Mould on or behind wallpaper: fix the cause first, then the wallpaper

How do you know if there is mould behind your wallpaper?

You can’t always see mould behind wallpaper. It grows between the wallpaper and the wall, where it is dark and damp, and only shows through once it has been going for a while. These signs point to it:

• Stains in black, grey, green or brown, often in spots or clouds that keep growing.
• A musty smell in a room, even when you can’t see anything yet.
• Wallpaper that comes loose, bulges or bubbles, especially in corners and along the ceiling or skirting board.
• Discolouration along the edges of seams, where the wallpaper absorbs moisture.
• A wall that feels cold or damp, usually an external wall.

If you are not sure, peel back a small piece of wallpaper in an inconspicuous spot. If you see stains on the back of the wallpaper or on the wall, the mould goes deeper than the surface. Also look behind large wardrobes and beds that stand against an external wall: the air stays still there, and that is where mould appears fastest.

Where does mould on wallpaper come from?

Mould needs moisture. So the question is always where that moisture comes from. Only once that is clear does new wallpaper make sense.

Condensation is the most common cause in homes. Warm, humid air condenses on the coldest surface in the room, and that is often a corner of an external wall. A sealed wallpaper layer such as vinyl also makes it harder for that moisture to escape from the wall again.

New-build homes bring something extra. New walls still contain construction moisture after the build, which only leaves gradually. If a sealed layer goes on too early, that moisture stays trapped behind the wallpaper. If you have a new home, allow for this in your planning: read about new-build walls releasing moisture.

Can’t you just wash the mould off the wallpaper?

On washable wallpaper you can sometimes remove visible stains. The biggest misconception is that this solves the problem.

Mould does not only grow on the surface. Paper and fleece absorb moisture, and the mould grows into the wallpaper and on through it, all the way to the wall. What you wash off the front is only the visible part. At the back it keeps growing, and the stains return within a short time.

Anti-mould paint over the wallpaper does not help either. You simply seal the mould and the moisture in under a new layer. If there is mould behind the wallpaper, the wallpaper has to come off and the wall itself has to be treated.

That applies to every type of wallpaper, including renovation fleece and fibreglass wallpaper, which you can normally repaint. With mould, removal is part of the job, so you cannot avoid taking renovation fleece off the wall.

What should you watch out for when removing mouldy wallpaper?

Mould does not belong in a home, and spores and dust are released when you remove it. People with asthma or another respiratory condition are better off not doing this job themselves.

• Work damp. Wet the wallpaper before you scrape. Scraping dry sends spores and dust flying through the room.
• Protect yourself. Wear gloves and a dust mask, and keep the door to the rest of the house closed.
• Ventilate. Open a window during and after the work.
• Clear up straight away. Put the wallpaper into a sealed bin bag immediately, then wipe the floor with a damp cloth.
• Let the wall dry. A wall that is still damp cannot be treated and finished.

After removal, adhesive is left on the wall, and mould can be hiding in that adhesive too. It all has to go. So take the time to remove wallpaper paste residue thoroughly.

What do we do about mould behind wallpaper, and what does it cost?

We remove the wallpaper, sand the wall and treat it against mould. We do this for an extra charge, on top of the standard wallpaper removal. There is no fixed price for it in our price list, because it varies greatly from wall to wall: a few stains in a corner is a different job from a whole external wall.

That is why we always assess it first during the site visit. We look at how large the affected area is, what wallpaper is on it and whether the wall is dry enough to treat. What we find is then stated in the final quote.

Prices exclude VAT. For homes more than 10 years old, 6% VAT usually applies. The VAT rate is stated in the quote.

The cause must be fixed before a new finish goes on. Otherwise the new wallpaper will be affected again before long. Once the wall is clean, treated and dry, we refinish it as part of the same schedule, for example with renovation fleece that you can repaint later. We only do that once the wall is ready for wallpaper.

Removal itself does have a fixed price, by type of wallpaper and per layer: what wallpaper removal costs.

Who does the work?

Our own people: Bouwsector België has 97 tradespeople on permanent contracts, including 40 wallpaper hangers and 32 plasterers. We remove wallpaper at an average of 100 m² a day; with mould we work more carefully and build the treatment and drying time of the wall into the schedule.

When you apply, tell us where you see the stains or smell the mustiness, roughly how large the area is and whether the cause of the damp has been found. You will then get a free quote for the removal within 24 hours, and we will know where to look first during the site visit.

Even without mould, you can have us remove your wallpaper.