Welding Floor Pans: Cost And Process

Welding new floor pans into a car can be a costly and time-consuming endeavour, with estimates ranging from $300 to $2500. The price can vary depending on factors such as the extent of the rust damage, the need for additional repairs, and the skill of the welder.

For those with the time, tools, and expertise, it is possible to weld new floor pans into a car as a DIY project. However, for those who lack the necessary equipment or confidence, it is advisable to seek the services of a professional welder or auto body shop.

The process of welding new floor pans typically involves removing the old pans, cutting and fitting the new pans, and welding them into place. This can be done through butt welding or lap welding, with butt welding being the preferred method for a seamless and stronger finish, despite being more challenging.

Before committing to the project, it is essential to assess the condition of the car's sub-frames, rockers, and other components, as additional repairs may be necessary.

Floor pan replacement cost

The cost of floor pan replacement depends on several factors, including the extent of the damage, the method of repair, the type of car, and the labour rate of the workshop.

Extent of Damage

If the hole in the floor pan is not too big, a patch repair may be sufficient. For larger repairs, a partial panel can be used to replace the damaged section. If the rust damage is extensive, a full floor pan replacement is recommended.

Method of Repair

There are several methods for repairing or replacing floor pans, including butt welding, lap welding, and spot welding. Butt welding is considered the most authentic and effective method, but it is also the most difficult and time-consuming. Lap welding is easier but leaves overlaps, and spot welding is quick but may not be as strong.

Type of Car

The type of car can also affect the cost of repair, as different cars have different floor pan designs and accessibility. For example, American-made cars typically have spot welds holding down their floor pans, which can be time-consuming to cut out.

Labour Rate

The labour rate of the workshop will also impact the overall cost of the repair. Bodywork is generally one of the most expensive parts of car repair, with rates ranging from $35 to $80 per hour or even higher for a good shop.

Additional Costs

There may also be additional costs involved, such as the cost of the replacement floor pan, rental car fees while the repair is being done, and the cost of prepping the car by removing interior components.

Estimates

Estimates for floor pan replacement vary widely depending on the above factors. Some forum users have quoted prices ranging from $300 to $2500 for labour, while others have estimated the total cost, including parts and labour, to be between $1000 and $2000 or even higher for more extensive repairs.

It is important to get multiple quotes from reputable workshops and to carefully consider the extent of the damage, the method of repair, and the labour rate when evaluating the cost of floor pan replacement.

Welding techniques

There are several welding techniques that can be used to install new floor pans in a car. The choice of technique will depend on factors such as skill level, desired authenticity of the restoration, and the condition of the existing floor pans. Here are some common welding techniques used for this process:

• Butt Welding: This technique involves welding the new floor pan directly to the existing metal without any overlap. It is considered the "right way" to do a replacement and results in a stronger weld. However, butt welding is more challenging and prone to ruining the panels. It requires precise fitment and good technique to control heat warpage.
• Lap Welding: Lap welding is easier than butt welding and is commonly used for floor pan replacements. It involves overlapping the new panel with the existing metal and welding them together. While lap welding is less aesthetically pleasing and leaves overlaps, it can still provide a solid weld.
• Plug Welding: This technique involves drilling holes in the new panel and the existing metal and then welding them together. Plug welding is quicker and simpler than butt welding but may trap moisture between the panels, leading to potential rust issues.
• Spot Welding: Spot welding replicates the original manufacturing process, as most American-made cars have spot-welded floor pans. It involves drilling out the old spot welds and creating new ones to attach the new panel. This method can be time-consuming and challenging, requiring special tools and techniques to cut out the spot welds effectively.

When preparing for welding, it is essential to clean and prepare the surfaces properly. Use tools such as an air-powered cut-off wheel or an electric grinder to ensure a shiny, solid, rust-free surface to weld onto. Additionally, consider using a weld-through primer to help protect against rust between the panels.

Before beginning the welding process, it is crucial to spend time fitting the new panel properly. Test fit the panel multiple times, make any necessary adjustments, and clamp it into place before starting to weld. Take your time and work in small sections to avoid overheating and warping the metal.

Removing old floor pans

Removing the old floor pans from your car is a necessary step in the repair or restoration process. Here is a detailed guide on how to remove old floor pans:

Assess the Damage

Before starting the removal process, it is important to assess the extent of the damage. Check for rust, rot, or holes in the floor pans. If the damage is limited to a small area, a patch repair may be sufficient. However, if the damage is more extensive, you may need to replace the entire floor pan.

Remove Interior Components

To access the floor pans, you will need to remove the interior components that are covering them. This may include seats, carpeting, and any other obstructions. Be sure to set aside these components in a safe place and label or organise them to make reinstallation easier.

Strip Old Seam Sealer

Once the floor pans are exposed, use a scraper or suitable tool to remove as much of the old seam sealer as possible. This will help you get a better view of the damage and prepare the surface for the new pans.

Drill Out Spot Welds

Most American-made cars use spot welds to hold the floor pans in place. To remove the old floor pans, you will need to drill out these spot welds. Use a spot weld cutting tool and a hand-held electric drill for this task. Work slowly and be patient to avoid damaging the surrounding metal. Remember to centre-punch the spot weld before using the cutter to prevent it from "walking" off its mark.

Cut and Remove the Old Floor Pans

After drilling out the spot welds, use an air-powered cut-off wheel or a suitable cutting tool to cut around the damaged area. Only cut away what is necessary, trying to preserve as much of the original metal as possible. Once the old floor pans are cut free, remove them from the vehicle.

Prepare the Surface

With the old floor pans removed, it is important to prepare the surface for the new pans. Use a grinder or sander to clean up the edges of the remaining metal. You want to create a shiny, solid, and rust-free surface to weld the new pans onto.

Treat with Rust Prevention

Before installing the new floor pans, treat the exposed metal with a rust prevention product to inhibit future rust formation. This step is crucial to prevent further corrosion and ensure the longevity of your repair.

Remember to wear appropriate safety gear during the removal process, including gloves, eye protection, and a respirator to avoid inhaling rust particles and fumes.

Trimming and fitting new panels

Trimming the New Panel

First, clean both the mating surfaces of the new panel and the floor. Then, test fit the new panel to the floor several times. Keep checking the fit until you are satisfied. Trimming the new panel may be required for a precise fit.

Fitting the New Panel

Once the new panel fits perfectly, clamp it into place, aligning everything up. C-clamps are often used to hold sheet metal in place while welding. Next, tack on a few welds to secure the panel. Then, put down the welder and check the fit again before final welding.

Welding Techniques

There are different welding techniques to consider. The original floor pans were likely spot-welded as it was cost-effective for the manufacturer. You could choose to duplicate the factory spot welds or run a complete bead around the new panel. Spot welding is more authentic, but running a bead is more comfortable and quicker.

For the actual welding process, butt welding and lap welding are the two main techniques. Butt welding looks better, leaves no overlaps, and is stronger. However, lap welding is easier. If you choose to butt weld, start by tack welding the parts that are touching first, then move on to the parts that are closer together. Continue tack welding until there is a tack every half inch. After tack welding, you can start plug welding.

Tips and Tricks

• Pre-drill the holes in the new panel if you plan to spot weld. Drilling the holes beforehand saves time and is more comfortable than drilling while crouched inside the car.
• To reduce distortion when welding a long seam on a flat sheet, weld small areas at a time and allow the panel to cool before welding nearby.
• Use a hammer shaft to press the floor against the flanges for welding if you don't have a large enough clamp.
• Before drilling out spot welds, spray a little cutting fluid or WD-40 on the cutting tip to keep it cool.
• To protect the new sheet metal, spray both sides with a zinc-rich primer.

Preventing rust

Rust is a common issue for car owners, especially if you live in an area with a lot of rain or snow. Luckily, there are ways to prevent rust from taking over your car's floor pans. Here are some tips to help you keep your car rust-free:

• Regular Cleaning: Wash your car regularly, including the undercarriage. Road salt and other chemicals used on roads can accelerate rusting, so it's important to rinse them off.
• Wax Coating: Consider applying a wax coating to your car's underbody. This creates a protective barrier that can help prevent rust.
• Rust Inhibitors: There are various rust-inhibiting products available, such as sprays and coatings, that can be applied to metal surfaces to prevent rust from forming.
• Paint: Paint acts as a barrier between the metal and the elements. Make sure any scratches or chips in the paint are repaired promptly to maintain this protection.
• Avoid Moisture: Water and moisture are key contributors to rust. Try to park your car in a garage or covered area, and if your car has been exposed to rain or snow, take steps to dry it off as soon as possible.
• Regular Inspections: Check your car's floor pans and other areas prone to rust regularly for any signs of corrosion. Catching rust early makes it easier to treat and prevents it from spreading.

Treating Minor Rust

If you do find minor surface rust on your car's floor pans, there are ways to treat it before it becomes a bigger problem:

• Grinding: Use a grinder with a wire wheel to clean off the surface rust and reveal the underlying metal.
• Sealing: After grinding, properly seal the affected area with a rust prevention product to create a barrier against future rust.
• Pinholes: For small pinholes, a sealer like POR-15 can be applied to fill the holes and prevent further rusting.

By following these tips and staying vigilant, you can help prevent rust from taking over your car's floor pans and keep your vehicle in good condition for years to come.

Frequently asked questions