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Need Advice with Skim Coat After Wall Repair

Need Advice with Skim Coat After Wall Repair


  #1  
Old 09-07-20, 11:48 AM
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Need Advice with Skim Coat After Wall Repair

Hi all,

DIYer here. This is my first skim coat attempt and I've read all of the how-tos and watched all of the YouTube videos. I realize this is 70% skill and 30% knowledge.

I'm doing a small bathroom. The paint job was peeling off so I was able to easily remove all of the paint from the room, but ended up with a lot of torn drywall paper. I sealed the walls with Roman Rx-35 PRO-999 and just put up the first skim coat layer.

I used USG All Purpose "green top" bucket, thinned down to what I think is "yogurt like", though it seemed to take a lot of water. I mixed it with a drill and a ribbon paint mixer.

Here's what I am struggling with:
  • I tried the paint roller trick but it just didn't work out for me. For starters, a 9" roller was too big to do most of this bathroom. I tried a smaller roller with 3/4" nap but that didn't work either.
  • I seemed to have better results just knifing the mud on as I went. I used a 12" taping knife.
  • What I am not understanding is how much mud I should be leaving on the wall? I realize if I were filling a texture, the mud would fill the gaps. In this case, I'm just trying to hide the indentations where the drywall paper is missing among some other wall imperfections. Several videos state the layer is around 1/8" thick or so, but as I'm smoothing out the mud, I frequently end up feathering out the mud thin enough that I can see the bare drywall. In many of the videos I've watched, I can hear scraping on the leading
  • I know this will likely take 2-3 skim coats, but what I am looking for are "milestones" for those coats.
  • When I smooth out coats, I frequently get what look like tears in the mud, but it isn't something dragging... It often looks like peeled drywall paper but isn't. Should I worry about these? If I continue to smooth out and press harder, they go away but then I end up taking off more mud than intended.. or so I think.
  • I think one hurdle here is that as I am pulling my knife, my walls aren't exactly flat.
  • So right now, my first coat is up and drying, but I have a lot of lines to scrape off or sand out. I couldn't seem to find a pattern to keep pressure on one side of the knife and lift the other because I was constantly changing directions. Given its a bathroom, there's the door, a linen closet door, and a shower tub to work around. Once I cleaned up the mud in one direction, as soon as I switch directions I would mess up what previously looked good. I would have maybe 14-16" between the corner and a door frame, and taking the knife from the floor up failed because this piece of drywall wasn't square and my knife wouldn't keep on the mud no matter how flat I had it to the wall... and then the corners were awful. So I would pull from the corner to the door frame, every 10" from the floor up, overlapping slightly.
  • Was I expecting too much out of this first coat?
  • Should I scrape off edges and do a light pole sand before the second skim coat?
 
  #2  
Old 09-07-20, 11:54 AM
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Should I scrape off edges and do a light pole sand before the second skim coat
you can... but probably shouldnt. 1/8" is probably too thick. If you can barely see through it, that could be a high spot on the wall so I wouldn't be too concerned. Drag one way only on the first coat. On your second coat try to drag perpendicular to the previous coat. Scraping is preferred over sanding. Typically you just scrape and apply the next coat. If anything was left REALLY high you might sand those areas, but sanding dirties up the wall and can cause adhesion problems. That's why sanding is usually last.

if you have a line in your mud, that's some foreign material in the mud or on the edge of your knife. It often indicates you got crap in the pan or dry bits off the edge of your bucket. Keep the bucket edges clean with a wet rag and the mud all scraped down flat. If you get crap on your knife, throw that mud away, dont put it back on your pan, that will just recycle it so it happens again. And I never put old mud back in the bucket.
 
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Old 09-07-20, 11:55 AM
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How many coats are needed for a skim coat job depend both on the condition of the wall/ceiling and the skill of the person applying the mud. I've never measured the thickness of any skim coat I've down but I suspect it's a lot thinner than 1/8" Normally there is no need to apply it thicker than you need to get the desired result. It's no big deal to go back and remud some areas. Use a little pressure to apply the mud but a very light touch to smooth it out.

I frequently get what look like tears in the mud, but it isn't something dragging... It often looks like peeled drywall paper but isn't.
are you sure it isn't trash in your mud?
 
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Old 09-07-20, 01:24 PM
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Thanks for the pointers.
Dragging in one direction makes sense but it doesn't seem doable given the number of corners / edges I need to keep sharp.

It isn't trash in the mud, but seems like the mud streaking or tearing from a low spot in the wall, or possibly an uneven coat of mud. They are like indents in a long "V" shape usually.

Should I be able to see the bare wall or previous coat under the coat I am applying? Or should I have a coat think enough that I'm hiding this?
 
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Old 09-07-20, 01:46 PM
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Are there any nicks in your blade?
Not all skim coats need to completely cover the underlying finish. As long as it's all smooth and relatively flat it should be good.
 
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Old 09-07-20, 02:12 PM
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Sounds like the voids that are produced when you dont have enough mud on the knife or arent putting enough even pressure on the knife. When you are spreading the mud you should be dragging it at a low angle with even pressure. If you go back to smooth it out, you feather it to one side by putting more pressure on one side of the knife and barely lifting the other.
 
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Old 09-10-20, 05:32 AM
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My second coat turned out much better than the first. Perhaps the smoother surface made the second coat easier... But one thing I did differently is thinned the mud down quite a bit less. I'm not sure where the "yogurt". consistency description came from but that seems like it is too thin, unless I just used it very wrong. I just did a splash of water in like 1/3 of a bucket of mud. It was still a paste, but one that would not hold its own shape.

Now, on the second coat, I got bubbles from time to time. Is there a way to prevent that?

Also, I can see a couple spots with bubbling drywall, probably from torn paper. I'm not sure how that happened since I applied the sealer, but is there anything I can do at this point to fix this? Do I just cut out the bubbles, put more sealer and re-mud?
 
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Old 09-10-20, 05:50 AM
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thinned down to what I think is "yogurt like"
Looks like you found the one thing that stood out to me, the mud was too thin.

I dont think you need to thin at all, a nice new bucket should be the consistency needed, and yes as the wall gets smoother the application gets easier.

Just knock down the imperfections, once you have a solid coat you should be good!
 
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Old 09-10-20, 05:59 AM
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I almost always thin my mud - it flows better. Can't really say how much I thin it as I eyeball it and know when it's in the neighborhood of being the right consistency. Bubbles are usually caused by over mixing with the drill. Not a big deal as once sanded or scraped down a thin coat of j/c will make them disappear.
 
 

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