Why do wallpaper seams open up and how can you fix them?

Here is one of the most dreaded things that can happen to your wallpapering project: you have finally finished installing your new wallpaper and it looks just like you imagined it. A few hours later you come back to take another glance and a sense of dread fills your heart: suddenly the seams are showing… How can this be possible? In this article we’ll guide you through the possible causes and explain how to prevent this from happening in future projects and how to fix this issue so that it becomes almost invisible.

I won’t blame you if your first thought is “it must be a problem with the wallpaper!”. However, this is unlikely to be the case. While in the past, paper-based models had to be soaked in wallpapering paste for a specific amount of time before hanging (resulting in expansion and contraction once they dried), modern non-woven varieties are made of a mix of synthetic and natural fibres, ensuring structural stability.

“So, what could be the issue then?!” I hear you say. You are asking the right people! With years of experience in wallpaper installation, we have come across this issue many times. As a result, we have put together this handy guide for you to uncover the possible reasons why those annoying seams might pop open and, most importantly, how you can prevent and fix this annoying issue.

What's causing seams to split?

There can be several reasons why your wallpaper seams might detach from the wall. Sometimes it's a single issue, but often it's a mix of things causing the problem. It’s important to understand what could have gone wrong so it won’t happen again in your next wallpapering project:

Did you prepare your surface appropriately?

I cannot stress enough how crucial it is to prepare the surface properly before wallpapering. If your wall is either too absorbent or not absorbent enough, those open seams are almost guaranteed!

Old layers of paint, patches of old plaster or any other uneven spots will cause problems. One of the safest ways to ensure a smooth result and even adhesion is to apply a coat of primer. It will seal the surface of your wall, preventing the water contained in the paste to soak through. This way the adhesive will stay on top, keeping the wallpaper in place. Check with your local DIY shop for the right primer for your wall. If the surface looks too damaged, consider adding a layer of wall lining paper. For a more detailed look at this topic check out “How to prepare the wallpapering surface”.

Did you use the right wallpapering paste?

Each wallpaper paste has its own characteristic, so pay close attention to the instructions that come with it as they’ll tell you everything you need to know. A basic rule always applies: investing in high-quality adhesive is absolutely worth it. You’ll see a noticeable difference compared to cheaper alternatives.

When you’re applying paste directly to the wall (for wallpapers with a non-woven backing layer), prepare one strip at a time. This way, you won’t have to rush or worry about the adhesive drying too quickly. Always make sure that you spread the paste a bit wider than the strip itself to ensure the entire width is well-covered. For heavier or coated wallpapers, you might need to add some dispersion glue (again, please take note of the instructions).

Did you pay enough attention to smoothing the wallpaper out?

Often an afterthought, especially for those DIYers with less experience, smoothing the wallpaper out thoroughly is crucial to guarantee a perfect finish and avoid open seams. Many beginners think of smoothing just as a way for getting air bubbles out from under the wallpaper. That is not correct!

This step is required to apply pressure to the wallpaper to ensure it sticks properly and also to push any excess paste out at the edges. If you just hang your wallpaper without pressing it down, it won’t have the adhesive strength needed to stay in place as it dries. Arm yourself with a good quality seam roller and focus on the edges of each wallpaper strip to increase adhesion.

Did you stick to the correct soaking and drying times?

This point is only relevant if you are installing a wallpaper with a paper-based backing as these models expand when wet. When you apply the paste to these types of wallpaper, you need to let it soak for a specific amount of time (exact numbers are provided in the instructions that come with each roll). It varies depending on the type of wallpaper and must be the same for each strip. Wait too long or not long enough or use different times for various lengths and you’ll end up with open seams.

Did you apply enough paste to prevent the edges from lifting?

Another point to remember when installing paper-based wallpapers is to apply enough adhesive to the edges.

You want to cover them thoroughly, without going overboard. When you fold the strips after pasting, ensure the edges are aligned or they might dry out.

Is the temperature of the room to blame for your open seams?

While this point tends to remain under most people’s radar, changes in temperature can be the reason behind the dreaded open seams as they affect the drying process. For example, if you are installing strips of wallpaper near an air conditioning unit, a heating element, or in an area facing direct sunlight, this area will dry faster than the rest, causing the wallpaper to pull and shift. That is why it is important to let your wallpaper dry as naturally as possible for a couple of days. Also, before starting the installation process leave your wallpaper in the room where it will be hung for at least 48 hours, giving it time to acclimatise.

Remember: The sweet spot for wallpapering and drying is around 18 degrees Celsius (about 65 Fahrenheit). If it’s too hot or there’s a draught, the wallpaper will dry faster than the adhesive, causing those annoying seams to split open. It’s therefore important to maintain this temperature for a few days after installing it.

What can I do to prevent open seams from appearing?

Even with all the advice, it’s always possible for something to be overlooked, especially if you are new to wallpapering. Besides following the above instructions to the letter, here are a couple of valuable tips to prevent unsightly seams from ruining the overall look of your room:

Try to match your wall with the colour of the wallpaper

The closer to the background colour, the more you can camouflage any potential open seams. You can also look for a coloured primer close to the hue of your wallpaper. It doesn’t have to be an exact match; as long as it’s close enough, any potential seams will be almost invisible.

Consider “banding”

Paint a vertical stripe down your wall where the wallpaper strips will meet. It’s the same concept as the suggestion above, but it saves you from painting the whole wall. You can just use a small sponge, dip it in a little water, then into the paint, and then run a stripe down the plumb line you’ve drawn on the wall.

Avoid gloss paint or thick layers of paint as otherwise the wallpaper may not adhere properly. Always let it dry completely. Of course, this means you will have to first calculate the width of each strip and measure where to paint, but it’s a small price to pay for the peace of mind it brings.

Do some preventive work on dark coloured wallpapers

Thick, dark wallpapers can pose a unique challenge: Since the vast majority of wallpapers are printed on a white base, the white edge might still be noticeable once installed. This often leads to the mistaken belief that a seam is visible when, in fact, it is just the side of the wallpaper showing. You can prevent this by lightly colouring the edge of the wallpaper roll with a crayon of the same shade as the wallpaper before hanging it on the wall.

My wallpaper is already installed, and open seams are still showing - what can I do now?

Open seams can happen to professionals, too - nobody is perfect, as we all know. Although it is not possible to close the seams once the wallpaper is installed and dry, there are several ways to significantly improve the visual appearance. The main problem of an open wallpaper seam is usually that the white background shines through or the white carrier paper of the wallpaper is visible. To solve this issue, you can try to:

Colour in the space between the open seams with crayons or felt-tip pens

Carefully paint the seam with a crayon or felt pen in a colour matching your wallpaper. Test it first in an inconspicuous area and make sure the results are to your satisfaction once the felt tip ink has dried out.

Use water colours in the same shade of your wallpaper

A similar solution that tends to bring even better results is using water colours. Either use a water colour paint box or buy a water colour brush pen. Make sure to pick a shade as close as possible to the one of your wallpaper, then apply it to the open seams with a fine brush (if you are using the paint box). Wipe excess paint away with a damp microfibre cloth. Any parts of the wall surface showing in the open seams will be coloured, making the seam in visible. Important: Like for the solution above, test it first in a hidden spot. Wait until dry and check the result before proceeding.

Trust us: In our experience, if you do this right, your seam will no longer be visible to the eye!

Conclusions

I understand how frustrating it can be to see those annoying seams ruining your beautifully wallpapered walls. So, let’s sum up which steps to take to avoid and fix open wallpaper seams:

1. Ensure the wall is properly prepared
2. Use the right wallpaper paste and don’t forget the edges
3. Smooth the wallpaper out thoroughly to ensure good adhesion
4. Take note of the right soaking and drying times for paper-based models
5. Control the room temperature during and after installation
6. Match the wall colour to wallpaper
7. Use crayons, felt-tip pens, or watercolours to match and colour open seams

Remember, wallpapering is an art that takes patience and attention to detail. Prep your wall well, take care of the little things, and you will achieve the flawless finish you seek. Happy decorating!