Plaster Walls and Ceilings

LIME plaster, as used by the builder, consists of slaked lime and sand impregnated with hair; the lime must be thoroughly slaked before use. Too-hasty use of the lime results in the presence of many unslaked particles which later may bubble and spoil the work. For this reason the handyman can, if desired, use one of the many alternative proprietary brands as they may be found easier to handle than the slaked lime plaster which requires much preparation and some delay. For all plastering, the surface must be well wetted, and all loose material, or old crumbled plaster, must first be removed.


Internal walls are plastered in three stages, the first coat being 1 in. in thickness of hair mortar, employed to roughly level the surface beneath. The second or floating coat of mortar, ½ in. to ¾ in. thick, is intended as a true levelling coat, and the final or setting coat is a io’n- to ½ in. layer of fine white plaster, designed to produce a smooth, hard surface. This finishing coat is also occasionally known as a skimming coat.

A good mortar contains three parts sand to one of lime, mixed to a stiff paste with the necessary water. Strength and tenacity are improved by adding one handful of soft, chopped hair or fibre to one bucketful of mortar. To accelerate setting, place the amount required on the mixing board, make a hollow in the centre and add plaster of Paris (one part to eight of mortar); mix with water, then combine the whole mass: this latter method should be adopted mainly for small areas of repair. The final coat may consist of one part slaked lime, one part plaster of Paris to two parts fine sieved sand. The less plaster of Paris mixed in, the slower will be the setting characteristics.

Lath and Plaster Partitions

In the case of partition walls covered with plaster on wooden lathing, make a close examination to discover the cause of any evident defect. The laths may be loose, decayed or broken, or the woodwork supporting them may have warped or twisted. In bad cases a suitable area of plaster must be cut away to expose the laths where these are nailed to the nearest studs, so that faulty laths may be replaced. Laths can be bought at a builder’s merchant, and should be matched for thickness with those of the partition. If laths are broken, cut them by a hammer and 1 in. chisel, midway on a stud of the partition, so that room is left to nail the end of the new piece there, and also the existing end of the old lath that has been left. In some instances it may be possible to do this without altering the position of the nail in the existing part of the old laths.

In dealing with old partitions it may be found that an attempt at extensive repairs may bring down adjoining areas of plaster. If this happens it will be fairly evident that the main area of plaster has badly deteriorated.

When, for example, the existing plasterwork crumbles away at a touch it is futile to attempt localized patching; the entire area should be stripped and re-plastered, a task that may require the services of a builder. The lathing having been made satisfactory, brush all dust and fragments of plaster from the bad portion. The plaster may be applied in two layers if the patch is fairly small, a coarse one which should adhere to and protrude behind the laths, and a fine coat which is to go on top and make a smooth surface. Before plastering, cut back the lower layer at the edges of the patch, so that the new plaster gets behind the old top coat and forms a kind of dovetail ‘key’ to the surrounding plaster-work; this can be done with an old, pointed kitchen knife. See that the spaces between the laths are freed from old plaster, leaving an interstice through which the new material may be forced so that it exudes at the back and spreads out, forming a key to the lathing and holding the plasterwork securely.

Material for the Patch

To repair a small hole, and for defects in plaster at corners or by door or window openings, use a quick-setting cement which may be obtained from a builder’s merchant. Several brands of quick-setting cements suitable for this type of repair are available under trade names. Keene’s cement, a preparation of plaster of Paris and alum, calcined and powdered, is an admirable example. Manufactured in two grades for rough and fine coats it sets to great hardness and strength in a few days. Of the two grades, coarse and fine, the latter is white and the former pink in colour. For small jobs it can be applied as a single layer to fill completely the hole or crack, the holes or cracks being cut back at the edge as described above. Parian cement, prepared from a combination of gypsum and borax, is another quick-setting cement which sets in about five hours. Another material that can be used for small jobs is pure plaster of Paris; it sets very quickly indeed and does not permit long for smoothing off after application. Proprietary quick-setting plasters can, of course, be used in extensive repairs for both under layer and top coats.

Quick-setting plasters should be mixed and used strictly according to the maker’s instructions. In one brand, for example, the plaster has to be mixed with an equal quantity of sand for use on lath work; for solid walls (no laths), two parts of sand to one of plaster are advised. Usually such plasters are recommended only when the space between the laths is not less than a ½ in.; however, the spacing is generally ¾ in. The proprietary plasters are sold in coarse and fine grades, and some also in haired plaster. Hair, it should be noted, is introduced into plaster not only to strengthen, but to bind the material together and is recommended for ceilings on that account. Enquiry of a builder’s merchant will aid the reader in selecting the best preparation for the nature of the work or repairs to be undertaken.

Method of Procedure

Spread a diist sheet or newspaper below the portion of wall to be treated. Damp the surface of lathing and the edges of the hole with a brush and water; a wide distemper brush is most suitable for large patches. Mix the plaster on a board, being sparing with water until it is seen, by experience, how the material works up. A brick trowel will do for small jobs, though a flat (plasterer’s) trowel would be more convenient for larger areas. Lay on the plaster, and press it well into the lathing, until a fairly level surface is produced up to the thickness of the surrounding under- layer. Score the finished work as, making criss-cross lines to increase the_ adherence of the next- coat, which will be applied several hours later, or next day, according to the setting characteristics of thef’£- ‘ plaster. To complete the job, damp the surface and edges with the brush and water if the top coat is applied next day; lay on the finishing coat, and trowel it off level with the adjoining surface. When using the trowel keep it wet with water, but do not resort to an excessive use of the trowel or it may be found that the patch will sag.

For small patches and other minor defects, damp the work well and fill in with the plaster selected. On solid walls the procedure is generally the same, except that a good bond should have been secured by roughening or pock-marking the surface to form a key, and by raking out the mortar joints. In patching the work, damp it well having first cut back the edges and brushed away all dust. In some cases it will be found upon removing the defective plaster that a metal mesh is secured to the wall. This mesh, which is another form of key surface, must be thoroughly cleaned and brushed, before applying new plaster.

Walls and. Ceiling Stains

These are usually met with in bedrooms and attics, and are commonly due to dampness arising from defects either to roof or gutter. See also WOODWORM AND DRY ROT. Smoke and soot may also cause discoloration as, for example, in old houses where the accumulated deposit may impreg- nate a plaster ceiling and this cannot be removed by washing.

The treatment of all stains consists of curing any dampness (at the source) and then sealing up the affected part by coating with flat oil paint, oil-bound distemper, or white shellac varnish. If this precaution is not taken, the stain will continue to strike through any number of coats of distemper. Where a ceiling is to be papered, it is better to use one of the many excellent damp preventive paints as a sealing agent.

Cracked Ceilings

Cracks may develop as a result of vibration caused by heavy road traffic, or by the natural settlement of a building. The treatment will depend upon (I) whether the crack is of a simple character, I.e. with both edges level, or (2) is of the more awkward type with one edge higher than the other. In either case it is necessary to wash off the old distemper or strip off any paper so as to produce a clean surface, before commencing repairs. Cut away the plaster at the sides of the crack, making a slight undercut, following the line of the crack. The area should be made wet with clean water brushed into the gap, then stopped or filled with, for instance, Keene’s cement, or plaster of Paris mixed with weak glue-size. The more thoroughly the plaster is worked in the recess, the less likelihood is there of further cracking. Finish it off flush,.

Where the edges of a crack are out of plane, I.e. not on the same level, the best and only permanent job is to cut out or widen the crack in order to disguise the fault on the surface.

It requires some courage, but the wider the channel cut out the more gradual will be the unavoidable slope, connecting the two edges.

The alternative would be the rather risky expedient of bevelling with plaster to build up a slope from the lower to the higher edge; perhaps with disastrous consequence when the door slams.

Sagging Ceilings

It is not difficult to ascertain the cause of this trouble, but the remedy is sometimes very simple. Occasionally, however, it involves the temporary shoring up of the affected part. It is a job within the capacity of the handyman, but a matter for careful discretion.

First of all, find out whether the ceiling is of lath and plaster, plaster-board, or of the plastered, re-inforced concrete type.

If of the last-named class, the structure will, usually, be sound, and making good consists of hacking down the defective plaster and replastering with one or two coats according to the thickness. If lath and plaster ceilings sag and there is evidence of floor sag in the room above, strut with wedges. Remove the floorboards in the room above, where the sagging occurs in the ceiling of the room below, and investigate the cause. If light hand pressure, however, will restore the plaster to its original position it is probable that only the plaster keying or laths, not the floor joists, have broken, and the former method of inspection should not be resorted to. Small areas of plaster may be nailed up to the joists with clout nails driven below the level of the plaster, and covered with plaster afterwards to conceal their presence. If serious sagging of the plaster or breakage of laths has occurred, the whole area of plaster must be removed, the laths replaced by new ones and plastering carried out as described previously. Plasterboard which may have come away from the ceiling joists may be made good by large-headed galvanized nails, along the line of the joists. While considerable pressure may be necessary to push back the bulging part, it must be remembered that this material is very brittle and easily damaged, therefore be particularly careful not to break the plasterboard when countersinking the nails or screws.

Where, as previously mentioned, severe sagging of the plaster exists, due to structural defects, the ceilings must first be shored or propped up from below and then secured or strengthened from above,.

A weak or broken joist will require a five foot length of 4in. X 2 in. timber bolted to one side to serve as a permanent splint. It is advisable to use preservative-treated or new sound timber for repairs of this type, thus reducing the risk of dry rot.

Hangers or short struts of wood are also quite effective as a means of supporting warped or sagging joists . Where the rafters are too old and weak to take the strain, an 8ft. Length of 4 in. x 2 in timber may also be fixed across the top of the joists and will provide means whereby shorter struts can be secured. It will help considerably, when working in a loft, to use any available spare boards as temporary planking, thus reducing the risk of further damage to ceilings immediately beneath.

Plaster Mouldings

Repairs are not easy. Small repairs may be made good in the following manner. Remove the defective plaster and treat the area as previously described for filling small areas. Apply plaster to the area and, using a metal straight edge that overlaps the extreme length of the patch, draw it lightly over the contour.

Another method is to draw a template, cut to match the contour of the moulding, over the plastered area; but the moulding must be simple.

The extensive repair of a heavily ornamented moulding is a highly skilled job, involving the manufacture of plaster moulds to match the form of the moulding, and a specialized understanding of the principles and materials involved. If the moulding is badly affected, it is advisable to obtain the services of a competent plasterer.

Papering a Ceiling

The important essentials for a beginner are: (I) good preparation of the surface; (2) good paste; and (3) a ceiling of less than 9ft. Across. Both (1) and (2) together with the use of tools and equipment.

White lining paper needs no preparation, but patterned paper requires trimming, I.e. the complete removal of one, and the partial removal of the other, selvedge. The pattern can then be matched arid the lengths cut, allowing a few inches at the ends for waste. Two step ladders and a plank form the scaffolding, and it is best to work from right to left when hanging the paper. A straight cornice mould is the best guide line for the first length, but where no cornice exists it will be necessary to rule a pencil line 2o1 in. away from the wall, and hang the first length in the reverse direction, taking care to keep the selvedge edge along the pencil line; other lengths are hung from right to left.

Pasting and folding must also be worked from right to left, to achieve the result indicated; it will then be easy to support the paper upon an odd roll held in the left hand, with the thumb gripping the folds. By employing this method it will be possible to release one fold at a time as required. The right hand remains free to unfold and attach the first few feet of paper to the ceiling and then to apply the remainder by brushing. See also PAPER AND PAPERHANGING. Waste ends should be systematically trimmed 0 so as to ensure a clean and accurate finish.

The main points to watch when papering a ceiling are: (a) to prepare each length of paper carefully if wall projections have to be negotiated; (b) do not overload the paper with paste; (c) do not use a stiff narrow smoothing brush.

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