A guide coat is a tool that should be used a lot more.
I’m guilty of it myself. I’ll be sat struggling on a repair or feeling as if something is not right, but I’ll not use a guide coat. Why? Because I’m an idiot!
And normally, after applying and rubbing the guide coat, the repair feels right and ready to send to paint. I could have saved myself the headache and used it earlier.
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what is a guide coat & what is it used for?
A guide coat is a thin layer of black powder of paint that can be used at both the repair and paint prep stages.
It doesn’t have to be black but it normally is. All that matters is that it’s a different color from your filler or primer so that you can see where you’re rubbing.
Guide coats are used to perfect repairs and get the panel shaped as if it was straight out of the factory. Any low will become obvious when using a guide coat as it will still have guide coat remaining in the low spot.
Another way that a guide coat can be useful is to understand the way that you’re rubbing a panel.
When using a sanding block, you’ll be able to see the difference between holding the rubbing block in one position versus another. This is helpful for understanding why you may be creating low spots in your filler work.
Rubbing filler actually takes a lot of thought and guide coat helps to make things more obvious.
What can I use as a guide coat?
The most obvious thing to use as a guide coat is an actual guide coat.
You can buy a guide coat in powder or spray form.
The main difference between the two is obviously the application method.
One of them you rub over the panel and the other one is sprayed onto the panel via a can.
There isn’t much difference between the two. They both do the same job.
If you don’t have a guide coat. You can use paint.
Lightly dust the paint onto the repair area and wait for it to dry before sanding.
This is worse than a guide coat as it takes longer to dry. It will do the job if you’ve run out and are waiting to get more.
Finally, pay attention whenever you’re rubbing the “crust” or top layer off of the body filler.
This also acts as a guide coat since low areas will still have the “crust” on top and look unrubbed.
When to use guide coat
I’m guilty of this myself. I don’t use a guide coat anywhere near as much as I should.
Guide coat is perfect for beginners to help understand the rubbing of body filler and glazing putty.
It’s also great for identifying lows and potential ripples in a repair.
For the time that it takes to apply and rub, there’s no reason not to be using it 99.9% of the time.
As you become more experienced, it’s understandable why you might not use it as much.
I’ve seen people 20 years in the trade not need it. Unless they’re using it for bodylines or repairs that they can’t get.
If you’re independent or a DIYer, it’s a consumable that can add up in costs if you’re always using it.
At the end of the day, it’s another tool that you can fall back on if required.
As soon as you start to struggle, the first step should be to slow down, think about it, and use a guide coat.
How to use guide coat
Applying a guide coat is super simple.
To apply the powdered guide coat, apply some to the foam pad that’s supplied and rub it across your repair or primed area.
The same logic works with a guide coat in a can. Simply spray it across the primed area or your repair and let it dry before rubbing.
If you do end up using paint because you don’t have an actual guide coat. It’s very similar to using a spray guide coat, just leave it a little longer to dry.
Sanding filler using guide coat
When using a sanding block correctly, a guide coat will tell you everything.
Keeping the rubbing block flat across the repair will help to identify low spots.
The same principle works with curved blocks too.
As you rub with a curved block, the area that the block doesn’t rub will stay black with guide coat.
This will tell you that you’re either using the wrong block, rubbing the filler the wrong way or that the area is low.
Continuing to rub the filler this way will flatten out the highs on either side or dig out the filler from either side.
Time & experience will teach you which situation it is. But if the rest of your repair is flat and level with the panel, the remaining guide coat is most likely a low spot.
It’s easy to beat yourself up over filler work. I do it all the time.
It’s a skilled trade though and time in the trade is the number 1 fix for poor filler work.
If you can, spend time on each repair with a guide coat to understand the way your block works. Pay attention to the difference each change you make has on your repair.
Over time, something will just click.
Guide coat powder vs spray which one should I use?
If you’re in a shop, use whichever one is supplied in the parts department.
The main difference between a guide coat powder and a spray is the mess.
A powdered guide coat can get literally everywhere. If you get this on your hands and touch your face, you’ll quickly look as if you’ve been working down a mine.
Knocking it over is also a huge pain and if you were to break the tub, you’re just as well putting it in the bin to save yourself the hassle that could follow.
Other than the mess I don’t think there’s much difference.
The powdered guide coat tends to cost a little more, however, it definitely goes further.
It’s all personal preference. Use whichever one you find best or can get your hands on.
Best powder guide coat
Whenever I can, I always recommend Mirka. They’re the leaders in the auto body industry for a reason
Sometimes you have to pay a premium for their products, but their guide coat is fairly priced.
For under $50 you’re going to receive 100g of dry powdered guide coat and a foam applicator.
This will last you as long as you make it last.
If you cake it on every single skim it will disappear quickly. If you apply it every so often with a nice even application, it could last forever.
It depends on the type of work you’re doing, but, you shouldn’t be buying this every week or even every month.
You’ll probably find with heavy use that it’s bought every 6 months or so.
If you own or work in a shop, the sundries charge will cover it anyway.
This is the best powder guide coat on the market, it doesn’t clog up your paper and is super easy to apply.
It’s used in every shop across the world, so why isn’t it in yours?
Buy Mirka Dry Powder Guide Coat From Amazon.com
Best spray guide coat
U-Pol is another industry leader that always comes recommended. They make most, if not all the fillers used in shops today.
Their spray guide coat is very competitively priced and can be picked up at any local auto store or on amazon.
It dries instantly and is ready to rub straight away without any clogging.
You can use it when both wet and dry sanding, so it’s great for painters.
It’s also great for panel beaters that want to identify lows, pinholes, and scratches too.
You can’t go wrong with this product.
I’ve chosen U-Pol, but the alternatives will work as well.
Buy U-Pol Guide Coat Spray From Amazon.com
Guide coat alternative
Using guide coat alternatives isn’t necessarily the smartest idea.
As long as the products dry well and don’t bleed into the paint or filler it’s fine. Using a wet product could increase the amount of sandpaper you use.
The main benefit of a dry guide coat is the fact that it’s very fine and breaks down easily. It just rubs off the panel straight into the atmosphere.
Other products will begin to clog up your sandpaper and start to change how you’re rubbing a repair.
The clogged-up paper should be changed as soon as possible otherwise it will start to create highs and lows in your repair.