Index > Articles > Solving decorative problems - Decorative Concrete
Solving decorative problems - Decorative Concrete
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In the October 2003 issue of CONCRETE CONSTRUCTION magazine, the Decorative Concrete column was about troubleshooting decorative problems. Many of these problems relate to basic concrete issues, although they may appear to be decorative problems when viewed through a colored concrete filter. Some problems, though, are indeed caused by the mechanics of decorative techniques. The following table is an attempt to pick up where the column on troubleshooting left off, listing some of the more common problems experienced in the field and what to do about them.
One material that can be used to solve problems for many of these situations is a stand alone product called "Spray Top," manufactured by Concrete Solutions, San Diego. It's a polymer cementitious material that can be sprayed with conventional paint spraying equipment. The application is very thin and can be used to solve problems relating to surface coloration issues. Also, when slabs won't accept chemical stains, they can be sprayed with white Spray Top and then successfully be stained.
For more information about "Spray Top," contact Concrete Solutions at 800-232-8311, on the Web at www.concretesolutions.com, or circle 12 on the reader service card.
Green slag concrete
Q. We're going to pour a lot of exposed architectural walls with an 8000 psi, 50% slag mix. In samples, the concrete has a very dark green color. Will the color eventually disappear?
A. On ARI's forum, Jan Prusinski of the Slag Cement Association answered: The color you describe is due to reactions between sulfur compounds in the slag cement and portland cement. When this occurs (and it usually does not), exposure to air and sunlight will eventually promote oxidation reactions, which eliminate the "greening." Greening is prolonged if the concrete is not exposed to air/sun during curing. Often, formwork that has been left on for some time can cause this. Of course, higher strength concrete such as yours also reduces permeability (which is good), but slows the process of going from green to white. If a new surface is continuously wetted (as in a new pool) the greening may never disappear.
Problem Reason Suggestion
Integrally Colored Concrete
Inconsistent Inconsistent Use the same ready-mix plant and
color slump the same portland cement
Check the slump for each ready-mix
truck and make them all the same
Don't add water while a ready-mix
truck is unloading
Efflorescence Try a light acid wash (not more
than 10%)
Try a light sandblast (owner
approval needed)
Seal concrete soon after initial
set with breathable sealer
Inconsistent Porous and hard-finished surfaces
finishing reflect light differently
Dry Shake Colored Concrete
Inconsistent Uneven coloring Develop better worker skills for
color color application
Arrange placements so that workers
don't throw colore more than 15
15 feet (re-color)
Spray a micro-topping polymer
cement over the surface
Damaged or Patch with a mixture of dry shake
scaled color (sift to remove silica
surface aggregate), add white or gray
portland cement to adjust and
balance the color, and polymer
bonding agent
Stamped Concrete
Surface Moisture loss Spray vapor retarders of fresh
cracking from surface concrete when weather causes
concrete surface to lose moisture
Fog the area using fog nozzles or
a pressuer washer
Accelerate the concrete so that the
base of the slab sets before the
surface of the slab does
Close cracks with a margin trowel
before initial set; re-texture
the surface at the same time
Broken or Concrete too Make patch material by mixing
chipped edges hard when water with the color hardener
along pattern stamped and patching affected areas
lines before initial set occurs
Mushy imprints Stamping Reduce the area of each placement
and "fins" started too or consider "step retardation"
between early to manage the stamping program
stamps better
Use stiffer stamps, which don't
move as much under the stamping
person's weight at the beginning
of the stamping process
Slab Cracking
Excessive Poor joint plan Plan for control joints according
cracking to American Concrete Paving
Association guidelines
Uneven slab Subgrade preparation must provide
thickness for even thickness concrete
placement; good compaction is
vital also
Control joints Weather conditions influence how
placed too fast concrete shrinks and gains
late strength; plan for control joints
accordingly
Consider early-entry saw cutting
Excessive water/cement ratio;
place concrete at 0.5 or less
Chemical Staining
Damage by other Oil droppings Remove with chemical cleaner
trades
Paint droppings Remove with chemical cleaner
Chalk lines Remove with chemical cleaner,
with lacquer followed by sanding or grinding
overspray
Concrete Inform the owner that patches will
patches take stain differently
Use eyes and tints to mask them
Drywall mud Remove with water
Tape marks Don't use tape--marks can be
removed by grinding and
re-staining, or covering the
marks with dyes and tints or
colored sealer
White color High moisture Remove the sealer, reduce relative
between the content in humidity in slab, and reapply the
concrete concrete sealer
surface and
sealer Stain residue Remove the sealer, re-clean the
shortly after not surface, neutralize the surface,
application; adequately and reseal
Stain doesn't removed
react
Curing compound Remove with chemical cleaner,
on surface surface, may need to be sanded
Liquid hardener Sand or grind to get below that
applied surface
Consider other decorative options
Surface is Create access to calcium hydroxide
hard-troweled in the concrete by sanding or
grinding the surface
Cement has low Consider using nonreactive stains,
alkaline or spray micro-topping over the
content surface
Patches won't Polymer in the patch material won't
take stain allow stain to penetrate; test
patch materials before using them
Covering the Prepare the owner and general
slab with contractor at pre-job meetings
nonabsorptive Do not allow a covering to be on
materials: very long--only while mess is
plastic, being created
mansonite, Stain and seal floors a day before
cure paper, other trades work on them
plywood
drywall piles
Sealer doesn't Residues from Wash with a buffing machine using
bond stain remain a brush head, remove residue with
on surface wet vacuum before it dries,
apply neutralizing wash to low
pH left by acid in the chemical
stain
Overlay Cement
Overlay cement Base slab Surface preparation is everything!
scaling preparation Prepare by sandblasting or
is inadequate bead blasting
COPYRIGHT 2003 Hanley-Wood, Inc.
COPYRIGHT 2003 Gale Group
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