Solving decorative problems.

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.

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