© OhioReady Mixed ConcreteAssociation, May 2009

CONCRETE

BASICS

CURING

MAINTENANCE

A HOMEOWNER’S GUIDE

TO HEALTHY CONCRETE

One other potential problem is too much ofa film build up on the surface may reducethe friction that keeps feet or tires from slip-ping. Applying film-forming sealerstoo heavily or in too many coats canalso cause the sealer to bubble, turnwhite, or flake off.

Penetrating Sealers - 'Dry Look'

Most penetrating sealers are madefrom derivatives of silicone calledsilanes or siloxanes. These materi-als are designed to penetrate into thepores of concrete, and once there,react with the alkaline materials and mois-ture to form silicone. The silicone filled pores

MAINTENANCE

then make your concrete water repellent.

While the silane and siloxane penetratingsealers are usually more expensivethan the film formers, they should lastlonger. Another reason that the pen-etrating sealers are gaining in popu-larity in spite of their price, is that,when properly applied, they don'tchange the appearance of the con-crete. Their biggest disadvantage,or at least the major concern in theirapplication, is that there can be noother membrane cure or sealer onthe concrete when applying and the

concrete must be over 28 days old.

OHIO CONCRETEOhio Ready Mixed Concrete Association

614/891-0210FAX: 614/891-2675

E-MAIL: ormca@ohioconcrete.orgWEB: www.ohioconcrete.org

Do

Not

Cop

y

CONCRETE BASICS

fig.1 A 15 year old air entrainedconcrete slab

fig.2 A 15 year old non-air entrainedconcrete slab exhibiting scaling

CONCRETE BASICS

Concre te driveways and walkways cangreatly enhance the appearance and valueof a property. Healthy concrete, however,does not happen by accident. Thoughtfulplanning, a quality mix, professional place-ment and the proper curing and mainte-nance can produce beautiful concrete thatwill last for years. The time to think aboutwhat you want from your concrete in termsof appearance, performance and mainte-nance is NOW - before the concrete isplaced.

You may hear many things about what to dowith your newly placed concrete - some aregood ideas, others are myths and miscon-ceptions. This brochure is to help you, thehomeowner, understand what is needed forhealthy concrete and to separate thesemyths from reality. While the information pre-sented will not make you a concrete engi-neer or contractor, it will help you to makeinformed choices when planning your con-crete driveway, walkways, and patios. In par-ticular, this brochure is designed to help youunderstand the curing and sealing pro-cesses and the homeowner's responsibilityonce the concrete has been placed and fin-ished.

Concrete Construction Responsibilities

Concrete construction is a complex set ofactivities requiring professional skills and anextensive understanding of concrete. Usu-ally several parties are involved -the generalcontractor, the home builder, the concretecontractor, the ready-mix producer and thehomeowner. The technical aspects of in-stalling concrete such as planning, prepa-ration, mix specification, placing and finish-ing are the responsibilityof the home builder,ready-mix producer, and largely, the con-crete contractor. The homeowner shoulddiscuss the type of curing used with the con-tractor to determine the appropriate type offuture maintenance (sealing). Ultimately, anyongoing maintenance is the homeowner'schoice and responsibility.

Concrete Concerns

Concrete is a blend of cement, mineral ag-gregates and other natural materials. There-fore, it may and most likely will have somenatural imperfections.

The mos t prevalent concerns ofhomeowners are scaling and uniform ap-pearance. Because of concrete's complex-ity, it takes a team effort to address thesepotential problems.

Scaling

Also called mortar f laking,scaling is the localized orwidespread loss of the con-crete surface, usually affectingthe top 1/16 to ¼ inch. Mostscaling can be prevented by:

The use of airentrained concrete - All ex-

terior concrete must be air entrained

Your ready-mix producer and concrete con-tractor control the amount of air entrained inthe concrete and the mix quality. In freeze-thaw climates, it is very important to placeexterior concrete with entrained air, as thetiny air pockets provide space for water toexpand into when it freezes.

Proper Finishing

The concrete contractor must be aware ofthe proper timing of the finishing operations,which can vary greatly depending on theweather. Finishing too early or over finishingcan result in a weak concrete surface, sus-ceptible to scaling. It is important to mini-mize manipulation of the surface, thereforeswirl finishes are not recommended.

Judicious Use of Deicing Salts

Calcium or sodium chloride salts on theirown will not chemically damage or etch yourconcrete, but the fact that they do allow thesurface to stay saturated with water candamage your concrete. Deicing productsand fertilizers made with ammonium nitrateor ammonium sulfate can chemically attackthe concrete, causing severe damage.

Deicing salts are not recommended in thefirst winter and over the life of the concreteshould always be used judiciously. Use plainsand instead during the first winter for trac-tion. Promptly remove any inadvertent deic-ing salts tracked onto concrete less thanthree months old.

Insufficient or No Curing

Failure to properly cure your concrete oftenresults in lower strength concrete, cracking,dusting, and a weak surface skin which willbe prone to scaling. Although proper curingshould be done by your concrete contrac-tor, it is absolutely necessary that you andyour contractor work together on this be-cause the curing method affects your plansfor ongoing maintenance.

Uniform Appearance

It seems that most homeowners are look-ing for their concrete to turn white quicklyand evenly. In reality, the longer your con-

Do

Not

Cop

y

CURING

crete keeps its darker color, the better it isretaining moisture. This will ultimately resultin stronger, healthier concrete.Your entire drive or walkway should even outin appearance over the first month afterplacement. Variations of dark and light ar-eas during this time are normal.

After reading this brochure, you will discoverthat you need to start at the end - that is theend result you want - and plan back to thebeginning of your concrete construction toproduce healthy, durable concrete. For tech-nical information on concrete mixes, designand placement, refer to Ohio Ready MixedConcrete Association's Industry Recom-mendation for Exterior Concrete Flatwork -availab le f or download atwww.ohioconcrete.org. If you have any ad-ditional questions regarding curing and seal-ing, we would welcome your call.

Curing Concrete - What Does it Mean?

When there's an unsightly concrete drive-way, everyone would like some way to 'cure'the problem, but that's not what we meanby curing concrete. It is true, however, thathad the problem concrete been properlycured, it may never have gotten sick. Cur-ing is the maintaining of a satisfactory mois-ture content and temperature in concrete fora sufficient period of time during its earlystages so that its desired properties maydevelop.

Strength

The amount of water in the concrete while itis being placed is normally more than mustbe retained for curing. However, concretethat dries out too quickly may not retainenough water needed for the hardening pro-cess - a chemical reaction called hydration.

Temperature also greatly affects the hydra-tion process. While hot weather can makethe concrete hardenand gain strength faster,it ultimately leads to a weaker concrete thanone that has been kept cool (but not withinfreezing range) during its first few days.

Thus, the goal in curing is to keep the con-crete cool and moist so that it gains itsstrength slowly but eff iciently. Laboratorytests show that moist cured concrete canbe twice as strong as concrete cured in adry environment.

Freeze - Thaw Resistance

Curing can also help concrete to be moredurable and resistant to damage caused byfreezing and thawing. As long as the hydra-tion process continues in concrete, the ce-ment portion hardens and becomes moredense. If the concrete is properly cured, itwill be less porous than uncured concrete,thus making it more difficult for water andsalts to penetrate.

Properly cured concrete is also more wearresistant and less susceptible to dusting andscaling.

Curing Concrete - How is it Done?

There are numerous methods for curing con-crete from covering with plastic sheeting orwet burlap or ponded water.

Moist Curing

Probably the best method for curing con-crete is to flood the surface continuously withwater for the first seven (7) days after place-ment. However, it is impor-tant that the concrete notbe allowed to dry out dur-ing this time. Often, con-tractors will recommend tothe home owner to wet thenew driveway for the firstweek after its completion.But, if the concrete is al-lowed to dry betweensoakings, this alternate wetting and dryingmay actually damage the concrete. So if youare going to water cure, plan on keeping thesprinkler going for at least a week.

Membrane Curing

The most common method of curing newconcrete driveways is the use of a liquidmembrane-forming compound normallycalled a curing compound. These materialsare usually sprayed or rolled on the concretesurface. Once dry, they form a thin film whichrestricts theevaporation ofmoisture from the con-crete.

The most important thingto remember regardingthe use of a curing com-pound is timing. The ap-plication of these productsshould be done as soonas the final finishing operations are completeor as soon as their application won't mar

the concrete's surface. So if someone says,"Let's wait until tomorrow to apply the cur-ing compound," you will know it's not a goodidea.

The next most important thing is applicationrate.A light sprinkling of the curing compoundon the surface will not do the trick. A suffi-cient coat according to the manufacturer'srecommended coverage rate (usually 150ft²/gal) is critical.

Curing with sealing in

mind

When choosing the cur-ing method and materialsthat will be used on yourdriveway, one importantaspect to consider is howyou intend to seal and

maintain your concrete in the future. Seal-ing your concrete is addressed in the nextsection, but for now let's look at how thecuring method can affect your sealing deci-sion.

The most common type of membrane cureused is referred to as a 'cure and seal'. Butlet's make one thing clear, this is not a onestep process for permanent concrete seal-ing. It does, however, dictate the use of afilmforming sealer unless the 'cure and seal'is removed or allowed to naturally wear off

over time.

If you plan to use a pen-etrating sealer for ongo-ing maintenance, thenyour concrete should ei-ther be moist cured orcured with an easily re-moved, dissipating con-crete curing compound.

MAINTENANCE

Do

Not

Cop

y

THE 'WET LOOK' VS. THE 'DRY LOOK'

tend to be less costly better stain protection (i.e., oil, grease,

etc.) usually compatible with curing method

used glossy to medium gloss look deepens and highlights the color of ex-

posed aggregate, colored or stampedconcrete

can darken the concrete may appear blotchy if not evenly applied will wear away, requiring more frequent

applications may create a slippery surface

Wet Look - Film Formers

MAINTENANCEMAINTENANCE

By making the sealing choice before thedriveway is installed, you can then informyour contractor on the curing method thatyou would prefer.

Maintaining Your NewConcrete

You wouldn't use a strongcaustic soap to clean yournew carpet. Nor would youuse acid to clean your newkitchen or bathroom fix-tures. In fact, you're prettycareful about how youclean and take care ofyour new home inside. But, what about out-side concrete walks, drives, patios, porchesand steps? Give the new exposed concretearound your house the same considerationas your pretty new interior! It's quality con-crete, but don't abuse it.

New concrete should be at least threemonths old before deicing chemicals - thosethat contain sodium chloride (common salt)or calcium chloride - are used. Remember,deicing salts are not recommended in thefirst winter. The only safe material to use tomake the concrete surface skid resistantduring the first winter is plain sand. Promptlyremove any deicers tracked onto or inad-vertently broadcast on new concrete.

It is helpful that a recommended surfacesealer be applied in the fall prior to theconcrete's f irst winter. Check with yourbuilder, contractor or ready mix supplier forrecommended quality concrete sealers andrefer to the next section on choosing seal-ers. These can be rolled or sprayed on anddo require re-application for continued per-formance.

Never use deicers containing ammoniumsulfate or ammonium nitrate. These prod-

ucts are commercial fertilizers used by farm-ers and have on occasion been packagedand soldas deicers. They will effectively meltsnow and ice, BUT they will also rapidly dis-

integrate concrete. Also,deicers containing mag-nesium or acetate arealso known to be harmfulto concrete and shouldbe avoided.

Clear snow and ice, in-cluding deicers , fromyour concrete surfacesas soon as possible.

Sealing Concrete - Ongoing Protection

Just as you paint the trim on your home orwax your car to keep them looking nice andprotect their base structures from detrimen-tal elements, you should seal your concreteregularly to protect it from moisture penetra-tion and prolong its life too. Although it seemsironic, it is true that when concrete is firstplaced, we want to keep the moisture in;once it has matured, we want to keep mois-ture out. This is especially true for concretethat will be subjected to freezing and thaw-ing. You can do this by maintaining your con-crete with a sealer designed to keep out wa-ter and deicing chemicals.

Choosing a Sealer

Choosing a product to seal your concretecan seem like a complicated process, butlet's try to cut through it all to some simplechoices. There are really only two types ofconcrete sealers -those that form a film onthe surface of your concrete, giving it a wetlook, and those that are designed to pen-etrate the concrete leaving it dry looking, yetwater repellent. Like any choice, each hasits advantages and disadvantages.

Film Formers - 'Wet Look'

The film formers are usually made fromacrylic compounds. They form a thin coat-ing on the surface of your concrete, leavinga wet look; much like varnish does on wood.These products generally tend to be less ex-pensive on a per gallon basis than their pen-etrating counterparts, but you'll probably findthat they will need more frequent applicationsince they will weather and wear away morequickly.

One significant advantage of the film form-ers is that there is usually not a compatibilityconcern with the method of curing used orwhatever previous sealer might have beenapplied.

The biggest problem that can develop withthe film formers is that they tend to darkenthe color of your concrete. This may not bea problem on decorative concrete where adeeper color is desired, but on plain con-crete the color variation may be objection-able. Just like varnish will enrich the colorof wood, these will do the same to concrete.And just like it may take several coats ofvarnish to provide an even, rich color, don'texpect the film forming concrete sealer toperform differently. If after one coat you getsome dark areas and some light, you maywant to apply another coat to make it evenlydark. These initial variations in color maybe caused by natural variances in the po-rosity of the concrete and/or uneven appli-cation, but they are quite normal.

Dry Look - PenetratingSealers

should not change the concrete’s ap-pearance

less frequent applications needed easy to apply

usually more costly not as effective as a stain protector cannot be applied over a film forming

compound

Advantages

Disadvantages

Do

Not

Cop

y