Stucco is an exterior cladding material that is applied wet as a “mud” and dries hard. Apart from perhaps stone, stucco has been employed as a building material longer than any other. It remains timeless because of both its storied durability and, its often heralded, flexibility, that is – stucco provides a limitless range of options in decorative finish.
Stucco is generally broken into two categories: Polymer-modified synthetic stucco and traditional cement-based stucco. Either can be fiber-modified (with fiber glass or acrylics). While materials and the resulting preparation processes have evolved in recent years, many of the considerations (like moisture management) and techniques required for physically applying a mix to a wall remain the same.
Traditional or three-coat stucco consists of Portland cement, sand, and lime and is applied in three-coats (hence the name, three-coat stucco). Components are blended in varying proportions with water, producing a peanut butter-like paste that is then troweled or sprayed onto a surface. Proper mixing, which varies based on the stage or phase of the “assembly,” is absolutely critical for the final appearance and longevity of the job.
|Tools||Materials||Skill Level||Estimated Time|
|• Trowels (rectangular, pointed, finish)||• Roofing felt (15lb) or stucco wrap||Advanced||5 days minimum|
|• Mortar board or hawk||• Galvanized casing bead or control joint|
|• Straightedge or scarifier||• Galvanized weep screed|
|• Whisk broom||• Wire lath (wire mesh)|
|• Masonry brush or browning brush||• Galvanized roofing nails (various lengths)|
|• Hammer (pneumatic nailer)||• Self-furring lath nails or galvanized 4d nails (depending on lath type)|
|• Aviator snips (right, left, straights)||• Crown staples|
|• Mixing trough (Wheelbarrow)||• Stucco base mix|
|• 5- gallon bucket(s)||• Stucco finish mix|
|• Hoe or low-speed mixer||• Plastic sheathing|
|• Masonry string|
|• Wood and cork floats|
|• Garden hose|
|• Eye protection|
|• Heavy-duty gloves|
|• Mortar mixer (optional)|
|• Cement sprayer (optional)|
Below I will describe the steps required for installing traditional three-part stucco; however, installing it in a whole-house context is really a job far beyond that of a single DIYer. It's a painstaking process requiring a mix of patience and precision that only a team of people could yield. Often you’ll find crews broken down according to the steps and functions found on the job. Like a drywall or masonry crew, these designations could include laborers, mixers, installers, as well as finishers.
Traditional stucco is applied in three layers: a base (or scratch) coat, the brown coat (which itself is addressed in two stages) and the finish coat. Each serves a unique purpose. Some installations may or may not be given a fourth coat known as fog coat, which could assign the stucco with its final color. While one-coat synthetic mixes are available, these products are better left for installers with knowledge of the “systems” they are designed for. One-coat stuccos will require the use of specialty products and procedures, specifically at the point at which the substrate is prepared.
1. Prepare for the Job
Stucco can be applied directly to stone, block, or brick, provided that these surfaces are clean and intact. These surfaces are often treated first with a bonding agent and effectively, the first step in the three-coat process can then be skipped.
In terms of exterior cladding, you will find it applied rather over the framed structure's shell, or sheathing. This substrate must be well-constructed and sound before the installation can begin. Traditional stucco is most often bedded in a “self-furring” wire mesh–aka lath, which is found both in sheets and rolls. The most common variations are a one-inch hexagonal “netting” or a diamond-shaped, dimpled lath.
Building codes vary based on region. Codes, in many cases, dictate specific fastening requirements for the lath. Lath is installed using self-furring, roofing, or other large-head, corrosion-resistant 4d nails–depending on the type of lath selected. The sheathing itself is fitted with roofing felt (15lb traditionally, installed in some cases in two layers), treated building paper, or more scientifically advanced weather barrier. These materials help manage the moisture that ultimately makes its way behind cladding.
These membranes are stapled with crown staples or nailed with capped (roofing) nails; either can be pneumatically-driven. Depending on the selected product, most self-seal. Some membranes may or may not require a construction tape during installation. (Installing house wraps, and other water-resistant membranes, is another discussion altogether.)
2. Prepare the Surface
At the base of the installation, a galvanized weep screed (or stop bead) is installed. It is typically installed as such that it laps the home's foundation by a few inches. Using a laser or line level, a chalk line is snapped along long stretches to ensure that this bead is installed level.
The bead is fastened to wood framing with roofing nails. Nailing should find framing members and penetrate at least ¾”. For fastening at the foundation, specialized fasteners are used based on the foundation type. Nailing occurs on eight-inch interval (or otherwise according to manufacturer recommendations).
Stucco weep screed comes pre-fitted with weep holes. At the base of an installation, these 1/8” or so holes allow any moisture that may get behind the assembly to “weep” out without issue. Take care not to damage, cover, or otherwise fill these holes while you work. Stop bead similarly is installed at the top of the installation, but of course, in reverse and facing down. It provides a capping edge for the installation and should be installed tight to the soffit.
Galvanized casing bead, designed to go around openings (windows and doors), is sometimes fitted itself with a short (four-to six-inch) strip of wire mesh. After starter strips are installed, install casing bead at doors and windows--the bead's long leg facing out.
With precision, cut the mesh and a part of the flanged portion of the galvanized piece, such that a single run can bend around at corners. Completing this aspect of the installation in as few pieces as possible creates a continuous plane, while minimizing failure points. Casing bead, and other trim elements, can typically be found in ten-foot lengths.
Working with a partner (or two), the wire lath is then rolled out and applied to the surface. Nailed with galvanized fasteners, it is brought fairly taught as not to contain kinks, bends, or sagging. Nailing is sometimes achieved in a grid fashion, where the four corners are nailed first.
Dictated in part by the substrate, the wire is then fastened throughout the field on nothing more than a 16-inch center. Spacing as small as six-inches can be utilized and is in fact common. The wire can appear to ride on, almost "hooking" on top of the installed nails, but often a slight bending of fasteners may be required. Galvanized beads as well as the wire lath can effectively be cut with aviator snips.
A consistent-nailing pattern with regular pressure is important during installation. This is important because compression in the netting can and does affect the stucco’s ability to "key" to it. At intersections where “sheets” meet, the mesh should lap ½ to one inch and one to two inches at horizontal and vertical seams respectively. Sections of netting are bound together with wire ties, which are then tucked back into this portion of the assembly.
This wire lath serves multiple purposes, including giving the base, aka scratch, coat a place to bond, bed, or “key”. This meshing also affords for some expansion and contraction at the insertion of varying building materials--the point between the stucco and the softer wood installation below.
Expansion and contraction in the assembly is further managed by control joints (as you’d see in say a sidewalk). Controls joints are installed either horizontally or vertically on longer wall spans and help prevent unwanted cracks and failure in the installation. Galvanized M or VV control beads are often nailed at structural breaks, like the transitions between floors, where framing members (joists) are present.
Both inside and outside corners can provide an opportunity to install control joints. These too can be fitted with casing or stop bead. Self-furring or “ribbed” lath allows the entire assembly to relieve itself of potentially damaging moisture.
3. Mixing Stucco
On Mixes: Stucco today may be purchased fully pre-mixed. Like mortar or concrete, stucco products can frequently be found in 50-or 80-pound bags. Bulk buys are also possible. Varying blends have differing component mixtures. These mixes target the individual phases of a three-coat stucco job. You’ll find a general-purpose base coat mix (some modified with fiber), a scratch and brown coat mix, as well as several types of finish coat mixes–with and without color addictive.
Most can be extended with “plaster sand,” but unmodified 80-pounds of stucco powder will yield roughly 15 to 20 square feet at about a 1/2” inch.
With that in mind, you (or your contracted pro) might opt for mixing components by hand. Doing so can offer a big win in terms of cost. There are countless recipes available online that pair cement, sand, and lime–again, the base components.
Recipes will vary not only on the phase of assembly--first, second, or third coat, but also on such factors as geographic location, climate, and even the prevailing temperature and precipitation expected on the day(s) of installation. Your masonry supplier should be able to assist both in estimating materials needed for the job as well as with an appropriate recipe.
Personal preference may also have a big impact on the qualities called out for ingredients. Many recommend replacing traditional Portland cement with a more workable plastic cement. In general, base coats will demand up to a three to one ratio of sand to cement in any given mix.
Mixing: When mixing, try thinking of this process as mixing the materials (the components) into your water. A perfect mix should stick to a trowel when it is held at roughly a 45-degree angle. You should be able to pick it up and almost roll into a ball. It should leave a residue in your gloved hands, but it should not stick to them.
On mixing for a whole-house installation, a mortar mixer (available for rent at home improvement or rental centers) can be utilized to speed this process. For smaller project areas, you may choose a low-speed mixer or drill working in one or more five-gallon buckets. More traditionally, you might mix your stucco with hoe in a wheelbarrow. Water can be added periodically throughout the mixing process to achieve the consistency needed. Once mixed, your mud has a limited working time of 45 minutes to an hour.
Color, in part, will be dictated by the exact proportions of your mix's components. If it is heavy on cement, the color produced will be a white-gray, if it is heavy on sand, the color will be a brown. In fact, this is indeed from where we get monikers like “brown” coat. Traditionally colors are achieved by mixing in coloring agents, oxide powders, with the finish coats. Some mixes come pre-colored and offer a modest range of colors. Others are "misted" on in an optional fog coat. Stucco, like concrete, accepts latex paint finishes as well.
Important! Inconsistencies in the mix, especially to the amount of water added throughout the job, can create the possibility for "flashing" or "ghosting," where sections of the surface will stand out in color undesirably. Because of this, it is of paramount importance that the mixing throughout the job remains consistent, often left to the same individual throughout the length of the job.
4. Applying Stucco
When installing stucco, think of it with this rhythm: mixer, mortar board, hawk, trowel, wall. Stucco once mixed is often moved to a mortarboard, where individual installers can then load their hawks (a smaller, more mobile mortar board). Mortar is than transferred from the hawk to the surface.
Stucco is cut from the hawk in a two-handed motion. Tilting your trowel away from your body, your trowel comes upwards, while your hawk almost moves back towards you. The stucco is applied using a rectangular trowel and where practical, in an upward stroke. Edges and tighter spots are addressed with a pointed and often smaller trowel.
Alternatively, you may consider renting a cement sprayer or hopper for a quick application. However, cement sprayers are designed only to deliver material to the surface, you will still need to provide significant trowel work to get the stucco exactly how you need it.
5. Applying the Stucco in Three Coats
The Scratch Coat: As the initial coat, the scratch coat is designed to be pushed through the wire mesh, such that when it cures it forms "keys"--a slumping in the stucco that utilizes gravity to grab onto the lath. Because of this, and while you'd expect this coat to finish at about 3/8" thick, you will more than likely actually be applying closer to a 1/2" of material.
Before moving away from the scratch coat, it is scarified, that is--scored or scratched. A specialty tool called a scarifier is designed just for this purpose. Comparable to a drywall knife in size, it is fitted with long tines that are gently raked across the surface.
Alternatively, a more seasoned pro might use the long edge of a rectangular trowel or may even build their own scarifier for addressing larger areas. The scratching done in this coat allows the more vital second coat to effectively bond. The scratch coat under good weather conditions is allowed to dry for four to six hours.
The Brown Coat: A browning broom or misting from a garden hose is used to spritz water and moisten the surface before the brown coat is to begin. The second coat gets its name from a traditional heavy use of sand. Your second coat may or may not truly be brown in color. Regardless, the second coat gives the stucco job its soundness. It is at this point within the assembly that the plane of the finished surface is established.
The brown coat is troweled on with a rectangular trowel in a manner similar to the scratch coat above. Seasoned installers will often drive roofing nails at intervals throughout the field of the installation. By running masonry string either horizontally or as a web between nails, installers then have a guide to help them set a four-by-four grid of nails, which is repeated.
Note: It is important to remain mindful of projections such as door and window trim as this is done. Your stucco should, of course, finish below them.
Later the string itself is removed. Mud in this stage is applied in a more pronounced vertical manner. This method is called "screeding." To smooth out larger sections or to identify low spots in the installation, reach for a perfectly true piece of trim board or a metal straightedge. In most cases, the nails left behind here are used as pivot points for checking plane and may simply become part of the final installation as the stucco is built-up.
Again dampening any dried surface area before applying new material, the final aspect of the brown coat is applied. The goal with this coat is to create a surface that is as free of imperfections as possible. A thin coat of additional material is feathered into any ridges created during screeding above. Additional water may be broomed over the surface at this point to make the process of feathering easier.
As the brown coat begins to cure, perhaps within an hour, a wood float can be used to create a flat yet gritty surface. The wood float is worked with a light circular motion over the entire surface.
Once this brown coat is in place, the entire installation to this point should be misted with the garden hose every 12 hours for the first 48 hours. Note: Allowing stucco to dry out can cause cracking in the short term and general brittleness across the life of the installation. Next, cover with plastic sheathing an additional two days.
6. Finishing the Job
The Finish Coat: Final texture can be applied after the brown coat has set for three to five days. This is the point at which presenting color is applied to the assembly.
One reason for stucco's timeless appeal is the versatility it affords in this final stage. It is here a texture is imposed and quite literally, a limitless set of options are available to finishers. This phase of the job should be very well thought out, and the approved texture should be practiced repeatedly in an inconspicuous location.
Use the home's architectural style or other nearby homes as a cue for choosing your texture. Common finishes include a floated (aka smooth) finish, slop-pebble finish, glass, and rock dash, or numerous others with antique origins. Textures created by stippling, jabbing, or scraping the surface are easiest, while smooth or splattered finishes are surprisingly harder to achieve. The trickiest part is staying consist across the entirety of the surface.
Finish-coat stucco is applied with a finishing trowel, but is often addressed with an additional implement--a cork float, brush, broom, sponge, wood block, etc. Mix finish-coat stucco as per manufacturer instructions or according to your chosen recipe. Each distinct texture may be accompanied with its own unique recipe. It is best to only apply finish coats in cooler temperatures when significant rains are not forecasted (a light misting is fine).
With traditional stucco, it is best not to disturb the finish for the first 24 hours after its application. Ideally the installation will then again be misted three to four times over the next two days. Covering the installation with plastic sheathing for at least one additional day allows the assembly to retain the required moisture it will need for proper curing.
Apply a “fog coat” or paint when appropriate to achieve any tweaks in color. Paints may be applied based on manufacturer recommendations. When in doubt, allow the stucco up to a month of cure time before painting.
A stucco seal coat can then optionally be applied. Follow all manufacturer recommendations, adhering closely to requirement regarding your specific installation and cure times.
7. Stucco Installation Service
Installing stucco is a big job that requires both a good bit of effort as well as a significant outlay in terms of materials. Some might refer to stucco as an artisans finish, meaning installers (many splitting time also as masons) have developed their craft through years of practice.
Because it is such a significant undertaking and because any misstep in preparing the substrate, mixing product or in the curing process can lead to a catastrophic failure, it again may be best to leave a big enough job to the hands of a professional for stucco installation.
For small or repair jobs, the most important aspect of the installation is finding the exact type, mix, texture, and color you are trying to match. While repair and one-coat products are available, it often best to follow steps that more closely resemble a new stucco installation.
Related Guides: Stucco Installation Cost