Patching Scaling Concrete Masonry
- Procedure code:
- Hspg Prepared For Nps - Sero
- Concrete Repair
- Last Modified:
PATCHING SCALING CONCRETE MASONRY
A. This procedure includes guidance on patching scaling
concrete with a mortar patch.
B. 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:
1. Overtroweling: Weakens the bond of the surface
concrete to the concrete below by bringing an
excess of fines to the surface.
2. 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
3. The use of concrete with low air contents in areas
exposed to severe winter weather.
4. Heavy application of salts and/or de-icing
5. The use of high slump concrete.
6. Improper curing methods or lack of curing.
7. Insufficient protection of fresh concrete during
C. See 01100-07-S for general project guidelines to be
reviewed along with this procedure. These guidelines
cover the following sections:
1. Safety Precautions
2. Historic Structures Precautions
4. Quality Assurance
5. Delivery, Storage and Handling
6. Project/Site Conditions
7. Sequencing and Scheduling
8. General Protection (Surface and Surrounding)
These guidelines should be reviewed prior to performing
this procedure and should be followed, when applicable,
along with recommendations from the Regional Historic
Preservation Officer (RHPO).
A. Scaling is the local flaking or peeling away of the near
surface portion of concrete or mortar.
1. Peeling: Thin flakes of mortar are broken away
from the concrete surface.
2. Light scaling: Loss of surface mortar without
exposure of coarse aggregate.
3. Medium scaling: Loss of surface mortar without
exposure of coarse aggregate.
4. 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
5. Very severe scaling: Loss of coarse aggregate
particles as well as surface mortar surrounding
aggregate, generally greater than 20 mm in depth.
B. Spalling is a more extreme form of scaling.
A. Check to see that all gutters, downspouts and other water
run-off systems are in good repair and clear of debris.
B. Correct conditions of "rising damp", splashback, and
C. Remove water-entrapping vegetation from on or near the
D. Do not use salt to melt snow anywhere near concrete
A. Thoro System Products
7800 NW 38th Street
Miami, FL 33166
A. Mortar Patching Material: Composition to be determined
by Regional Historical Preservation Officer (RHPO)
B. Bonding Agent or Cement paste such as "Acryl" (Thoro
System Products), or as specified by RHPO
C. Rebars and/or stainless steel pins as required
D. Epoxy as required
E. Clean, potable water
A. Hammer and chisel
C. Mortar board
D. Masonry drill
3.01 ERECTION,INSTALLATION, APPLICATION
A. Cut back damaged area to stable material. Roughen the
surface with a hammer and chisel.
CAUTION: AVOID GRINDING THE MATERIAL IN THIS PROCESS,
BECAUSE IT LEAVES THE SURFACE TOO SMOOTH TO ACHIEVE A
B. Remove all rust from any exposed rebar.
C. Cut out any rebar which is severely corroded and splice
in new rebar- consult RHPO.
D. Paint freshly cleaned rebar with an epoxy coating to
prevent further rusting.
E. If the patch is unusually large, drill holes into sound
substrate and insert stainless steel pins anchored with
F. Remove all dust and debris by water blasting, air
blasting, or with a broom or vacuum.
G. Square off the perimeter of the area to be patched so
that a feathered edge will not be required.
H. About 1 hour before making repair, moisten surface of
area to be patched.
I. To insure a good bond between patch and substrate, brush
substrate surface with either a cement wash or a bonding
agent such as Acryl.
J. Apply patching material, with a trowel, in 3/4" layers,
compacting thoroughly after each layer.
K. Work the finished surface carefully making sure to match
texture and appearance of surrounding surfaces.
NOTE: PATCHING MIX SHOULD MATCH AS CLOSELY AS POSSIBLE,
THE TEXTURE AND COLOR OF THE ORIGINAL.
END OF SECTION