How do you use guide coat?

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If you have never used guide coat before see below:

Can I do without using a guide coating?

Guide coat is a tool. You are free to use are not use any tool . Using Guide coating is not required.

Guide coat tells you when to stop sanding, not using it causes you to do 3 things:
1. not sand enough
2. sand just right
3. sand too much

You won't know which of the four pertain to you until you start painting, you'll know if something is wrong right away on the first coat, and then it's too late. To be clear ,we are talking about proper block sanding, not just roaming around with sand paper in a random pattern,

This page will attempt to answer these common questions about guide coat use in car refinishing.
what is it?, "why should I use it?". " how do I use it?", " " Is one type better than another?" "
1.What is it?
Guide coat is a film of contrasting color that when applied over a repaired area, will get in to all the scratches, pinholes and flaws in the surfaces that that are being repaired . As the guide coat is block sanded it will make the high and low areas stand out and be easily seen, and also tell you weather or not the surface is flat and straight and that any contours are the proper shape. If a whole car is primed it will insure that when the final sanding is done , any missed areas can easily be seen.

2.Why should I use it.
Guide coat is the simplest and most inexpensive way to insure a high quality finished paint job, it will speed up the straightening and set up time on any refinishing project. If you have ever seen a beautiful classic car with a great looking custom paint job , then you looked a little closer and down the side to see what resembles a wavy washboard with sanding scratches and pin holes, you will understand why you should use guide coat.

3. How do I use it.
When using plastic filler to straighten a damaged area, the guide coat can be applied right from the first coat to the final sanding. Apply the filler , when it is cured, cover with guide coat. When the sanding begins it will show early problem spots (low spots). often the pro's will stop right there and add more filler in the low areas.( powdered guide coat will not effect the adhesion of the filler) As the straightening continues, guide coat is added after every application of filler, continuing until the repair is shaped properly . The area can now be feather edge with 180 paper and the filler lightly sanded to remove large sanding scratches. Next step is to apply polyester putty to take care of any slight imperfections and scratches. The putty is then guide coated and sanded with 180 grit paper in the same way as the filler ,until flawless and straight. (this will sometimes require additional applications and more polyester putty) After priming with 2K primer , use the guide coat again and sand flat with 180 sandpaper until no flaws show. Re-prime the area, or if it's an overall , the whole car.
Unless you have a heated spray booth the primer should be left to cure for at least 4 days, this depends on the climate around the car. ( it's better to let it sit for a week if you can). By letting the primer and fillers completely cure out, you will avoid the risk of scratches and flaws from shrinkage showing back up after the paint is applied. The car now will need to be guide coated again and sanded with a fine grit sand paper, 400, 500, 600, 800 grits are standard, Depending on the type and color of the paint . If you are using a single stage paint, then 400 grit will usually be fine enough to achieve a clean finish. ( if all the body work was sanded properly the car can be dry sanded by machine with 400 DA paper) The two and 3 stage paints will show flaws more easily and should be block sanded with wet or dry paper, 500 , 600 or 800 grit. Sanding with finer grit paper is pretty much a wast of time and can actually cause ripples and adhesion problems. Dry sanding is faster and not as messy. Using wet sand paper with plenty of water also works well and the paper is less likely to clog. Next Paint the car and say goodbye to the guide coat. it can't help you anymore.

. 4. Why is one type better than another?

Guide coat usually comes in aerosol cans or in dry powder form. You can make your own by spraying a thin coat of a different color primer or paint over the car. Making your own is the least desirable method, As it is messy, time consuming and can cause problems like clogged sandpaper , over spray. and worst of all paint reactions. Unless you are a pro and know which paints are compatible , Do not make your own!. Take this advice from someone who has painted hundreds of cars and trucks over the past 35 years. since homemade guide coat is sprayed and therefore is in the seams and all the hard to reach places everywhere on the car, if it reacts, it's hell to fix, a horrible nightmare!. The aerosol guide coat comes in different colors will not react and is the least expensive way to go, however the can nozzle tends to clog , the surrounding areas need to be masked, the cans spray an uneven pattern (especially when trying to spray on an overall job) and some brands will actually clog sandpaper , leak and run out of propellant. Dry powder works the best , it is wiped on with an applicator and can be sanded right away with wet or dry sandpaper. Masking is not required. and the dry powder forms a very thin and even film that will never clog sandpaper, effect adhesion or react with any paint system known. The powder goes a long way and can be used freely over large areas, quick and easy. The powder is safe to use and washes off with soapy water. A big drawback of using powder is that Some powdered guide coat brands charge hefty prices for there products ,while at the same time skimp on the powder , ( 50g. and some even add fillers). This is due mainly to the high cost of advertising (how else can you get someone to pay over $60.00 for a few dollars worth of powder) All these methods work ,but dry powder works the best. Use powdered guide coating if you can, if not use some form of guide coating, it will make a big difference in the final outcome

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