How Long Will Spray Foam And Bondo Last? (Solved)

Even before answering this question, mixing spray foam and Bondo isn’t something we would recommend. No matter how severe or significant the rust spots are on your car, there are better methods of dealing with the rust, and this shouldn’t even be on your list.

However, if someone has recommended spray foam and Bondo as temporary fixes to your car rust problems, we will look deeper into this matter and give you a prediction of how long it may last.

You would be very lucky if spray foam and Bondo lasted for more than a year. Bondo is formulated to adhere to carbon fiber, wood, metal, and foam.

However, it will not hold on to Styrofoam. So, if this is the type of foam that you intend to layer Bondo with, you can start looking for other alternatives.

As we were saying, Bondo body filler is strictly formulated for particular surfaces. On foam, it can hold on for a while. But the structure on which Bondo is holding in is weak.

Therefore, it will collapse after a considerably short period. This may happen in a few weeks or months. If you plan to use spray foam and Bondo to repair scratches, then expect it not to last for long.

how long will spray foam and bondo last

Is It Worth Layering Bondo Over Spray Foam?

The primary use of spray foam is to insulate the voids on a car to provide better temperature control and shield outside noises.

This product is not only famous for improving ride comfort, but due to its physical characteristics, it can easily fit in the crevices of your vehicle and doesn’t have to be molded by hand.

You can use it on the wheel wells, ceiling, floor, door panel, and any other place that you may consider applicable.

However, even if your goal is to use spray foam for insulation purposes, adding a layer of Bondo can affect the lifespan of both materials.

Bondo will weigh down the weak structure of spray foam, and this will cause it to fall off after a while.

Layering Bondo over spray foam isn’t worth spending your time, effort, and money. If you are dealing with rust, there are better solutions out there.

Should I Use Spray Foam as a Base for Body Filler?

Having seen that spray foam and Bondo don’t last very long, we must address the use of spray foam as a base for body filler.

If you are researching how long spray foam and Bondo last, chances are, you want to use spray foam as a base for body filler. Bondo is used as a filler during car paint and repair. On the other hand, spray foam is used for installation.

Another reason why you may be interested in knowing how long spray foam and Bondo last is because you are interested in a cheaper method to fix rust spots.

You need to understand that you will always get exactly what you pay for when it comes to bodywork.

In this case, using spray foam as a base layer for Bondo may look decent at first, but there will be no strong structure beneath, and the Bondo will fall off as you are driving one day.

Not unless you want to spray the foam over the already rusted metal and use it as a surface to hold the two. But then again, a rusted piece of metal is equivalent to a space.

Because rust spreads and weakens the metal. Eventually, it will spread around the foam, and that part can fall off.

Instead of spraying foam as a base filler, we would recommend cutting off the rusted metal, riveting, or welding a new piece of metal, and then applying high-quality Bondo over it.

You can add primer and sealer alongside the Bondo to protect the newly installed piece of metal from rusting.

The good thing about Bondo is that it can conceal the added piece of metal from being visible. You, therefore, get a decent finish and a permanent solution against rust.

Can I Replace Spray Foam with Paper?

What you have to understand about bodywork is that the more wrong products you use, the shorter the repairs will last. Back in the day, people used newspapers as base layers for Bondo.

If one had a rust hole, they would patch it up with newspapers and add Bondo to the surface. Other than this being an old-school trick, you have to think twice about the strength of the structure supporting the Bondo.

Newspaper is light, and when it gets wet, it crumbles easily. Using that as a base layer for Bondo is completely absurd.

If you want Bondo to last for longer, use it on metal. If a particular area of your car has been eaten away by rust spots, don’t hesitate to rivet or weld a new piece of metal before sealing it off with some Bondo. Forget about spray foam and paper.

How to Fix Rust Holes with Bondo and Spray Foam?

As a website dedicated to giving you tips, guides, and information on all car matters, we will still explain how you can fix rust holes using these two.

Even though we don’t recommend it, spray foam and Bondo are excellent alternatives if you are interested in a low-cost and quick method of fixing rust spots.

You can use this method if you have an upcoming state inspection and don’t have the money or time for proper bodywork.

Let’s get started on how you can fix rust holes with spray foam and Bondo.

1st step – Apply the Spray Foam on the Holes

In terms of quickness and easiness, this method stands out to be one of the best. However, welding or riveting a piece of metal is a much better alternative if you want a durable fix.

Back to spray foam. You can apply this product directly to rust holes in your car. The spray foam will fill in the rust holes, and even though they won’t attach permanently, it will get you through the next few months.

2nd step – Cut the Protruding Foam to Create an Even Surface

After filling the rust holes with spray foam, you will realize that it’s a little bit thick. To make the surface even, cut the foam to at least an inch thick from the car’s surface.

You can use a razor. You don’t need to be very consistent because Bondo will squeeze the foam deeper.

3rd Step – Prepare and Apply Bondo

For those who have used Bondo in the past, you are aware that it needs to be mixed with a hardener. So, combine these two in the appropriate ratio.

Don’t forget that too much Bondo can cause the mixture to harden quickly, thus affecting your working time.

Once the Bondo and hardener are mixed in the correct proportion, spread it on the foam and surrounding area. Depending on how uniform you want the surface to be, you can spread it to a more extensive surface area.

4th Step – Spray Matching Paint

Give the Bondo some time to cure. Once that happens, you can grab your spray paint of choice and spray it on the Bondo. Choose spray paint that matches the color of your paint so that the finish looks decent.

That sums up the process of using Bondo and spray foam to cover rust holes. That can last for up to a year or several months, depending on the conditions your car is exposed to.

Why Shouldn’t I Use Spray Foam and Bondo to Cover Rust Holes?

We can think of many reasons you shouldn’t do that, and we will list all of them.

1. If you love your car, don’t go with this option.

Rust is the last thing you can ever expect to find on your vehicle. Rust lowers the resale value of your car, and if not dealt with, it can spread to other parts and render the vehicle unusable.

You haven’t dealt with the rust when you spray foam and Bondo over rust holes. You have just concealed it. The rust will spread beneath the new paint, Bondo, and spray foam.

The effects of rust may not be visible at the moment, but they can be drastic in the future.

2. It’s a quick method that doesn’t last for very long.

Bondo can last for years as long as it’s applied correctly. But, if you use it over foam, it won’t stick for long. After a few months, you will notice the Bondo falling off alongside the paint.

This can be avoided by welding metal over the rust holes and eliminating any corrosion on the surface. This latter method allows you to Bondo over the surface and watch it hold still for years.

3. Spray foam doesn’t conceal the hole on the other end.

When you spray foam and Bondo a rust hole, in most cases, you will only work on the visible part. The other part on the inside is left naked.

Holes in a car should be covered on both sides. If you leave the other side naked, the durability of this repair will be affected.

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