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Old 02-03-2014, 07:17 PM   #1
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How to get flat walls after mudding & sanding?


I'm looking for some advice on techniques to mud & sand drywall to a reasonably flat finish.


I'm doing three coats of mud then sanding with the help of a 500W worklight at an oblique angle. After this, there is a lot of residual dust on the walls. To prepare for painting, I use a a dry cloth to remove the remaining dust. However, it usually takes 5-10 passes before the mudded areas don't rub off dust when touched. When all is said and done, the walls look less than smooth when lit at an oblique angle.


For example, this is a horizontal joint after sanding and dust removal:

http://i.imgur.com/LgXUxrP.jpg


Any suggestions?


Is this bad sanding technique, bad mud technique, or something else entirely?


Thanks in advance.

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Old 02-03-2014, 07:23 PM   #2
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How to get flat walls after mudding & sanding?


Really bad finishing job. Looks like you went up and down across the seams, instead of along the seams.
What size knife where you using and what material.

The whole key to drywall finishing is thin coats, looks like you used way to much mud!

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Old 02-03-2014, 07:36 PM   #3
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How to get flat walls after mudding & sanding?


Really looks like it needs another coat, but go out wider. use at least a 12" knife
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Old 02-03-2014, 07:45 PM   #4
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How to get flat walls after mudding & sanding?


Should be sanding in a ciruler motion not just up and down.
Where's the tape?
No way should there be those big blobs of compound that far away from the repair.
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Old 02-03-2014, 07:55 PM   #5
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How to get flat walls after mudding & sanding?


What are you using to sand with? Remember all low spots must be filled all high spots must be sanded.
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Old 02-03-2014, 08:53 PM   #6
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How to get flat walls after mudding & sanding?


Thanks for the feedback. To answer your questions:

I'm using general purpose mud with a 12" knife and am sanding with a 220 grit sanding sponge.

The wall was much smoother before dust removal. Wiping down the wall with a dry cloth to remove loose dust causes the mud to disintegrate, leaving behind bumps and visible ridges.

If I don't wipe down as thoroughly, chunks of mud tend to come off during painting.

Last edited by tc113; 02-03-2014 at 08:58 PM.
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Old 02-03-2014, 09:14 PM   #7
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How to get flat walls after mudding & sanding?


Somethings is not right. You shouldn't have chunks of mud coming off. I usually just prime right over the dust with a roller or sprayer so you shouldn't need to wipe it down at all. Is it old compound? Did it freeze? Was it dried out and you added water to it?
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Old 02-03-2014, 09:43 PM   #8
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How to get flat walls after mudding & sanding?


Was the mud thoroughly dried before you sanded? Did you knock off all the ridges and boogers on each coat before going on to the next? Waited 24 hours between coats? Can you give a picture a bit further back, it's hard to get perspective/scale.
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Old 02-03-2014, 10:38 PM   #9
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How to get flat walls after mudding & sanding?


Definitely sounds like the mud was not completely dry. No way way a dry rag can do that to dry mud. A wet rag can soften it back up but not dry.
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Old 02-03-2014, 10:38 PM   #10
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How to get flat walls after mudding & sanding?


Definitely sounds like the mud was not completely dry. No way a dry rag can do that to dry mud. A wet rag can soften it back up but not dry.
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Old 02-03-2014, 11:11 PM   #11
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How to get flat walls after mudding & sanding?


Also could we have exact brand/type of mud and how you prepared it. You go roughly 1/8 inch each coat and then smooth out, or did you go heavier? You go with increasing width of mud each coat? Example 6, 8 then 10. This is a tapered not butt joint right? I know sometimes pictures can end up flipped. Also, I'm very much a novice with drywall, so take my 2 pesos advice, the guys posting above me are much more knowledgable.
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Old 02-04-2014, 06:19 PM   #12
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How to get flat walls after mudding & sanding?


Thanks again for the feedback. To answer your questions:

Here is a wider view of the wall under normal lighting. (I did remove the thermostat and seal the air return before sanding.)

The problem area is a tapered joint.

I waited 24h between mud coats but didn't do any other clean up between them. It sat for about two weeks before sanding.

I used Certainteed Easi-Fil joint compound mixed with a little water.

Can joint compound be weakened by adding too little water when mixing?
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Old 02-04-2014, 08:03 PM   #13
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How to get flat walls after mudding & sanding?


Not unless you added a lot.

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