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-   -   How to get flat walls after mudding & sanding? (http://www.diychatroom.com/f101/how-get-flat-walls-after-mudding-sanding-195453/)

tc113 02-03-2014 07:17 PM

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.

joecaption 02-03-2014 07:23 PM

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!

ToolSeeker 02-03-2014 07:36 PM

Really looks like it needs another coat, but go out wider. use at least a 12" knife

joecaption 02-03-2014 07:45 PM

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.

ToolSeeker 02-03-2014 07:55 PM

What are you using to sand with? Remember all low spots must be filled all high spots must be sanded.

tc113 02-03-2014 08:53 PM

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.

TotalHomeworx 02-03-2014 09:14 PM

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?

Jb1234 02-03-2014 09:43 PM

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.

ToolSeeker 02-03-2014 10:38 PM

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.

ToolSeeker 02-03-2014 10:38 PM

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.

Jb1234 02-03-2014 11:11 PM

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.

tc113 02-04-2014 06:19 PM

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?

ToolSeeker 02-04-2014 08:03 PM

Not unless you added a lot.


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