News Article

Installing Stucco Finish on ICF Walls

Stuc­co pro­vides a beau­ti­ful fin­ish for insu­lat­ed con­crete forms (ICF) like the Bau­tex Block Wall Sys­tem. Apply­ing stuc­co over ICF pro­vides a mois­ture-resis­tant and durable fin­ish. Stuc­co is also rot‑, rust‑, and fire-resis­tant. There are three gen­er­al types of stuc­co sys­tems: tra­di­tion­al stuc­co, exte­ri­or insu­la­tion and fin­ish sys­tems (EIFS), and thin-coat stuc­co. Each type has its advan­tages and dis­ad­van­tages. Bau­tex Block Wall Assem­bly uti­lizes the thin-coat stuc­co method because it has all the ben­e­fits of tra­di­tion­al stuc­co and EIFS (dura­bil­i­ty and mois­ture-resis­tant, fire-resis­tant, design flex­i­bil­i­ty). Yet, thin-coat stuc­co is quick­er to install, less expen­sive, and more durable in the long-run.

Successful Stucco Application

The suc­cess of each of the stuc­co meth­ods is depen­dent on prop­er instal­la­tion, includ­ing details at open­ings, tran­si­tions, and the edges of the wall cladding.

The prop­er instal­la­tion of a com­pat­i­ble weath­er-resis­tant bar­ri­er (WRB) under the stuc­co is of par­tic­u­lar impor­tance. The pur­pose of the WRB is to stop water from enter­ing the wall assem­bly should it get behind the stuc­co sys­tem, and to, low­er air infil­tra­tion into the build­ing over­all. In fact, Sec­tion R703.6.3 of the Inter­na­tion­al Res­i­den­tial Code (IRC) man­dates that the water-resis­tant bar­ri­er used under stuc­co have a per­for­mance at least equiv­a­lent to two lay­ers of Grade D paper1. Prop­er instal­la­tion of a WRB under stuc­co is essen­tial for cre­at­ing a mois­ture-resis­tant ICF struc­ture and should not be skipped.

Traditional, EIFS, and Thin-Coat Stucco

Traditional stucco is an exte­ri­or wall fin­ish made from Port­land cement, sand, and lime. The tra­di­tion­al stuc­co method involves apply­ing three coats of mate­r­i­al over a met­al lath that is mechan­i­cal­ly attached to the wall. The lath is attached over the WRB and to the exte­ri­or of the struc­ture (typ­i­cal­ly on con­ven­tion­al wood-frame con­struc­tion, mason­ry, or con­crete). The three coats include a scratch coat, base (brown) coat, and an expan­sive acrylic-poly­mer fin­ish (top) coat that reduces the poten­tial for crack­ing. The three coats pro­duce a 7/8‑inch- to 1‑inch-thick cladding that resem­bles clay or con­crete.

The pri­ma­ry dis­ad­van­tage of tra­di­tion­al stuc­co over thin-coat stuc­co is that tra­di­tion­al stuc­co is more time and labor inten­sive, there­fore more expen­sive, than thin-coat stuc­co sys­tems in most cas­es. Tra­di­tion­al stuc­co is also more sus­cep­ti­ble to crack­ing over time due to the nat­ur­al shrink­ing of Port­land cement as it cures.

Exterior insulation and finish systems (EIFS), or syn­thet­ic stuc­co sid­ing, is mul­ti­lay­ered but looks like tra­di­tion­al stuc­co. EIFS includes a lay­er of up to four inch­es of rigid insu­la­tion, attached either adhe­sive­ly or mechan­i­cal­ly, or both, to the sub­strate. EIFS also con­sists of a rein­forced base coat, a fiber­glass mesh, and a tex­tured, pro­tec­tive syn­thet­ic stuc­co top coat. Drainage EIFS incor­po­rates a sec­ondary mois­ture bar­ri­er and a drainage mat with weep holes in the bot­tom that let the mois­ture drain behind the stuc­co but exte­ri­or to the wall itself. EIFS is more flex­i­ble and soft­er than tra­di­tion­al stuc­co, so it allows for ornate key­stones and cor­ner­stones that tra­di­tion­al stuc­co pre­vi­ous­ly could not hold. Because of its inclu­sion of an rigid insu­la­tion lay­er, EIFS is also more ener­gy-effi­cient than tra­di­tion­al stuc­co. The poten­tial down­side of EIFS is that it may be slight­ly more expen­sive than tra­di­tion­al stuc­co and is more sus­cep­ti­ble to impact dam­age due to the thin stuc­co lay­er and soft insu­la­tion.

Thin-coat stucco (one-coat, two-pass, thin-coat, or fiber­glass-rein­forced stuc­co) sys­tems speed up and sim­pli­fy the process of installing stuc­co. Thin-coat stuc­co has one base coat with a thin fin­ish coat that is typ­i­cal­ly applied while the base coat is still wet; thus, also called two-pass. In some cas­es, the base coat is a com­bi­na­tion of Port­land cement, fibers, and pro­pri­etary addi­tives. Some abuse-resis­tant one-coat stuc­co sys­tems replace the Port­land cement with a min­er­al-based cement like mag­ne­sium oxide which cre­ates a hard­er and more durable fin­ish that is high­ly resis­tant to crack­ing and dam­age.

Each mate­r­i­al has its own Inter­na­tion­al Code Coun­cil (ICC) Eval­u­a­tion Ser­vice (ES) report that man­dates the instal­la­tion details. Thin-coat stuc­co pro­vides the same ben­e­fits as tra­di­tion­al stuc­co and EIFS (dura­bil­i­ty, design flex­i­bil­i­ty, and fire resis­tance), yet saves mon­ey because it takes half to the time to apply, which reduces con­struc­tion time and labor.

Application of the Thin-Coat Stucco over Bautex Block Wall Assembly

Bau­tex uti­lizes a min­er­al-based thin-coat stuc­co method because it is the most cost-effec­tive, prac­ti­cal, and quick­est way to install a stuc­co fin­ish to the Bau­tex Wall Sys­tem while cre­at­ing a robust and abuse-resis­tant build­ing assem­bly. Apply­ing thin-coat stuc­co over the Bau­tex Block Wall Assem­bly, includ­ing the Bau­tex AMB 20 air and mois­ture bar­ri­er, ensures that if any mois­ture gets behind the stuc­co, it will stay to the out­side of the wall sys­tem. The thin-coat method is also aes­thet­i­cal­ly pleas­ing, durable, and rust‑, rot- and fire-resis­tant. For more infor­ma­tion on installing stuc­co fin­ish on ICF walls, please watch our YouTube video Installing Stuc­co fin­ish on Bau­tex Block Walls.”.

1The Amer­i­can Soci­ety for Test­ing and Mate­ri­als (ASTM) stan­dards for what con­sti­tutes best prac­tice for the ingre­di­ents and the appli­ca­tion of port­land cement plas­ter, or stuc­co. Accord­ing to R703.6.3 of the Inter­na­tion­al Res­i­den­tial Code, instal­la­tion of exte­ri­or plas­ter must be in accor­dance with the fol­low­ing,

  • ASTM C 926, Stan­dard Spec­i­fi­ca­tion for Appli­ca­tion of Port­land Cement-Based Plas­ter
  • ASTM C 1063, Stan­dard Spec­i­fi­ca­tion for Instal­la­tion of Lath­ing and Fur­ring to Receive Inte­ri­or and Exte­ri­or Port­land Cement-Based Plas­ter