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Decorating Defects - their cause and cure

Faults in Paperhanging

Faults in paperhanging may arise from carelessness or bad workmanship, but are frequently due to insufficient familiarity with the characteristics of the different types of wallpaper and failure to adapt the technique to their individual properties. The following are the defects most likely to be en­countered:
Bad Joints.-These may result from incorrect trimming, excessive use of the seam-roller, or not making sufficient allowance for the shrinkage of the paper when it dries. Friction caused by a too vigorous pressure of the roller will produce a sheen on the joints, emphasising their presence and making them too much in evidence.
Blistering.-Faulty pasting or the employment of too weak an adhesive may result in the formation of blisters, which may be caused, also, by in sufficient use of the smoothing-brush after the paper has been hung. The trouble often occurs with embossed papers which must be smoothed with caution lest their raised portions are unduly flattened, but care must be taken that, so far as is possible, the air is effectively expelled in all areas where the paper makes contact with the wall surface.
Darkening at the Joints.-This defect is mainly confined to those papers which are varnished after having been hung, and is the result of faulty sizing which permits the varnish to penetrate behind the joints, the oil in it staining the paper. Two coats of size should always be given to prevent the possibility of " misses" occurring. The trouble is especially liable to take place if the joints of the paper are bad, e.g. if they lap slightly or do not butt closely; in such circumstances, the size may bridge over them, and, in drying, contract so that it does not form a continuous coating.
Again, if the adhesion of the paper generally is not good, the shrinkage of the size may exert sufficient pull to cause the edges of the length to curl outwards slightly-possibly to such a small extent that it is not easily detected, but sufficient, nevertheless, to allow the varnish to "strike" through at the paper. There is no cure for this defect and it will be necessary to strip the wall and repaper.
Delay in Drying.-This may be caused at times by over-soaking the lengths or by the use of too fluid a paste, but more frequently takes place when the paper is hung on an impervious ground, such as old paintwork or old varnished paper.
That a paper hung on a surface of this kind takes rather longer to dry is due to the fact that owing to the impermeability of the ground, the moisture in the paste must evaporate outwards through the paper, whereas, when the wall has a certain amount of porosity, some of the moisture is absorbed by it.
It is important to remember that in such circumstances drying out will be slower, especially when the paper is subsequently to be varnished. The application of varnish over a paper which is still slightly damp may induce blooming.
Effiorescence.-This defect takes the form of patches of a white powdery substance on the face of the paper. For information on the conditions which may occasion it.
Fading.- The fading of wallpapers is usually due to the use of fugitive colours in their manufacture, and is thus beyond the control of the decorator. On occasion, however, it may be caused by the addition of too much alum in the paste, as a result of which some of the more delicate colours will be affected.
On new walls, fading, bleaching, or discoloration may take place as the result of the action of free lime in the plaster which attacks certain colours which are not proof against alkali. As a rule, greens and blues are particularly liable to be affected. It is wise, therefore, to postpone papering new plaster until the wall has dried out properly and no moisture is present which can actify any alkaline matter which may be present.
Failure to Adhere.-This may be due to poor paste or faulty pasting but commonly occurs when paper is hung over an impervious surface, or over smooth, hard-faced plaster, without a lining paper having previously been used. Old paint or varnish work should be well rubbed down with waterproof abrasive and a fairly strong solution of sugar soap or soda, in order to "cut" the film and provide a key. Hard-faced plaster, such as Parlan or Sirapite, should, when costs permit, always be lined.
If wallpaper, after it has been hung and dried out normally, tends to detach itself and come away from the wall, the trouble can nearly always be traced to damp. If this occurs on an outside wall only, it is usually due to penetration of moisture through the wall structure, in which event the paper will probably show water stains on both sides. If the other walls in the room are also affected in this way, it is reasonable to suppose that the defect arises from condensation or perhaps from the presence in the plaster of hygroscopic materials, though in the latter event, the paper will probably be bleached in patches.
Joints Springing.--See "Failure to Adhere" above.
Mould.-On occasion, mould growths may make their appearance on papered walls, usually in the form of black spots, though the colour may vary according to the species of the mould, the spores of which find nourishment in the paste, size, or paper itself. For further information on the conditions which induce this defect and on suitable treatment.
Shadiness.-Rolls of wallpaper of the same pattern but made from different reels of raw material may show slight variations in tone or hue when the lengths are hung, though such differences may not be very evident from a superficial examination before hanging. Careful comparison should therefore be made and sorting carried out so that adjoining lengths on anyone wall are as uniform in appearance as possible. Any discrepancies which may occur in the paper itself can usually be minimised by reversing alternate lengths when hanging.
Stains and Discoloration.- The most common form of discoloration is from paste getting on to the face of the paper, due to carelessness in pasting or slovenly workmanship. (Any paste which happens to get on to adjoining paintwork should be at once wiped off while it is still wet, since in drying it will contract strongly and may cause cracking and flaking of the paint.)
Discoloration due to damp walls or to alkaline action has already been discussed above. Soiling may also arise from dirt deposition, which can be removed with fair success by means of bread or other cleaning agents , though a good deal will depend on the hardness and texture of the paper. Fine dark lines or streaks on the paper-especially on or near the chimney-breast-usually denote hair cracks in the plaster under­neath.
Shrinkage.-All wallpapers expand in a greater or less degree when made' wet with paste and contract again in drying, but certain types are more susceptible than others to these movements.
Paste for those which tend to shrink excessively should be on the stiff side and well brushed out, or there will be considerable risk of trouble from bad joints. Paperhangers often try to save time by pasting four, five, or even more lengths at once, and while this may be practicable with certain types of paper, which need a good deal of soaking, it cannot be safely done with others.