FREQUENTLY ASKED QUESTIONS
How do I calculate the amount of coating required?
First, see the “Calculations” page under tools and links on this web page – estimate the area to be coated then calculate coverage by dividing film thickness into 1604.
Example: if thickness is 16 mils then coverage is 1604/16 = 100 sq.ft. per gallon. Divide area by coverage to get an estimate of consumption – remember, this is theory – always allow a little more for wastage and losses.
Note: the coverage calculation only works for solvent-free coatings like TFT – if the coating being used is solvent based this coverage is reduced.
Can I add solvent to a solvent-free TFT coating?
It is possible to add a compatible solvent such as MEK when TFT products are used in thin films, say 40 mils maximum. In thicker films the addition of solvent can cause problems because of slow release from the film. As a guide, a 12oz can of solvent in a 2 gallon kit of TFT coating is about a 5% addition. This will cause a significant reduction in viscosity.
Note: Remember at all times that epoxy solvents bring with them health, flammability and odor problems. Avoid inhalation and ensure that there are no sources of ignition in the project.
What Surface Preparation is required?
More is better! At a minimum it is necessary to remove loose surface contamination such as grease, loose rust and dirt which will seriously interfere with adhesion. Some TFT coatings are designed for application to wet, or even underwater, surfaces. Adhesion is excellent so long as rust and marine fouling is removed.
What is the effect of temperature?
Drying, or curing, of solvent-free coatings is an entirely chemical reaction. Ordinary paints contain solvent which just has to evaporate into the atmosphere in order to begin the drying process. Increasing temperature speeds up the reaction between epoxy base and curing agent. As a rough guide, increasing the temperature by 18°F, (10°C), doubles the rate of reaction. This means curing time is halved however potlife, or working time, is also halved.
What is “Potlife”?
After the two components of epoxy base and curing agent are mixed there is a chemical reaction which begins immediately. Obvious effects of this reaction are an increase in temperature, or exotherm and an increase in viscosity. The stated Potlife is the length of time after mixing that the material is still usable. Potlife is usually measured in the lab using small quantities of about 100 grams, in practice, with larger volumes, the potlife can be appreciably shorter. In practice it can appear that viscosity is manageable some time after mixing – however this may be the result of strong exotherm heating, when the product is brushed onto a cool surface it can thicken up instantly and look like chewing gum.
Why do “paints” contain solvents?
Coatings are made up from only a few “families” of raw materials. These are: Firstly, the resins which bind the coating together and which adhere to the coated surface. Next come the pigments which provide opacity, color, hardness, slip resistance and other functional properties such as corrosion or fouling resistance. After this come the “additives” which are small amounts of specialized chemicals which provide properties such as package stability, better pigment dispersion and so on. Regular paints also have an appreciable quantity of solvent, or thinner, in their formulas. This solvent dilutes the mixture of resins and pigments making it possible to brush or spray them. It is fair to say that the solvent exists to serve a useful purpose only during the application process, outside of that it causes nothing but problems:
- Paint solvents are health hazards, air polluters, flammable and smelly.
- Solvent residues remain in the paint film long after application and can cause severe blistering upon immersion and cracking due to continued film shrinkage even months after application.
- Solvents are no longer cheap and contribute only costs to the final coating job.
How do solvent-free coatings work?
These are the latest generation coatings. Rather than using solvents the resins used are advanced, low viscosity polymers. Careful formulation yields coatings which are easily applied by pad, brush or roller. When larger projects require spray application we use heat, rather than solvent, to reduce viscosity. Using heat has several advantages over solvent:
- Heat doesn’t smell! Ventilation requirements in enclosed spaces are much reduced.
- Heat begins to dissipate immediately after the coating leaves the spray gun. After reaching the relatively cool surface it is quickly lost to the “heat sink” and the coating recovers its gelled viscosity to prevent runs and drips.
- Blistering problems and shrinkage cracks caused by solvent residues are no longer a problem and the cured film is denser and more protective.
What is the effect of humidity during application and curing?
Look at the Product Data Sheets of most paints and coatings and you will see a note to the effect that those materials are not to be applied when humidity is 85% RH or higher. Most normal paints and coatings have a problem with humidity which causes “blooming” or “blushing” on the surface. Not only do these effects appear unsightly but they can seriously interfere with intercoat adhesion. This effect is primarily due to the unfortunate fact that many curing agents are not really totally compatible with epoxy resins and, as the molecular weight of the epoxy/curing agent reaction product increases during curing it can squeeze out free curing agent which comes to rest on the surface of the coating as a greasy film.
Typical TFT base and curing agent mixtures are totally compatible through all phases of curing as well as being extremely hydrophobic. Unlike mixtures susceptible to moisture attack they repel moisture and even cure with a glossy surface after application and curing underwater. Because of these attributes there is never a problem coating with TFT products under humid conditions.
When is the best time to coat concrete?
There are two answers to this question. The first is that the concrete should be aged at least 20 days after pouring.
The second answer is that the best time of day for concrete coating is late in the afternoon when things are beginning to cool off. Prior to this there can be problems with bubbling from trapped internal air in the concrete which expands throughout the early day as the sun heats up concrete slabs. When the surface is suddenly covered by a layer of uncured coating this expanding air seeks to escape by blowing bubbles through the coating – usually coming out as streams through the same spots. As the concrete cools the opposite happens and coating is sucked into the concrete surface – which is a good thing.
How should concrete be prepared for coating?
There are several methods and factors to consider:
When concrete cures it forms a thin and weak surface layer called “laitance” on its surface which is formed from cement and very fine aggregate. This layer is so weak that when a strong coating applied to it is stressed it will be the weak link which breaks resulting in detachment of the coating system. Obviously laitance has to be removed before coating.
Mechanical methods are by diamond grinding, open air/abrasive blasting or centrifugal shot blasting can all work well. Centrifugal blasting using “Blastrac” or similar equipment does a great job however requires a decent sized project because of its mob and demob costs.
Chemical methods involve etching with an acid –usually 10% hydrochloric, (or “Muriatic”), acid followed by neutralizing with soda ash and thorough rinsing.
This can work however it is messy and can cause severe stains in adjacent areas such as driveways. A sheetrocked garage can suffer sheetrock damage from accidental soaking. If acid etching is used make sure that the surface is properly neutralized and thoroughly dried after rinsing before coatings are applied.