DeHaven Construction Company
"Specializing in Stucco, Stucco Repair, Interior Painting, Exterior Painting, Texture Coating (Texcote™) & Elastomeric Coatings"
Stucco - Open Frame Application
Metal reinforcement must be applied on all open frame structures, whether of wood or metal frame, that will be plastered. The frame should be complete and carry the entire dead load of the structure prior to plaster application. Interior finishing may begin after exterior stucco work is complete, but vibrations or impacts against the exterior wall from the inside should be avoided.
In open-frame-wood construction, the structure frame should be properly braced and rigid. Where wire-mesh lath is used, a soft annealed-steel wire, No. 18 gauge or heavier (often called line wire), is first stretched horizontally across the face of the studs about 6 in. apart. The wire is stretched by nailing or stapling it to every fourth stud. It is tightened by raising or lowering it and securing it to the center stud.
Next, the wall surface is covered by a waterproof building paper or felt that is nailed over the wire strands. The paper or felt should be lapped shingle fashion at least 2 in. The line wire provide back support to minimize bulging of the paper or felt between the studs when plaster is applied and to help ensure a uniformly thick scratch coat.
Hexagonal-wire mesh (stucco netting) is applied over the waterproof building paper or felt, using furring nails that hold the mesh out ¼ to 3/8 in. from the framing or self-furred lath with attachments made at furring point. As the plaster is applied, it is forced through the mesh opening and against the backing, completely embedding the metal lath in plaster.
In open-frame-wood construction, junctions or laps should be avoided when installing metal lath at reentrant or external corners. The lath should be started at least one full stud space away from the corner and bent to conform to the corner.
Paper-backed diamond mesh and paper-backed welded-wire mesh lath can also be used in open frame construction. These types of lath can be applied directly over the studs
Stucco and Sheathed Frame-style Construction
The use of sheathing over wood or metal frame eliminates the necessity for wrapping the horizontal strands of annealed line wire around the structure. Sheathing materials include exterior gypsum board, insulated board, expand polystyrene, wood, or plywood. Wood sheathing should be applied horizontally and securely fastened to each stud. Whenever plywood sheets or insulating boards are used as sheeting, allow 1/8 in. space between adjoining plywood sheets or insulating board sheets to accommodate possible expansion of these materials.
Waterproof building paper or felt should always be placed over the sheathing, followed by the accessories, and then the metal reinforcement. Then the surface is ready for plastering. The lath and paper are lapped at the ends and sides for uninterrupted coverage of the surface. Metal reinforcement should be installed with its long dimension at right angles to the wood or metal stud supports.
Metal reinforcement must be attached to supports rather than the sheathing. In wood frame construction, metal reinforcement is fastened to the studs with furring nails or staples. Nails or staples for attaching the metal reinforcement to the wood studs should be galvanized or corrosion resistant. Aluminum nails should not be used where they will be in direct contact with the wet plaster in service. Cement reacts chemically with aluminum, causing corrosion and cracking. Wire ties, metal clips, or other means of attachment which afford equivalent carrying strength and corrosion resistance are used to attach metal reinforcement to metal supports.
Cement plaster can be proportioned using a variety of cementatious material and available aggregates to produce a hard surface that is resistant to abrasion and unaffected by dampness. Proportions should be adjusted to suit the use and climatic conditions that will prevail at the jobsite.
A properly proportioned plaster mixture is characterized by its workability, ease of troweling, adhesion to bases, and resistance to sagging. Batch-to-batch uniformity in scratch, brown, and finish coat mixture will help assure uniform suction, color, and serviceability.
Water content of plaster discharged from the mixer should be as high as can be tolerated for either hand or machine application. Water content of plaster after the finishing operation for a particular plaster coat has been completed will be lower than the water content of the plaster as discharged from the mixer.
Successful performance has been achieved by the combinations of cementatious materials aggregates. These proportions are recommended for scratch-and-brown coat applications. Note that the volume of aggregate is based on the sum of separate volumes of cementatious materials. When selecting the plaster mix, basic considerations include: suction of the base, its surface irregularities, climate extremes, extent of surface exposure, type of base, method of application.
These plaster mixtures can be prepared choosing combinations of cementatious material and local sands. The sand content of the plaster is given as average to allow the specifiers to select high strength, dense plaster where needed. A good rule is to select a mixture with the largest aggregate-to-cement ratio to reduce shrinkage and cracking. The use of an air entrained plaster is recommended for geographical areas with freeze-thaw temperature cycles and for all locations where deicer salt solution may be splashed against the plaster. For the brown coat plaster that is applied over scratch coat, the specifiers should select the same plaster type with equal or larger aggregate-to-cement ratios. This design practice places the lower strength mixtures with corresponding lower shrinkage characteristics toward the exterior.
Lime or other plasticizers should not be added to the mixture where masonry cement or plastic cement are used, since these cements already contain plasticizers.
For the finish coat, a factory prepared finish coat mixture should be considered, if locally available. The manufacturer's instructions should be closely followed for factory prepared finish coat plaster mixtures. Alternatively, the finish coat may be proportioned and mixed on site. If the finish coat plaster is mixed on site, truer color and a more pleasing appearance can be obtained by using white cement with a fine graded, light colored, washed sand. If coloring compounds are added during mixing, preweighted quantities should be introduced in the same sequence while charging the mixer. Close control of all quantities of mix ingredients is required to achieve consistent color.
Finished coat plaster to be prepared on site should be selected. The aggregate used for the finish coat plaster need not comply with grading requirements for basecoat plasters. Unless otherwise specified , all of the aggregate should pass the No.16 sieve and should be uniformly graded from coarse to fine. The sand should be selected for its ability to produce the desired surface texture.
Proportioning of plaster mixtures for texture and appearance is more an art than a science. Designers and specifiers should explore the many surface finishes available, or develop new ones, for the third or finish coat. Sample panels prepared prior to construction are an effective way to develop procedures, provide an acceptance standard for acceptance of work on the structure, and establish performance characteristics. A sample panel should represent that acceptable finished work in the structure and be at least 4 by 8ft.
Successful plastering depends on proper batching and mixing of individual and combined materials. The plaster should possess proper consistency and body to be either spread by hand or machine. Although batching by shovel is still the most common procedure, proportions should be checked daily by using volume measures. Full bag quantities of cement (and lime, if applicable) should be used if proportioning allows. The volume of plaster in the mixer, when a batch is properly proportioned, should be noted. Water additions should be batched by volume with calibrated measures (containers of known volume), a quick-fill tank, or a water meter.
Mixing should produce a uniform blend of all materials. The accepted procedure is to :
Ideally, mixing should be completed in a paddle type mixer within 3 to 5 minutes after all the ingredients are in the mixer. Where machine application is used, this mixing period may slow the plastering operation, so the mixer speed (rpm) should be adjusted to allow for shorter mixing periods. The proof of adequate mixing is the uniformity of the plaster as received and judged by the plasterer.
The water content of the plaster should be determined by the plasterer. The plasterer can best judge the correct water content by observing its ease of application and the degree of bonding to the substrate. Bonding to the substrate can easily be assessed by removing some the applied plaster and observing the degree of wetting of the substrate. Water is the only plaster ingredient that should be reduced or increased during on site adjustment of the approved mix.
Stucco Application InformationStucco & Stucco Repairs
Open Frame Stucco Application
Machine and Hand Application of Stucco
Application of Stucco to Bases
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