How do you prep a Unigrit disk?

[Shinystang]

I'm going to try damp sanding using a PC7424 with Unigrit 6" 1500 sanding, finishing and 3000 finishing. The car is a black 79 Trans Am that was repainted about 20 years ago and seems to have been parked in the sun most of that time.

I know the speed to keep the PC is between 3-6 and mist the surface with plain water, not soapy water.

My question is about the prep of the Unigrit disks prior to use. Should they be soaked in water like hand-held sandpaper or is misting the dry disk and the painted surface enough?

Also, what is a good rule of thumb to decide whether to start with 1500 sanding or 1500 finishing disks?

Should the sanding disks be used with or without the foam backing pad?

Thanks for the advice and I'll post some before & afters.

Jeff

 

[rohnramirez]

Just out of curiosity, why not soapy water?

Haven't tried DA sanding yet, but using a foam backing pad will give you cushion when applying pressure and help distribute it evenly over the disk, but in turn lessens its cut a bit.

I'm not sure if you're supposed to soak the disks too like regular sandpaper.

 

[Mike PhillipsMike Phillips is verified member.]

Apologies ahead of time that my article on damp-sanding is long, but it's not a procedure a person wants to enter into without some head knoweldge first....

Here's the article,

Damp-Sanding Tools, Tips and Techniques by Mike Phillips



And in post #5, the how-to section, here's an excerpt... see the red text...

Water Volume?
Damp-sanding is using only a few mists of water. Meguiar’s new Unigrit Sanding and Finishing Discs MUST be used wet but not over-wet. All you need is a mist or two of clear water to the face of the pad and a few mists of water to the surface to be sanded. Damp-sanding should not be a wet-mess on the car, or on the ground surrounding the car.

• Too much water will hyper-lubricate the surface and reduce cutting action.

• Too little water will increase cutting, clog disc and wear disc out prematurely.

Unigrit Sanding and Finishing Discs are always used wet. Use water only - no sanding lube (soap).


Use a clean water source - no soap or sanding lube

It's safer to error on the side of caution and use an extra mist or two of water until you get a feel for the right balance for your environmental conditions. Temperature, humidity, airflow, affect all machine sanding process including the Unigrit Sanding System so there can be no hard and fast recommendations. Practice makes perfect.

VITALLY IMPORTANT
It's vitally important that you stay focused on the amount of water you're using when damp-sanding because if you use too much water and your disc hydroplanes, you can mis-read this to mean the disc is spent of used-up and no longer cutting.

If the disc is in fact still good and you throw it away because you used too much water then you waste a good disc and these are not inexpensive.
​

Remember, it's not wet sanding it’s damp-sanding
I took the below picture after completely sanding down a 1969 El Camino. Note the water level in the clear spray bottle.

Only 16 ounces of water used to sand an entire 1969 El Camino

This is a 32 ounce spray bottle and I never refilled it during the sanding process, this means I used approximately 16 ounces of water to sand down a full size, domestic vehicle.


Downward Pressure?
Light Pressure. When machine sanding you only need to use the weight of the machine and whatever more pressure it takes to keep the pad flat to the surface with no hopping or skipping. It’s vitally important to maintain disc rotation so you don't want to use too low of a speed setting.


Tool Speed Setting?
Fast. With an air powered D.A. Sander you're going to be on 3/4 to full throttle With a Meguiar's electric polisher you’re going to use the 3.0 to 6.0 speed setting depending upon whether you're sanding a flat surface or a curved surface. It's safer to turn the speed down anytime you're sanding small curved areas or hard to reach areas.

 

[Mike PhillipsMike Phillips is verified member.]

My question is about the prep of the Unigrit disks prior to use. Should they be soaked in water like hand-held sandpaper or is misting the dry disk and the painted surface enough?

Also, what is a good rule of thumb to decide whether to start with 1500 sanding or 1500 finishing disks?

Should the sanding disks be used with or without the foam backing pad?

Thanks for the advice and I'll post some before & afters.

Jeff

I cover the above in my article but maybe not as clearly as I should have...

Should they be soaked in water like hand-held sandpaper or is misting the dry disk and the painted surface enough?

As it relates to the Meguiar's Unigrit discs, do NOT soak the discs, only mist water onto the paint and onto the face of the discs.

Also, what is a good rule of thumb to decide whether to start with 1500 sanding or 1500 finishing disks?

Factory paint, (thin and hard paint), #3000 foam, if you're brave, #1500 foam.

Repaint, that is paint you think or know is thicker and hopefully easier to work on, for removing Orange Peel and Surface Texture, you start at #1500 Sanding Disc, not 1500 Foam Finishing Discs.

Should the sanding disks be used with or without the foam backing pad?

You can use an interface as an option, an interface will decrease the aggressiveness of the cut, no interface will maximize the cut of the grit level chosen.

 

[rohnramirez]

Mike, why not use soapy water? Is it because of of overlubrication?

I'm just curious of the difference in machine sanding, i've been using soapy water when wetsanding by hand. Thanks.

 

[Mike PhillipsMike Phillips is verified member.]

Mike, why not use soapy water? Is it because of of overlubrication?

I'm just curious of the difference in machine sanding, i've been using soapy water when wetsanding by hand. Thanks.

The manufacture states not to use soap as a lube, my guess is because they don't want the soap to interfere with the slurry that embodies the abrasives.

I can check but regardless, the manufacture knows their product best and they don't recommend using a lube, so that's how I wrote the how-to article. I know this goes against what most people are used to but that's the idea behind "instructions".

 

[rohnramirez]

I see. Sorry i haven't had the chance to use it yet. I totally agree with you that the manufacturers' instructions are the best way to use their product, i usually do not stray away from it, especially with paints.

Thanks for taking some of your time to clear that out, Mike. Good day.