Cast-In-Place Concrete

Q: We are a cast in place concrete contractor. Our clients like our work because the concrete we cast comes out tight in appearance, but we are always trying to do better. How should we reduce our surface voids or "bug holes?

A: There are many means and methods your crews can become expert in doing, careful placing of concrete in controlled lifts, minimizing the "free fall" of the concrete and of course, expert consolidation of concrete between the forms. The next thing you can do for your crews is provide them with a high performance chemical form release agent. The high performance form release agents are totally fuel or in layman's language "diesel fuel" free. The form release agents your crews need are very low odor and function by reacting with the lime water released from the concrete.

The released water, out of the concrete, is part of the "bug hole" forming problem. A premium form release agent allows the water droplets to rise up and out of the formed face region, fuel form oils do not.

We suggest your company try DEBOND® FC™ by LATICRETE® and continue your quality approach to cast concrete.

Rehabilitating Concrete Floors

Q: We are trying to justify coating and rehabilitating the existing concrete floors to a very budget sensitive client, any thing you can share with us to promote nice looking floors?

A: Attractive, well maintained floors speak volumes about your client to the prospective customers he brings into his facility. In the case a business has a dependency on making a good first impression, attractive floors, beautifully maintained always make a great first impression. The beauty of the floor will provide the impression his company has pride in all the things they do.

Nice looking coated floors also, send a good message to your clients employees. The employees can see a commitment to cleanliness and safety with beautifully sealed floors. Coated and sealed floors are less expensive to maintain and keep clean, this should appeal to your client.

LATICRETE® has concrete repair and coating products to make an old floor appear new and a new floor appear beautiful. You are giving good advice to your client, when you ask him to repair and coat his floors.

Concrete Surface Powder

Q: We have a new concrete slab on grade. The surface is smooth and hard. The surface is beginning to dust or give off a fine white powder. What can we do without removing the slab or installing an expensive overlay? The dust is getting on the inventory and that must stop.

A: There are many causes for a concrete floor surface to dust. In this case the cause is not the concern. The solution is the immediate need. The best product for the immediate dustproofing of the floor at your property is SEAL HARD™. Seal Hard is odor free and clear. You could apply the Seal Hard and open the floor up to traffic in the same day.

The wise thing to do is a test panel on the worst area of the floor and watch the for the dust free performance. You can then make an informed decision.

Concrete Slab or Foundation Cracks

Q: My concrete contractor failed to coat the finished slab foundation with a curing agent. The next day two hairline cracks appeared that ran from one side of the foundation to the other side. After two weeks, these cracks have not gotten any larger. Should I be concerned about foundation failure later, or are the two cracks simply cosmetic problems?

A: I get the impression the cracks are in a slab upon ground. I also am thinking the slab is roughly rectangular in shape. The cracks are not just cosmetic, they probably go through the depth of the slab of concrete. The trouble I imagine is a rising dampness and water ingress into your structure through these cracks.

One thing before we continue, concrete cracks by nature, it is a matter of jointing it so the cracks are pre-engineered to occur in useful or expected places.

If I owned your concrete, I would have the contractor come back and answer your questions, I would ask him to hire a concrete expert and have the expert design a joint system for your concrete and then fill the joints with a high grade poly urea joint filler. This should get you the performance a reasonable man could expect.

Concrete Slab Moisture Vapor

Q: We want to apply one of your membrane sealers on a warehouse floor. The problem is that moisture is visible upon the surface of the concrete in early morning. The floor is six months old and we think the moisture is condensation and not moisture vapor from within the slab... what can we do to tell the difference?

A: My experience from other, similar circumstances leads me to tell you to use a thin piece of sheet metal and place it on the dry floor surface. The piece of sheet metal should be large (about 20 square feet in size). Tape the sheet metal down with some duck tape in order to seal the entire perimeter edge. Allow it to lay in place at least overnight. Examine the top, exposed surface of the sheet metal the next morning for the presence of moisture. If water is present because of atmospheric condensation, the water will be present upon the top surface of the sheet metal and when you lift the metal sheet, the surface will be dry. There may be a minor amount of moisture under the sheet. This would be from the normal vapor transmission. If, however, the underside of the metal sheet is highly condensed, the problem is probably due to excessive moisture rising through the slab. This may or may not be a problem depending on the origin of the moisture.

LUMISEAL WB™ is an effective, user-friendly membrane that can even be placed over concrete releasing a moderate amount of moisture vapor. LUMISEAL WB™ is a low-odor, non-yellowing, low-gloss sealer. It has excellent tire marking resistance. If you're not quite sure of your particular application, or the right LATICRETE® product to use to solve your problem... just give us a call - We always appreciate questions from the industry.

Concrete Oil Stains

Q: We are always fighting the same fight at the end of every concrete floor project. Dirt, mud stains, rubber tire marks and sometimes rust stains sticking to our once clean concrete floor. Our crew pours the concrete and gives it a smooth and clean finish, as soon as we leave the other workers dirty the floor so bad, we have to clean the floor at our expense before receiving our final check. What can we put on the floor to minimize this problem?

A: The first thing to do is develop a "understanding" with the general contractor's onsite supervision. This understanding should give knowledge or meaning to your reoccurring situation. You want to promote a sense of caring, if even in a small way, for the cleanliness of the new concrete floor. I know that sounds futile, but you have to communicate your concern to the leadership on site. Once you have done that, I suggest examining the contract and if the specification language calls out a cure and seal product, use it.

The choice of the product may come from a suggested or approved list in the specifications language, or it may be a performance specification. The product you want should produce a "skin" or membrane on top of the concrete. Your plan is to lock out as much dirt and stains as possible, without going overboard. Many of these membrane cures are rated in moisture retention ability, and that is good, you want moisture retention and you want film thickness, too. Luck would have it, these two properties usually coincide.

Look for a cure or a cure sealer meeting the new ASTM C 1315, this requires 25% solids as a minimum and a moisture retention ability greater than low solids formulas from the past.

The idea is to bond a tough membrane to the surface of your clean, smooth concrete and minimize the mess you have to deal with from the other trades at the end of your contract. I suggest using our DRESS & SEAL WB 30™, or LUMISEAL PLUS WB™, and always check to see if the specifications' language permits these membrane-producing products.

Concrete Block Wall

Q: We have a concrete block wall with a northern exposure, we have insulated and finished the inside and enjoy the improved looks and warmth the insulation and wallboard provide. We have observed the outside of the wall stays wet or damp for days after a rain or snow melt. Can we improve water resistance of the out side face of our wall? We suspect the water will create problems over time.

A: The concrete block surface exposed to the water from rain and snow melt will become a problem. Historically, the water will find a way to get to your finished surfaces.

I would like to recommend AQUAPEL PLUS™ as a clear, liquid applied treatment to the exposed face of the block. AQUAPEL PLUS™ is easy to apply and is odor free. The concrete block wall will repel the water in the future versus letting it soak in and ruin your finished spaces.

Exposted Aggregate - Water Protection

Q: We have a dusting problem on a new concrete floor we pumped, placed and finished last winter for our best customer. The floor surface is very porous and weak, and in some areas appears to be covered with white flour. We sweep it and scrub it but it returns the next day. Some areas are even showing the surface of the coarse aggregate. A review of our placement records shows that we did everything according to the book, but now we have this awful situation. What do you think happened and what can we do?

A: Your letter further explained that the concrete mix was not too wet or high in slump. Troweling was not done too early. The surface was hard and firm when your crew completed finishing. Lastly, the surface did not crust or dry out before it was covered in some cases and cured in other cases.

Here is what I suspect went wrong. Your floor is a victim of the cold weather scourge of concrete: Carbonation. Fossil fuel heaters give off high levels of carbon dioxide gas. If not properly vented to the outdoors carbon dioxide gas from the heaters will float down to the surface of fresh concrete and react chemically with the fresh cement paste, halting its set. Carbonated concrete surfaces will fail to properly set or harden completely and instead will dry out to a weak, porous finish, which in severe cases as the one you describe evidences itself as a fine powdery dust. The depth of this weak carbonated concrete surface will vary due to the degree of exposure to carbon dioxide gases.

To prevent dusting from carbon dioxide gas use indirect fired heaters or fireboxes vented from and to the outside. The combustion air and combustion chamber need to be outside in fresh air. Do not allow the heater to combust the recycled interior air or the air will become more laden with carbon dioxide and soon destroy the integrity of the newly placed concrete surface.

To minimize or eliminate the effects of carbonation on an already placed concrete floor a number of costly steps will be required, depending upon the severity of the carbonation. For lightly carbonated surfaces, many of our customers have found the application of SEAL HARD and CHEM HARD in multiple coats has yielded satisfactory results. On more severely carbonated floors a more expensive, but necessary, treatment may be required which would involve surface grinding of the floor using a FGS (Flat Grinding System) to remove the weak, carbonated cement paste, polish the remaining floor, which is then reinforced with a two-coat application of SEAL HARD™. Finally, in areas where coarse aggregate is already showing, carbonation has done its maximum damage. The remedy for these distressed surfaces requires grinding in preparation of a properly bonded latex-modified floor topping like our DURATOP HP™.

Carbonation can be scientifically identified on a suspicious surface. Generally a good concrete lab can determine the presence and depth of carbonation. It is necessary that concrete cores be taken from the areas in question for this test.

It is always a good idea to consult with your LATICRETE® technical representative to review the project condition and to allow us to help you. Thanks for bringing up this costly, yet easily prevented problem.

Concrete Plant Floor

Q: We have an expansion adjoining our existing plant. The floor in the existing plant was treated with iron shavings and cement. We can see the iron shavings on the worn parts of the floor. Our existing plant managers told we cannot use it in the new adjoining floor, too much dust from the iron and cement shavings. We have to treat our new floor. What can we do?

A: Contact your project engineer and discuss this situation with him. The information you are about to see is to be used in combination with the meeting with your project engineer.

SEAL HARD™ by LATICRETE® is a liquid applied hardener and is totally dust free. SEAL HARD™ is not an iron hardener and it contains no cement dust. Your plant engineers may have very legitimate reasons for a no dust process.

The construction activities will not be altered. The concrete can be placed as planned and the concrete floor can be finished as specified. The SEAL HARD™ liquid can be placed upon the finished floor in as soon as the floor is three days old or older. There is no odor associated with it and absolutely no dust. The SEAL HARD™ treated floor will resist dusting and wear. The color is clear.

Waterproofing Concrete Floors

Q: We treated our plant floor five years ago with a water proofer and it had the picture of a seal on the label. Can we retreat our plant floor with your SEAL HARD™? We cannot tolerate an odor because this time the plant is in operation.

A: Yes, you can treat your concrete floor with SEAL HARD™. I am pretty sure I know the product you are describing, as being used in the past. The process this time would be to degrease the floor with CITREX™ and then treat the floor with odor-free SEAL HARD™. You can do the floor in phases or you can slip in on nights and week ends and do larger areas. Using SEAL HARD™ will be a good investment to keep your floor in good order for years to come.

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