Frequently Asked Questions
What happened to the gloss?
UV sunlight damages film forming sealers the same way it damages your skin. Over time, sealers develop micro cracking and pitting that detract from gloss and appearance. Although plenty of sealer may remain, it has lost the initial cosmetic appearance and may need repair.
When do I need to reapply sealer?
That depends upon your expectations of the sealer. If your intention is to protect your concrete from water penetration, freeze/thaw damage and staining, then it needs to be reapplied when the film is no longer there. If you have decorative concrete that relies upon gloss and color development from the sealer, it should be addressed when the appearance no longer suits your taste. At this point the question you need to ask yourself is whether you need to repair existing sealer, or reseal.
How do I tell if there’s any sealer still left on my concrete?
There are two easy ways to assess whether your concrete is adequately sealed for protection. One is to place some water on the concrete and observe whether the concrete darkens, indicating it has been absorbed. If water is able to absorb, there is insufficient sealer to protect your concrete.
A second option is to drip a small amount of household vinegar on your concrete. Vinegar will react with unsealed concrete to bubble or fizz, indicating it should be resealed. If there’s no bubbling or fizzing, your concrete is sealed.
Should I reseal my concrete, or repair the weathered sealer that’s already there?
The answer to this question really depends upon how much sealer remains on the concrete. If concrete is resealed too frequently (every year, for example), the film thickness builds up over time like wax buildup on your coffee table. Increased film thickness will reduce breathability and can cause a whole host of problems, including whitening and delamination.
Why did my sealer turn white?
Concrete may seem like a solid material, but it’s actually very porous. As a result, there’s always water vapor originating in the soil and passing upwards through the concrete into the air. Sealer that is applied too heavily or too often will create an impermeable barrier and trap that water vapor beneath it. If enough pressure is created by trapped water vapor, the sealer can delaminate from the concrete surface, and might even take some of the concrete paste with it! Those areas of delamination appear “white”.
Tech Tip: If your sealer is solvent-based, use a xylene (or xylol) wash to re-solvate and redeposit sealer onto the concrete surface. If your sealer is water-based, this solution may work within the first 24 to 48 hours of sealer application.
Why are there bubbles in my sealer?
Bubbles form for a variety of reasons (see June, 2013 article on bubble formation) but are commonly associated with fast solvent evaporation, over application of sealer, resealing, and a variety of environmental factors including solar energy and air movement. Bubble formation is more frequent in low-VOC formulations in states with restrictive VOC limitations.
Tech Tip: A light xylene (or xylol) mist will often “knock down” the bubbles. Gentle back rolling may be required as well.
Why does my sealer appear milky or cloudy?
Sealer that appears milky or cloudy may have several causes. If your sealer is water-based, it may indicate the application took place when the concrete or ambient air temperature were too low (water-based sealers require both substrate and ambient air temperatures above 50° F). Water trapped in the sealer as it cures can also cause a milky or cloudy appearance.
Tech Tip: If your sealer is solvent-based, use a xylene (or xylol) wash to re-solvate and redeposit sealer onto the concrete surface. If your sealer is water-based, this solution may work within the first 48 hours of sealer application.
What caused my sealer to turn yellow/brown?
Some sealers use resins that are not light stable. Long term exposure to UV sunlight can cause them to become yellow or brown in appearance.
Tech Tip: Don’t reseal over a sealer that has turned yellow or brown. Allow the sealer to completely wear away, and then apply a sealer with a fully non-yellowing resin. Stripping sealers is a difficult process that often results in loss of nearby landscaping, lawn, etc. and should be considered as a last resort.
Why is my sealer “blotchy” or uneven in appearance?
One cause of blotchy or uneven appearance is application of a sealer on freshly poured concrete. New concrete is very high in alkalinity, and requires a cure & seal product rather than a simple sealer. Another cause can be uneven application.
Tech Tip: Using a xylene (or xylol) wash to more evenly distribute the sealer will improve the appearance of solvent-based sealers, or water-based sealers within 48 hours of application.
Why does my sealer appear to have dark “stripes” or roller marks?
Sealers, particularly solvent-based sealers, will darken concrete. If unevenly applied, it will create light areas where there is less sealer, and darker areas where there’s more. If applied by sprayer, it may appear like “stripes”. Uneven roller application may leave darkened roller marks.
Tech Tip: Apply sealer evenly to avoid uneven appearance. Always maintain adequate air pressure when spray applying. Use a xylene (or xylol) wash to more evenly distribute the sealer will improve the appearance of solvent-based sealers, or water-based sealers within 48 hours of application.
Should I use a water-based or solvent-based sealer?
Both have different aesthetic and performance characteristics that will be desirable to different customers for different applications. Those differences can be expressed in the form of pros and cons:
- Typically less expensive
- Generally more environmentally friendly
- Non-flammable, low odor
- Minimal darkening of concrete
- Easier to use at higher temperatures
- More chemical resistant
- Not usable at low temp
- Lower gloss
- More sensitive to some environmental conditions such as high humidity and low temperature
- Develops a deeper, richer gloss
- Will “wet out” antiquing release on stamped concrete
- Increased color development on colored concrete
- Can be used & stored at lower temps
- Improved recoatability
- More expensive
- Faster evaporating, less user friendly at higher temperatures
- Darkens light concrete
- Solvent fumes