Priming is an important step that should not be skipped. A primer seals the existing wall surface, creating a uniform substrate for the skim coat. It improves the adherence of the drywall compound and reduces the absorption rate, ensuring a consistent, durable finish.
Go over wall with 150 grit paper, to smooth down any rough areas, apply one mist coat, any further imperfections will show up, so fill & rub down any areas where needed, then apply a second mist coat, then your top coat(s),second one if needed.
For the skim coat get a box or bucket of light joint compound, this is thinned with water, so that it can be applied with a roller. Use something like a 1/2'' nap roller to apply it and skim it off with the widest drywall knife you can handle. Then sand lightly to smooth things out and use PVA drywall primer over that.
Yes. Skim coats, if done correctly, should not require much sanding at all. You want to be careful of over sanding skim coats.
However, we'd recommend leaving it for at least two weeks if possible to be safe. In the wrong conditions, plaster can even be known to take up to four weeks to dry! The colour of the plaster should help you tell whether or not your walls are ready to be painted.
Cons of the Skim Coats
Skim coating walls seems to be more tedious than expected. It can consume more time for those who aren't familiar with the steps used to repair walls. This process can also be intensive labor-wise and energy-consuming.
Give the final coat a full day to dry, then you'll sand the drywall for that ultra smooth finish. In color, it may not look perfectly even, but as long as it's super smooth, the primer will do the trick to even the color prior to paint.
You should prepare to apply at least two coats, in order to achieve a smooth finish. However, if you can still see obvious grooves and indents after the second coat dries, you can trowel on a third coat using the method mentioned in Step 7 of this guide.
Don't paint directly over new plaster walls because the glossy surface can prevent the paint from adhering effectively.
If you've plastered yourself, or if you can see a few spots and bumps (which could be a splash of PVA or plaster), you can lightly sand these back to avoid them showing up once you've painted. Overly sanding the surface will create additional shine, not ideal for adhesion when you start to apply the paint.
In addition to smoothing out walls, painters may also do a bit of cleaning, remove stains, tape over trims in the room, and remove outlet covers. These steps can take a good chunk of time to complete but is especially important for ensuring the paint job isn't for nothing.
If the paint is in good condition and not in need of any maintenance, it is perfectly fine to skim over it with plaster. However, if the paint is old, flaking, or damaged, it is recommended to remove it before plastering.
Drywall compound rollers are not only effective, durable, and easy to clean, but they offer versatility for tasks such as texturing, and skim coating. The LEVEL5 drywall compound roller is available in 9” and 12” sizes, and created with a higher nap to hold more compound than competing brands.
Drying time for skim coating typically ranges from 24 to 48 hours per coat, depending on the thickness of the application and environmental conditions like temperature and humidity.
The Ceresit primers recommended for skim coat application are: Ceresit IN 10 and Ceresit CT 17 Profi.
After the last coat dries, pole-sand the wall with 120-grit paper. If you have too many peaks and valleys, hit the walls with 100-grit first.
The first alternative is to use joint compound rather than skimming the surface with plaster. The compounds are for filling joints between plasterboard or any gaps and holes. However, you could use it to give an entire wall a smooth coat. You apply it with a trowel or putty knife.
SHELF LIFE: SKIM COAT has a shelf life of 12 months when stored properly in a dry location, protected from moisture, out of direct sunlight, and in an undamaged package.
Temperature and Humidity Changes: Fluctuations in temperature and humidity can cause materials to expand and contract. This movement can lead to cracks in plaster over time, especially if the plaster and the substrate have different rates of expansion and contraction.
Another common blunder is using too little or too much joint compound. Uneven application can cause visible seams, cracks, or bulging joints, compromising the overall appearance of your walls.
Adding dish soap or No-Pock Pro can help, but the compound may still “pock,” just not as bad. The only recourse is thinner coats with some type of air assist drying and work the bubbles out with your knife.