Q. Who can apply Gemite materials?
A. Gemite material systems should only be applied by well-trained professional contractors. Please contact Gemite or one of our Distributors for advice.
Q. Cold weather application – what do I need to do?
A. To apply any cement based material during the winter months, or when the temperature is expected to fall below 4 deg. C (40 deg. F) it is necessary to heat the application area.
Do NOT use gas or oil heaters – you may get severe carbonation and carbonation cracking.
Use electrical heaters to keep the working environment above 4-5 deg. C (40 deg. F) during and after the application. The materials must not freeze the first night, and should be kept warm while curing (wet or dry curing). The length of heating time depends on material – contact Gemite technical Service for advice.
Q. What is the difference between dry and wet process shotcrete?
A. In the dry processes the dry mix of cement, aggregates, additives and possibly fibers are blended and delivered by the hose to the nozzle by compressed air. The mixing water is added at the nozzle, mixed with the dry material while being delivered to the area of placement.
In the wet process the mortar or concrete is premixed with water in a mixer and pumped through a hose to the nozzle. The compressed air brought to the nozzle delivers the mix to the area of the placement. Both processes have their advantages and disadvantages and both are used in concrete restoration. For more detailed information please see a presentation titled Shotcrete in Concrete Restoration.
Q. What is the function of microsilica in shotcrete?
A. The microsilica is a very effective pozzolanic admixture, and increases the strength, decreases hydraulic permeability (water tightness), and provides mix cohesion in the wet process shotcrete. For more information on microsilica, please refer to presentations on Adi-Con CSF (R).
Q. What is a Pozzolan?
A. The Pozzolan is an amorphous silicon dioxide capable of reaction with calcium hydroxide generated by the hydration of Portland cement. It could be synthetic such as condensed silica fume, fly ash or slag, or natural, for example volcanic ash.
Q. What type of fibers are you using?
A. Gemite mortar mixes typically use alkaline resistant glass in combination with polymer fiber. The specialty concrete mixes may contain polymer or steel fibers.
Q. What is the function of fibers?
A. Fibers are used to improve the fracture toughness and control drying shrinkage cracking, and in some special Gemite materials they improve tensile and bending strength.
Q. How do I prepare the surface of new, or existing concrete?
A. ALL concrete surfaces need thorough cleaning.
Old surfaces need cleaning to remove any bond preventing dirt, or contamination.
New concrete surface always has laitance present, which MUST be removed.
For more details, please see Technical Note – Surface Preparation Instructions.
Q. Is it possible to bond to oil contaminated concrete?
A. Yes, it is not easy, but possible, using a special procedure utilizing Cem-Kote Barrier Coat 100. Please contact Gemite Technical Service for advice before starting such project.
Q. What is the difference between positive and negative side waterproofing?
A. Positive side waterproofing – when the water is on the side of the waterproofing (swimming pool).
Negative side waterproofing – when the water is on the opposite side (waterproofing a basement from inside).
Q. What is the difference between Damproofing and Waterproofing?
A. Damproofing – protection against penetration of wind driven rain (minimum pressure), such as damproofing of an exterior wall.
Waterproofing – protection against penetration of water under water-head pressure (usually below grade).
Q. What is the function of Reinforcing Fabrics?
A. The Reinforcing Fabric reinforces Cem-Kote Flex and other cementitious membranes, and provides a higher tensile strength, toughness and cracks bridging.
Q. What is the difference between standard crystalline waterproofing and Cem-Kote CW Plus?
A. Standard crystalline waterproofing use only one (1) mechanism – penetrating silicate, which reacts with lime and forms crystal plugs within the capillarity of cement based concrete and mortar.
Cem-Kote CW Plus uses two (2) waterproofing methods – crystalline + in addition it functions also as a membrane. This unique composition provides faster waterproofing when compared with conventional crystalline waterproofing, and is a much stronger and tougher coating.
Q. What is the difference between Cem-Kote Flex ST and Cem-Kote Flex CR?
A. Cem-Kote Flex ST is based on Portland cement; Cem-Kote Flex CR is based on aluminate the latter one has a considerably better performance to microbiologically formed sulfuric acid in wastewater treatment facilities, lift stations (pumping stations) and manholes.
Q. What waterproofing product should be used in sewer systems?
A. For a layer thicker than 1/4 in (6 mm) use either wet shotcrete applied Spray-Con WS ST or hand applied Fibre-Patch OV. If only a thin section is required, use Cem-Kote Flex CR. Depending on hydrogen sulfide concentration, the layer of Spray-Con WS ST may have to be coated with Cem-Kote Flex CR.
Q. Is pH information sufficient for establishing the corrosive nature of the chemical on concrete?
A. It is not, it is also important to find out what acid it is, its concentration, exposure frequency or continuous submersion, quality of concrete and if possible how long the concrete has been exposed and what is the section thickness loss.
Q. Why epoxy and other polymer coatings fail on concrete in wet environment?
A. There are several reasons for that. It could be capillary pressure at the polymer coating/concrete interface due to water penetrating from behind the coating (e.g. sump pit coated on the positive side), but getting the ground water from behind. Or it could be pinholes and micro-cracks in the coating. The penetrating water from the positive side creates high capillary pressures at the polymer coating-concrete interface and causes de-bonding. It could also be a combination of both effects.
Cement based coatings do not have these problems, since they are breathable and also they are able to reduce the capillary pressures at the interface by absorbing the water into the porosity of the coating at the concrete interface.
Q. What is breathability and vapor barrier?
A. The breathability of the coating is the ability to pass the water vapor. It is defined by water vapor transmission, permeance and permeability. For more detail, see ASTM E-89 Standard.
The vapor barrier is a coating with none, or very minimal ability to pass the water vapor through the coatings.
Q. Are all cement products breathable?
A. All cement-based products manufactured by Gemite are breathable; the extent depends on formulation and thickness.
Q. What products can I use over an existing brick wall?
A. Use clear penetrating sealers based on either silane or oligomeric siloxane, such as Rain-Shield SX SL, Rain-Shield SX WB or Gem-Gard SL ST. These do not reduce the breathability of the brick. When a color sealer must be used, contact Gemite Technical Service to discuss each project separately.
Q. When do I need Tuff-Flex, the flexible wall coating?
A. When there are cracks in the wall
Q. What is the longevity of Gemite wall coatings and sealers?
A. The longevity of Tuff-Flex, Tuff-Cote and Rain-Shield Stain WB is in excess of 25 years, and we have many projects lasting even longer. The penetrating wall sealers, such as Rain-Shield SX / SL, Rain-Shield SX WB last for about 6-7 years. Then they need to be reapplied to maintain the damproofing effectiveness.
Q. What is the difference between penetrating and film forming wall sealers?
A. The penetrating sealers based on silane and oligomeric siloxane do not form a film and have very little or no effect on breathability of the substrate, which in some cases may be important, e.g., in damproofing of brick walls.
The film forming sealers form a very thin, physical film on the surface. Depending on the formulation and the substrate porosity they may penetrate to some extent or just form a surface film. The film forming sealers, e.g. Gem-Seal MB, Rain-Shield MB WB will reduce breathability to some extent. They are not recommended for brick walls and are used only on concrete or concrete block walls.
Q. What is microsilica and how does it affect the properties of concrete?
A. Microsilica is a very fine particle, amorphous silicone dioxide with pozzolanic properties. It reacts with lime generated by hydration of Portland cement and forms additional products of hydration. Condensed silica fume is one of the microsilica types of pozzolans, produced during manufacturing of ferro-silicones. The addition of microsilica increases compressive strength, decreases hydraulic permeability hence increasing durability and improves chemical resistance. Gemite supplies Adi-Con CSF (R), which is a formulated product, which includes a superplasticizer and polymer fibers and Adi-Con CSF, which is a raw microsilica. The latter product, when used in concrete, requires an addition of a superplasticizer.
Q. What is the function of fibers in Adi-Con CSF (R)?
A. The main function of polymer fibers in Adi-Con CSF (R) is to control plastic shrinkage cracking of concrete and to some extent drying shrinkage cracking. The fibers do not replace the necessary use of fogging shortly after the finishing and good wet curing
Q. What admixtures should I use for underwater concreting?
A. Use Adi-Con AWA 100 and 200 anti-washout admixtures. These control the cement wash out of cement when casting concrete under water.
Q. What is the difference between Sure-Flo ST and Sure Flo Plus?
A. Sure-Flo ST is typically walk-able the next morning; the Sure-Flo Plus is walk-able in several hours after the placement. The actual times will depend on temperature, relative humidity and the ventilation of the areas.
Q. What product can I use as a finished topping?
A. Use Sure-Flo FT 100
Q. Do I need to coat Sure-Flo FT 100?
A. It is recommended to use a color sealer, such as Gem-Cote WA ST and then clear sealer Gem-Seal WA ST, since it is difficult to obtain a uniform color with these types of products, due to variation in substrate porosity, the layer thickness, air movement during curing and variations in mixing and placement.