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For most trowels used for floor-covering installations, the correct angle to hold the trowel is 45 degrees to the floor. There is a reason for this angle. First, the angle creates a bit of a hydraulic pumping action by compressing the liquid adhesive and forcing it through the notches. If you were to hold the trowel at a 90-degree angle to the subfloor, you wouldn’t get the compressing action and would just cut through the adhesive on the floor. Without the compression from the 45-degree angle placement, the adhesive may actually skip through the trowel notches and leave you with an undesirable result.

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Why should I be concerned about moisture content in a concrete slab?

Because you will be directly touching it with an adhesive and flooring material, both of which may not function properly when in contact with a damp substrate. For example, if your goal was to install a solid vinyl sheet flooring over a damp concrete slab using a wet-lay, water-based adhesive, once you covered the adhesive with the sheet vinyl there would be nowhere for the moisture in the adhesive to absorb into; the existing moisture would remain in its liquid state and the installation would be a mess. Another example would be to install prefinished solid wood flooring using a urethane adhesive over a damp concrete slab. The urethane adhesive would cure nicely because it cures by coming into contact with moisture, but the wood flooring would absorb moisture coming from the slab and cup, warp, curl or swell – causing a nightmare of a problem. The bottom line is that there's a reason for the moisture-limits statements of adhesives and flooring materials. As such, the installer should calculate the appropriate measurements for moisture to determine if he can proceed or if he needs to do something more to isolate that moisture from the flooring installation. Learn more here:

What does "working time" mean?

This term refers to the amount of time, after the open time or flash time (if any), during which the adhesive you just applied will accept the flooring material and still provide an adequate bond. If you leave certain adhesives open to the atmosphere for too long, they will skin over or cure out and not be wet/sticky enough to accept the flooring material. In other words they will dry out. It is important to note that working time is often affected by the ambient temperature as well as the ambient humidity. For example, in arid parts of the country when the temperature is very high, working times will be much shorter for water-based materials but much longer for moisture-curing materials. Areas of high humidity and high temperature will have longer working times for water-based materials but potentially shorter working times for moisture-curing products. Cold temperatures are going to slow everything down whether the products be water-based or moisture-curing. For reactive adhesives like epoxies or epoxy-modified polyurethanes, temperatures will greatly affect the working time. Reactive adhesives are very sensitive to temperature, so cold conditions will extend the working time and hot conditions will speed things up.

Should I be concerned about moisture content in a plywood substrate?

Excess moisture in a plywood or wood substrate is a probably just as damaging to a floor installation as high moisture content in a concrete slab. According to industry standards, the moisture content of a plywood substrate should be in the range of 10% to 15%. Dryer than that risks extreme adhesive absorption and subsequently poor adhesive transfer to the flooring. Wetter than that (such as through exposure to rain before installation) and the adhesives will take longer to dry; then when you have installed the flooring and the plywood has dried out, you will see the result of the plywood panel shrinkage through the surface of the flooring. A critical success factor for any floor installation is to make sure that the substrate you are working on is stable and acclimated to the working environment. Anytime you step outside that playing field, you will find yourself in trouble.

What’s the problem with OSB as a substrate?

Traditional OSB is a problem for resilient and wood flooring installations because of the nature of its construction. Traditional OSB is made from large chips of wood that will swell when exposed to humidity and moisture, causing the texture of the chip structure to show through on resilient floors. According to the Engineered Wood Association, OSB is only suitable as a substrate for stretch-in carpet, which isolates the texture of the OSB from the flooring with a layer of carpet pad. The association goes on to recommend applying a 1/4" layer of underlayment over the OSB for installation of resilient and wood flooring. The main thing to remember about traditional OSB is that it is very absorptive and swells when exposed to moisture (such as rain). This swelling is not good for floor installation. Having said that, there are new OSB products out there that are “engineered” materials, making them different from traditional chip/strand OSB. Some of these new engineered OSB boards have much better moisture resistance and can handle water contact without a change in dimensional properties.

Why did my concrete crack?

There are many causes for cracking in concrete. Concrete goes through many changes as it hydrates or hardens. Allowing the concrete to harden and achieve strength before these stresses arise will eliminate a large portion of these cracks. Proper curing, a good mix design, use of shrinkage-reducing admixtures and the addition of fibers are all good ways to help minimize some types of cracking.

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How much water do I need in my concrete mixture?

ACI provides guidelines as suggestions or recommendations on the water content to provide the desired compressive strength. Never add more water than what is necessary to provide the desired workability. More water equals lowered strength.

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Why do I need air in my concrete?

Adding air to the concrete (air entrainment) allows the concrete to withstand freezing and thawing cycles as it provides room for the water present in concrete to expand without putting stresses on the concrete itself.

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What is the best time to pour concrete?

Concrete can be placed in a wide range of ambient conditions. ACI guidelines explain the range of these conditions. Avoid placing concrete below 40°F or above 120°F without proper protective measures. Also avoid windy conditions without a wind break as this will expose the fresh concrete to premature surface drying, which can lead to cracking or a weakened surface that is prone to “dusting” and discoloration.

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How soon can I apply Mapelastic AquaDefense membrane over a sloped mud bed?

After creating a slope with a fresh mud bed using MAPEI's 4 to 1 Mud Bed Mix, the area should be allowed to cure for at least 24 hours per inch (centimeter) plus one day before application of MAPEI's Mapelastic AquaDefense. For example, if the mud bed is at 2" (5 cm) depth at its highest level, then you must wait three days before the application of Mapelastic AquaDefense. Curing time is based on a temperature of 73°F (23°C). Cooler temperatures will require longer curing times. If your project is on a fast track, consider Planislope RS mortar, which can receive waterproofing in a matter of hours.

Surface Preparation Requirements Reference Guide RGT0309

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How should I cure my concrete?

Curing is one of the most important steps in protecting your concrete and ensuring a long service life. The use of sprinklers, wet burlap and curing agents allow the concrete to gain structural integrity (strength) while protecting it from premature surface drying. Utilizing curing compounds and using sealing agents are the best ways to keep the concrete surface protected from the environment and ambient conditions, which would otherwise deteriorate the concrete surface.

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Why isn't Mapelastic AquaDefense membrane bonding to the cement board?

New cement board will often come with a fine dust on the surface of the board. So, it is very important to clean the surface of the cement board and to allow the surface to dry before applying Mapelastic AquaDefense. Usually, wiping the cement board with a damp (not wet) sponge will effectively remove the dust.

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