How To Repair Spongy Or Crumbling Cast Concrete Wall

Efflorescence on concrete masonry. Photo courtesy of Portland Cement Association.

Efflorescence is a fact of life with most concrete. We are hearing more than about efflorescence related issues because of the popularity of stained floors. As the trend to accept exposed concrete floors grows, the industry is struggling with the problem of unsightly efflorescence, particularly when it is trapped under a film forming sealer. This is non to say that exterior decorative concrete is immune from efflorescence problems, but problems with interior floors pose a greater challenge and are the focus of this give-and-take.

This commodity is meant to exist a common sense overview of the major efflorescence issues. Nosotros will suggest realistic preventative measures to control the conditions that encourage efflorescence and nosotros will offer remedial suggestions. Nosotros will offer useful explanations of this complex phenomenon in applied terms without a lengthy detailed chemic analysis.

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Decorative physical contractors usually get the first telephone call when efflorescence shows up on a stained floor. Many things may have contributed to a particular efflorescence plagued project, the least of which may be the work performed by the stain contractor who in near cases is unaware of the preexisting weather condition that caused the efflorescence. Stain contractors, physical finishers, builders, general contractors, the design community and owners are all affected by issues related to efflorescence. Nosotros hope this discussion clarifies some of the problems and so that efflorescence is better understood and the appropriate measures are taken to prevent its occurrence. The costs associated with efflorescence prevention are minimal when compared to the cost and inconvenience of the remedies, especially when the space is occupied. Efflorescence in itself is not a health problem although it might indicate moisture levels sufficient to back up mold. Efflorescence is non a structural issue. It is an aesthetic issue, an issue we would all similar to avoid.

WHAT IS EFFLORESCENCE?

Efflorescence is the white powdery substance on the surfaces of unsealed concrete and the white blush seen with sealed floors. Efflorescence is acquired by vapor migrating through the slab bringing soluble salts to the surface of the concrete. Efflorescence is unremarkably worn off or washed away on unsealed concrete surfaces. In stubborn cases, a mild acrid rinse or fifty-fifty a calorie-free sandblasting may exist necessary. Efflorescence that becomes trapped under sealer is cruddy and is even more conspicuous on darker floors.

In worst case scenarios where the vapor cannot pass through the pinnacle coat, a urethane and/or an epoxy for instance, hydrostatic pressure can build to create water blisters indicating delamination of the top coat from the concrete. Baking is rarely seen with acrylics. Acrylic sealers let the vapor to pass through, but the common salt deposits remain behind creating the unsightly blush that prompts owners to phone call the stain contractor.

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WHAT CAUSES EFFLORESCENCE?

Efflorescence requires the movement of wet. Without wet movement in that location would be no efflorescence on the surface to create the problem. Unfortunately, too many finishers (non-ACI Certified Finishers) routinely introduce large amounts of unnecessary "water of convenience" to the mix in order to facilitate physical placement.

Primary efflorescence is caused past the h2o in the physical evaporating from the slab leaving behind the soluble salts on the concrete surface. The fact that these salts are really more soluble in colder temperatures coupled with increased drain water in common cold weather increases the likelihood of efflorescence showing up subsequently winter concrete placement. Contributing further to efflorescence with cold weather condition pours is the use of calcium chloride to accelerate the fix time. Loftier slump concrete and the addition of calcium chloride are major contributors to efflorescence.

Secondary efflorescence is often described every bit h2o coming from underneath the slab or h2o that is introduced from the surface. Probable sources of secondary efflorescence would exist a saturated base material, an improperly drained site or excessive amounts of water used by the decorative floor contractor during his cleaning procedure - rinsing off the acid stain residue, for example. When extra mix water and extra soluble salts from calcium chloride are added to concrete placed in cool weather followed by more than h2o from the decorative processes, some caste of efflorescing is bound to occur.

HOW TO REMOVE EFFLORESCENCE

What are the options when efflorescence rears its ugly caput? A fast fix might be to use toluene, xylene or another coat of solvent base acrylic which reemulsifies the original sealer and clears the chroma. If vapor continues to come up through the slab though, the condition volition most likely reappear. Be enlightened that if the space is occupied at that place can be health issues because of solvents like toluene and xylene.

The most prudent class of activity includes stripping the sealer in order to conduct a test to determine the rate of vapor transfer and and then develop a remedial strategy. It is important to get it right the second time so have time to diagnosis the causes as all-time you can with the data bachelor. 1 of the more expensive hand held digital instruments may prove to be a valuable tool because they are able to get accurate wet reading below the surface of the slab. In one case the wet levels are established a sealer can chosen based upon the manufacturer's recommendations.

Think that some manufacturers accept the vapor inhibiting, non-moving-picture show forming sealers that we mentioned before. These may reduce the vapor transmission rate to a level appropriate for a heavier bodied more abrasion resistant top coat for apply in high foot traffic situations.

Where slabs have continued to take efflorescence issues even after the application of a lithium or silicate densifier contractors accept used a finish or polish, which are industrial grade "mop and glow" - low build, low solids micronized acrylic water based products every bit the final treatment. These finishes and polishes can also be used over film forming sealers to add together abrasion resistance.

In almost efflorescence cases, the decorative flooring contractor inherited the problems that contributed to creating the efflorescence. Diagnosing the causes of efflorescence after the floor has been sealed can exist difficult. It is important to determine how much moisture exists in the slab, the source of the moisture and too whether conditions, like seasonal ground water might contribute more than moisture in the future. Consider vapor testing and resist the quick fix. Finally, contractors may elect to avert warranty language where sealers are concerned or they may choose to specifically ascertain typical vapor transmission problems. The decorative adage of "exam, test, and examination" holds especially true for interior stained floors. Information technology means doing a VTR test whenever you suspect there may be the potential for efflorescence problems. Happy staining and call up – you don't have to take every job that comes your way.

HOW TO Forbid EFFLORESCENCE

Efflorescence reducing measures are: site surface drainage; a well graded concrete mix with a water reducer to minimize paste; concrete not exceeding a 4" slump; that the concrete be well consolidated (ane man vibratory screeds exercise a corking job); placed directly on a vapor retarder and cured in some style. All these factors contribute to a physical that has a minimum corporeality of drain water with a lesser pore and capillary network that will resist rather than facilitate absorption and movement of wet...in other words, a dumbo and relatively impermeable concrete slab.

Now for more specifics...an option to the vapor retarder is a waterproofing admixture to assist prevent efflorescence. This is added to the concrete at the plant, but it has a downside. Information technology can pose existent problems for the stain contractor since a mutual ingredient, stearic acid, is hydrophobic in the same style that powdered release agents for stamped physical are so the waterproofed physical does non readily accept either acid stains or h2o base stains. Suggestions in this instance would exist to open the surface with a sanding screen or a gelled acid to create some degree of profile enabling a better mechanical bond for the water borne stain.

Not an Uncommon Fix of Circumstances:

Scenario of potential efflorescence consequences of a fast track project:
Imagine the consequences of a fast track project...restaurants have to be the worst...with an acid stained floor on a slab as we just described, a few months one-time poured tardily in the twelvemonth. The thou opening is early spring. The decorative contractor, being the sincere person he or she is, has proposed an upgrade from the acrylic sealer in the specifications to an epoxy or urethane because of the heavy foot traffic. The proposition was canonical, epoxy sealer it is. Our contractor goes into the project without a clue almost the sub grade conditions, vapor retarder, mix design, admixtures, etc. At that place is 1 more complexity all too familiar to staining contractors...the schedule. The superintendent greets our contractor friend on Monday with the news that the floor needs to be serviceable Friday forenoon so that the kitchen stoves and ovens can be dragged in. Our contractor feels a bit overwhelmed, but plans the work: clean up the drywall mud today; stain tonight; make clean the residual Tuesday, use epoxy Wednesday, Th is cure day, Friday is open for light traffic. This seems workable, life is adept. No matter that the heat is not nevertheless on in the building and the floor is not fully cured out. Our contractor friend, by the way, does not take floor scrubbers. Mops and buckets brand up the clean up and water removal equipment. This is not an uncommon ready of circumstances. What do y'all suppose the chances are that the stained and sealed floor will escape with no efflorescence?

Helpful mix design factors include ordering a well graded a mix from the ready mix producer. The advantage gained from a well graded mix blueprint is the reduction of the weakest part of concrete, the cement paste (cement and water), making for a denser physical than with a standard mix. Another important mix pattern consideration is the replacement of 15% to 20% of the Portland cement with wing ash which contributes significantly to lessening efflorescence. Fly ash brings three of import benefits to reducing efflorescence. Fly ash reduces the amount of Portland cement and free lime as well as chemically binding upward a portion of the free lime and salts that cause efflorescence. In addition, fly ash requires less water over again resulting in a denser paste which aids in keeping wet from traveling up from the bottom and from the top downward. Water reducers of form, are as well helpful at minimizing the amount of water and a reduction of cement (paste).

The closer a mix design gets to the desired water cement ratio of .45 pounds of h2o to pounds of cement, the fewer efflorescence issues arise, especially with a mix including fly ash. And forget the one-time notion that you tin can't employ integral color with fly ash, y'all can. Keeping multiple pours consequent with the mix design, sub grade conditions and finishing practices will produce consistent results. Heads up on this one... common cold concrete and cold ambience temperatures encourage efflorescence because the salts are actually more soluble in colder temperatures plus concrete tends to drain more in cooler conditions further encouraging the upward transportation of moisture and its passenger, soluble salts. Follow ACI 306 Cold-Weather Concreting procedures whenever possible including raising the placement temperature of the physical to 60 degrees and then encompass overnight to retain the estrus. This will encourage a more dense pore and capillary structure and assist shut down the moisture transportation routes.

Curing becomes important equally nosotros recognize that wet moves much more than slowly through denser concrete from either management. When physical is kept moist for a longer period, specially the first few days, more capillaries and pores fill partially or completely to course a denser and more impermeable matrix that discourages the migration of moisture and soluble salts. Conversely physical that is placed at a high slump and not cured acts as a sponge, full of miniature raceways allowing easy movement of moisture from the bottom up and summit downwardly. Cure and seal membrane type cures poses a trouble in that the membrane has to be removed to accept acid stains, and so they are non often used. One manufacturer has a thermal degrading wax that breaks downwardly with hot water. H2o borne stains are becoming popular and manufacturers are working to formulate compatible curing membranes that will take subsequent staining. Wet curing is difficult considering it must be continuous and may create discoloration if a plastic canvas has wrinkles.

Some contractors are following the awarding of acid stains with silicate type non-film forming sealers generically described as chemical hardeners, densifiers and soluble chloride reducers within a few days of concrete placement.

A Calcium Chloride Test is a skillful surface moisture test for determining the current vapor transmission rate of concrete. Photo Courtesy of Vaporprecision, Inc.

TESTING FOR VAPOR Transmission

Even if some answers are provided information technology behooves the contractor to practise some independent fact finding to determine the current vapor transmission charge per unit (VTR). Probably the oldest examination method is the Plastic Sheet Test (ASTM-D-4263) which is taping down a clear 18" X 18" sheet of poly and checking 16 hours subsequently for condensation or for a darkened concrete surface. Both are indications of vapor manual. Another surface moisture test is The Calcium Chloride Test which quantifies the charge per unit of vapor transmission. This is a covered dish that is weighed before and subsequently a twenty 4 hr period. Both are cost effective measures in determining whether vapor is active.

A note of caution when using these testing methods...the plastic sail and chloride tests will track moisture move near the peak merely. When the atmospheric conditions are like to the slab weather condition the tests might non bespeak significant vapor transmission because movement happens when the ambient weather differ from the slab conditions. Moisture migrates and moves toward cool temperatures. Vapor emissions migrate and move toward rut. Imagine the consequences of the following unpleasant, simply very real scenario... the project is completed, the contractor has been paid, the delighted owner takes possession and turns on the HVAC causing vapor in the slab to move towards the warmth or the lower humidity of the conditioned space bringing the whitish minerals with information technology. If the sealer is acrylic the vapor will laissez passer through leaving the efflorescence. If urethanes or epoxies are on the floor, hydrostatic pressure may build and possibly crusade delamination. Efflorescence tin can occur months or even years afterwards the contractor has left the job due to circumstances similar to those but described or from seasonal ground water seeping nether the slab. Testing the surface may not exist enough to guarantee an efflorescence gratuitous project for years to come up. It is important to make up one's mind the source and the rate of vapor transmission before prescribing a remedy.

Make up one's mind ahead of time if efflorescence is a probable problem waiting to happen on your project:

• Are there signs of efflorescence now?

• Is the property properly drained?

• Does surface water run towards the foundation?

• Is there a French drain system?

• How old is the slab, what fourth dimension of year was it poured?

• Was the concrete placed on a saturated sub course?

• Was the concrete placed straight on a vapor retarder?

• Was a granular material placed over the vapor retarder (vapor bulwark being the outdated term) and was the base saturated?

• If a vapor retarder was used, was it carefully taped at penetrations, around the plumbing, for instance? Did the mix design include fly ash?

• Was a waterproofing admixture used?

• Was calcium chloride used?

• How much "water of convenience" was added to the physical?

• Was a curing compound or liquid densifier applied?

Answers to at least some of these questions can give a decorative contractor a heads upward earlier wading into a project completely uninformed and unprepared.

More authentic, but also more expensive, testing technology such as the Protimeter Moisture Measurement System (ASTM Standard F-2170-02) uses a probe to measure the presence of moisture on and below the concrete surface along with the relative humidity, dew point and temperature. 2 non invasive paw held devices using similar technology are the Aquant, which measures surface wet to a depth of 10 – 20 mm and the Tramex Concrete Run across Wet Meter which transmits a signal ½" deep and projects a wet measurement for 4". The benefit of these tools is their accurateness in measuring the moisture levels well beneath the surface whether there is whatever current movement or non. Given the financial risk, non to mention impairment to a contractor'southward reputation it makes sense for a contractor to explore procedures that more clearly signal subsurface weather condition in club to avert the efflorescence issues caused by moisture.

Nosotros mentioned that a well tuckered site and a vapor retarder are deterrents to efflorescence. The example tin be made for placing the concrete directly on the vapor retarder or over granular textile on top of the vapor retarder. The statement against the granular fabric is that information technology may become a saturated "blotter" before the slab is poured adding even more h2o that has only one way to leave. Finishers contend that there volition be too much bleed water resulting in dusting, merely a four" slump with water reducers and a well graded mix volition show very little bleed water. Elevated slabs are quite mutual in commercial construction and they are not placed on a blotter material. The really important factor hither is minimizing h2o in all the important areas...the sub grade, the concrete and the procedures performed by the decorative contractor. These all require some amount of water, but keeping water to a minimum helps ensure that efflorescence is controllable.

To give an idea how much water may exist available to bring soluble salts to the surface when these factors are not given any consideration let us consider a typical residential slab pour...assume nosotros have a 2" thick blotter class of sand residing between the physical slab and a vapor retarder. Dry sand weighs approximately 100 pounds per cubic pes. Wetted to achieve compaction, this sand could easily contain 10% moisture past weight, or 10 pounds of h2o per cubic foot of sand. Information technology will take approximately 167 cubic feet of sand to comprehend 1,000 foursquare feet of vapor retarder. That figures out to each ane,000 square feet of concrete surface having i,670 pounds, or 200 gallons of water sitting on the underside of the slab with no where to go simply up! Add that amount of water to another threescore or seventy extra gallons of "h2o of convenience" added by the finisher and nosotros may take 270 gallons of extra h2o moving towards the surface whenever surface conditions are warmer or drier than the slab itself. There is another aspect of this foreboding movie...this porous slab nosotros have described acts like a difficult sponge with big pores and capillaries throughout the matrix, able to wick wet upward and quite willing to human activity every bit a hard sponge, capable of absorbing hundreds of pound of water from the cleaning processes employed past the decorative flooring contractor.

WHAT OPTIONS DOES A STAINER HAVE?

Engineering that might offering double relief from efflorescence related issues involves the use of chemic liquid densifiers and hardeners. Offset, manufacturers say chemically hardened floors do non require a membrane sealer. This eliminates the trapped efflorescence problem and also greatly reduces maintenance costs. The chemicals include silicates, silicaonates, polysiliconates, silanes, siloxanes and the new lithiums, to name a few. Some of these are used in the conjunction with polished physical floors. Some are used on floors already acid stained or dye stained and could receive a membrane type sealer. Some of these chemicals accept been used for years and some are relatively new to market place. Claims vary from production to product and from manufacturer about how far the chemicals penetrate, their permanence and the levels of smooth and slip resistance. Nosotros know for sure that the big box stores are getting away from vinyl and going to bare concrete. Decorative flooring contractors would exist well served to explore this technology even for smaller residential stained floors.

Secondly, some contractors are following the application of acid stains with silicate type non-film forming sealers generically described as chemic hardeners, densifiers and soluble chloride reducers within a few days of concrete placement. Efflorescence is reduced as the silicate causes the matrix to become denser as we described earlier. The contractor has the option of adding conventional membrane forming sealers if subsequent VTR tests indicate acceptable levels.

Doug Bannister is possessor of The Stamp Store in Oklahoma Urban center, OK, which provides a complete line of decorative concrete materials including products, equipment and training. www.thestampstore.com

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EFFLORESCENCE Q&As

Chris Sullivan is a decorative physical expert who answers technical questions from contractors and homeowners concerning efflorescence and other bug.

Efflorescence on black physical

Question: Final week, we poured a band of integrally colored black concrete. It looked smashing for three days, simply so it rained a picayune the nighttime of the third mean solar day, and by the next forenoon all the blackness colour had disappeared, hidden by a grayish-white surface discoloration. What happened, and how do I fix this?

Deposits of efflorescence make black concrete expect grayish-white.

Respond: This is i of the near common but least understood phenomenons with concrete. Efflorescence is a chalky white salt residual that can occur with any product containing cement. Every bit wet migrates upwards to the surface of the concrete, it carries along with it calcium salts from inside the concrete. When the salts reach the surface, they react with CO2 in the air and form insoluble calcium carbonate. This white, dusty, scaly salt can exist minimal or dramatic, depending on the corporeality of free calcium salt present in the concrete. Exposure to rain, continuing water, and sprinklers only make the situation worse, every bit water triggers the reaction and creates more than efflorescence.

Efflorescence is non as noticeable when it occurs on gray concrete, but even a little efflorescence on colored concrete can be a contractor's worst nightmare. Efflorescence makes ruddy look pink, brown look tan, and black look greyness or even white. The good news is that it will eventually go away on its own as the free calcium is depleted. The bad news is that this tin can take as long as 15 years. And in this situation, you can't wait.

To fix the problem at this point, clean the surface with a mild acid or efflorescence remover (some manufacturers make special efflorescence cleaners) followed past sealing. To avoid the problem altogether on future projects, consider using a colored curing compound or cure and seal to match the colour of the concrete. To learn more near efflorescence, read my post on the topic: Causes of Efflorescence on a Stamped Overlay and Efflorescence Hides Integral Color

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Stampable overlay efflorescence - How is it removed?

Question: A few days after placing a stamped overlay, I noticed that the overlay was covered with efflorescence. The picture shows two minor samples of the overlay taken from material left in the mixing bucket. The sample on the left side shows textile that was exposed to the air, and the sample on the correct shows fabric that was up confronting the side of the bucket. Why is the sample exposed to the air loaded with efflorescence while the other sample has no effloresce and is the proper colour?

These two samples come from the same bucket of overlay mix. Notwithstanding only the one on the left shows efflorescence.

Respond: This is a corking example of how efflorescence works. Information technology also shows just how many variables decorative physical installers deal with on whatever given project.

Efflorescence is a natural phenomenon that occurs in any material that contains cement (lime) and comes in contact with water. The procedure involves natural salts migrating out of the physical (or mortar, block, or brick), in a. chain reaction triggered by water and carbon dioxide. In an try to escape from the concrete, efflorescence will have the path of least resistance. The physical's surface profile, color, water-cement ratio, and porosity all play a big function in the process.

The sample on the left side of the picture has a rough, open surface and is very porous, which allows for like shooting fish in a barrel water migration. The sample on the right shows the backside of the piece that was up confronting the bucket, which was made of non-permeable plastic. This sample likewise has a smoother, denser surface that inhibits water migration. What this illustrates is that a smoother surface (such equally that produced with a steel trowel) volition retard water penetration and efflorescence movement more an open, porous surface (such as a float stop). In addition, materials that are darker in color will show efflorescence more readily than lighter-colored materials. In fact, I have seen decorative concrete and concrete overlays that have astringent efflorescence just are lite in color, so the efflorescence is barely noticeable. When it comes to the water-cement ratio, less water is always amend. And never add water to the surface. Employ an evaporation retarder instead.

While y'all can never eliminate efflorescence, controlling the factors outlined above will help minimize its furnishings.

Efflorescence on a stained floor slab

Question: Nosotros take a stained concrete floor slab on form in our Houston home. We accept salts that our escaping and clouding the floor. During the iii years we have lived in the house, our builder has tried various things to fix the floor. First, he tried redoing the stain and sealer, only the same discoloration happened. Near six months ago, the architect removed the sealer and waxed the floor to allow it to breathe and the salts to rise through the flooring. The salts are now hands wiped away, but the wax is wearing off, onto our socks, shoes, the dog's paws, etc. Can annihilation be washed to salvage the floor? Nosotros have idea about tiling over it, but are whatever special preparations necessary, such equally applying a thin-ready mortar or a moisture barrier?

White efflorescence caused by high water motility pushing salts out of a concrete floor slab.

Respond: It sounds like y'all have a chronic efflorescence problem. Efflorescence is a process where salts leach out of the concrete, carried by water, and end upward on the surface as a white dusty residue. Since you accept had this issue since y'all've lived in the home, information technology seems to be chronic and ongoing. Since water is the trigger, practice you have a high water table, flood evidently, or other situation that's causing water to get nether your concrete foundation? Annihilation y'all can practice to minimize water migration under your concrete will help. This would include installing French drains or possibly regrading the slope of your property.

No matter what y'all do, the efflorescence problem will demand to be mitigated. Efflorescence will not but cause problems with a stained concrete floor, information technology can too delaminate tile and warp wood floors. The best approach would be to strip all the sealer and wax off the concrete. Once the sealer and wax are removed, a moisture examination should be conducted and then you lot can become an idea of how much h2o is moving through the slab. The test results will dictate your next footstep. If the water movement is depression, a penetrating sealer designed to terminate or dull efflorescence can be used. After the sealer is applied, you can reapply a stain or dye to the floor. If the h2o motion is high, a more drastic and aggressive topical waterproof blanket may take to be used. If you and then want to restain the floor, a cement and polymer topping would demand to practical to create a new canvass on which to apply the stain. If you desire to tile over the flooring, the same water mitigation procedures would have to be completed.

Source: https://www.concretenetwork.com/doug_bannister/efflorescence.htm

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