Help With Skim Coating Horse Hair Plaster
JoeJoyce
| Posted in General Discussion on
Hi,
I could use some guidance on skim coating horse hair plaster. I have put on a skim coat and sanded using 220 grit paper, either by hand or with a sanding pole. I find that there are little holes or what look like poch marks left in some places that I’ve sanded. Not everywhere, but more than I expected.
Does this mean I should skim coat again or just touch up the areas where the poch marks are? Or am I expecting it to be perfect after one skim coat and some sanding and that isn’t realistic? I’ve done a decent amount of DIY drywalling and this has always baffled me.
Thoughts and recommendations very welcome!
Joe, Boston, MA
Replies
It could be a few things. Not mixing the mud well enough, over mixing or mud is too dry. In general as you progress through coats of mud you add a bit of water with the top coat. The water thins the mix a bit to help with smooth troweling and helps remove trapped air in the mix. When skimming we usually add the largest amount of water, so much so that we can use a paint roller to apply the mix and follow with a large trowel to smooth out. It works very quickly. The skimming will not cover large defects, so those should be handled first. Also, we usually use a high bonding primer on the walls first for better adhesion. For the existing poch marks as you are describing just touch them up. Apply a bit of pressure to get new mud into the holes when troweling and sand very lightly as to not pull the mud out of the holes.
Thanks for the feedback. I have done some of what you said (like the water part. Part of the issue I am running into is that half the wall had no cracks and I skimcoated it and it looks good, the other half had mucho cracks that I repaired with Fibafuse. Getting a smooth finish on that is hard and that is where some of the tiny bubbles are appearing, for the most part. I will move up to 400 grit sand paper for the rest of the sanding.
400 grit?
Is that too fine or should I stay at 220?
Joe,
I usually use screens, called medium for knocking down spots or ridges of the pre last coat. Then a “fine” screen after last coat where necessary........but honestly I rarely use the medium. It’s in the bucket but will usually use the fine and lay on it heavier. With screens you use more of a circular motion on the final as back and forth may leave very fine lines (scratches).
Another beauty of the screens, you can wet (damp) sand between coats or as a final when wanting to keep the dust down. Working in retail stores on repairs or display changes I’ve done this often. Of coarse a vac sander would be the ticket but unnecessary for such small jobs. Then again I’ve followed drywall “companies” and walked away whiter than I started....
I used to fold 100 grit paper for inside corners, but found a foam block at my drywall supplier. One edge is 45’d and it does nice work. One pass up or down and it finishes a nice clean corner.
I asked about the 400 as I’ve never gone more fine than 100 when I used sandpaper. I’d think it was way too fine, fill faster and ...... never thought about it.
The tiny bubbles that end up as holes, I find these if I skim over a sealed or painted surface when doing a patch. A damp sponging of the dust left on the surface usually fills them and they don’t often reappear on subsequent coats.
PS, You’re not related to the umpire that stopped a Tiger pitcher’s no hitter with 2 down in the ninth?
And yet another ps.
Patching or skimming over plaster I will first apply plasterweld.
A few times I found problems with compound adhering to bare plaster. A couple of times on the other side of bathroom or kitchen walls. I would guess from moisture transmission through the wall. Once I coated the area before the patch with plasterweld, no problems.
Thanks Calvin for the insights. I did graduate to a screen on this project (I had never used one before) and like the way they work and will use circular motions (I was using back and forth). I am joint compounding over many cracks in our dining room, so it is a painted surface. I tried something new this time - the Fibafuse rolls and sheets as there were so many cracks in certain areas it made sense to me to cover them all at once. I was lulled into a false sense of "this looks great" because the compound is white and doesn't show imperfections until a light is run over it, then I noticed about a million areas I missed or didn't look good. I also decided to skim coat the plaster that wasn't cracked so that I had the same wall texture throughout the room. Trying to get the skimcoats smooth over the fibafuse is challenging, but I have to get it near perfect cuz it is the dining room!
So I will try your suggestions. And no, that was not me. I would never do that to a pitcher, or would at least change my name if I made that decision......