Two Schools of Thought when Hand Sanding - Straight-lines or Crosshatch Pattern

[Mike Phillips]

Two Schools of Thought when Hand Sanding - Straight-lines or Crosshatch Pattern

Copyright ©PBMA - Autogeekonline.net® All Rights Reserved


There`s two schools of thought on the correct method or best method on which direction to move your hand and backing pad when hand-sanding.

Straight-line School of Thought
This method means to to sand in only one direction with all sanding steps. The perceived benefit is it will keep all your sanding marks in the same direction. Then, if you want to take this thought deeper this would mean if you don`t get all your sanding marks out of the paint then at least they`re all running in the same direction and my guess is most people will think this won`t look as bad as sanding marks left in the paint that are in a crosshatch pattern and to some level straight-line scratches might be less noticeable and less unsightly than crosshatch scratches.

Crosshatch School of Thought
This method means that with each change in grit size of sanding or finishing papers, you sand in a different direction 90 degrees away from the previous direction. The goal is as you move to a higher grit paper you completely sand-out all the previous sanding marks that were running in the 90 degree angle opposite from the direction you`re sanding with in subsequent steps.

Now assuming you sand all the previous sanding marks out you would then only be left with sanding marks running in one direction. If you don`t remove all the sanding marks from previous sanding steps you`ll have a crosshatch pattern of sanding scratches in the paint of varying depths. At this point you can either re-sand and try to remove the 90 degree sanding marks or move on to the compounding step and try to remove all the sanding marks with a rotary buffer. If you don`t remove all the sanding marks using a rotary buffer then you`ll be left with a crosshatch pattern of sanding marks in the paint and these will tend to be easier to see than sanding marks all running in one direction.

Sanding in Circles
Don`t sand in circles. Circular motions work great for spreading out of coat of wax over a painted panel but don`t work well for sanding on car paint. One reason for this is because the idea behind sanding paint in the first place is to remove some type of defect, a lot of times this will be orange peel or some type of damage that caused deeper scratches or etchings. Whatever the defect is, the goal is still the same and that is to only remove as little paint as necessary to remove the defect so you leave the most amount of paint on the car so it will last over the service life of the car.

Now follow me on this...
When you sand in a repeatable pattern, for example straight-lines, you have some measure of control over the pattern of sanding marks you`re putting into the paint and also the number of strokes and thus the amount of material being removed. If you sand in random, overlapping circles you have realistically no control over your sanding mark pattern and little or no way of gaging how much paint you`re removing while you`re sanding. Wet-sanding paint is already difficult and risky, there`s no good reason to make it more difficult or more risky so I`m not going to recommend sanding in circular motions and common sense dictates to also avoid sanding in circles.

Big Picture
Of course the big picture goal is no matter how you sand the paint, in the end you remove ALL sanding marks and then there isn`t any issue with which method you used. This is easier said than done and paint hardness is a crucial factor as to how easy or difficult it will be to buff out the sanding marks and film-build or paint thickness will be the limiting factor as to how much paint you can remove with both the sanding and the buffing process. (So be careful).


Personal Preference
Because in my life I`ve met seasoned Professionals that are proponents of both methods, choosing the best method becomes a personal preference. As long a there`s enough paint or film-build on the car to work with then theoretically, both methods will work.

Ultimate Goal - Leave the most paint on the car
The most important part of any hand sanding project is to use the highest quality finishing papers you can obtain as this will reduce the potential for uneven sanding marks while leaving the most amount of paint on the car and making the removal process faster and easier.

Machine Sanding
And in this writer/detailer`s opinion, generally speaking, machine sanding is a better option than hand sanding as it will leave more uniform sanding marks that will be a lot easier to remove and the machine compounding process will always be faster and easier versus trying to remove hand sanding marks.


Related Topics
Wet-sanding - Fresh Paint vs Factory Paint
Basic Hand Sanding Techniques
How long will a half sheet of wet/dry sandpaper last before it stops cutting and you need to replace it?
RIDS and Feathersanding - A Highly Specialized Technique by Mike Phillips
Removing Orange Peel & Sanding Marks with the Griot`s ROP and the Wolfgang Twins

Related Tools
Meguiar`s Unigrit Sand Papers 8 Sheets - Mix and Match Grit Sizes


Defelsko PosiTest DFT Combo Electronic Paint Thickness Gauge




Direct Drive Rotary Buffers - Circular Polishers
Easiest Rotary Buffer to learn how to use!
Flex 3403 Lightweight Rotary Buffer
11.5 Amps
1100 to 3700 RPM
5 Pounds
1 Year Limited Warranty




Tools & Accessories Quick Reference List

Here`s a Quick Reference List that will take you to the different categories of products related to machine polishing

Electric Buffers - Main Landing Page for everything in this list.
Buffing Pads for Dual Action Polishers
Buffing Pads for Rotary Buffers
Buffing Pads and Accessories for the Cyclo Polisher
Bonnets
Hook And Loop Backing Plates
Grit Guard Universal Pad Washer - Foam Pads and Wool Pads - All Machines
Autogeek System 2000 Pad Washer for Rotary Polishers Wool Pads and Rotary Buffers
Brinkman Maxfire Dual Xenon Rechargeable Spotlight
Autogeek Detailer’s Tool Bag
Pinnacle Detailer’s Tool Bag
Wolfgang Detailer`s Tool Bag
Defelsko PosiTest DFT Combo Electronic Paint Thickness Gauge
DP Polishing Pad Rejuvenator
Defelsko PosiTest DFT Combo Electronic Paint Thickness Gauge
Foam Pad Conditioning Brush
Duo Spur Wool & Foam Pad Cleaning Tool
Pinnacle XMT Polishing Pad Cleaner
Pinnacle XMT Polishing Pad Conditioner

Copyright ©PBMA - Autogeekonline.net® All Rights Reserved

[cartoysautospa]

wet sanding , it`s all about the pattern. just as in polishing the paint.

[Maknmony]

Hey Mike,

What`s the lowest number of Mills of paint that you will wet sand?

[cartoysautospa]

1 mil

[bigron62]

great write up thanks

[(901)]

1 mil

Thats crazy talk cartoy ^^^^^

You must really like those red dots

[cartoysautospa]

well go below 1 mil and see what happens (901)

[(901)]

well go below 1 mil and see what happens (901)

Uh, no thanks. I will leave that to the experts like you

[Mike Phillips]

I was asked something like this on AG last week and the point I made was that a Paint Thickness Gauge, at least the ones that are affordable, measures total film build, not just a specific layer of paint, so you never know the actual thickness of the top coat whether it be a single stage or a bc/cc.

If I were asked to sand a car there`s other considerations besides the thickness of the paint and what I`ve been practicing and offering as a suggestion to others is instead of evaluating the paint first, evaluate the customer first. Make sure the customer is someone you want to work for and make sure you can match your services to their expectations.