With the basics now under your belt, it won't be long until you reach one of those problem areas...but don't worry, help is at hand!
All those tricky areas can easily, with some thought and patience they'll be wallpapered to perfection. These tips will slow you down but will give you the best results, there is nothing worse than having to look at a lop-sided pattern in a corner.
Before you start, you do need to acknowledge that continuity of pattern will be lost in corners and similar places, even a professional decorator cannot avoid this, however they will match the pattern as closely as possible and that is what we hope to emulate.
Sometimes you can't Match it..
Things would be far easier if all corners were perfectly square, however they very rarely are. If this is the first time you have decorated a full room you are likely going to discover that those angles that looked perfectly squared are anything but. There are patterns that help disguise and those that will emphasise any untrue corners, the most difficult of patterns hide problems are ones with a simple small and regular repeating motif, the loss of continuity will be easy to spot even it small errors are made. The same can often be true of large designs, with either of these pattern types a lot more time will be involved and it may take a couple of hours to hang wallpaper around a single window reveal.
Sloping ceiling lines are another problem area and certain patterns will show it up clearly. The nuisance of a sloping ceiling can be imagined if your wallpaper pattern had a regular row of motifs / flowers, your first drops will have full motifs and as the ceiling slopes you will loose the motif slightly with every drop used. Conversely, if the ceiling slopes upwards you see more sections of the motif with every drop, even when hung perfectly this may appear unsightly because of the motif pattern.
Internal & External Corners
Before you hang wallpaper around a corner, you must hang your last full length before the corner.
You will need to measure from its edge into the corner so you can prepare the next length that will be carried round onto the new wall, use a steel tape. As your corner will most likely be untrue, measure the gap to the corner at the top, middle and bottom of the wall.
For an internal corner add around 12mm (1/2 inch) to the largest measurement to allow that excess to go around the internal corner onto the new wall, the offcut left can be used to start the new wall and overlaps the 12mm strip that turned the corner (where the corner is an external corner add 25mm (1 inch) to the longest measurement).
So cut your wallpaper length to the size measured including the excess required (don't forget to match your wallpaper pattern up to the previous length), put the off cut to one side for now.
Prepare this strip and apply to the wall smoothing flat and taking it into the corner and out onto the new wall, tap your wallpaper hanging brush into the corner so the wallpaper goes tightly into that corner.
As you can imagine to butt join the wallpaper that now sits on the new wall would be very difficult and most unsightly with the offcut made earlier, so we overlap to create a neat finish. To continue with a true vertical hanging we must use a plumb bob or long spirit level to create a vertical line to work from (as you will have done when starting out wallpapering). Measure the width of the offcut piece and mark your line that distance away from the corner, prepare this length and apply to the wall butting up to the level line and overlapping the small excess. You should aim to match the pattern as closely as possible, as the paper overlaps this will not be perfect but this is unavoidable and will not be, in any case be noticeable as the overlap is tucked into or round the corner out of sight.
Only ever try to take a narrow strip around a corner, if you try to take a large length around you will find your paper will end up with a large crease going into the corner and the pattern becoming askew on the new wall.
Wallpapering Around Windows
Unless you are only papering a feature wall or two walls within a room you eventually reach a window reveal that will need wallpapering. Here pattern matching is the enemy, the simple sections above and below the window shouldn't be too difficult provided you are working in a logical order. Do be prepared for a lot of cutting when making the strips for the two sides and the top of the reveal to ensure the pattern matches paper on the facing wall. To help you hang these strips, it would be advantageous to mark or number each one to know where to use them.
You must ensure that you do not end up with a seam on the edge of a reveal, this can easily lift and will be susceptible to knocks. Ok so lets have a go, before we start on the window wall, take a roll of your wallpaper and lets estimate how many lengths will fit between the window and the nearest corner. If it looks like you will have a join within 25mm (1 inch) of the window reveal, move the starting point slightly so that when you get to the window, the seam will have moved away from the edge of reveal. Where the lengths of wallpaper are positioned on the window wall obviously depends on the position of the window, the size of it and the width of the wallpaper.
Ideally we would want the last full strip we hang before we reach the window to leave us with a width of wall and the window reveal that when combined is just less that the width of your wallpaper roll. This would allow us to hang the next length so its upper parts hang above the window, the lower part will hang on the wall below it and with a with just two scissor cuts, the middle section could neatly fold into the window reveal and fill its depth entirely allowing you to crease the paper against the window frame a trim neatly.
You can now go onto hanging the short lengths of wallpaper above the window, the first one can be a short length which can be overlapped by the last drop (or overlap a larger piece and cut at 45 degrees across using a wallpaper straight edge and snap off knife, cut though both pieces and remove excess from under the large drop just hung and the excess from under the small length just hung), then again crease at the window frame and neatly trim.
The remaining lengths should also be short pieces that only need to be long enough to cover from ceiling to the underside of the top window reveal, again trim them neatly against the window frame. Have a look at the following images to help you visualise the method.
When you reach the point where the reveal on the opposite side of the window is less than one full width of wallpaper away from the edge of the last length hung, you should stop and repeat the paperhanging process under the window from the sill to the skirting board, trimming neatly as you proceed.
Completing the Reveal:
You are now able to move on to the next full length, work in the same way that you hung the first side of the window.
You should first use the plum bob again to get your truly vertical line to work back from, this may mean the final length to complete the reveal hangs over the last pieces you hung, both above and below, the window.
You'll then need to trim any overlap on the final window length if needed (this will the allow the rest of the lengths on this wall to be hung truly vertical).
You'll often find that this final length does not fill the entire reveal at the side of the window - if this is the case, then you will have to cut matching strips to fill in the gap. Both in the side window reveal and above the window... Good luck, it's all in the practice.