Cottage Building in Cob Pise Chalk and Clay Part 13

Chalk in all these forms, if fairly dealt with and reasonably protected from the weather, is a most amenable and satisfactory material to build with.

The last-named method particularly seems to promise results that should satisfy the most exacting critics of the unconventional, as it a.s.suredly does those who inhabit the cottages so constructed.

The several systems of chalk construction are fully dealt with in the pages that follow.

_Chalk Compost: Historical._--At the Ancient British village on West Down, Chilbolton, some five miles south of Andover, delving archaeologists have brought to light undeniable fragments of chalk "Daub," with the wattle marks still clearly showing upon them.

This discovery is chiefly of academic interest, though it is a pretty refutation to those who regard any building material save brick and stone as "new-fangled," and it should also serve to hearten the doubters and the timid amongst us who seek historic sanction for any departure from current building practice.

_Composition and Uses._--In the Andover district Chalk Compost or "Chalk Mud," as it is called locally, is prepared and used as follows:

The chalk is dug out in the autumn, and the frost allowed to play on it during the winter. In the spring building starts, and the weathered chalk is spread all around the outside of the walls. Straw is sprinkled on it and it is then well trodden, usually by the workers, but sometimes by horses. Sometimes chopped straw is added, sometimes unchopped straw is sprinkled on. The quality of the walls depends very largely on the preparation--that is, in getting the mud to the right consistency--and the old hands know by experience when it is ready.

The compost is lifted on the wall by a fork and another man stands on the wall and treads it in. It is then chopped down straight with a spade. Some of the naked walls at Andover show traces of the courses, which are usually something under 2 ft. in height.

Where a course has to be left unfinished it should be ended with a diagonal ramp so as to splice in with the work that follows.

Some of the old builders seem to have been somewhat catholic in their conceptions as to what const.i.tuted "chalk," and vague patches of earth, loose flints and other stray substances not infrequently mar their work and sometimes seriously reduce its strength.

As a general rule, the finer the chalk the stronger and more durable is the walling.

What is aimed at is a conglomerate of small chalk k.n.o.bs cemented together by a matrix of plastic chalk and straw, the whole forming as dense a ma.s.s as possible.

Grinding in a mortar-mill would probably reduce all the chalk to an amorphous powder, which would not be desirable, and in any case such mechanical mixing is quite unnecessary.

Building by ramming the moist compost between timber shutterings does not appear to have been practised in the past, though there is nothing against the method except its tendency to delay the drying out.

The drying of each course takes several days, depending on the weather.

A course is usually laid right round the building. It must be covered up at night in case of rain, and when it is hard another course is laid on, and so on till completion. The aim is to build during the summer and autumn, and when the moisture has dried out, to render the exterior.

Where brickwork is used with chalk compost it is generally bonded in in the ordinary way, but block-bonding the depth of a chalk course is a better way of doing it.

The exterior corners of chalk buildings are the vulnerable points, and these should therefore be well rounded off.

_Timber._--In the old work nothing seems to have been done to prevent woodwork built in to the compost from decaying, though in many cases it has survived surprisingly. In any new work, however, proper ventilated air-s.p.a.ces should be contrived or the timber ends treated with some preservative.

The door and window frames are fixed to fairly large pieces of wood built in across the thickness of wall, and other woodwork is fixed to wood blocks built in in a similar way.

Picture-rails should be provided in all rooms, as chalk walls are apt to flake and chip if nails are driven into them.

Lintels are usually of wood, and when plastering is carried down over these some form of key must of course be provided to hold it.

[Headnote: Winter Work Barred]

_Frost._--New work must not be exposed to frost or there will be danger of collapse, and winter work is barred out for this reason.

_Repairs._--Chalk compost walls are not easily repaired in that material, and bricks are generally used, well bonded in.

_Chimneys._--Chimneys, too, are usually of brick, though there would seem no reason against the flues being carried up in chalk, especially if clay pipe linings were used.

The chimney-stacks above the roof might well be built in flint, the corners being rounded off in deference to the peculiarities of the material.

_External Rendering._--It is of the first importance that a good weather-tight skin be maintained, and many old buildings have suffered through neglect of this precaution.

The rendering was often of the poorest quality, more mud than lime, and the constant repairs that the indifferent materials necessitated has resulted in many of the old cottages becoming patchworks of variegated plaster blotches, when not whitewashed over, which give an impression of dilapidation by no means warranted by the facts.

_Rendering._--Given a good skin, however, of cement or cement and lime, a chalk conglomerate wall will last indefinitely. So vital is the skin that it is as well to put it on in two good coats--rounding off all the corners and finishing it either with slap-dash or rough from the wooden float.

Also, to ensure its proper adhesion throughout, wire-netting may be used as reinforcement--being secured to the face of the chalk wall by means of cross netting or wires laid on the wall as the building rises.

If the netting be of a fine mesh it also serves as an absolute barrier to vermin, though pounded gla.s.s incorporated in the base of the wall is equally effective.

_Strength._--Provided the wall has dried out thoroughly, any of the ordinary loads occurring in a two-storied house can be borne with ease.

Chalk conglomerate walling, however, has no great lateral strength, and it should not be asked to stand up to thrusts.

The roof, therefore, must be well tied, and should sit on the building merely as a lid.

[Ill.u.s.tration: +Details of Chalk Construction at Amesbury.+ (From a sketch by W. R. Jaggard, F.R.I.B.A., the copyright of the Department of Scientific and Industrial Research.)]

[Ill.u.s.tration: +Chalk Construction at Amesbury, Wilts.+ (From a sketch by W. R. Jaggard, F.R.I.B.A., the copyright of the Department of Scientific and Industrial Research.)]

_Roof._--Though thatch is the traditional roofing material of chalk cottages, any other will serve that is permanent and good of its kind.

The only special demand that chalk walls make is that the eaves shall be generously overhung for their better protection from the weather.

Where, in later years, the boldly projecting thatch has been thoughtlessly replaced by a slate roof with meagre eaves, or with none at all, the walls have suffered accordingly.

[Headnote: Garden Walls]

_Garden Walls._--A chalk garden wall must be afforded just as much protection as the wall of a house and on both sides.

The hat with which it is provided is of the highest importance to the health and longevity of the walling.

Examples of garden wall copings are given in the sketches shown below.

[Ill.u.s.tration: WALL COPINGS.]

_House Walls._--Chalk conglomerate walls rarely exceed 18 in. in thickness, and are usually the same upstairs as down.

A plinth of the same thickness as the chalk wall it supports is usually carried up 6 in. to 18 in. above the ground level in rubble-work, flint, or brick, being known as the "Underpin Course." Any of the stock damp-courses are suitable, but they must be well and truly laid, as damp feet are nearly as deleterious to a chalk wall as a leaky or inadequate hat.

No special tools are required for this method of building, an ordinary farm fork for lifting and a spade for the final chopping down of the wall faces being all that are necessary.

A house built during the summer is usually fit for occupation the same autumn.

_Old Examples._--Those who may wish to see buildings in chalk conglomerate, both old and new, would do well to visit some such typical chalk district as that lying about Andover in Wiltshire.