Can You Bondo Over POR 15? (Explained)

Yes, you can use Bondo body filler over POR 15. The manufacturer of POR 15 clearly mentions that it’s okay to do so in their FAQ section.

However, there is a requirement on how you are supposed to go about this. First, the POR 15 must be painted on the rusted area. Only when the POR 15 is dry to the touch can you apply Bondo.

POR 15 should dry within three to six hours, depending on the weather. If you are in a hurry, you can always use the POR 15 dry time accelerator.

Bondo over POR 15
“Bondo Layered Toyota” by Alexander Pfeiffenberger, Flickr is licensed under CC BY 2.0

Reasons People May Want to Use Bondo Over POR 15

Before we get to the details of whether Bondo is an excellent fit for POR 15, we must figure out why someone may be interested in such a project.

We all know that Bondo is a polyester putty commonly used in the auto industry as a body filler. What about POR 15?

POR 15 is a rust preventative paint applied directly to rusted surfaces. Someone would want to Bondo over POR 15 because they want to fix a rust dent or hole on their vehicles.

The Bondo will fill the rust spot or hole, and the POR 15 will deal with the rust. This is a brilliant idea, and there is a good chance that it will work out well. You have to follow the instructions provided by POR 15.

What are Some of the Concerns Associated with Applying Bondo Over POR 15?

There are always concerns associated with nearly every project in the auto industry. Using Bondo over POR 15 isn’t free of these concerns. The main concern is that body fillers are always required to be applied over bare metal.

The reasoning behind that is that Bondo absorbs moisture. Therefore, if you apply Bondo over POR 15, it could absorb moisture and eventually fall off.

Though the above concerns are valid, there is a way you can ensure your Bondo adheres to the POR 15, and that is by scuffing up the surface.

Once the POR 15 dries up, you can lightly sand over it to rough up the surface. That will give Bondo something to adhere to. About the concerns that Bondo will absorb moisture.

Many detailers apply body filler over primer, and it works out perfectly. Therefore, you don’t have to be very worried about Bondo absorbing moisture.

As long as you prepare Bondo with the right ratio mixture with the hardener, it should fix the rust holes and sit over POR 15.

If you doubt bondo’s ability to stick to POR 15, you can always use POR 15 fillers instead. For those of you who didn’t know, POR 15 makes and sells body fillers.

They claim that their body fillers are much stronger than typical ones. They go on to explain that their fillers harden like steel.

We are recommending POR 15 filler instead of regular Bondo because you can never go wrong with products from the same company. POR 15 is very clear that one can apply body filler over their paint.

To be safe, it would be better to use a product that the same company has formulated. As a result, you can avoid incompatibility issues.

Should Bondo Go Under or Over POR 15?

When you look up this debate on popular forums, you will see that it’s a hot topic with many contradicting yet convincing arguments. However, we are always keen on following the right procedure.

POR 15 recommends Bondo be applied directly over its paint. On the other hand, Bondo is known to stick when applied over coatings such as primers as long as they are sanded first. It would be the same thing with POR 15.

The argument here is that you can apply Bondo over POR 15. However, it would be best if you let it dry first. And, to ensure the Bondo has something to stick to, you can scuff up the dried POR 15 and then apply the Bondo.

When you do this, you shouldn’t run into any issues. When sanding POR 15, we recommend using ultra-fine sandpaper.

The reason for that is to prevent you from removing all the POR 15 paint and leaving the surface unprotected. You mustn’t forget why you are using POR 15 in the first place.

You shouldn’t use Bondo under POR 15 because the latter is formulated to adhere best to rusted surfaces and not Bondo. When you Bondo first, the POR 15 may have adhesion issues.

Will Bondo Fall When Applied Over POR 15?

Bondo will only fall if you mix it wrongly or apply the POR 15 incorrectly. Here are some things that can cause Bondo to fall prematurely after being applied over POR 15.

• When it is applied on POR 15, that hasn’t fully cured.

• When you don’t mix Bondo with a hardener in the right ratio.

• When you spray the POR 15 incorrectly.

You need to wait until the POR 15 has fully cured. Otherwise, if you go straight in with the Bondo, it will fall off because the POR 15 is still wet. Also, if it’s still wet, how are you going to sand over it?

Moving on to the second reason, Bondo has a mode of application. It must be mixed in a correct ratio with the hardener. Ensure that you follow the manufacturer’s instructions and use the correct amount.

Finally, make sure that you spray or apply the POR 15 correctly. Applying POR 15 over rust is fairly easy. Therefore, the odds of making a mistake during the application of POR 15 are very minimal.

Your goal should be to ensure the rusted surface is covered in POR 15, and that’s it. However, while we are still on POR 15, contributing to the short lifespan of Bondo, there have been allegations that POR 15 doesn’t stick well to metal.

Upon further inquiry into these allegations, we found out that POR 15 sticks best to well-prepared surfaces. It doesn’t matter whether the surface has rust on it or not. As long as you have degreased the area, POR 15 should bond pretty well.

POR 15 Patch vs. Bondo

In the past, people who had to use Bondo over POR 15 struggled a lot with Bondo not holding up after application. This issue was, however, resolved when the POR 15 patch was introduced.

Most of you may be familiar with Bondo, and therefore, you may hesitate to use the POR 15 patch. But it is a sandable seam sealer designed to work perfectly with POR 15 rust protective coating.

Like Bondo, it dries into a rock-hard substance that can stay put for years. Unlike Bondo, you don’t have to worry about the POR 15 surface being too smooth for the patch to hold.

If possible, instead of Bondo, you may want to give the POR 15 patch a try. If you run into any issues, you can always return to the good old-fashioned Bondo.

Should I Sandblast Before Applying POR 15 and Bondo?

Rust is a threat to all car owners. No one ever likes seeing rust on their cars unless you are into patinas.

Therefore, if you are fixing the rust on a car, you may want to do everything you can to remove it completely. For instance, you may consider sandblasting the rust and then applying POR 15 before covering it with Bondo.

There is no need for that. Sandblasting and POR 15 do the same job, which is to stop and prevent the spread of rust. If you decide to sandblast, you can skip the POR 15 and spray an epoxy primer followed by Bondo.

But if you want to use POR 15, there is no need to sandblast. Spray the rust protective coating on the corrosion and let it do its job.

How to Make Bondo Hold onto POR 15?

Bondo is one of the easiest products to work with. As long as you meet its requirements, it should hold pretty well on any surface, even POR 15. Here is how you can make Bondo adhere to POR 15.

The surface of the POR 15 needs to be dry. Some car owners recommend that Bondo be applied over tacky POR 15, but that’s a discussion for another day.

Anyway, when the Bondo dries, you should scuff it up slightly. That will give Bondo something to hold on to. Make sure that you use adequate Bondo to fill the hole deeply.

If you have trouble with the Bondo staying in place, it can be temporarily held with cardboard until it cures. Once it cures, you can sand the Bondo to get a uniform surface and finish.

Because Bondo Absorbs Moisture, Will It Go Through the POR 15?

Rust restoration jobs can be pretty overwhelming for those new to such. You need to understand POR 15 and Bondo’s purpose in this scenario. Bondo is the putty that will be used to fill rust holes.

POR 15, on the other hand, deals with the rust by creating a hard coating over the metal. Even though Bondo contains talc, which is hygroscopic, as long as there is POR 15 on the metal surface, the moisture will not get inside.

Therefore, when Bondo and POR 15 are used together, you are assured of stopping rust. Also, if you are worried about Bondo attracting moisture, you can always apply a sealer on top.