Bondo is a super versatile product that is effective for a range of repair and restoration applications. It is a favorite among homeowners, DIYers, and woodworkers.
There are multiple fillers on the market, but what makes Bondo particularly popular is its quick drying time. With Bondo, you can complete a project in no time as it cuts back the painfully long wait time experienced with similar products.
But how long does Bondo take to dry? Bondo dries within 15 minutes of an application under normal conditions and is good to sand. You’ll wait up to 45 minutes for a complete cure, after which it can be painted.
Notwithstanding, a couple of factors alter the drying rate of Bondo, which can ruin your plans if it is not ready at the expected time.
So before embarking on any project, continue reading this article. You’ll learn more about Bondo, what factors influence drying duration, and how to check whether it is ready.
What Is Bondo?
Bondo is so good that it is often used as a generic term for restoration fillers; you know, the way we refer to all bandages as Band-Aids. However, it is also a brand on its own.
There are several different types of products by the same brand, including wood filler and all-purpose putty, but Bondo is known as a 2-part body filler made from polyester resin. It is putty-like and is usually mixed with a peroxide cream hardener to become rock solid.
It comes in a distinct reddish tin accompanied by a tube of cream, which is the hardener that acts as a catalyst. You can work it in gorges, dents, and dings on wood surfaces to restore them to their original smooth appearance.
Rot in windows, joint gaps, chipped parts, and unwanted holes can all be remedied using Bondo. It is a go-to for a myriad of other indoor and outdoor cover ups and structural repairs depending on one’s creativity and not just surface restoration.
Originally, Bondo was designed for automotive body repairs, but today it is more diversified. There is a multipurpose Bondo and another variant for wood repairs. Bondo’s fame is attributed to the many desirable characteristics it possesses.
Bondo is sandable and can conform to any shape you desire. It is also paintable and takes all types of paint very well, including oil and latex-based paints for professional and home use.
Unlike other fillers that will budge to stress and outdoor elements like wetness and UV, Bondo remains exceptionally strong. It is permanent, waterproof, and does not crack after some time or outdoor exposure.
It does not shrink after drying, providing a sturdy reinforcement. Your patch will be seamless, and the substrate will be as good as new. It is also waterproof and not affected by rain or snow.
But what really sets it apart from wood putty and other fillers is its quick drying time. If you’ve used wood filler before, you can attest to the fact that it dries sluggishly.
You have to wait for hours for it to dry, and same-day project completion is at times impossible. But not with Bondo, which dries in 10-15 minutes if prepared correctly and within a room temperature of 77°F.
That said, you may experience a surprisingly shorter or exceedingly stretched drying time with Bondo. And when this happens, you might wonder whether you got the fluke of the batch or a counterfeit.
Don’t worry – it is pretty normal for the drying time of Bondo to vary depending on certain factors that influence it. Let’s look at each one of them.
Factors That Influence The Drying Of Bondo
Among the most frequently asked questions about Bondo is why the product is taking so long to dry. That’s probably because these users already know that Bondo is a fast-drying filler.
But what they are unaware of is that certain contributing factors could potentially change the drying rate. The following two factors are the primary influencers of how rapid or slow the drying rate of Bondo is.
Temperature
On many occasions, temperature alters chemical reactions. High temperatures usually accelerate a chemical reaction while lower temperatures drag it.
Without putting you off with complex science terms, if you remember your science, heat is energy. It makes molecules collide and vibrate faster hence hastening chemical processes. The same is true for Bondo.
Mixing Bondo initiates a heat-generating chemical reaction. When the surrounding temperatures are higher, the process is quickened. Consequently, the Bondo will set faster.
If you reside in tropical climates where it is primarily temperate, you can expect Bondo to dry even faster. It may dry in just 5 minutes instead of the regular 15.
If you are not so lucky to have the sun all year round, summer would be ideal for repairs. The ambient heat from the blazing sun will make Bondo repairs set quickly.
On the contrary, the drying of Bondo lags in cool temperatures. It would take much longer than expected for a seal on your furniture in a mountain cabin to dry than in warmer places.
The same concept applies if you choose to get some restoration done during winter or a frigid day. The Bondo will dry slowly, especially outdoors, as interiors are customarily heated.
You can expect Bondo to dry in at least 30 minutes in cool conditions.
Filler-Hardener Ratio
The second factor that could result in Bondo deviating from the norm with regards to drying rate is the filler to hardener ratio.
The amount of hardener you use impacts how fast or slow the Bondo will dry. The filler is always sold with a separate hardening cream. The two must mix for curing to take place.
The filler usually comes in a sizable tin. The hardener is, however, comparably small. You’ll only need a tiny amount of hardener as compared to the filler.
The best practice is to measure a ratio of 50 parts filler to 1 part hardener. That’s like a dollop of filler or the size of a golf ball and a one-inch strip of the hardener. The hardener comes in a tube and squeezes out in a strip.
That’s the optimal ratio for Bondo to set within 10-15 minutes. However, you can adjust the quantity of hardener up a bit to advance the drying speed of your Bondo. The more cream hardener you use, the speedier the drying duration.
So, if that’s true, can you reduce the proportion of hardener to slow down the hardening process? Yes, you can, but you shouldn’t.
Using an even smaller quantity of hardener will buy you more time for workability as the filler will dry much slower. But before you consider it, you should know that the results may be permanent.
Cutting back on the hardener will certainly make Bondo pliable for longer. That’s great news if you are slow and need extra work time, but on the flip side, the Bondo may take an insanely long time to cure or fail to cure at all. It can remain soft because there wasn’t enough hardener to react with or too little such that it dries soft, not solid.
There is no adverse effect of using more hardener to speed up drying. However, sometimes Bondo may dry with the appearance of minuscule holes. These holes are air bubbles attributed to using too much hardener.
The hardener is a catalyst. As you increase it, so does the reaction which produces heat and gas. The increased gassing is what causes the holes as air tries to escape faster.
If you’d like a visual tutorial here’s a great video from Ron Budman on YouTube.
How To Make Bondo Dry Faster
So, now you know the drying rate to anticipate with Bondo and what influences it, what’s the significance of this piece of information?
You could say proper planning. Since Bondo dries faster on a hot sunny day, it would be the ideal time for quick repairs. But sometimes, repair cases can’t wait for the next season. And for other folks, sunny days are rare.
You can turn things around to help your Bondo dry faster by introducing a heating device. Space heaters and heat guns can be used to raise temperatures to help quicken the curing process of slow drying Bondo.
Another practical application of this knowledge is when you need to do the opposite; extend the drying time of Bondo. You are probably wondering, why would anyone want their job to take longer?
Well, you might be carrying out a big job. It makes sense to mix a large batch of the product that will be sufficient, right? However, you do not want to do this with Bondo, especially on a hot day. Why? Because Bondo is a fast-drying filler.
It will start congealing before you can complete the job. With every passing minute, the putty becomes gooey and harder to work in gaps resulting in wastage. Since for a big job you need a longer working time than the Bondo can stay manageable, there are two options.
The first one is to either choose a cold day so the Bondo takes extra long to dry or introduce a cooling device to lower the temperatures where you’ll be working.
The second and more reliable option is to mix the Bondo in several small batches. Not all at once, of course. You can make a new batch after every section until the whole project is completed.
How Long Does Bondo Take To Dry Without A Hardener?
Bondo cannot dry without a hardener. Remember, it is a two-part filler. When purchasing Bondo, the filler tin comes together with the hardener tube as one purchase.
The filler and hardener are like a two-piece puzzle. One is incomplete without the other, as they were designed to work together to thicken and solidify permanently.
When Should You Sand And Paint Bondo?
One of the best things about Bondo is that it can be sanded to knock down any raised spots and to contour the patch as required to blend in with the design.
You might be unsure when precisely the right time to sand Bondo. Bondo is ready to sand usually within the first 15 minutes of application.
At this time, it is no longer mushy but still rubbery and much easier to sand. Notwithstanding, you do not have to do it then. You can wait if you’re not in a hurry as Bondo remains sandable days after complete cure.
You will, however, sacrifice the ease of sanding as you’ll need more muscle work then, as it will have hardened further. For best results, use a coarse 60-80 grit sandpaper sanding by hand or using a motorized sander.
What about painting? How long should you wait to paint Bondo? You’ll wait a bit longer to paint Bondo than you would to sand it. It must be completely cured before painting over it.
Painting over uncured Bondo will seal it while it is still off-gassing. Consequently, your layer of paint won’t be durable.
If mixed correctly, Bondo cures in a maximum of 45 minutes and is paint-ready then. Like sanding, you don’t have to do it immediately. You can wait a week or two.
How Can You Tell If Bondo Is Dry?
If you are a first-time Bondo user, it may be a bit difficult to tell if the Bondo is cured. The natural instinct is obviously to poke it with your fingertip, but do not do that.
If it is not dry, you’ll leave a pit that will require an extra layer of Bondo to remedy. So then, how do you know it is ready?
First, you can brush over or pat the surface lightly using the back part of your finger just below the nail bed. If it feels dry, it certainly is.
Another way is to check the color. When filler and hardener are mixed, the resulting mixture is usually a pale salmon pink. The Bondo then dries to a very light grey color.
And the third way is, of course, the time test. As long as 15 minutes maximum has elapsed, your Bondo is already cured enough for sanding and 45 minutes for painting. So take note of the time you started mixing. Set a timer if you must.
Wrapping Up
We hope it is now clear what Bondo is, how long it takes to dry, and what can be done to change the waiting duration as per your needs. Let’s quickly recap the main points.
Bondo is a reputable polyester resin-based filler for professional and home interior and exterior repair and restoration. It is two-part and comes as a filler and a hardener.
When mixed, it becomes a pliable putty that is workable inside dents, gaps, cracks, dings, etc. It patches up the surface so well without a trace of the stress or trauma that existed before.
Bondo is loved for its inherently great qualities. It is sandable, paintable, stable when dry, strong, and resistant to outdoor elements.
Where Bondo shines brightest is its brief drying time, something its competitors cannot brag about. At average room temperature, it will dry within 10 minutes for sanding and cure in 45 minutes for painting.
However, this time is largely dependent on two things: the temperature of the surroundings and the amount of hardener combined with the filler.
Heat speeds up the drying rate, and cool temperatures drag the process. As for hardener, more of it produces faster drying results, and less keeps the Bondo softer for longer. However, too little and the Bondo won’t dry.
Therefore, you can use heating devices or more hardener if your Bondo doesn’t seem to be drying within the acceptable time frame.
Bondo is an excellent product that places the full control of the drying speed in your hands. Be sure to use it in a well ventilated area as it emits gaseous solvents during the drying process.
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