The problem of Bubbling Wallpaper, Gaps appearing at seams and Lifting of the paper...

Hanging most wallpaper including traditional wallpapers such as embossed papers, lining papers or prints is not ‘rocket science’ and a beautiful finish will result so long as a few basic steps are followed. As with any other decoration work investing time in the preparation and using good quality materials will pay dividends in the end.

One of the most common problems encountered when hanging wallpaper is bubbling, shrinkage and lifting, this article is meant to be a practical aid, (rather than an exhaustive technical article) to avoiding the issue or at the very least to understand in all likelihood what has gone wrong. Understanding the basic science of what is happening helps in preventing all the above.

NB; in this article we are referring to traditional wallpapers rather than technically different paste the wall or non-woven wallpapers.

The basic science bit...

The first thing to understand, if you don’t know already of course, is that a traditional paper based wallpaper expands in dimensions when it is pasted (soaked) with adhesive (paste). Typically a 52cm wide wallpaper will expand 6 to 8mm or more (around 5/16 of an inch or more in old money) across its width –which is over 1.5%. It will also expand at a similar rate along its length.

Why does this expansion occur? The paper fibres are a natural cellulose material and they expand when they come into contact with water.

Remember, paper is wood based and we all know wood expands when its wet, most of us will have experienced wooden doors that suddenly don’t open easily in wet weather for example.

The second thing to keep in mind, again, if you didn’t know already, is that it takes time for the paper to expand fully – generally the thicker the paper, the longer the soaking time – depending on the wallpaper type you will see soaking times between 6 minutes and 15 or even 20 minutes.

So the first important rule then; when hanging traditional wallpaper is to let it soak for the correct time – in our opinion the very minimum time should be as stated on the label and as a general rule a little longer is better than not enough time.

So why are we droning on about this? because Bubbling occurs because of inadequate soaking time…

The simple point is if the paper is not allowed to expand fully on the paste table then it will carry on expanding on the wall – the classic cause of bubbling wallpaper. If the bubbling is not excessive then it may go flat as it dries out when the paper shrinks in the areas that have bubbled…

So what about Gaps and Shrinkage at Seams?

This is the reverse of expansion issue we have already talked about above; If paper expands when wet then it will want to shrink when it is drying…

This is why the wall preparation and the quality of paste you are using is so important because the paste doesn’t simply bond the paper to the wall but its job is also to permanently hold the wallpaper in its expanded state whilst the paper and wall dries out.

What about the surface the Wallpaper is being applied to?

The first thing to consider is the condition of the wall.

For a start it may well be ‘OK to go’, especially if the plasterwork has old paint on it and there is nothing flaking or loose material. The perfect surface is a slightly absorbent one – too absorbent and it will suck all the water out the paste and weaken/compromise the bond, not absorbent enough and the paste may not be able to bond and grip the wall…

So does the wall need sealing or sizing? Try the ‘flick test’ to give a good indication; flick some water from a saucer at the wall – if it soaks into the wall it needs sizing – if it runs down the wall it doesn’t.

So the water soaked into the wall and it needs sizing, what do I do next? We recommend a PVA based size diluted to the manufacturer’s instructions and painted onto the porous area. On a molecular level PVA is smaller than starch based sizes so gets deeper into the wall for a better job.

Don’t go over the top and put so much PVA on that it forms a skin on the wall – this could lead to bonding issues.

It is important not to go over the top or you could end up with a totally non-absorbent surface that is not compatible with the paste you are using and this will result in a weakened bond or no bond at all.

Non porous smooth surfaces will need a light sanding to form a ‘key’ and stability for the paste to bond to.

Paste and paste application;

Once the wall is prepared you are ready to hang the paper – remember to soak it as described earlier and then use a paste of suitable quality;

If the manufacturer is recommending a good quality ready mixed paste – don’t ignore it as the reason will be they believe the superior adhesion characteristics of a good quality paste are required and these qualities are more commonly found in Ready Mixed Pastes; A good ready mixed normally contains higher quality ingredients such as PVA for example. Ready mixed pastes also have a much higher percentage of bonding agents in than flake types, around 20% for ready mixed and only 4 or 5% for flake type pastes.

Use the paste to the instructions recommended – typically for example you will need at least a kilo of ready mixed paste per standard roll.

So, how do I prevent Gaps and shrinkage occurring?

As we have explained, paper expands when soaked and it naturally wants to shrink back to its original dimensions as it dries. The paste’s job is to hold the paper in its expanded state as the paper and paste dries and stop it shrinking back - not just simply to stick the paper to the wall. The bond has to be strong enough to do this and a cheap paste or one past its ‘use by’ date may not be good enough to do this whatever it says on the packaging.

If the paste doesn’t do its job, either because it is not suitable or because of wall preparation, or both, then the paper will shrink and you will see gaps opening up at the seams as the paste loses its fight against the paper wanting to shrink – in really bad cases the paper will lift off completely towards the edges.

So why does the lifting only occur at or close to the Seams?

When the paper wants to shrink, the maximum tension is at the furthest distance from the centre point of the sheet of paper. At the centre point there is no tension and as you move further out towards the edge the shrink tension increases.

Drying times and drying conditions

Always allow plenty of time for the wallpaper to dry out especially when the surface is going to be painted or overhung with decorative wallpaper – as with our products. The manufacturer’s instructions will offer guidance but conditions vary greatly so the drying times will inevitably vary.

Never try to speed up the process by advancing the drying process – such as turning the heating up in the room. This can result in the paper drying much more quickly than the paste behind meaning the paste does not have the time to bond the paper in its expanded state before it shrinks too quickly with the heat being applied – the result will again be lifting and shrinking

All the above is especially important when the surface is going to be painted or overhung with a decorative product – as is the case of most of our Wallpapers.

For example, most modern paints are ‘water based’ so when the paint is applied to the surface of the wallpaper the paper will try to expand – if the bond is fully cured and as strong as it should be, the surface will not be able to expand and a very satisfactory finish will be the result. But if the bond strength is inadequate then once again lifting, especially at seams will result.

Please note the paint will not penetrate all the way through the paper and be able to weaken the paste bond directly – the paint can only cause shrinking if the bond with the wall is too weak.

Conclusion

We want you to enjoy using our products but if that’s not possible at least for you to enjoy the results and following a few basic rules will we hope ensure this.

The old saying ‘don’t spoil the ship for a ha’porth of tar’ holds true in this case…