How to Skim Coat Walls

Skim coating walls is a process of applying a thin layer of joint compound or skim coat plaster to smooth over textured or damaged walls. A proper skim coat helps create a blank canvas to apply paint or wallpaper. With some basic tools and materials, skim coating can be done as a DIY home improvement project to transform the look of a room.

Benefits of Skim Coating Walls

There are several advantages to skim coating walls in your home:

Creates a smooth, uniform surface for decorating. Skim coating embeds drywall joints, repairs cracks and covers wall imperfections to give walls a flat, consistent appearance. This allows paint, wallpaper or other finishes to go on smoothly without flaws showing through.
Can change wall texture. Applying a skim coat layers over any existing wall texture, such as knockdown or orange peel, to create a blank slate. This allows you to alter the look of a room without replacing drywall.
Prepares damaged walls for refinishing. If walls are heavily textured, peeling, cracked or just dated, a fresh skim coat renews them at a fraction of the cost of new drywall. Skim coating provides the ideal, flawless surface for repainting walls.
A more affordable option. Skim coating over existing drywall is much cheaper than replacing drywall or extensive drywall repairs. The thin skim coat uses less joint compound than sanding bumps or heavy textures down completely.
Can match patched drywall areas. A skim coat helps blend patched drywall spots seamlessly into surrounding walls. This disguises seams between old and new drywall.

Overall, skim coating greatly improves the appearance of flawed or damaged walls and drywall while saving time and money over more extensive repairs.

Supplies Needed for Skim Coating

Skim coating requires some specific tools and materials to do properly:

Joint Compound

Also called drywall mud or skim coat plaster, this is a thin, fluid coating that dries to a smooth, hard surface. It comes as a powder mixed with water before using. All-purpose and topping compounds are best for skim coating.

Drywall Knives and Trowels

A 6-8 inch taping or drywall knife applies initial coats. A wider 10-12 inch finishing knife or trowel goes on for final thin layers. Stainless steel offers durability.

Sandpaper and Sanding Pole

Fine 120-150 grit sandpaper smooths the skim coat between applications and removes dust. A sanding pole with sandpaper wraps around the head for sanding hard to reach areas.

Paint Rollers and Trays

A high nap 3/4 inch roller sleeve on a roller frame spreads joint compound smoothly. Disposable paint trays hold compound for rolling.

Paintbrushes

Angled sash brushes cut neatly into corners and along edges. Softer paintbrushes blot up drips or excess material.

Drop Cloths

Protect floors and furniture from mess with canvas drop cloths, plastic sheeting or large tarps.

Dust Mask and Eye Protection

Wear a N95 mask to filter out airborne dust when sanding. Safety goggles keep compound splatter out of eyes.

Drywall Primer

Primer specially formulated for drywall seals in the skim coat layer once finished and ensures paint adheres properly.

Having the right skim coating tools and materials on hand makes the job much easier. Buy supplies at any hardware store or home improvement center.

Skim coating takes some practice to master but following key steps leads to smooth walls. Be sure to read and follow any safety directions on compound or equipment packaging.

1. Prep the Wall Surface

Skim coating works best on already painted drywall. Remove any wall-mounted items. Wash walls with TSP substitute cleaner to remove dirt and grease that prevents adhesion. Fill any holes or cracks with joint compound and let fully dry. Lightly sand glossy paint for better bonding.

2. Setup Your Workspace

Cover floors, furniture, cabinets and trim with drop cloths. Have all materials and tools nearby. Ventilate the room by opening windows or turning on fans to help dry the skim coat faster. Wear safety goggles and a dust mask.

3. Mix the Joint Compound

Pour dry powder into a bucket or pan. Add water a little at a time, mixing constantly with a drill and paddle attachment. Mix to a thin, creamy, lump-free consistency like thick pancake batter. Let stand 10 minutes before using.

4. Apply Base Coat

Use a 6-8” drywall knife or trowel to cover walls with a thin, even coat about 1/16” thick. Work in sections, spreading upward in 18”x24” areas. Apply lightly but completely to fill imperfections. Let dry 2-4 hours.

5. Sand Base Coat

Once dry, sand to smooth any ridges or lumps. Use 120-150 grit sandpaper wrapped around a block or sanding pole for best results. Vacuum dust before continuing.

6. Apply Second Skim Coat

Mix more compound. With a 10-12” knife or trowel, add a second thinner coat within 12”x12” sections. Glide knife at a 45 degree angle with sweeping “S” motions to flatten previous layers.

7. Sand Second Coat Smooth

When dry, lightly sand again with fine sandpaper. This removes any high spots and creates an ultra-smooth surface for finishing. Remove all dust.

8. Add Final Skim Coat

For the smoothest results, mix a final batch of thinned joint compound. Roll or brush a tight, thin layer over entire wall with overlapping strokes. Immediately go over the wet coating with a trowel to flatten.

9. Let Fully Dry

Allow the skim coat to dry thoroughly overnight before sanding or painting. The wall may appear blotchy until completely dry. Proper drying prevents cracks or paint not sticking.

10. Prime and Paint Walls

For best results, apply a high quality drywall primer to seal the skim coat. Once primed, finish walls with desired paint or wallpaper. Enjoy your smooth “new” walls!

Tips for Skim Coating Success

Apply thin coats and build up gradually. Thick layers dry unevenly and are hard to sand.
Keep a wet edge when working in sections so edges blend seamlessly together.
Fill any missed low spots as you go. Avoid skim coating over bumps or ridges.
Only mix enough compound that can be used in 45 minutes before drying begins. Discard any stiff leftovers.
Be extremely thorough sanding between coats. Lumps or swirl ridges show through paint if not smoothed.
Allow double drying times in humid climates. Compound dries slower than label estimates.
Use bright work lights angled across walls to check for any imperfections before priming and painting.

With the right prep and techniques, skim coating can transform flawed walls. Durable results come from multiple thin coats, thorough sanding between layers and allowing proper drying time.

Skim Coating vs New Drywall

While skim coating offers a cheaper alternative to new drywall, there are tradeoffs to consider:

Skim Coating Pros:

Significant cost savings over new drywall and labor to install
A weekend DIY project versus major drywall work
Maintains existing wall height and trim
No demolition mess or disposal fees

Skim Coating Cons:

Very time and labor intensive process
Achieving an ultra-smooth finish takes skill and effort
Joints and some wall defects may still faintly show through
Limited thickness buildup to cover severe flaws

New Drywall Pros:

True smooth, flawless surface and blank slate for decorating
Opportunity to update wall layout, add features
Thick enough to cover major wall defects
Professional results when installed by drywall contractors

New Drywall Cons:

Extremely expensive material and installation costs
A major project requiring drywall expertise
Existing trim may no longer fit neatly
Major demolition and disposal work involved

If walls have extensive water damage,bugling seams, or layers of outdated texture, new drywall often makes the most sense for a renovation. For smoothing over minor flaws or changing texture, skim coating is usually preferable. Assess the wall condition, project scope and budget to decide the best option.

Skim Coat vs Plaster

While both skim coating and traditional plaster create smooth finishes, they have some differences:

Plaster uses lime putty or gypsum plaster applied in thick layers requiring specialized skills. Skim coat uses thinning drywall joint compound rolled or troweled on easily.
Plaster takes longer to mix and apply properly, while pre-mixed skim coat compound is faster.
Skim coating only requires basic tools like trowels and sandpaper versus complex plastering tools.
Plaster requires a base layer of wood or metal lath. Skim coat goes directly onto drywall.
Skim coat builds up in very thin layers of up to 1/8” thickness. Plaster can be 3/8” or thicker in just a few coats.
Skim coat dries quickly while plaster drying takes days. This allows skim coating sections at a time.
Plaster provides a more durable, solid base for tiles or stone. Skim coat is meant for smoothing drywall.

For most DIYers, skim coating is preferable to traditional plaster methods. However, plaster creates a uniquely smooth, solid wall base in historic homes. Evaluate each method for the specifics of your project.

Skim Coating Ceilings

Applying a skim coat to ceilings follows the same process as walls but requires a few extra considerations:

Covering floors and furnishings from above is extra challenging. Use heavy drop cloths secured tightly.
Stand on a sturdy ladder or scaffolding high enough to reach the entire ceiling comfortably.
A plaster pump attachment on a drill mixes and sprays compound overhead more easily than a mud knife.
Start skim coating in the corners and work out towards the middle. This avoids excess buildup in corners.
Apply very thin coats or gravity will cause drips before drying. Feather out edges.
Use a pool trowel or 12” drywall knife to reach across ceiling flat without drips.
Division lines between ceiling drywall sheets are hard to disguise without rejointing.

Take all safety precautions when working on ladders or scaffolding. Having an assistant makes overhead skim coating much more manageable.

Skim Coating Concrete

Applying a skim coat helps disguise imperfections and resurface damaged or uneven concrete floors, walls, foundations, and slabs. The process is slightly different than drywall:

Clean concrete thoroughly and etch with muriatic acid first for proper bonding.
Use concrete-specific skim coat material rated for exterior use rather than just drywall mud.
Primer helps the skim coat adhere to slick concrete surfaces.
Apply very thin coats and allow extra drying time. Moisture prevents curing.
Rub coloring agents into the final coat to hide patches or unevenness.

With proper primer and high strength material, skim coating transforms rough, stained concrete into a uniform surface. Hiring a concrete professional is recommended for large exterior projects.

Skim Coating Plaster Walls

For traditional plaster walls, apply a “plaster wash” skim coat to hide defects and create a smooth painting surface:

Remove any loose plaster and reattach where needed. Fill large holes with plaster first.
Mix a thin vinyl polymer-modified joint compound to coat directly over plaster.
Dampen walls slightly first to prevent moisture absorption unevenness.
Apply a tight 1/16” base coat, filling any divots fully Allow to dry overnight.
Apply an extremely thin final coat using a wider knife or trowel.
Lightly sand any imperfections that remain and dust walls.

With the right plaster wash ingredients and methods, skim coating helps salvage hard plaster walls that would be difficult to replace.

Skim Coating Vs Wallpaper

Sometimes simply applying wallpaper or wallcovering can also disguise flaws:

Pros of Wallpaper Over Skim Coat:

Much faster application than multiple skim coats
Additional patterned texture hides small defects
Wallpaper adhesive fills minor divots and holes
Thicker wallpaper hides cracks better than paint

Cons Over Skim Coat:

Seams may ripple or edges peel up over uneven areas
Glossy wallpapers highlight uneven textures rather than hiding
Removing wallpaper can damage drywall worse than before
Moisture under wallpaper can create bubbling

If wall flaws are limited mostly to seams and cracks, a thicker wallpaper may perform well enough without skim coating. For knocking down heavy textures or smoothing major damage, take the time to skim coat first.

FAQs About Skim Coating Walls

How long does skim coat plaster take to dry?

Skim coat compound dries in 2-4 hours between coats. Final coats take up to 24 hours to fully dry and cure. Drying times vary based on temperature, humidity and ventilation.

Do you need to primer before skim coating?

Priming first is not mandatory but helps the skim coat adhere, prevents moisture absorption and seals the surface. Always use drywall primer after the final skim coat before painting.

Can you skim coat over semi-gloss paint?

Lightly sanding semi-gloss or glossy paint allows skim coating to bond but fully deglossing is ideal. The shinier the existing paint, the more prep needed.

Should I skim coat or replace drywall?

For minor flaws, skim coating is preferred to save time and money. For widespread water damage or mold issues, new drywall may be the best option for whole wall repairs.

Is skim coating hard to do?

Skim coating is labor intensive but does not require specialized skills. Allowing adequate drying times between multiple thin coats is key. Achieving very smooth results takes some practice.

How much does it cost to skim coat walls?

DIY skim coating costs $2-$6 per square foot depending on materials used and how many coats needed. Hiring a drywall pro ranges $6-$15 per square foot including labor and materials.

Conclusion

Smoothing over damaged or textured walls with a skim coat of joint compound creates the ideal surface for decorating a room. By following proven techniques, applying multiple thin coats, allowing proper drying time between layers and thoroughly sanding, you can achieve professional looking results. Skim coating helps transform any worn-out wall into a primed canvas ready for paint, wallpaper or other finishes.