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Discussion Starter #1
In the middle of sanding my joints, I noticed I'm having to work a little harder to smooth out lines and tiny ridges in my mud. I put on a fresh sanding screen only to find it's leaving scratches and grooves behind on the mud. I gently rolled the screen to soften it and it helped a little, but it's still leaving a lot of texture behind where there was none. I've tried to sand very gently to no avail. Any tips to avoid this?
Thank you!
 

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Use the 150 and go in a different direction. Any scratches you see are probably from the courser grits. Paint will easily cover any "scratches" made by the 150. You could also finish sand with a 180 grit sanding sponge if it's just a small area.
 

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Discussion Starter #5
By coarser grits, do you mean that there are spots on the screen that are coarser than the intended 120? They're quite significant in area and sometimes very deep. I did my best to minimize sanding, but I have a lot of smoothing to do. Maybe I can find something to sand to wear the screen down a little.
 

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80 is courser than 120. 120 is courser than 150. If you sand with 80 grit, you have to sand with 120 until you get ALL the scratches out that the 80 made. Then when you sand with 150, you have to sand until you get all the scratches out that the 120 made.

You also may not know that "screen" and "sandpaper" are 2 different things. Quit using screen, and use sandpaper for your finish sanding.
 

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Should you be so unfortunate To have to sand down a lot of mud, a screen is great. For finish sanding, I am always sandpaper. And as noted sandpaper technique is the same as technique you use when you sharpen your chisels.....start with a grit suited to the amount of material yuo need and keep getting finer, each grit cleans up the scratches for the previous. For chisels, I usually end at around 3000....but for drywall 150 should be fine, 220 if you want to get really particular.
 

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Discussion Starter #8
80 is courser than 120. 120 is courser than 150. If you sand with 80 grit, you have to sand with 120 until you get ALL the scratches out that the 80 made. Then when you sand with 150, you have to sand until you get all the scratches out that the 120 made.

You also may not know that "screen" and "sandpaper" are 2 different things. Quit using screen, and use sandpaper for your finish sanding.
Ah, I see. The scratches I'm talking about were not left by any other grit than the 120. I hadn't sanded the joints with anything else so I am completely certain it was the new 120 screen I put on.
I am aware of the difference between screen and sandpaper, but I hadn't heard to finish with sandpaper instead. What is the benefit?
 

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Another thing is to use very light pressure when sanding. I was using a 120 grit sanding screen and using what seemed to be a light touch and noticed sanding lines. I then backed off and used very light pressure, just keeping the sanding head & screen in contact with the wall and the lines disappeared. That said I found it a little difficult to use such light pressure consistently and started hand sanding using a 150 grit foam block which was easier to control and gave better results even though it was more laborious.

I have not tried the higher grit screens, which should help, but my sense was that it might still scratch if one is still a novice with a sanding pole (I am speaking of myself being the novice here.). Another factor is the type of finishing mud you used. I have not done a head-to-head test but it was my sense that a regular all-purpose is harder and would work better with a 120 grit screen. I was using a lighter weight all-purpose and it seemed softer when sanding.
 

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I generally use 120 grit screen with my sanding pole. About the only time I use sandpaper is when dressing up certain areas ... and then I'm prone to use a sanding sponge. I don't recall sanding scratches ever being an issue once the primer is applied although if there were any I'd fix them along with any defects in the finish without giving it a 2nd thought.
 

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Discussion Starter #11
Thanks for your response!
I too am a total novice with this. I did try to be very, very light on pressure and there were still nasty scratches. I am using all-purpose with 120 screen.
I gave the screen a couple swipes back and forth on the floor boards and that seemed to minimize the scratches quite a bit.

Another thing is to use very light pressure when sanding. I was using a 120 grit sanding screen and using what seemed to be a light touch and noticed sanding lines. I then backed off and used very light pressure, just keeping the sanding head & screen in contact with the wall and the lines disappeared. That said I found it a little difficult to use such light pressure consistently and started hand sanding using a 150 grit foam block which was easier to control and gave better results even though it was more laborious.

I have not tried the higher grit screens, which should help, but my sense was that it might still scratch if one is still a novice with a sanding pole (I am speaking of myself being the novice here.). Another factor is the type of finishing mud you used. I have not done a head-to-head test but it was my sense that a regular all-purpose is harder and would work better with a 120 grit screen. I was using a lighter weight all-purpose and it seemed softer when sanding.
 

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Discussion Starter #12
Thank you for your reply!
I'm using 120 on a pole and switch to sanding sponge when needed too.
I'm happy to hear the scratches won't show up through primer. I wasn't sure, but it was hard to scratch up the mud I put so much effort into laying on smooth.

I generally use 120 grit screen with my sanding pole. About the only time I use sandpaper is when dressing up certain areas ... and then I'm prone to use a sanding sponge. I don't recall sanding scratches ever being an issue once the primer is applied although if there were any I'd fix them along with any defects in the finish without giving it a 2nd thought.
 
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