Sealcoatings are wonderful for protecting and preserving asphalt pavements. For optimum performance though, it is imperative that sealcoatings be applied on structurally sound pavements that are clean and free of defects. Defects in asphalt pavements can interfere with the sealcoat’s performance. While examining sealcoating failures, it’s important to look at the pavement itself and ask from where the problem is originating. Property owners have to be made fully aware that the sealcoatings are not repair products and their performance depends on the condition of the pavement.
The major problems that may show up in sealcoatings originate not only from the top of the pavement but from the deeper structure (base and sub-base). Some of the frequent complaints on sealcoated surfaces are listed as below:
The appearance of white/ tan streaks along the cracks in the pavement, on sealcoated surface. The first reaction of the property owner and in some cases the sealcoating contractor is to call the manufacturers and complain that the sealer is faulty and breaking down, releasing clay and fillers. This reasoning is actually far from what is really going on. The most common reason for such complaints is poor drainage of the pavement, compounded by a situation with high water tables. Water collects in the base and sub-base and as the hydro-static pressure builds up, it pumps out though the cracks bringing up fine limestone/clay particles which are seen as white/tan streaks. The remedy is not to apply another coat of sealer, but fix the drainage so that the water drains away from the base.
Shiny silvery streaks coming though the sealcoated surface are not caused by any sealer component coming out of the sealer, but by the presence of an iron ore contaminant (pyrites) in the pavement. Depending upon the quality of aggregates available in a region, DOTs allow a certain number of rust spots per square yard of the paved surface. With weathering, iron changes into iron oxide, thus causing brown spots and streaking on the pavement surface. If you pay close attention, you’ll probably come across such brown spots and streaks on bare unsealed asphalt and even on concrete surfaces. Even after sealcoating, iron continues to oxidize, creating streaks – initially appearing silvery and before changing to brown streaks and spots. For such pavements a specialty rust-inhibiting primer should be applied prior to sealcoating. This will retard the reactivity of the iron contaminant and the reappearance of streaking. Priming is a maintenance step, not a permanent solution, meaning that priming may have to be repeated along with the sealcoating application.