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Wet Sanding Guide

What is the Goal of Wet Sanding?

The goal of wet sanding paint is to remove all the texture and make it as flat and mirror-like as possible. The intent of the following steps is for 'show' quality paint, and achieving the best results possible.

When sighting down the panels of a vehicle, you don't want to see any ripples in the paint, all the edges of the panels should be completely flat. Perfection is the goal.

What are the steps to wet sanding?

Following are the basic steps of wet sanding, there will be more detail in the following sections.

  1. 1.   P600 grit with a hard block (True Blox)
  2. 2. Dry guide coat (Mirka)
  3. 3. 1,000 grit with either the same hard block, or a softer block
  4. 4. Dry guide coat (Mirka)
  5. 5. 1,500 grit with a softer block
  6. 6. Dry Guide Coat (Mirka)
  7. 7. 2,000 grit with a softer block
  8. 8. Dry Guide coat (Mirka)
  9. 9. 2,500 grit with a softer block
  10. 10. 3,000 grit: foam 'tri-zact' pads
  11. 11. 5,000 grit: foam 'tri-zact' pads

What types of sanding blocks should be used?

There is typically two different types of sanding blocks used for wet sanding. The initial sanding is to remove the texture/orange peel from the paint. For this, the sand paper must be against a hard surface, like acrylic. A hard surface allows the sand paper to cut sharper and not follow the texture of the paint; the point is to shave off the top of the texture until it is completely flat. If your sanding block is soft at all (like a durablock), the paint will not be as flat.   This block is the purpose of the True Blox Wet Sanding Blox.

The second type of sanding block used is a softer block. There are a lot of different brands on the market, one of the popular ones is Motorguard. They are usually a type of foam/rubber, and a lot of times have two sides with different densities (I always use the harder side)  

While a hard block is absolutely necessary, they do need to be followed by a softer block to help smooth the paint out. Sand paper grit acts more aggressive on a hard block, so finishing with a soft block leaves finer sand scratches as well.  

****Very Very Important!!**** 

A sanding block can be hard and flexible at the same time. As a matter of fact, it is very important for the sanding block to be at least a little bit flexible. When wet sanding paint, the sanding block must follow the contour of the panel being sanded in order to sand the paint flat. This means if there are any ripples in the body work of the panel; they are staying there! The wet sanding block has to follow those ripples so at least the paint can be completely flat. This is very crucial, and a very big key to getting paint sanded flat.

Choosing the right sanding block

There are 5 True Blox wet sanding blox, now which one should you be using? The main difference is how flexible they are. It isn't too often the thickest block is used, since not many panels are flat enough, or straight enough. Remember, the sanding block must follow the shape of the panel. This means it is almost always better if the block can flex at least a little bit.  

The proper sanding block should take just a small amount of pressure to make it follow the shape of the panel. If it feels forced, or can't follow the shape; the block is too rigid. If the block feels too loose, or there is no tension at all to follow the shape, it is probably too flexible of a block.  

Here is a break down of the blocks (starting with the thickest) and their uses:

1. (the thickest): This block is 1/4 thick and made of acrylic. Technically it can flex, but barely. To use this block, the panel should be flat, or a small amount of a positive curve to it. It should not be used if there is a concave shape (this includes ripples/waves in body work). Sometimes this block works good to sand down a heavier area, and then switch to something a little more flexible.

2. This block is probably the most commonly used, and made of 1/8" acrylic. It flexes slightly, just enough to follow the shape of most panels, and even works great for panels that are completely flat.  

3. This block is also used a lot, and made of 3/32" polycarbonate. This material makes it highly flexible, and nearly impossible to break or crack. It is a very good block to use on any vehicle that has a little more shape to it (positive or negative), think something like a 1932 Ford.  

4. This block is a little narrower, and is made of 1/16" polycarbonate. It is meant to be quite a bit more flexible than the first three blocks. This block isn't usually used on open panels, but rather in areas that have quite a bit more shape. These areas are usually transition areas, or the edge of panels, like up to a head light or tail light area. This can also be a good block to use on some parts or areas that need to be wet sanded flat, but the body work might be more ripply/wavy. It can get the clear mostly flat, and have a much lower chance of sanding through. It is an excellent block for certain areas.

5. This block is the narrowest, and meant to be very flexible. It is the same material as the previous block, but being narrow allows it to flex even more. This is a great block for areas with a lot of shape, either concave or convex.  

General Concepts

The coarser the sand paper, the sharper it will sand, and the flatter the paint will be. Remember, we are shaving the texture off the top of the paint. Obviously, there is a limit to this, typically 600 grit is a great place to start.

If you can't get the paint flat with 600 grit, chances are, you won't be able to with 1,000 grit. Everything must be sanded out in this first step: all edges should be flat, there should be no orange peel left over; nothing left behind.  

When a panel is squeegeed off, you can sight down it and pay attention to the reflection. You should be able to see if there is any remaining texture or ripples in the paint. Look at it from as many directions as possible, and really pay attention to what you're looking at; it's easy to over look something.  

Along with sighting down panels, you should be able to feel if there is texture left in the paint while you're sanding. Using hard blocks, you will feel everything. It will feel slightly bumpy if there is some texture left, this is a surprisingly good way to tell. The key is, pay close attention, do not just go through the motions.  

Pay attention! This alone might be more important than anything else.  

The best success will be had when every step is very thorough, not leaving anything for later on. Using good lighting helps with this.

 

Sanding Techniques

The general rule of thumb is to sand at roughly a 20-30 degree angle and about 6-10" strokes, and alternating directions. Use a light amount of pressure, basically enough just to hold the block and sandpaper against the panel.   Try to sand as evenly as possible across the panel, so that roughly the same amount is sanded the entire panel. There's no need to be so picky to count the amount of sanding strokes, just don't sand a lot more in one area. Typically, about a 2-3 foot area should be worked at a time. This depends on the panel, but breaking a panel up can help keep you focused and stay thorough and miss less.  

For the most part, the sanding block should be parallel with the shape of the panel. It tends to help sand better if the block is angled just slightly (so it's almost parallel with the shape).  

How do you hold onto the Blox?! This is a great question, without a great solution. A big part of True Blox, is they need to work, without compromising anything, at all. That means comfort takes a back seat to results. True Blox is a brand only focused on world class results. Having handles on the wet sanding blocks effects how they flex and work too much.   That means I apologize in advance if your hands cramp up a little at the end of the day.  

The sandpaper is basically used as a handle for the wet sanding blocks. Wrap the paper around the block, and where the two flaps of the paper meet, hold those flaps together. Between holding the flaps of sandpaper, and holding onto the block itself a little bit, there shouldn't be too many issues.  

Runs, Sags & Heavy Areas

These areas can be the most stressful to get fixed. The first thing is to make sure the clear is dry enough to sand. It will stay rubbery for much longer than the rest of the paint, and it will sand a lot easier after it is completely dry. Also something to remember with the dry time of a run, is that it has more solvent in it than the rest of the paint. What does this mean? A run can not only take longer to dry, but there's more to dry out of it. So, if you sand a run completely flat before it's completely dry, it can sink in slightly after all the solvent is completely dried out of it. This doesn't always happen, but it is definitely something to be aware of.  

600 grit is aggressive, but probably not aggressive enough to sand some runs out. Most of the time, using 400 or 320 grit dry works very well. Use this on a hard block, and take your time carefully sanding. Only sand on the run, and slowly get it sanded down, staying off the surrounding paint. Being careful is the best 'trick' to it. Using dry sandpaper allows you to see exactly what is being sanding. When the run is very close to being gone, it can be guide coated and switch to 600 grit wet to finish sanding it out.  

What block to use depends on the area, sometimes a block that flexes a little can work better, and sometimes a rigid block is needed. Don't be afraid to try a couple of them and see what works best. There's no real secret, just try it, and find out what works for your exact situation.  

Razor blades. Very very rarely should a razor blade be used. The best use for one is to cut a drip of clear off. Otherwise, they can be too risky to scrape over a run. It is very easy for them to make the paint chattery, or rip, or anything else. Try to block as much as you can. There are rare occasions when a razor blade is useful, but usually not.  

Of course, be careful with edges. Sometimes it works great to knock down a heavy edge with 400 grit, but don't get too carried away, and just use some caution.  

Guide Coat

Dry guide coat is the best thing you will ever use when wet sanding. It is an absolute must. (ok, obviously it's possible to not use it, but it makes life far better.)  

What is the point of it?? There are a few reason to use dry guide coat. It shows you where you have sanded, which helps keeps from over sanding, leaving more paint on the panel. It obviously shows you where you haven't sanded enough (use plenty of good lighting). Guide coat lets you see if you got the edges sanded enough, or if there are any groves, or scratches missed. It shows everything; if the guide coat is gone, it is sanded good enough. Water doesn't wash it off, and it doesn't effect how the paper is sanding, and it doesn't created any scratches or any other issues. The only down side, is it looks messier.

Use it like you mean it!! Guide coat is useless if enough isn't used. It needs to be everywhere on the panel, and rubbed in very good to make sure it's actually in every single sand scratch.  

Mirka! They are absolutely not a sponsor, it just works far better. Mirka also offers white guide coat, and their black guide coat is much darker than the 3M version. 3M tends to leave a bit of a residue that can be a little harder to sand through, while its pretty much impossible to tell anything is on the panel with Mirka.

Trouble Areas

There is almost always some area that seems to be impossible to get the paint flat. Unfortunately this is reality, and even more unfortunately, these areas still need to be right. Here is a sanding technique that can help dramatically, but should only be used when nothing else works.

The first possible solution is to try a more flexible block. So, put down the 1/4" thick block and grab something that flexes. This is a very common misconception. Remember, the block needs to follow the shape of the panel, so many more times than not, a blocks that flexes will do a better job getting paint flatter than a totally solid and rigid block. If that doesn't work, keep reading:

The idea is to sand only in the direction that you sight down the vehicle. So, if there's an area that is slightly hallow, or low, it can be very challenging to get the paint flat through that section. The only effective solution is to sand essentially in straight lines.  

Warning!!!!: This part is very important!: The sanding block can NOT be used in a straight line; the corners will dig groves into the panel. The key is to hold the block at an angle, and your sanding stroke be going in a straight line. Also, you absolutely need to be using a block that can flex a little bit, so put that 1/4" thick block down, it's part of the problem you're having.

 

Other Supplies: Water, Sandpaper, sprayer, etc..

Here are a few other items needed for wet sanding, and some reasons we believe it's the best methods.  

• A Spray bottle, rather than a bucket of water. This ensure the water is always clean, and you can spray the sanding residue off of the panel as you're sanding. But mostly, the water needs to be clean.

• Straight water; no soap. Soap acts as a lubricant. While it may not cause issues directly, part of this process relies heavily on the sand paper grits working just as they do. Adding something that lubricates the sand paper might not cause each grit to sand the paint properly. There's really no need for soap.

• Sandpaper brand. There are more than likely brands available that are better, but just the normal 3M sandpaper is just fine. Feel free to use something that's better, but just don't use that as an excuse; you can achieve the best results with 3M.

•Soaking the sandpaper: isn't exactly necessary. Sure, it might help it be a little more flexible for the first 25 seconds of using it, but it always seems to just be a waste of time. The exception might be if you're trying to sand a complex area that has a lot of shape in it. Otherwise, if you're having issues, more than likely it's not because of this.  

 

Warnings & Disclaimers

All of these wet sanding techniques are meant for the highest quality, 'show quality' paint. That means the steps and techniques are definitely more aggressive than most other techniques, requiring a lot of care and attention to every detail and action made.

Every job done with the above techniques has 6 coats of clear, at minimum 5 coats. These steps cannot be done with 2 or 3 coats of clear coat.

ALWAYS pay very close attention to everything that is done. Paying attention is, by far, the most important factor to achieving great results.  

STILL HAVE ANY QUESTIONS?

Advice@TrueBlox.com

Polishing

Some General Ideas

•The GOAL: Paint that is completely scratch free, with as little to no texture as possible in it, and as clear as possible.
•The following guidelines are all assuming that the paint being polished has been wet sanded, and thoroughly finished in 2,500-3,000 grit.  
•A major key to great polishing results, is quality wet sanding. Using guide coat to help not miss any scratches, and being thorough. If random scratches have to be buffed out, there should have been more care taken while wet sanding. More often than not, it's better to go back and sand these out, rather than buffing them out.  

Polishing Pads

  • •True Polish pads are meant to be used as a system.  

    •There are essentially two ways to polish paint; heat or abrasives.
     
    •The cooler the paint stays, the better and clearer the end result typically is. Heat can cause too many issues, especially on a hand crafted panel with fresh paint. The concentrated heat in one spot can actually make the metal move around. Heat can force remaining solvents out of the paint, causing die back. It will seem like you just can't quite get the paint clear enough. Concentrated heat can also force problems out of body work, like making a small air pocket buried in the filler (pin holes) show up as a bubble, which otherwise would never show up.

    •Using abrasives to polish paint helps avoid heat going into the panel. With the proper rubbing compound, and an aggressive enough polishing pad, the scratches will 'mechanically' come out, rather than heat burning the paint to a polish.

    •Wool is used for step one because of its more aggressive nature. The True Polish wool is a perfect balance of being able to obtain a shine quickly, but not cut gouges into the paint.  

  • •Green Foam is the second step. This foam is fairly aggressive, making easy work of polishing out the wool swirl marks when paired with a medium cut polish. It is tempting to want to skip this step. Without it, the final polish is being asked to do a lot, and too much heat can be created, and a lot of time struggling with polish. Use the green pad, you'll be happy you did.


•Black foam is the final polish pad. If all the previous steps have been followed properly, this step should be quick and easy. All that should need to be polished is some light swirls from the green foam pad, thats it. If there is more, go back to the green pad, or better yet, the wool pad.

  •  

Polishing Speed

SLOW!!  
Every step should be done with the buffer running slow. Slow is 600-900 rpm's. If the correct pads and polishes are being used after the correct sanding steps, there is no need or reason for any more buffing speed.  

Polishing Compounds

•Polishes work best when they are used on clean paint. While going through the buffing process, polish builds up fairly quickly on the paint. The more that build up can be cleaned off, the bette the polish will work.   Polish is a water based product (as opposed to solvent), so that means a water based product will remove it. Water borne cleaner used for paint prep works very good to clean the painted panel with. Isopropyl alcohol can also be used, and works even better, but beware, it can be aggressive! Normally, the more the panel can be cleaned, the better.

•The recommended polish compound is Menzerna. It is clean, doesn't create dust, works very well, and goes a long way.

•Don't be afraid to use an aggressive enough compound. It is actually safer and better to use something more aggressive, there will be less passes with the buffer, and the sanding scratches will come out faster and better.   Menzerna 1400 is recommended.

•Step two should be a medium cutting polish. It is possible to use the same compound from step one, but with the medium foam pad. This will just make more work polishing. It's better to have the correct medium polish and save time and have better results. Menzerna 2400 is recommended.

•Final polish is Menzerna 3800.  

Lighting

Lighting is crucial!!

•Two different styles of light will be used during the buffing process. Each of the lighting types will highlight different things.

•Fluorescent tubes should be used with step one (which is a wool pad). The goal of this first step is to not only buff wet sanding scratches out, but also and more importantly, to remove all texture from the paint. This texture looks almost like leather; but it is actually left over wet sanding scratches that are almost polished out. The fluorescent lighting does a great job of showing texture in the paint.  

Cleaning the Paint

Use a water borne cleaner throughout the buffing process. This removes the compound and polish from the paint, allowing you to buff directly on the paint more effectively. A lot of times, when it's a struggle getting an area buffed out, stopping to clean it with water borne cleaner will help quite a bit.

Why water borne cleaner? Buffing compounds are water based. So in order to remove it, a water borne cleaner is needed. A solvent based cleaner won't take polish off. Isopropyl alcohol can also be used, but be very cautious, it can be quite aggressive on fresh paint.  

Metal Prep

Epoxy

These steps are assuming that all the welding, adjust, and any other metal work is complete, and the car is ready for body filler. This is also assuming the car has already been stripped down to bare metal in a previous stage of the build.

  1. Clean! The first step is very important. Clean the metal very well by rinsing it and wiping it with lacquer thinner. This will be sure to get any oil or sharpie marker out of corners, or small weld voids, or anywhere else you can’t tell it’s contaminated. There are a lot of times that the metal looks clean, and as soon as lacquer touches it, all the sharpie comes out. If the metal is clean right away, it will be a much better start and foundation to everything else.
  2. Sand Blasting. The entire car does not need to be sand blasted. The only areas needing blasting are any rust pitting left over, any weld seams, and any sharp inside corners. The corners, are only to help with adhesion for the epoxy, since it isn’t always as easy to get sand paper in these corners, so the blasting will help ensure there will be something for the epoxy to hold on to. The pitting and welds should basically be seen the same way. They both need to be “whited out”. This isn’t always easy, but they both need to be clean. The pitting cannot have any dark coloring in it, that just means the rust is still there. It needs to be completely white and clean metal all the way to the bottom of the pit. The welds must be the same way. If the seam is completely smooth, with no voids at all, it probably isn’t necessary to sand blast it. Any weld seam that has an little bit of voids, or anything else in it, needs to be blasted. Nothing properly sticks to welding coloring or porosity.  
  3. Epoxy should not be applied to sand blasted metal; at least not with the caliber of work we are aiming for. There is far too much dirt left behind from sand blasting, and it’s not worth that being the foundation of all the body work and paint. So, once the sand blasting is done, the metal is ready to be cleaned.
  4. Step one of cleaning the metal, is to use a red scotch brite (The rule of starting finer, and working down) and a metal cleaner. Be sure the metal cleaner is not and acidic based cleaner! We are not trying to etch the metal. Glasurit makes a very good metal cleaner, that doesn’t leave anything behind. Scrub all of the metal good with the scotch brite and metal cleaner.  
  5. Once the metal cleaner is done, clean the panels with a solvent based wax and grease remover and towels, to make sure all the cleaner is off the metal.
  6. Using 150 grit and a D/A, sand the panels very thoroughly. 150 grit does a great job of cleaning, as well as making sure there is at least 150 grit for the epoxy to stick to, incase anything is missed with 80 grit(which is next)
  7. With 150 complete, move down to 80 grit on a D/A. Be sure that the paper is sharp, you want to make sure there is plenty for the epoxy to bite onto.  
  8. With 80 grit complete, it’s time to clean again! Do not use lacquer to clean the metal. Lacquer thinner tends to hold/absorb moisture in it, and there is a chance that it will leave a small amount of moisture on the metal, leaving small rust droplet spots.  
  9. Clean very well with wax and grease remover. Spray the cleaner on the metal, and wipe clean. Repeat this until the towels stay completely clean. Yes, this is possible.
  10. Once the panels are all clean, they are ready for epoxy!  
  11. Spray two medium-wet coats of epoxy, following the tech sheet for the proper flash times. It should probably be at least 1-2 hours(or more) between the two coats, this will help make sure the epoxy is able to dry enough.
  12. After the epoxy is sprayed, it is very very very important that it is completely dry before body filler goes on top of it. A good infrared lamp is the best way to speed up the cure times. It should still go through several long heat cycles, like an hour of heat at a time, and 3 or 4 times. If there is no infrared lamp, bake the epoxy in the paint booth, with several bake cycles, and allow the epoxy at least 2 days to sit, even with the bake cycles.
  13. Once the epoxy is dry, it needs to be prepped for filler.
  14. Scuff the epoxy with a red scotch brite. Don’t get too crazy, it just needs to be gone over.
  15. After scuffing, 100 grit, or 80 grit, can be used by hand to scuff up the epoxy as well. You have to be careful here, the sand paper pretty easily cuts through the epoxy. Lightly sand it just enough to make it look like it has all been sanded.  
  16. Blow off and clean with wax and grease remover again to get rid of sanding dust.
  17. Make sure the wax and grease remove is completely dried out before using filler. I would recommend allowing at least a couple minutes, just to be sure.
  18. Filler time!

Bare Metal

These steps are also assuming that the vehicle is already in bare metal from a previous part of the build. It also assumes that all metal work is completed, including welding and adjusting panels. For this route, it is possible to leave all the panels on, and not worry about the jams and some other areas until later on. Judgement needs to be used for this. If the bottom, or jams, or engine bay need a lot of blasting, it might need to be done right away. The next chance will be when the car comes apart for the paint process. I will assume, for this purpose, that everything (floors, engine bay, jams) is clean, and not needing much prep work.

  1. Clean! The first step is very important. Clean the metal very well by rinsing it and wiping it with lacquer thinner. This will be sure to get any oil or sharpie marker out of corners, or small weld voids, or anywhere else you can’t tell it’s contaminated. There are a lot of times that the metal looks clean, and as soon as lacquer touches it, all the sharpie comes out. If the metal is clean right away, it will be a much better start and foundation to everything else.
  2. Sand Blasting. The entire car does not need to be sand blasted. The only areas needing blasting are any rust pitting left over, any weld seams, and any sharp inside corners. The corners, are only to help with adhesion for the filler, since it isn’t always as easy to get sand paper in these corners, so the blasting will help ensure there will be something for the body filler to hold on to. The pitting and welds should basically be seen the same way. They both need to be “whited out”. This isn’t always easy, but they both need to be clean. The pitting cannot have any dark coloring in it, that just means the rust is still there. It needs to be completely white and clean metal all the way to the bottom of the pit. The welds must be the same way. If the seam is completely smooth, with no voids at all, it probably isn’t necessary to sand blast it. Any weld seam that has an little bit of voids, or anything else in it, needs to be blasted. Nothing properly sticks to welding coloring or porosity.  
  3. A 3M clean & strip disc is the first step in prepping the metal for filler. These discs do a great job of cleaning, and the don’s miss anything; they create a very smooth and even surface. This can be used on a 3” grinder. Be careful not to use too much speed, creating too much heat into the panel. It is fairly easy to heat the panel up too much.
  4. Clean the metal with wax and grease remover. The metal won’t be able to be wiped down after it is ground with a roloc, so this is a good chance to make sure the metal is clean, since it’s still smooth enough.
  5. Grind the metal, carefully, with a 3” roloc. They type of roloc will determine what grit to use. The goal is for it to feel like the metal is almost fuzzy from the grinder. If it still feels smooth, the roloc isn’t sharp enough. I prefer the 3M purple cubitron roloc, in 60 grit. These last a lot longer than most grinding discs, and the grit is so much sharper, it grinds the metal nicely. For the 3M green corps discs, I prefer 36 grit to prep for filler. This line isn’t quite as sharp, so it takes a little bit lower of a grit to grind the metal well enough. Make sure to pay attention that the roloc is sharp enough. It will continue to look the same, but the metal is actually smooth. So, just always check and feel the metal to make sure. This step is important, it’s what everything will be hanging on to.
  6. Blow the metal off very well, and it is ready for filler. Don’t use wax and grease remover here, since the rag will stick to the metal too much and make a mess.