No_3_October_1963 — Page 125

HHHH

(a) Bridging by earth

(c) Bridging by rendering

Water-resistant floor finish

Porous screed

HARHHH

(b) Bridging by path

(d) Bridging by mortar pointing

(e) and (ƒ) Bridging by floor screed

(g) Bridging by mortar dropping

in cavity

on

મ

walls. there is no such regulation for solid floors. Some solid floors incor. porate damp-proof membrane beneath the floor screed, others rely

the floor finish to serve as moisture barrier. Unless care taken, it may be possible for the screed, which is usually porous, to transmit moisture from the wall be- low d.p.c. level to that above (Figs.

120

IS

Screed

D. P. C.

Fig. 2. (a)–(g) Bridging of damp-proof

course

2e and f). With this form of con- struction the position of the mois- ture barrier must be carefully plan. ned and a vertical d.p.c. may be needed to join the wall d.p.c. to the membrane in or on the floor.

REMEDIAL MEASURES

be

No hard and fast rules can laid down for the treatment of ris-

ing damp; the measures decided on will depend on the cost and estimat- ed effectiveness of the treatment, as seen against the value.

the value, condition and probable life of the property. Some of the causes of rising damp- ness described above can be dealt with fairly simply for instance. earth or paths above d.p.c. level, or rendering or pointing bridging the d.p.c. but where there is no is damp-proof course, or where it defective, more radical measures are necessary. There are three possible approaches to the problem.

First. a complete moisture barrier may be provided. by inserting a d.p.c. this should lead to a per- manent cure. There are also various proprietary methods that aim to produce a d.p.c. by the injection of water-repellent substances: these are probably more appropriate for walls too thick or too unstable for a con- ventional d.p.c. to be inserted. Secondly, it may be possible to re- duce the amount of moisture in the wall, by hindering the access of water to it and by increasinng eva- poration from it. With any of these measures, it will also be necessary to replace any decayed plaster and remove accumulated salts.

Thirdly, many of the methods available for dealing with walls heavily contaminated with salts can be used alone to conceal the rising damp. These involve battening out or lining the inside of the wall, or using various barrier layers which prevent the damp and salts affecting the decorations. The rising damp is not stopped by such measures, and will often be driven higher; but where it is causing no structural damage such steps are useful where the property has a limited life or more drastic treatments are too cost- ly. It may, of course. he appropri ate to use measures of the second category reducing the moisture content of the wall in conjunction with such a lining treatment.

METHODS TO PREVENT RISING DAMP

Inserting damp-proof courses

The traditional method of insert- ing a damp-proof course is to cut out a course of bricks, a short length at a time, and replace it by a course of dense engineering bricks or slates, Digest 107 (first series)

THE HONG KONG & FAR EAST BUILDER-VOLUME 18, NUMBER 3

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