Specification:Patching scaling concrete masonry

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=GENERAL=

SUMMARY
 This procedure includes guidance on patching scaling concrete with a mortar patch. Scaling of concrete masonry is the local flaking or peeling away of the near surface portion of concrete or mortar. It is often caused by:  Overtroweling: Weakens the bond of the surface concrete to the concrete below by bringing an excess of fines to the surface. Insufficient concrete strength: Often a result of cool temperatures that do not allow the concrete to cure properly and gain sufficient strength to withstand freeze/thaw cycles and the application of de-icing chemicals. The use of concrete with low air contents in areas exposed to severe winter weather. Heavy application of salts and/or de-icing chemicals. The use of high slump concrete. Improper curing methods or lack of curing.</li> Insufficient protection of fresh concrete during cold temperatures.</li> </ol> </li> See Specification:General project guidelines for general project guidelines to be reviewed along with this procedure. These guidelines cover the following sections: <ol> Safety Precautions</li> Historic Structures Precautions</li> Submittals</li> Quality Assurance</li> Delivery, Storage and Handling</li> Project/Site Conditions</li> Sequencing and Scheduling</li> General Protection (Surface and Surrounding)</li> </ol> </li> </ol> These guidelines should be reviewed prior to performing this procedure and should be followed, when applicable, along with recommendations from the State Historic Preservation Officer (SHPO).

DEFINITIONS
<ol type="A"> Scaling is the local flaking or peeling away of the near surface portion of concrete or mortar. <ol> Peeling: Thin flakes of mortar are broken away from the concrete surface.</li> Light scaling: Loss of surface mortar without exposure of coarse aggregate.</li> Medium scaling: Loss of surface mortar without exposure of coarse aggregate.</li> Severe scaling: Loss of surface mortar 5 to 10 mm in depth with some loss of mortar surrounding aggregate particles 10 to 20 mm in depth so that aggregate is clearly exposed and stands out from the concrete.</li> Very severe scaling: Loss of coarse aggregate particles as well as surface mortar surrounding aggregate, generally greater than 20 mm in depth.</li> </ol> </li> <li>Spalling is a more extreme form of scaling.</li> </ol>

MAINTENANCE
<ol type="A"> <li>Check to see that all gutters, downspouts and other water run-off systems are in good repair and clear of debris.</li> <li>Correct conditions of "rising damp", splashback, and foundation wetness.</li> <li>Remove water-entrapping vegetation from on or near the concrete walls.</li> <li>Do not use salt to melt snow anywhere near concrete walls.</li> </ol> =PRODUCTS=

MANUFACTURERS
<ol type="A"> <li>Thoro System Products 7800 NW 38th Street Miami, FL 33166 305/597-8100</li> </ol>

MATERIALS
<ol type="A"> <li>Mortar Patching Material: Composition to be determined by State Historic Preservation Officer (SHPO)</li> <li>Bonding Agent or Cement paste such as "Acryl" (Thoro System Products), or as specified by SHPO</li> <li>Rebars and/or stainless steel pins as required</li> <li>Epoxy as required</li> <li>Clean, potable water</li> </ol>

EQUIPMENT
<ol type="A"> <li>Hammer and chisel</li> <li>Trowel</li> <li>Mortar board</li> <li>Masonry drill</li> </ol> =EXECUTION=

ERECTION,INSTALLATION, APPLICATION
<ol type="A"> <li>Cut back damaged area to stable material. Roughen the surface with a hammer and chisel.</li>

<li>Remove all rust from any exposed rebar.</li> <li>Cut out any rebar which is severely corroded and splice in new rebar- consult SHPO.</li> <li>Paint freshly cleaned rebar with an epoxy coating to prevent further rusting.</li> <li>If the patch is unusually large, drill holes into sound substrate and insert stainless steel pins anchored with epoxy.</li> <li>Remove all dust and debris by water blasting, air blasting, or with a broom or vacuum.</li> <li>Square off the perimeter of the area to be patched so that a feathered edge will not be required.</li> <li>About 1 hour before making repair, moisten surface of area to be patched.</li> <li>To insure a good bond between patch and substrate, brush substrate surface with either a cement wash or a bonding agent such as Acryl.</li> <li>Apply patching material, with a trowel, in 3/4" layers, compacting thoroughly after each layer.</li>   <li>Work the finished surface carefully making sure to match texture and appearance of surrounding surfaces.</li>  </ol>