PM

 My afternoon...

Gemini:

Car repair; I'm about to actually start using Bondo putty for smallish patches on a white Subaru. I have two products: the actual putty with the hardener in a separate tube... and a glazing and spot putty. The latter seems easier to use to me: no mixing, out of the tube. I am wondering what the maximum area that might be good for is. I really don't want to mess things up!! 

It is understandable that you want to avoid mistakes, as bodywork requires a bit of patience to get right. To give you the best advice for your Subaru's repairs: do not use the Glazing and Spot Putty as your primary filler.

The two products serve fundamentally different purposes in the repair process, and using the wrong one for a "patch" will likely lead to the repair cracking or falling off over time.

The Critical Difference

Body Filler (The 2-part mix): This is structural. It is designed to fill depth, bond to the metal, and withstand the vibrations and temperature changes a car experiences on the road.

Glazing & Spot Putty (The tube): This is cosmetic. It is meant to be used only as a "finishing" layer to fill tiny pinholes, fine scratches, or minor surface imperfections left after you’ve already sanded your body filler. It is essentially a high-build, lacquer-based paste. It is not strong enough to hold a patch or fill any depth.  

"Maximum Area" and Usage Rules

Because Glazing and Spot Putty is not structural, there is effectively no minimum or maximum area for it, other than "as little as possible."

Rule of Thumb: If the area you are trying to fill is larger than a dime or deeper than a fingernail scratch, you should be using the 2-part body filler.

If you try to use the tube putty to cover a larger area (like a quarter-sized dent or a rust hole patch):

It will shrink: As the solvent evaporates, the putty will "sink" into the hole, leaving you with an uneven finish.  

It will crack: Because it lacks the chemical strength and reinforcement of the 2-part filler, it cannot flex with the metal of your car.  

It will fail: It will likely flake or chip off when the car is exposed to sun, heat, or vibration.

Recommended Workflow for Your Patches

To ensure your repairs last, follow this sequence:

Prep: Strip the area to bare metal (about 3 inches beyond the damage) and ensure all rust is completely removed.

Body Filler: Use your 2-part filler to fill the actual depth of the patch. Shape it, sand it, and get the contour as close to the original body line as possible.

Glaze: Once the body filler is shaped and you see tiny pinholes or slight surface imperfections remaining, apply a very thin skim coat of the Glazing and Spot Putty.  

Finish: Sand the spot putty with a finer grit (320–400) to get that "glass-smooth" finish before you prime and paint.  

A quick tip for your Subaru: Since you are working on a 2014 white model, ensure you thoroughly clean the area with a wax and grease remover or alcohol before applying any product. If you skip this, even the best filler will struggle to bond to the metal.

How deep or wide are the areas you are planning to patch? Knowing that will help determine if you need any additional steps, like using a metal mesh or fiber-reinforced filler first.

I'm not sure how to handle the body filler product: one needs to mix in some strengthener, and once applied it should dry in 8 minutes before the next coat. What happens to the product I have already prepared; surely it too will dry in a few minutes!!??

You have hit on the exact reason why body filler (often called Bondo) can be intimidating for the first-time user: the clock starts the second you mix the hardener.

You are absolutely correct: any filler left on your mixing board will harden just as quickly as the filler you just spread on your car. You cannot "save" mixed filler for later. Because of this, the secret to professional results is working in small, manageable batches.

Here is how to manage the "ticking clock" so you don’t waste product or panic while applying it.

1. The "Golf Ball" Rule

Never mix the entire contents of your can at once. Even for a medium-sized repair, start small.

Scoop out an amount of filler roughly the size of a golf ball onto your mixing board (a scrap piece of metal, a plastic spreader, or a dedicated mixing board works best).

Add the hardener according to the manufacturer's ratio (usually a "ribbon" of hardener across the center of your pile).

2. Speed and Technique

You don't need to rush like you're in a sprint, but you do need to be deliberate:

Mix thoroughly: Mix the hardener into the filler until the color is perfectly uniform (no streaks). If it isn't mixed well, you will get "soft spots" in your repair that will never cure.

Apply quickly: Use your spreader to firmly press the filler into the surface of the metal—this ensures good adhesion—then build up your desired thickness in one or two quick passes.

Stop shaping: Once it's on the car, stop touching it. If you try to over-work or smooth out the filler while it’s starting to set (going from "gummy" to "rubbery"), you will pull it away from the metal and create bubbles or tears. Let it harden completely.

3. The "Dry" Window

The 8-minute window: That 8-minute timeframe is the working time (before it becomes too stiff to spread). It will usually be sandable within 20–30 minutes, depending on the temperature and humidity in your garage.

Hardening on the board: If you have leftover filler on your mixing board, just let it sit there until it's hard. Once it is a solid, hard puck, you can usually peel it off a plastic board or scrape it off a metal one to reuse the board.

Practical Tips for Success

Don't try to build all your depth at once: If the dent is deep, it is much better to apply two thin layers of 2-part filler than one giant, thick blob. The second layer will bond perfectly to the first one after you sand it flat.

Keep your tools clean: If you have a second plastic spreader, use one to hold the filler and the other to apply it. Immediately wipe your spreader clean with a rag and a little acetone or lacquer thinner before the filler hardens on it. If you let it harden on the tool, it's a pain to scrape off.

Temperature matters: Since you are in Montreal, keep an eye on the weather. If it is very hot, the filler will set even faster than 8 minutes. If it is cool, it will take longer. Always test a tiny bit of your mixture on the corner of the board to see how fast it's setting before you commit to the car.

One final piece of advice: If you have never mixed this before, do a "practice run" on a piece of scrap metal or even a piece of cardboard first. It will help you get a feel for the consistency and how quickly it changes from a paste to a solid.

Do you have a dedicated mixing board, or are you planning to use a specific surface to mix the hardener in?

Help me find applicator tools for Bondo putty. I shop at Canadian Tire...or Dollarama...

You are looking for plastic body filler spreaders. These are the industry standard for DIY bodywork because they are flexible enough to follow the curves of your Subaru's body panels and inexpensive enough that you won't worry about ruining them.

While you could check at a local Dollarama, these are specifically categorized as automotive repair tools and are most reliably found in the automotive section of Canadian Tire or at a dedicated auto parts store. They are almost always sold in multi-packs (usually sets of 3) containing different sizes, which is perfect for your project since you can use a small one for detail work and a larger one to smooth out your filler.  

Recommended Applicators

These spreaders are specifically designed to be flexible and reusable. Once the filler hardens on the plastic, you can usually just "pop" it off, or wipe them clean with a bit of acetone while the filler is still fresh.  

Bondo Plastic Spreader Set

This is the standard, widely available option you will find at most Canadian Tire locations. It includes three sizes to handle everything from small dings to larger patches.  

Dynatron 3 Pack Plastic Spreaders

Another excellent and highly-rated alternative that functions identically, offering the same flexibility and ease of cleaning.

Bondo Spreader 357

A staple in automotive repair kits, these are very reliable and effective for achieving a smooth, consistent finish.  

                                                                                 

A Quick Tip for Your Purchase:

Avoid Metal "Spreaders" for now: While you may see metal applicators or putty knives at the hardware store, stick to the flexible plastic ones. Metal tools are often too rigid for beginners and can accidentally gouge the filler or leave "tracks" as you try to smooth it out.

Mixing Surface: Since you are buying tools, grab a clean, non-porous surface to act as your mixing board. If you don't have a dedicated one, a piece of flat, scrap sheet metal or a clean, flat plastic surface works great. Some DIYers even use a dedicated "mixing board" pad of peel-away sheets (also found at auto parts stores) so they can just tear off a dirty layer when finished.

If you like, I can look for a simple guide or video recommendations that demonstrate the proper "pressure and swipe" technique for using these spreaders to get that smooth finish on your Subaru. Would you like me to do that?

You were right to suggest a practice run: I cut myself while opening the can of putty, and things went downhill from there. It needs the hardener to set, but is still very sticky without it. The side of my right hand has a putty residue which will be with me for a while.

I am so sorry to hear that! Please make sure you clean that cut thoroughly—even small nicks from metal can be prone to infection, especially when working with chemical products like automotive fillers.

To get that stubborn, sticky filler off your skin, do not keep scrubbing with just soap and water, as it will likely just smear it around. You need a solvent to break the chemical bond.

Removing Putty from Your Skin

Since the filler hasn't been mixed with hardener yet, it is essentially a resin-based paste. Try these steps, in order of effectiveness:

Use a Waterless Hand Cleaner: If you have something like GOJO or Fast Orange (commonly found in the automotive aisle of Canadian Tire), these are designed exactly for this. They contain pumice and solvents that break down resins without being as harsh as pure chemicals.

Acetone or Lacquer Thinner (Use with Caution): If you have acetone (often used for thinning fiberglass resin or cleaning paint brushes), it will dissolve the sticky resin almost instantly. However, use this sparingly since it is very drying to the skin. Put a tiny amount on a paper towel, wipe the residue off, and then immediately wash your hands with soap and water and apply hand cream.

The "Oil" Method: If you don't have solvents, try rubbing a generous amount of vegetable oil, baby oil, or even butter onto the sticky spot. The oil can sometimes help break the resin's grip on your skin's natural oils. Let it sit for a minute, then wipe with a paper towel and wash with dish soap.

A Few Safety Reminders for Your Next Attempt

Since this was a rough start, let’s ensure the next attempt is much smoother:

Protect your hands: Use nitrile gloves when working with body filler. They provide a barrier so you don't have to worry about the resin sticking to your skin, and they make cleanup as easy as peeling off the gloves. You can find these in the paint or automotive section at Canadian Tire.

Handle the cans carefully: Body filler cans can have sharp edges, especially once you've pried the lid off. Use a sturdy screwdriver or a dedicated paint can opener (which has a hook specifically for this) to avoid slipping.

Wear eye protection: If you are sanding or prepping, little bits of metal or dust will fly. Safety glasses are a must.

Once you have cleaned up and the cut is taken care of, do you have someone nearby who can help you hold the lid or assist with the next mixing attempt, or are you planning to jump back into it solo later?

I used nail polish remover on the side of my hand: mostly gone. For the cut, I used a little wipe they use before injections: it burns like anything, but is a sound disinfectant. Put a household plaster aound the finger. I mixed a small amount of putty and hardener with a plastic spoon. And spread it on a fruit can top. It hardens nicely, but there is a quite regular pitting on the surface...I have bought sandpaper of various GRIT values and will be trying out GRIT400 on my can cover. 

This is for informational purposes only. For medical advice or diagnosis, consult a professional.

It sounds like you have successfully navigated the "emergency" phase and are now into the testing phase—which is exactly where you want to be before touching the Subaru.

Those little "pits" you are seeing are extremely common in body filler work. They are usually caused by air trapped in the filler during the mixing process or tiny pockets that didn't fully settle against the surface.

A Few Notes on Your Current Progress:

The "Pitting" Reality: In the world of auto body work, these are often called "pinholes." Even professionals get them. This is exactly where that Glazing and Spot Putty (the one in the tube you mentioned earlier) will save the day. Once you sand your base layer, you’ll likely still see some of those pinholes. You just apply a tiny "skim coat" of the glazing putty, let it dry, and sand it again to fill those microscopic gaps.

The 400 Grit Test: Starting with 400 grit on your can cover is a good "finishing" test, but don't be surprised if it feels like it’s taking a long time to remove material.

400 grit is for the final smoothing.

80–180 grit is for the "heavy lifting" (shaping the main blob of filler).

If you find that 400 grit isn't making a dent in the shape, don't worry—your filler isn't defective, you just need a coarser grit to get the initial contour right before refining it with the 400.

A Tip on Mixing (to avoid the pits)

When you mix with that plastic spoon, try to "fold" the hardener into the filler rather than whipping it. Whipping it creates thousands of tiny air bubbles, which eventually become those little pits you see on the surface. Imagine you are folding egg whites into a cake batter: press down and pull across rather than stirring in circles.

A Quick Word on the "Injection Wipe"

Since you are in the Montreal area and it is currently mid-June, keep an eye on that finger. Even a small "plaster" (bandage) can get damp and irritate a cut if you are sweating or working in the humidity. If it starts to look red or feels hot, definitely give the bodywork a break for a day or two to let it heal properly.

You are building a great process: testing on a can lid is the exact method a pro would use to check how the filler behaves in the current temperature and humidity.

Are you planning to tackle the actual car panels today, or are you going to keep practicing on the can lids until you're completely confident in the finish?