Funny thing about water slides: They’re not exactly waterproof.

Just as a river will smooth rock to stone, thousands of gallons of rushing, chemical-laden water and abrasive swimsuit-clad bodies will take an eventual toll on fiberglass flumes.

Water slides are durable, not indestructible. Chips, scratches, cracks, scummy build-up and other indicators of a well-loved slide add up to a rough and potentially hazardous ride.

Though routine, ongoing maintenance will go a long way toward keeping these towering attractions operating safely, repairs are inevitable.

Faced with a slide in need of face-lift, facility managers either can use their in-house crew or turn to service professionals to restore those giant, spiraling tubes to their former glory.

By the way, it’s September. The season is winding down. Tackle each slide one by one and your facility will be ready well before spring. But before you call in the cavalry, know what you’re getting into.

Water slide restoration requires meticulous attention to detail, plus the physical ability (and nerve) to crawl around the dark contours of these massive funnels, keeping your eyes peeled for defects. A headlamp is highly recommended.

It may sound like a daunting task, but better that you discover whatever snags may be lurking around the bend than learn about it from complaining guests.

Warning signs

So what exactly are you looking for? The list ranges from simple cosmetic blemishes to serious safety concerns, but here are some of the most common red flags.

Bare fiberglass — A new slide fresh from the factory comes with a protective top coat over the fiberglass laminate. Most manufacturers use gel coat. Though durable, gel coat will wear away over time. That creates the potential for the fibers to protrude through the laminate surface. Fiber bloom, as it’s called, is nothing you want your guests to encounter. Look for these rough spots around twists where the surface is susceptible to more friction due to centrifugal force.

Unaligned seams — Check each seam closely to ensure they’re flush. Problems occur when panels fall out of alignment, creating positive and negative seams. A positive seam happens when the edge facing the slide’s exit juts slightly above the entrance-facing edge. (Like this: –_). While not exactly a hazard, it can be briefly uncomfortable for the rider. Far more dangerous is the negative seam, which faces the rider head on (Like this: _ –).

Blisters — These occur when water gets trapped between the fiberglass and resin, or when off-gassing creates tiny volcanos on the surface.

Spider cracks — More than a cosmetic issue, these cracks could indicate a structural failure that should be closely investigated.

Weathering — Perhaps the sun does more damage than continuous coursing water and sliding bodies combined. Punishing UV rays result in chalking, fading, yellowing and alligator-like scaling over time.

Prep for perfection

“No matter what you’re going to put down, even a good quality gel coat, you’re going to have to have the most immaculate surface for that to adhere to,” advises Bill Hamilton.

The manager of water quality and pools at a major Florida waterpark can’t stress that enough.

“Because of the friction that takes place between the rider and the [tube], that surface is precious,” he adds. “It has to be pristine.”

That means sanding off the existing top coat, smoothing away rough patches and grinding out chips and repairing cracks with waterproof filler. Use a power washer to blast away the dusty remains and consider giving the slide a thorough scrubbing with trisodium phosphate to remove any oils.

You might have to get creative with some of those hard-to-reach spots. Firms that specialize in this line of work are accustomed to scaling the heights of intimidatingly steep speed slides with a rope and pulley system, or they might employ hydraulic aerial lifts.

Because you’ll have workers in awkward places of height, carefully go over safety standards, insurance matters and other risk factors, especially if you’re hiring contractors.

“There are a lot of reputable companies that can do a job for you, but at what cost? If they’re cowboys swinging off the rafters like rebels, man, one accident and that good bid is shot away and gone,” Hamilton warns.

Seams good?

Examine the seams closely. As previously mentioned, offset panels can create an uncomfortable, potentially dangerous speed bump. Even properly aligned, seams can trap debris, which builds up over time with back-scratching consequences.

“We’ll sand through the original gel coat into the fiberglass to get those seams aligned perfectly,” says Andrew Fischer, co-owner of Fischer Bros., LLC, a water slide maintenance and restoration firm in Eau Claire, Wis.

In preparing the surface of the riding path, some water slide pros suggest running a diamond cutter around the circumference of the seam to make it slightly wider. That way, when it comes time to apply the laminate, the seam is more defined. Don’t paint over it.

“Depending on the manufacturer, some of those seams are pretty tight … and we don’t want that layer of gel coat to attempt to bridge over the seams,” Fischer cautions.

Preventing leaks really is only an ancillary benefit. Properly caulked, seams not only create smooth transitions between panels, they allow for some flex. Painting the seams would make the slide stiff and prone to crack.

A question of coatings

This is where things get controversial. Some say resurfacing slides with anything other than gel coat is folly. But manufacturers of alternative coatings claim their products are, in many ways, superior to the industry standby, boasting-chlorine resistant properties and added UV protection.

However, some say it’s not a matter of which application is better than the other, but how it’s applied. Simply applying a layer of gel coat or other epoxy over an improperly prepped surface can cause big problems down the line.

Tony Perry sees it all the time.

“The No. 1 enemy of a restoration process is a failed coating,” says the customer relations manager of Safe Slide Restoration. Headquartered in Missouri, the firm has worked on some of the biggest waterparks in the U.S., including Legoland Florida and Busch Gardens. As an example of what-not-to-do, Perry points to a water slide in Illinois that was refurbished by a competitor. The slide developed jagged, sharp edges as a result of an improperly applied top layer.

“It was done so poorly it had to be taken down,” he says.

Anthony Sabo is sticking with gel coat. The rides maintenance supervisor at Ohio’s Columbus Zoo and Aquarium — the only zoo in the nation to boast a full-fledged waterpark — recalls the mess his predecessor left behind when he resurfaced some slides using an experimental paint product. Water became trapped between the fiberglass and coating, causing it to bubble and chip.

“Honestly, we had nothing but issues,” Sabo says.

One structure was damaged beyond repair and had to be removed.

Sabo hired Safe Slide Restoration to give the attractions a top-to-bottom refurbishment. The crew scrutinized each slide for problem spots and presented Sabo with an action plan.

“We also use them as third-party inspectors,” Sabo says.

Sealants also have their critics. Though sealants may give slides a wet luster, some say that it doesn’t significantly protect colors from fading. Even worse, some claim that inferior products can wear away, leaving bits and pieces in the pool, which could clog the filter.

In short, you get what you pay for. Budget-strapped municipalities are more likely to experiment with cheaper alternatives and hire the lowest bidder to freshen up their public waterparks. The results are hit-and-miss.

“We remove those regularly,” Perry says of painted rider paths, which can fail after one season’s use. That means the Parks and Recreation Dept. could be out another $50,000 to mend the slide. “That’s an expensive mistake to make,” Perry adds.

Check the specs

Off the shelf, so to speak, slides generally come with a layer of gel coat 18 to 24 mils thick. When resurfacing, try to replicate manufacturer’s original top coat.

“We really want to go back to the original manufacturer’s specs,” Perry says.

Tip: Using precise metering spray equipment, layer it on between 20 and 27 mils. That way, you’ll achieve a dry film thickness of 18 to 24 mils when it cures. To put that in perspective, 18 mils is about half as thick as a dime.

A question of colors

Colored gel coats are available in a variety of pigments. Some hold up better than others. It can take as little as six months for some to drastically fade in a hot, sunny climate, so choose wisely.

Here’s how different colors react under continued sun exposure.

White, clear and off-white — The benefit of whites and clears is that dull patches of gloss don’t show up as well as they do on darker hues. However, they can become yellow with age. For best results, use a coating with high UV defense.

Deep — Blacks, blues, reds, burgundies and greens chalk as they weather. They may chalk at the same rate as other colors, but because these colors are darker, unsightly chalking is more pronounced.

Bright — Blues and greens are subject to fading, while yellows and reds can turn into ugly, darker shades. Some pigments also can bleach out under a steady stream of acids and alkalis.

While it’s best to stick with the manufacturer’s specifications when resurfacing the interior, an exterior paint job is an opportunity to improve upon the slide’s original finish. Some contractors use a high-grade paint, suitable for water towers, that’s able to withstand the elements better than conventional coating.

In fact, freshening up the exterior is the quickest, most affordable way to give your facility a whole new look.

“Often we hear park owners or park managers say the following year, ‘Man, everyone thinks we got new slides,’” Fischer says.