali83 kali83
 

Hi Kali83,

 

Each trade does their specific portion of the job. The unions have worked this out over the years.

 

All stucco finished construction uses sheathing. Normally this is osb or plywood as the local codes requires.

 

The foambord is for insulation only and does not add structural strength to the building.  EIFS systems are the latest development in insulation and stucco finish systems.

 

Below if have included information from The Minnesota Lath and Plaster Bureau on these systems.

 

 

 

 

 

THERE ARE TECHNICALLY FOUR TYPES OF EIFS

 

 

(1) Class PB or Polymer Based EIFS:

Uses expanded polystyrene insulation board which is adhered to the substrate with proprietary polymer based adhesive that is applied with a notched trowel to the back of the insulation board. In most cases the adhesive that is used in this process is the same material that is used for the base coat and may or may not include portland cement in its composition. After the board has been allowed to set, the surface of the insulation board is often rasped to flatten out high spots and break the surface for a better key of the base coat. The base coat is then troweled onto the surface and a reinforcing mesh is encapsulated by embedding it with a trowel into the base coat. In some instances it is necessary to add more base coat to completely encapsulate the mesh. This process is then followed with an acrylic decorative finish color top coat, floated to the desired texture. Typical thermal values of expanded polystyrene foam board are R3.65/inch. Typically wall thicknesses of these systems are installed from 1" to 4". Larger thicknesses are often used to create the look of heavier decorative features, such as quoins, bands, classic entablature and other decorative shapes.

 

 

(2) EIFS with Drainage:

In most cases is similar to that of PB EIFS with the exception that a liquid applied water-resistive barrier is installed over the substrate to provide a level of redundancy for moisture protection. These liquid membranes are troweled, roller, or spray applied, generally over a substrate of glass fiber faced gypsum sheathing, oriented strand board or plywood, depending upon the manufacturer's requirements. Combined with compatible reinforcing fabrics and membranes, penetrations and joints between the sheathing boards are treated to help prevent moisture from breaching the assembly and getting into the cavity or framing of the building. The expanded polystyrene insulation board is adhered with a proprietary adhesive with a notched trowel. The adhesive is oriented in a vertical direction on the back of the insulation board, to provide a medium for the drainage of moisture between the liquid applied membrane and the insulation board. After the board has been allowed to set, the surface of the insulation board is often rasped to flatten out high spots and break the surface for a better key of the base coat. The base coat is then troweled onto the surface and a reinforcing mesh is encapsulated by embedding it with the trowel into the base coat. This process is then followed with an acrylic decorative finish color top coat floated to the desired texture.

There still exist more rudimentary and complex forms of these types of systems, which include mechanically attaching housewraps or building paper, drainage mediums of tangled plastic netting, furring, channeled and compartmented insulation board. While many manufacturers still carry these products, they have fallen out of favor in lieu of the newer more user friendly and advanced technology.

 

 

(3) Class PM or Polymer Modified EIFS:

Uses planed or sanded extruded polystyrene insulation which is mechanically attached over a water-resistive barrier and substrate with screws and plastic washers or discs. The reinforcing mesh is generally attached using the same fasteners as are used in attaching the insulation board. The base coat is mixed with the addition of cement, sand, water and a liquid polymer to make a coating that is applied 1/4" to 3/8" thick. This is followed by a texture able acrylic decorative finish color top coat. Because of its thickness, coefficient of expansion and contraction and its affinity to similar stucco compositions, PM systems require mechanical control joints to provide stress relief from panel to panel. Typical thermal values are approximately R5/ inch of extruded polystyrene foam board. Limitation to this product's use is higher cost of materials while being much more labor and skill intensive than the PB system. Competitive in the 1980's with the more popular PB systems, PM systems are not used to any great extent today, although many manufacturers still carry them as part of their product line.

 

 

(4) Class PI EIFS:

PI in this reference refers to Polyisocyanurate Insulation boards. PI boards generally have a higher density than extruded or expanded polystyrene insulation board, with a higher thermal value of approximately R7/ inch. They are distinct in that the core is yellow in color and a fiberglass facer is installed over the surface of the board. Because of these physical characteristics, PI board is typically installed mechanically with screws and polypropylene discs over substrates generally of sheathing board. Because of the fiberglass facer, rasping of the board is prohibited. Like PB systems however, a proprietary polymer base coat is applied over the surface of the insulation board and a fiberglass reinforcing mesh is embedded into it. Finish is applied in a similar manner to PB EIFS. PI systems have had a larger following in the residential market because of their simplicity of installation. Occasionally they are used in a commercial setting as a substrate for darker pigmented finishes. This is because the in-service temperature of the PI board exceeds that of expanded polystyrene. Like PM systems however, their use have diminished over the years in favor of products that have been developed for EIFS with drainage.

 

I hope this answers your question

Mike,

 

 

Posted 2012-09-06T17:36:33+0000  by Mike_HD_OC

"Why is it that carpenters only sheath the corners of a house..."

The amount of plywood sheathing is usually an engineering specification; Shearing the corners is usually the most effective way to add shear value. If you want to go the EIFS route you need atleast Exterior gypsum sheathing and eifs mesh over the house wrap.  Styro-foam board out-sulation is not required but check local codes.

Posted 2012-11-08T01:02:05+0000  by gbconstruction
 
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