IN its simplest form, distemper is probably the oldest kind of paint in existence. Many primitive peoples used coloured earths with a water-soluble binder for wall paintings and other decorative purposes, and even to-day, what is usually described as ‘ ordinary ‘ distemper consists, in essentials, of similar materials. Its popularity in this and other countries is still very great, though the latter has, to some considerable extent, been affected by the introduction of oil-bound and other types of washable distemper or water paint.
No doubt much of this popularity is due to the fact that distemper, or colour wash, as it is sometimes called, is cheap, made of ingredients which are readily available, is easily prepared and quickly applied, but it has other advantages which should not be overlooked. It possesses great opacity, is hygienic, gives pure tints and a pleasant mat coating, is fire-retarding, and can be speedily and inexpensively removed when it is no longer required. Against this must be set the fact that it is very susceptible to damp and consequently cannot be washed or used on exterior work and that, from the point of view of durability, it does not compare favourably with most other forms of applied decoration.
Ordinary distemper, as made up by the painter, consists simply of whiting, glue size, the necessary pigments for tinting, and water. If the best results are to be obtained, more care should be exercised in selecting the first three of the materials mentioned than is usually shown. It is well worth while to pay a little more and get a good-grade gilders’ whiting; cheap whiting is frequently a poor colour, contains an excess of moisture and too many impurities – mostly of an alkaline nature. So far as the binder is concerned, either cake glue, concentrated size, or jellied size will serve, but whichever is preferred should be of good quality and prepared by a reputable firm. Low-grade glues are frequently adulterated and erratic in both their setting and adhesive properties.
Mixing Size Distemper
There are minor differences of opinion as to the precise way in which distemper should be mixed, but the following represents the method very generally adopted.
Break up a sufficient quantity of whiting into small lumps, place it in a clean vessel and add sufficient cold water to cover it well. Let it stand until the whiting is thoroughly soaked, which may take a few hours. In another vessel prepare, by melting, the size or glue which is to act as binder, and in a third, place the dry distemper colours which are to be used for tinting, and add water to reduce them to a paste.
Before adding the size and the colouring matter to the whiting, all water which has not been absorbed by the latter should be drained off, and the whiting beaten with a clean paddle or stout stick until it is free from lumps and of the consistency of stiff cream. Many painters prefer to knead the whiting with their hands and this is quite a satisfactory method, always providing their hands are perfectly clean. Now add the colour, stirring well in and pouring it in a little at a time until the desired shade is reached.
The pigments should never be added in dry form; if this is done, there is some risk that they will not be uniformly distributed throughout the mass, with the result that, when the distemper is applied, streaks of darker colour will be left on the surface. The size, which should be warm rather than hot, should then be added slowly, stirring all the time. Finally, strain the mixture through a distemper strainer or cheesecloth into a clean container and allow it to get cold; it should not be used until it reaches this condition.
The proportion of binder to whiting will depend primarily on the strength of the size as well as on the amount of water which the whiting has absorbed, and both these factors are subject to considerable variations. It is consequently difficult to give any precise guidance on this point, but, on the average, about half a pound of concentrated size to every six pounds of whiting should be a suitable proportion. Experienced painters can usually tell, by the way in which the material works under the brush, whether approximately the right amount of binder has been added; if, on starting work, the mixture should prove too thick, a little cold water can be stirred in.
Owing to the size content, a distemper made in this way will not keep sweet indefinitely, particularly if the weather is at all hot. It is highly desirable that a little carbolic acid, formalin, or similar preservative agent should be added, in order to prevent decomposition.
Some painters are in the habit of adding alum to their distemper; this has the effect of hardening the binder and making the coating less soluble, but, because of this, of making it more difficult to wash it off when the time comes round for renewing the decoration. Alum does not agree with all the pigments commonly used for tinting distemper; so long as it is not added to excess, it probably does little harm, but, on the whole, its incorporation is not to be recommended.
Colours which may be Used in Distemper
Only certain pigments can be used with distemper, as the whiting, being slightly alkaline, may affect the others. Following is a list of those colours which may safely be used, and as these may be mixed, a large variety of different tints and shades can be obtained:
Sienna, raw and burnt.
Umber, raw and burnt.
All the black pigments.
In mixing the particular tint required it must be remembered that distemper is very much darker when wet than it is when dry. By painting a little on a piece of paper and holding it at the fire, the tint when dry can be more or less accurately ascertained.
Before distemper is applied to a surface, whether the latter be new and untreated or an old ground from which the existing decoration has been stripped, the suction must be equalised, or, if too great,-partially satisfied. This is done by means of a coat of clairecolle – also spelt ‘ clerccole,’ ‘ clearcole, ‘ and in other ways – which may be described as a kind of undercoating for size-and-whiting distemper, and which is made in a manner similar to that in which distemper is prepared, but with a far greater proportion of size or glue. Here, again, no exact figures can be given, but for most purposes, three pounds of whiting will require the addition of about two pounds of concentrated size, or about half that quantity of glue, but these amounts are subject to adjustments according to the porosity of the ground.
Many painters continue to knock up ordinary distemper in their own shops or on the job, but it is also available ready-prepared, in paste or powder form, needing only the addition of water to reduce it to working consistency. One advantage of the factory-made article is that, if manufactured by a reliable firm, it ensures that the proportion of binder to pigment is correct. This is important because if there is too little binder, the coating will lack strength and rub off easily, while if there is too much, there will be a tendency for the coating to crack and flake, owing to too great a degree of contraction in drying.
We turn now to the class of material known as washable or sanitary water paint or distemper. These were introduced to supply a demand for a finish which would be cheaper in first cost than oil paint, would, like size-and-whiting distemper, be capable of being quickly and easily applied, but, unlike it, would have rather more resistance to moisture, so that it would provide a coating which, to some extent, would be washable.
Washable distempers differ widely in formulation according to the ideas of the firms which make them and represent far more complex mixtures than do ordinary distempers. The pigment portion consists of such whites as barytes, Paris white, blanc fixe or zinc white, with the addition of coloured pigments which are not affected by alkali ; for the vehicle, a variety of ingredients is employed, among them linseed oil, casein, soft soap, glue, and, on occasion, varnish – sometimes in the form of varnish ‘ foots.’
While the composition varies according to brand, washable distempers can, broadly speaking, be divided into two main classes: oil-bound distemper and casein-bound distemper, although a proportion of casein may also be employed in conjunction with oil. It is pertinent to add that although some authorities attempt to make a distinction between a washable ‘ distemper ‘ and a washable ‘ water paint/’ in practice no hard-and-fast differentiation seems to exist, so that the two terms may be regarded as interchangeable.
In oil-bound distempers, the medium consists principally of oil, such as linseed, which is converted into a soap by means of a suitable alkali and thus made capable of mixing with water. This type of distemper is widely employed and is put up in paste form, to be reduced either with water or with special thinners, known as petrifying liquids, to make it suitable for application. After it has been brushed or sprayed on to the surface, the binder gradually oxidises and a hard film is formed which has some resistance to moisture, although, compared with one of oil paint, it is relatively porous.
In good-quality oil-bound distempers, little or no whiting is used, for this pigment, though very opaque when mixed with water, becomes semi-transparent in oil; any substantial proportion of it would consequently reduce the obscuring property which is so valuable a feature of all distempers. If the distemper is made by a firm of repute, it may generally be assumed that all pigments employed are proof against lime and that most of them are also fast to light.
Oil-bound distempers can, as stated above, be thinned either with water or with petrifying liquid. The latter varies greatly in formulation according to the firm which prepares it, so that it is necessary to use only the brand made expressly for the particular make of distemper which is being employed.
Petrifying liquids have the effect of reinforcing the binder and of introducing additional vehicle into the mixture ; they should be used in preference to water for thinning purposes where the surface is unduly absorbent, or where there is considerable local variation in the suction. On very porous groundwork, it may be desirable, at times, before applying the distemper, to give a preliminary coat of petrifying liquid or, again, the latter may be used as a binding agent on plaster which is inclined to be friable.
Oil-bound distempers are frequently used on exterior surfaces, such as brickwork, in which case they should be thinned with petrifying liquid to improve their weathering properties. Although the coating they provide is rather less durable than one afforded by an oil paint, it should be capable of withstanding exposure, if it is of good quality and properly applied, for two or three years under normal conditions, without disintegrating to any great extent. Being more porous than oil paint, however, it does not possess the same waterproofing qualities.
It should be noted that clairecolle, which, as already explained, is employed as an undercoating for size-and-whiting distemper, should never be used for this purpose beneath a washable-type distemper ; if an under-coating is necessary for this type of finish, either petrifying liquid by itself should be used, or the first coat of distemper should be thinned with the latter, in place of water. Special priming sizes are also available from some manufacturers.
Casein is derived from milk and is prepared in the form of a fine white powder. It is not soluble in water alone but can be made so if a small proportion of a suitable alkali, such as borax, is added to the water ; it then dissolves to a thick, transparent viscous material with strong adhesive properties. Washable distempers in which casein provides the major portion of the binder are sold in stiff paste or in powder form.
As a general rule, washable distempers can be safely applied on strongly alkaline surfaces such as those of Portland cement or lime plaster, although, in the case of oil-bound distempers, there may be some slight danger of the oil content of the binder being attacked and saponified by the free lime. With the casein-bound type, this risk is avoided, since the casein combines with alkalis and is thus unaffected. Once a distemper of this kind has dried out, there is little or no further change in its chemical composition.
Although both oil-bound and casein-bound distempers are correctly described as ‘ washable,’ this description should be interpreted only in a modified sense. They are not, for instance, scrubbable; they can be cleaned by sponging with a damp cloth wrung out in lukewarm water, with or without the addition of a mild soap or weak solution of sugar soap, but more than this should not be expected of them, and any more vigorous treatment will result in the loosening of surface pigment particles. Decorators would do well to impress this on their customers who, because of the description ‘ washable,’ sometimes attempt to subject coatings of this kind to the same kind of cleaning methods as are used on films of oil paint, with unfortunate results. It may be observed that most coatings of washable water paints take some time to harden and do not reach their maximum degree of hardness until about seven or eight months after application. Their ability to withstand washing is in proportion to their hardness, so that in the first few months of their existence they must be treated very gently.
Preparation of the Surface
The ground over which distemper is applied should be clean and dry. If an ordinary distemper has previously been used, care should be taken that the washing off is thorough and that no remnants of it remain on the surface, or the adhesion of the new coating will be affected. Similarly, if the plaster has been papered and the paper has been stripped off, see that the surface is free from traces of paste or size. Notes on the stripping of old washable water paint have already been given proves successful is to use a casein type of distemper, which should cover solidly and prevent the stains from bleeding through. If this material is employed, it is essential that the distemper should be of a type containing a high percentage of casein.
Application of Distemper
The application of distemper, although it does not involve any very great skill, demands a certain amount of method and dexterity if the best results are to be obtained.
The brush used may be a distemper brush of the flat, two-knot or three-knot type, according to preference, and should be as large as can conveniently be handled on the job, though it should be remembered that though a heavy brush will probably take up more material, it will also be more tiring to use – a point worth bearing in mind if large areas have to be decorated.
Before work begins, take the usual precautions to ensure that all furniture, etc., is properly protected by dust sheets ; it is a good plan to cover the floor for a foot or two nearest the skirting with old newspaper, particularly if it happens to be polished or stained. Keep a watchful eye open all the time for any splashes of distemper which may fall on woodwork or surrounds, and have a damp sponge or cloth ready to wipe them off as soon as they occur ; if they are allowed to harden, their removal may be difficult.
All windows and doors should be shut during application to prevent movement of air which would hasten the drying too much. Begin the work from the main source of light, which, in most cases, will be the window, Apply the material freely, covering only a small section at a time – say, a strip from 12 to 18 in. wide, taking care to keep the edges ‘ alive,’ so that distemper applied to the next section blends into it without showing any laps or joins. Take care, also, that there are no ‘ misses,’ for it is not easy to touch them up later on without a difference in texture being evident, once the work has begun to dry. Use only the tips of the brush and swing it over the surface in any direction lightly and freely. Make no attempt to cross the work, as when oil paint is being used.
As soon as the whole of the surface has been covered, open the windows and doors and allow as much ventilation as possible.
Grounds for Distemper
Distemper can be used on plaster, cement, brickwork and similar surfaces, and on certain types of wallboard. It is not successful on woodwork, though it is sometimes applied to it when a cheap, temporary decoration is wanted, as on exhibition stands ; it is, on occasion, used as a primer on woodwork, under oil paint, in order to check any tendency of the latter to blister. Its application over various types of existing decoration will be described later on in this post.
The best type of ground is one which has uniform but moderate porosity. If there is too much suction and the distemper is applied direct, too much of the vehicle will be absorbed, leaving on the surface a coating of underbound pigment which will have little adhesion and will soon flake. It is easy to tell when there is too much porosity as the distemper will not work freely, and, in extreme cases, tends to pile up under the brush.
The suction must be partly satisfied before the distemper is put on. This is done by means of a coat of clairecolle, when ordinary size-and-whiting distemper is being used, or by one of special priming size or petrifying solution (preferably with the addition of a little of the distemper itself), when one of the washable type is being employed. As an alternative, in the treatment of interior plasterwork, a coat of clear size may be applied to the surface, which is then hung with lining paper; this makes an excellent ground for the distemper.
If, on the other hand, there is too little suction in the surface and the distemper is applied directly to the latter, flaking is also likely to occur at an early date. The material will go on easily enough and dry out normally, but unless it receives some help from the texture of the ground and this provides a certain amount of key, the coating will have no real gnp.
Hard-faced plasters, such as Parian, often give trouble in this way, especially when, as is not infrequently the case, they have been trowelled to a smooth, marble-like finish, and it is not unusual to find that flaking takes place, again and again, within a few months of application. The difficulty can generally be overcome either by fining the walls or by applying a coat of special priming size, as made by most of the leading makers of distemper. In such instances, however, it is questionable whether a coat of flat paint will not prove a more satisfactory alternative to a distemper finish.
Distempering over Wallboard
Many types of wallboard offer a good ground for distemper, the only preparation needed, so far as the bulk of the surface is concerned, being a coat of size to satisfy suction. The main complication likely to be encountered by the decorator is how to prevent the joints of adjacent boards from being too conspicuous.
The easiest way of doing this is by means of mouldings, but this may not always be feasible. It is useless merely to level up the joints with stopper, because atmospheric changes will cause a certain amount of movement in the wallboards and this will displace the stopper. One method is to line the wallboards with paperhangers’ canvas or scrim , hang lining paper on top of this, and then distemper.
This, though sound practice, is expensive. A cheaper process, which is quite effective if carefully carried out, is to fix strips of cheesecloth, about 6 in. wide, across the joints; to do this, first apply size to a strip of wallboard about four inches wide on either side of the joint and, when this is dry, coat it with stiff wallpaper paste and roll the length of cheesecloth into place, pressing down well. When dry, apply a coat of size. After this is dry, take strips of lining paper at least two inches wider than those of the cheesecloth and hang them over the latter, using paste of fairly stout consistency. When they are in position, turn up the edges on either side to a depth of not more than an inch. When the paste has dried out, tear off these turned-up edges; if properly done, this will leave an irregular edge which will not show through the distemper, after this has been applied, so definitely as would one which had been clean cut and sharp.
Previously Decorated Grounds
If a surface previously finished in size-and-whiting distemper is to be recoated, either with similar material, with washable distemper, or, in fact, with any form of applied decoration, it is imperative that the existing finish be removed – a task which should not involve any great difficulty, since ordinary distemper yields easily to water, particularly if the latter is warm and a little sugar soap or soda is added. It is quite useless attempting to apply the new finish on top of the old, since the water content of the new will soften the size binder of the old and loosen the film, which will be detached by the subsequent contraction of the new distemper when it dries.
Although ordinary size-bound distemper can be washed off without trouble, the removal of old washable water paint often presents something of a problem to the painter, unless he possesses one of the steam-generating stripping appliances, designed primarily for removing wallpaper but equally effective in the case of water paints. It will frequently be found that though old washable distemper is flaking from a wall in parts, the bulk of it remains obstinately in place and with-stands the application of hot water or alkaline or acid solutions. In such circumstances, the majority of painters are inclined to apply the new coating on top of the old, and though this can often be done without trouble resulting, it must be emphasised that there is always a certain amount of risk in doing it.
Old paintwork, which is adhering firmly to the surface, can be recoated with fresh paint almost indefinitely, because its natural adhesion is considerable, because comparatively little contraction takes place when the new paint is applied, and because the liquid portion of the latter has very little, if any, solvent effect on the old. Washable distemper behaves differently, when recoated, in all three respects. The strength of its adhesion is far less than that of oil paint, and although the binder of the old coating has some resistance to water, it is affected to a certain extent by the moisture content of the new distemper, particularly if the old finish has been on the wall for some years. Moreover, distemper is applied in thicker and heavier coatings than oil paint ; in drying, it contracts strongly, and, in doing so, exerts a considerable pull on the underlying film, weakening the grip of any parts which are not firmly attached to the surface.
Two, three, or even more coats of washable distemper can, on occasion, be safely superimposed on the original finish, but there comes a time when the weight and strain are too much and the bond gives way. It is not possible to lay down any rule or even to give any indication as to when this is likely to occur; all that can be said is that the application of new washable water paint to an old finish of a similar nature must always be attended by some danger of premature failure.
The situation is further complicated by the fact that not all brands of washable distemper necessarily agree with one another ; the rate of contraction and expansion of one based on an oil-emulsion composition may, for instance, be sufficiently different from that of one based on casein, to cause trouble. Unless the painter has some knowledge of what type has previously been used, it is not possible for him to identify it from a superficial examination, and, in recoating, he may unwittingly use a brand which ‘ quarrels ‘ with what is already on the wall. Instances are not unknown when old washable distemper which has seemed to be adhering firmly to the wall, with no signs of cracking or peeling, has flaked exten-sively within a few weeks of a new distemper being applied on top of it, simply from this cause.
Although the safest policy is always to remove the old distemper coating before applying the new, it is recognised that there are many occasions when, because of the additional cost, this is not practicable. The question then arises as to what treatment can be given to minimise the risk of trouble.
In such a case, the first operation is to remove, by brushing and scraping, all loose matter or any of which the adhesion seems at all doubtful. Rub the boundaries of any bare patches to a feather edge with sandpaper. This done, probably the best course is to apply a thin coat of oil paint. The purpose of this is two-fold: it helps to bind down the existing coating which the oil penetrates and converts, in some degree, to an oil paint, and it also assists in making more uniform, all over the surface, the suction which is bound to be greater where loose material has been stripped.
The paint used should not contain too much oil ; if it does, the coating it provides will be too impervious for the distemper, which is to be applied on top of it, to adhere properly. Nor should it be over-pigmented, for, if it is in the nature of flatting, it will not have sufficient spare oil to penetrate the old distemper.
An alternative to oil paint, favoured by some painters, is to give a coat of what is known as ‘ varnish size,’ made by mixing equal parts of oak varnish and turpentine. In no circumstances should a coat of glue size be given with the idea of binding down the old water paint; far from doing this, it will probably cause it to flake away, since the glue, in drying, shrinks and thus tends to pull away from the surface any parts of the existing distemper which are not firmly attached,
In most cases, for reasons of hygiene, it is desirable to strip old wallpaper before applying distemper to the wall, and when this is done, it is important that all traces of old size or paste should be removed from the plaster before the water paint is applied.
For the sake of economy, however, it is often necessary to apply the distemper without removing the paper, and if reasonable precautions are taken and the work properly carried out, good results can be obtained. One substantial advantage is that saving the wallpaper also means saving on the making-good, for the paper usually conceals hair-line cracks and minor defects which would need stopping. It is arguable, too, that leaving the paper in place comes to much the same thing as lining the walls. Steps should be taken to ensure that the paper is adhering well, and any loose lengths should be repasted and given plenty of time to dry out before the distemper is applied.
One difficulty which may arise is that with some papers, the pattern – or parts of it – persist in showing through the distemper, even though several coats of the latter are put on. This is often the case when the wallpaper in question is printed in oil colours, because the suction of the patterned portion is different from that of the ground. But even in papers printed in water colours the same trouble occasionally arises, due to the nature of the colours or dyes employed. It may be necessary to apply a coat of flat paint or, alternatively, one of shellac varnish, to prevent this, though in such an instance it may prove more economical to strip the paper.
Oil or Gloss Paint
An oil- or gloss-painted ground is far from being an ideal foundation for distemper, but there are times when the last-named type of decoration is required and is preferred to flat oil paint. The difficulty lies chiefly in the fact that the paint film, being more or less impervious, does not encourage the adhesion of the distemper, which is consequently more prone to flake than from a ground which possesses a greater degree of suction.
The best procedure is to break down the gloss of the existing finish and etch the surface by washing with a fairly strong solution of sugar soap or soda, rubbing down with waterproof abrasive and rinsing off carefully before the distemper is applied.
If the old paint happens to be of a flat type, there is less risk of trouble later, since it probably has a certain amount of porosity and rather more texture to afford a key. Even though, in such a case, there is no gloss to be broken down, the same procedure should be followed, and the washing fluid be strong enough to ‘ bite ‘ into the paint film.
Durability of Washable Distemper
Provided the surface is properly prepared, a washable distemper will be reasonably durable in normal conditions, though it compares unfavourably with an oil paint in this respect, since it contains a higher proportion of pigment to binder, and the pigment itself is not so finely ground as that employed in an oil paint; nor has the binder such strength as has the medium used for the latter.
While washable distemper gives good service in living-rooms, bedrooms, halls, and similar interiors where the atmospheric conditions are generally favourable, too much should not be expected from it in bathrooms or kitchens, or in rooms where there is fairly heavy condensation. It is sometimes preferred in them because, presenting a slightly warmer surface than paint, it tends to reduce condensation and also absorbs a good deal of such moisture as is deposited on to it, whereas on films of oil paint, condensation is both heavier and more in evidence. It must be remembered, however, that a washable distemper, however good its quality, has only a limited resistance to water, and that the alternate wetting and drying out, when condensed moisture forms on, and then evaporates from, the surface, progressively weakens the binder and consequently the adhesion of the coating.
An expedient sometimes adopted to prolong its life is to apply over it one or preferably two coats of varnish, either over all the surface or on the lower portion, to act as a dado. This is quite a sound plan for halls, public rooms, etc., where the varnished part takes the rough wear of shoulders pressed against the walls, or for bathrooms, where it offers resistance to water splashed against it. The varnished portion will be rather darker than the rest, but the contrast of colour and texture is by no means unpleasing.
If this treatment is given it is important that the distemper should be perfectly dry before the varnish is applied. Any moisture trapped beneath the film may result in a patchy finish or severe blooming of the varnish, or both.
A cheap form of treatment for brickwork, plastered surfaces, or stone, and extensively used for outbuildings, factories, and workshops, cottage property, and similar structures where a more expensive finish is not required, consists of the application of limewash. In its simplest form, this is made by breaking freshly burned lime into small pieces and adding it, bit by bit, to a tub about half-filled with clean water, stirring it briskly all the time with a stout wooden paddle; the slaking process causes the lime to generate heat and the mixture to bubble up, and the stirring should continue until this effect has ceased. The wash should then be of the consistency of rather thin milk. It is common practice to add a little lime-blue, which should first be soaked in a separate container and added to the mixture; this tends to improve the colour. If desired, the wash can be tinted by incorporating other lime-resisting pigments, such as Venetian red or lime-green, in a similar manner.
The surface to which the wash is applied should be clean, dry, and free from grease. The coating, while still wet, will seem thin and lacking in opacity, but will dry out to a more solid covering.
Such washes have little to commend them except their cheapness, since they have little resistance to exposure and tend to rub off easily. However, they can easily be renewed; in practice this is done almost invariably without removing the old coating, with the result that it is not unusual to find on old buildings, which have periodically been finished in this way, that the coating is of considerable thickness.
In order to make limewash better able to withstand abrasion or the weather, various ingredients are often added, such as oil, glue, or casein, and there are, in fact, a great number of recipes in which one or the other of such materials are used. One of the best is to place a bushel of quicklime with approximately 20 lb. of tallow in a barrel, slaking with hot water and covering with sackcloth, to keep in the steam. If a coloured wash is wanted, the pigment, which must be lime-proof, is added before slaking. When cool, the mixture is run through a fine sieve before it is used.
Another simple recipe is to mix three parts of lime and one of Portland cement, dry, and add the mixture to water, constantly stirring until a thick creamy consistency is reached. Any dry pigments wanted for tinting should be mixed with the dry lime and cement; if the latter is inclined to be lumpy it should be sieved before being added to the water.
It should be added that both the mixtures quoted above were among those tested by the Building Research Station some years ago and reported on, in the periodical Notes issued by the Information Bureau of that body, as having given ‘ fairly good ‘ results on brickwork. They are probably as reliable as any other limewashes, and more so than most.
The behaviour and life of a limewash coating depend, not only on the materials used in its composition, but to some extent, also, on the nature of the surface to which it is applied. On a ground of more than average porosity it will tend to fail fairly soon, owing to too much of the binder being absorbed. As a general rule, too, limewash is more durable on a rough-textured surface than on one which is relatively smooth.
The recoating of limewashed surfaces often gives a certain amount of trouble, especially when five, six, or more previous applications have been made without the old material having been stripped, and in such instances it will frequently be found that the new coating dries out very patchily. This is because, on any building, some portions are more exposed than others, and consequently the limewash disintegrates more rapidly on these; such areas are more porous than the remainder of the surface and absorb more of the binder from the new coating, leaving the underbound lime a lighter shade. So long as white limewash is used, the fault is not obvious, but the use of colour shows it up.
Limewash is without doubt a useful form of treatment and, if properly made and applied, gives good service in view of its low cost. Those who decide to employ it in preference to paint or a good washable water paint should bear in mind that it is far from easy to remove, and that it makes an impossible ground for any other form of decoration, should a change ultimately be required. It is quite true that the use of dilute acid solutions, such as muriatic, will soften it to some extent, but since the acid may damage the structural material and traces of it may attack paint or other coatings subsequently applied, its use is not to be recommended. Prolonged soaking and scraping are the only practical methods of stripping old limewash, and they take both time and money. It is quite hopeless to attempt to paint or distemper on top of a coating of this kind since its porosity varies, its adhesion is never certain, and there is the further risk, especially if paint is applied, that the lime may attack the new film. A good distemper may cost a little more in the first place than limewash, but it should last longer and will probably cause less trouble in after years.