When I first started working as a corrugated steel culvert supplier 12 years ago, I thought waterproofing was just about slapping a sealant on the metal and calling it a day. I learned real quick that anyone who’s ever dealt with a culvert failing because of water damage will tell you: waterproofing corrugated steel isn’t a one-size-fits-all job. It’s a mix of choosing the right material, understanding the site conditions, and staying on top of every step from manufacturing to installation. Let me walk you through what I’ve seen work (and what’s landed customers back in my shop with repairs that could’ve been avoided) over the last decade. Corrugated Steel Culvert
First off, let’s get one thing straight: corrugated steel is strong—way stronger than concrete culverts for most rural and municipal projects I work on. But steel rusts when it’s exposed to consistent moisture, and corrugations are just little nooks where water can get trapped, holding more moisture than a smooth metal surface. That’s the core problem we’re solving with waterproofing. The method depends entirely on where the culvert’s going: is it a buried rural road crossing, a storm drain under an urban sidewalk, or a water conveyance culvert for a reservoir? Each site has different water pressures, soil chemistry, and traffic loads, so you can’t use the same waterproofing on a job in North Dakota’s clay soil as you would on a project in Florida’s sandy, salt-laced groundwater.
Let’s start with the most common method I recommend for standard buried culverts: fused-applied liners. Wait, not just any liner—high-density polyethylene (HDPE) or polyvinyl chloride (PVC) liners that get heat-fused directly to the inside of the steel corrugations. Here’s how that works in practice. When we’re fabricating the culvert at our plant, we first blast the inner steel surface to get rid of mill scale, rust, or any leftover debris from corrugating. That rough surface is key—whatever we apply next has to stick, and a smooth, oily mill scale means no adhesion. Then, we prime the surface with a special epoxy primer that’s designed to bond metal to plastic. The liner sheets are cut to fit each culvert section, and we use a hot-air welder to fuse the seams together so there are no gaps. For curved or odd-sized joints at the ends of the culvert, we use flexible sealant made from the same material as the liner to keep it consistent.
Last year, we did a 1,200-foot culvert for a county road in southern Ohio that runs through a wetland area. The original plan was just a spray-on sealant, but when we dug test pits at the site, we found the groundwater table was sitting only 18 inches below the culvert’s invert—way higher than the 3 feet we usually see for standard buried culverts. We switched to the fused HDPE liner, and that’s saved the county from having to do any extra repairs. I’ve seen too many projects where someone uses a cheap spray-on sealant here, and within three years, it’s peeling off because the constant high water pressure pulls at it. The fused liner acts like a second barrier, almost like a plastic pipe inside the steel one, but it’s light enough that it doesn’t add much weight to the culvert, which cuts down on installation costs.
That said, fused liners aren’t for every job. If you have a culvert that’s going to be exposed to high traffic from heavy trucks, like under a highway overpass, the friction from vehicles carrying gravel or asphalt can wear through a plastic liner over time. For those projects, we go with a different method: mill-applied zinc-rich primer followed by a powder coating. Let me break that down. The zinc-rich primer is made with tiny zinc particles, so when it’s applied to the blasted steel, it acts as a sacrificial layer. If any scratch or chip happens to the coating, the zinc will corrode first, protecting the steel underneath—this is called cathodic protection, and it’s a huge plus for high-traffic areas where dings and scratches are inevitable. Then we apply a polyester or epoxy powder coat, which is electrostatically sprayed on and baked at high temperatures so it melts into a hard, smooth layer that’s super resistant to abrasion.
We did a culvert for a state highway project in Pennsylvania a few years back, right after a 100-year storm had washed out the old concrete culvert. The new culvert needed to handle 80,000-pound semi-trucks daily, so the fused liner was out. The powder-coated steel has held up way better than expected—we checked in last year, and there was only one small chip from a falling guardrail part, which the crew fixed with touch-up paint in 10 minutes, no big deal. A lot of people ask if powder coat can stand up to groundwater, and yes, as long as it’s applied correctly. The key here is the blast process: if we don’t get that steel surface to a near-white metal finish, the powder won’t stick, and you’ll get peeling within a year. I make sure our guys don’t cut corners on the blast—we spend 10 to 15 minutes per section, and we do a visual check and a tape test to make sure the surface is ready.
Now, what about culverts that are used for water conveyance, like for agricultural irrigation or drinking water pipelines? Those need to meet drinking water standards, so we can’t use any materials that leach chemicals. For those, we use food-grade HDPE liners that are fused just like the standard ones, but we test every batch of liner material to make sure it’s approved for contact with potable water. Last year, we worked with a local farm co-op on a 500-foot culvert that connects a reservoir to their crop fields, and they later asked us to supply the liners for their irrigation pipeline’s end connections too. The nice thing about HDPE is that it’s flexible, so it can handle slight settling of the soil without cracking, which is a big deal for long-term waterproofing. I always tell customers that settling is the biggest culprit for culvert failure that no one talks about—even the best waterproofing will crack if the ground shifts, so we use flexible sealants at the joint sections between culvert sections to absorb that movement.
Wait, I should also mention the old-school method of bituminous coatings, because I still see it used on smaller, lower-budget projects. Bitumen is that black, tar-like stuff, right? It’s cheap, and it works for temporary applications, but it has downsides. It gets soft in hot weather, especially down south, so it can run off the steel, leaving gaps. It also breaks down over time when exposed to UV light, so if a culvert is partially above ground, the top half will lose its waterproofing much faster than the buried bottom half. I only recommend bitumen for small, buried culverts where the budget is super tight and the water pressure is low. Last year, a small town used bitumen on a 200-foot side road culvert, and by the next summer, the bitumen had peeled in two spots, leading to rust spots on the steel. We fixed it by sandblasting those areas and applying a zinc-rich primer, and it’s held up ever since, but that’s an extra cost the town didn’t plan for.
Installation is just as important as the product we apply at our plant, by the way. I’ve had customers show up with culverts that look perfect, only to mess up the waterproofing when they’re setting them in the ground. For example, when you lower a culvert into the trench, you can’t drag it across sharp rocks—those rocks can scratch or tear the liner or coating. We always tell crews to lay a 6-inch layer of crushed stone at the bottom of the trench before setting the culvert, so the surface is smooth. Also, when connecting two culvert sections, you have to make sure the sealant or liner seam is aligned correctly, not bent or stretched. I once had a customer who tried to save time by not cleaning the corrugations before applying the joint sealant—dirt and mud got in the way, and the seal didn’t hold, leading to water leaking in along the joint. It was a quick fix, but it could’ve been avoided if they’d followed our installation guidelines.
Another thing I’ve learned over the years: regular maintenance keeps waterproofing intact. Even the best culverts need to be checked every 3 to 5 years, especially after heavy storms. You don’t have to pull the whole culvert out—just send a crew to inspect the inner lining or coating for scratches, chips, or peeling. Small repairs are way cheaper than replacing a whole culvert. Last year, we did a check-up on a highway culvert we installed 7 years earlier, and we found a few small scratches from a road grader. We touched them up on site with epoxy touch-up paint, and the culvert is good for another 10 years at least.
I know a lot of people look for the cheapest option when it comes to culverts, and I get that—budgets are tight for municipalities and farms alike. But cutting corners on waterproofing is never worth it. I’ve seen culverts fail in 3 years instead of 50 because someone used a cheap spray-on sealant, and then they have to pay for emergency repairs, road closures, and all that extra cost. The right waterproofing method is an investment that saves you money in the long run.
At the end of the day, every project is different, and that’s why I don’t push one method for every job. I take the time to walk the site with the customer, ask about the water levels, soil type, traffic loads, and any other factors that matter, then recommend what will work best for their specific needs. If you’re planning a project that needs a corrugated steel culvert, and you want to make sure the waterproofing is done right, I’d be happy to talk through your options with you. We’ve got materials for every type of job, and we’ve installed culverts in all kinds of conditions, from rural farms to urban highways. Don’t take my word for it, though—just ask any of our past customers, most of whom come back to us for repeat projects because they know we do the job right.
If you’re ready to discuss your corrugated steel culvert project and find the best waterproofing method for your needs, reach out to us to start the conversation. We’ll work with you to find a solution that fits your budget and your project’s requirements.
Lightning Protection Steel Tower References
- Corrugated Steel Pipe Association. (2020). Waterproofing and Corrosion Protection Guidelines for Corrugated Steel Culverts. CSPI Technical Report 20-03.
- American Association of State Highway and Transportation Officials. (2019). Standard Specifications for Highway Bridges and Culverts, Chapter 10: Drainage Structures.
- National Rural Water Association. (2021). Design and Maintenance of Agricultural Corrugated Steel Culverts: Waterproofing Best Practices. NRWA Publication 412.
Hebei Yifeng Steel Structure Co., Ltd.
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