Can I use joint compound over wallpaper?

Whether you can use joint compound over existing wallpaper depends on several factors. Joint compound, also known as drywall mud, is a pasty material used for finishing and repairing drywall seams and patches. It creates a smooth surface for painting or applying wallpaper. Using joint compound over wallpaper is possible in some cases but not recommended in most situations.

What is Joint Compound?

Joint compound is a paste-like material used in construction and repair for finishing drywall panels. It is applied over the joints between drywall sheets and screw holes to create a seamless surface. Joint compound comes as a powder that you mix with water to create the plaster-like consistency. It hardens as it dries.

There are several types of joint compound:

• Pre-mixed – comes ready to apply from the container
• Powder – needs to be mixed with water
• Lightweight – contains perlite for easier sanding
• All-purpose – used for all stages of drywall finishing
• Topping compound – extra smooth finish for final coat
• Setting compound – hardens quickly without needing to air dry

Joint compound is an essential material for finishing drywall installation. It creates a seamless surface ready for decorating with paint, wallpaper, or other wall coverings. Using joint compound requires some skill to apply smoothly and evenly. Multiple coats are often needed, allowing each layer to dry before adding the next.

Can You Apply Joint Compound Over Wallpaper?

In most cases, it is not recommended to apply joint compound directly over existing wallpaper on walls. There are a few reasons why joint compound and wallpaper don’t mix well:

• Adhesion issues – Joint compound doesn’t bind well to wallpaper. It may peel or chip off over time.
• Moisture issues – Water-based joint compound can loosen wallpaper adhesive, causing the wallpaper to release from the wall.
• Uneven surface – Seams and bumps from underlying wallpaper layers will show through the joint compound.
• Difficult to finish – The texture of wallpaper makes it hard to smooth and finish joint compound.

Applying joint compound over wallpaper often leads to the joint compound cracking, flaking or failing to adhere properly. The uneven surface of wallpaper prevents the joint compound from forming a durable finish.

When Can Joint Compound Be Used Over Wallpaper?

In limited situations, it may be possible to apply joint compound over wallpaper successfully:

• Over painted wallpaper – Joint compound generally adheres better over wallpaper that has been painted rather than the raw wallpaper surface.
• Thin skim coat – A very thin, light layer of joint compound may work over wallpaper without adhesion issues.
• PVA primer – Applying PVA or wallpaper primer before the joint compound gives it something to bind to.
• Stable wallpaper – Joint compound is more likely to adhere properly over wallpaper that is well-adhered to the wall and doesn’t have loose seams or edges.

Even in these situations, results can be unpredictable and the joint compound may still fail. Test a small area first to see if the joint compound sticks to the wallpaper without problems.

Alternatives to Putting Joint Compound Over Wallpaper

Instead of applying joint compound directly over wallpaper, consider these alternatives:

• Remove wallpaper – Take down existing wallpaper before applying joint compound for the most reliable results.
• Skim coat over wallpaper – Use a dedicated skim coating product rather than joint compound.
• Prime before applying joint compound – Use an appropriate primer like Gardz or Draw-Tite to prepare the wallpaper surface.
• Hang new wallpaper – Apply fresh wallpaper over the existing, then apply joint compound over the new wallpaper.
• Install new drywall – For severely damaged wallpaper, it may be best to remove it completely and install new drywall panels rather than trying to resurface over wallpaper.

A skim coat is a very thin layer of a smoothing product that can help minimize the texture of wallpaper before painting or applying new wallpaper. Gardz and Draw-Tite sealers help create a more sound surface for applying joint compound or skim coating.

Tips for Applying Joint Compound Over Wallpaper

If you decide to try using joint compound over wallpaper, follow these tips:

• Fill any loose seams and gaps in the existing wallpaper with caulk or spackle first.
• Sand down any rough or lifted edges in the wallpaper.
• Wash the wallpaper with TSP or mild detergent and water solution to remove dirt and residue.
• Apply primer like Gardz to seal the surface.
• Use light coats of joint compound and allow to fully dry between applications.
• Only apply a thin skim coat no thicker than 1/16th of an inch.
• Use a setting-type joint compound for a harder finish.
• Consider using fiberglass mesh tape over cracks or seams to reinforce the repair.

This helps provide a more suitable surface for the joint compound to bond to. But preparation alone can’t overcome inherent adhesion issues of applying joint compound to wallpaper. Expect that problems may still arise down the road.

Conclusion

Applying joint compound over existing wallpaper often leads to adhesion failures, an uneven finish, and other problems. It is generally advisable to remove old wallpaper before repairing walls and ceilings with joint compound. Priming, light skim coats, and proper surface preparation may allow joint compound to work temporarily over wallpaper in some cases. But for the most reliable results, take down wallpaper before applying drywall joint compound.