Unusual moisture problem on interior walls

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Unusual moisture problem on interior walls

NATIONAL RESEARCH COUNCIL CANADA

DIVISION OF BUILDING RESEARCH

UNUSUAL MOISTURE PROBLEM ON INTERIOR WALLS by

D. C. Tibbetts and D. R. Robson

Internal Report No. 235 of the

Division of Building Research

OTTAWA Nov ernbe r 1961

PREFACE

A most unusual moisture occurrence on the walls of one room of a house heated by a ceiling panel system is now reported so that it

may be more widely known and studied. The authors are research officers on the staff of the Atlantic Regional Station of the Division at Halifax, the senior. author as officer-in-charge. In the course of their work of providing a building information service "to the Atlantic Provinces they are able to study and report on field problems as a contribution to the improvement of building in Canada.

Ottawa

November 1961

N. B. Hutcheon, Assistant Director.

UNUSUAL MOISTURE PROBLEM ON INTERIOR WALLS by

D. C. Tibbetts and D. R. Robson

On 2 Sept errib e r 1958, the Station was asked by a local architect to assist with an unusual rnois tu r e p r o b l ern in a rOOITl of a one - story hous e in Halifax. The initial visit to the hous e was rna d e on that date with the architect's representatives. The house was architect designed and at the ti rn e of the investigation was three years old.

The rOOITl in which the wall p r o b l ern exists is app r o xi.rnat eIy

12 by 12 ft and is located in the SE corner of the house (Figs 1 and 2). Darnpn e s s occur s on the surface about 2 ft below the ceiling on all four walls in a continuous band a.pp r o xi m at e l y 6 in. wide. Detailed e xarrrin at i on indicated that this condition does not exist in any other part of the hous e.

The darnpn e s s COITles and goes but is associated with prolonged periods of hurni d weather in SUITlITler. It has never been a p r o b l ern during other seasons. A detailed exarrrination of exterior and interior wall

construction s e ern e d to rule out all possible causes of da rnpn e s s with the exception of surface condensation or adsorption.

The rOOITl is equipped with three double -hung wood windows, two on the south wall and one on the east wall, fitted on the outside with

steel co mb inat ion windows and screens. Windows can be opened top and bottorn in conjunction with st o r m s to provide dir ect or indir ect ventilation. Heating is provided by a hot water radiant ceiling panel s y stern, Water is returned fr orn the panels to the boiler by piping down the outside wall to pipes e rnb e dd ed in the p e rim et e r of the concrete floor slab. The ceiling coils are suspended below g yp s urn lath and covered with rn et a l

lath; the plaster is placed over the rn et a l lath so as to e rnb e d the pipes. The space between ceiling joists above the lath is floored over and well insulated. The heating s y stern rio rrrial l y is operated all year at 72°F. The attic is ventilated by gable end vents. This ventilation is au grn ent ed in SUITlITler by opened windows at either end of the attic (west and east) with a fan also installed near the opened window in the east end. An e xarnin at i o n of the heating s y st ern showed no evidence of leakage. The heating plan revealed nothing unusual in the design that could be related to the particular condition in the affected rOOITl. The s y st ern s e ern e d to be properly designed, and irist r urn ent at ion indicated very little te rnp e r at u r e variation throughout the house.

The exterior cladding is generally of board and batten on walls with wood shingles at the gable ends. Gutters are recessed and equipped

2

-with electric de-icing cables. One downspout to the east of the front entrance is connected to the city sewer. There is nothing unusual about the site. The rear yard is level for approximately 30 ft from the house and then is terraced upwards. Efflorescence was evident on the concrete foundation wall about 1 ft below the level of the water table trim. In the spring of 1961 paint was peeling from the gable ends and around some

gutter trim.

INSTRUMENTATION

On 2 September 1958, two hygrothermographs were placed in the house, one on a high dr es ser in the affected bedroom near the southeast corner of that room and the other on the fireplace mantel in the living

room at the opposite end of the house but near the centre carrying partition. Charts were replaced on 8 September and the instrument from the living room was transferred to the NE corner of the NE bedroom at the same end of the house as the affected room. On this date three surface

temperature thermometers were placed on the west wall of the affected room, one 4 in. below the ceiling, one at the height of. the moisture band, and one immediately above the baseboard. Both instruments and all thermometers were removed on 12 September. Information pertaining to this 1958 period is contained in Appendix A and Figs A-I and A-2.

On 10 August 1960, three hygrothermographs were placed in the house, one in the attic at the east end, one at dresser level, and one at the level of the damp band in the affected bedroom. With the exception of the period of 15 August to 22, relative humidity and temperature records at these locations were obtained until 23 September. Glass and polyethylene were also taped to the walls for part of this period to establish if surface condensation were indicated. Unfortunately for test purposes, an unusually dry summer did not create the conditions necessary for dampness to appear in this room. Records for the 1960 period are contained in Appendix B, Figs B-1 and B-2.

GENERAL OBSERVATIONS

In 1958 some experimenting was done by opening and closing

bedroom and bathroom doors and by various window ventilation arrangements, and also by a combination of these in an attempt to correct the situation.

Streamers were fastened to the ceiling of the adjoining hallway; what little air movement was detected was in the direction of the affected room. A ventilator was also installed in the bathroom. From these experiments it was learned that when conditions were severe enough to cause dampness,

3

-they could be corrected by isolating the room or by window ventilation. No experimenting was conducted during the 1960 instrumentation period.

In the spring of 1961 plaster samples were taken for analysis of the materials used in its composition. It is perhaps interesting to

note that the line of dampness occur s at an elevation at which it is common to fold back during the normal plastering operation. A common practice when plastering is to do the ceiling and about 18 to 24 in. down the wall in one operation. The lower portion of walls is usually done from the floor after staging has been removed, and may not take place on the same day as the ceiling is done.

The period of instrumentation shown in Table I and Figures B-1 and B-2 (September 1 to 15) for 1960 is only half the period for which records were kept; it is representative. however, of conditions throughout the instrumentation period. It also covers the period for which records were kept in 1958.

SUMMARY

From the 1958 observations it would appear that a moisture problem exists under certain conditions. Alteration of these conditions by isolation or ventilation seemed to alleviate the problem. Although no dampness occurred in 1960. records kept during this period together with those obtained in 1958 indicate a critical level of air moisture content above which the condition can exist. For purposes of graph interpr etation this level has arbitrarily been called the "median line". It appears that when the moisture content does not exceed 60 per cent R. H. or .0100 Ib of rno i s tur e per Ib of dry air for an extended period that darnpn e s s does not appear.

If weather conditions are suitable during the summer of 1961, it is intended that additional information be obtained to substantiate this interpr etation of the cho s en "median line".

Plaster samples from dry and darnp areas of the wall were

analyzed. The analysis showed that no material difference existed between the two samples. Paint could readily be scraped from damp area sample whereas it was nearly impossible to scrape paint fr orn th e other sample. The results of the plaster analysis are contained in Appendix C.

HYGROTHERMOGRAPH

HYGROTHERMOGRAPH

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South elevation (front), SE corner where affected room is located.

North elevation (r ear) showing terradng of backyard.

APPENDIX A

Table I

(See Figs A-I and A-2)

1958

Date Inside Conditions Outside Conditions

of _R.H.

_#

_Moisture of _{R. H.}

_#

_Moisture Sept. 2 72 71 .0122 63 88 .0108 3 71 62 .0101 59 63 .0072 4 73 61 .0106 59 75 ,0080 5 73 75 .0130 65 83 .0110 6 72 76 .0127 64 72 ,0105 7 72 76 .0127 65 89 .0117 8 72 71 .0121 66 80 .0110 9 73 47 .0080 65 66 .0086 10 7i 50 .0081 60 81 .0090 11 71 54 .0087 60 71 .0079 12 72 50 .0083 54 56 .0049

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APPENDIX B Table I

(See Figs B-1 and B-2)

1960

Date Inside Conditions Outside Conditions

OF _R.H.

_#

_Moisture of _R.H.

_#

_Moisture Sept. 1 74 54 .0100 67 73 .0105 2 73 51 .0090 65 55 .0073 3 71 46 .0075 61 61 .0071 4 71 43 .0071 61 65 .0075 5 71 41 .0066 61 69 .0078 6 71 38 .0061 60 60 .0066 7 71 40 .0064 61 63 .0074 8 75 49 .0090 70 67 .0104 9 73 56 .0098 65 74 .0098 10 72 63 .0110 65 87 . 0116 11 71 54 .0089 60 72 .0081 12 71 62 .0102 63 96 .0120 13 71 61 .0100 65 85 .0115 14 70 60 .0094 63 74 .0092 15 70 49 .0076 59 64 .0068

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APPENDIX C

Analysis of Plaster (ASTM Method C26 -54) Percentages

Sample from Dry Area Sample from Damp Ar ea

1 2 Average 1 2 Average Free H 2O 0.20 0.21 Combined H 2

°

6.38 6.30 Fe 20 3

+

A120 3 0.48 0.39 0.43 0. 36 0. 31 0.34 CaO 36.31 36.06 36.18 36.71 36.29 36.50 MgO 17.82 18.33 18.07 18. 11 18.42 18.27 S03 14.50 14.85 14.67 14.23 14.82 14.52

Note - because of similarity of per centage of CaOJ MgO and SO3 it was thought

unneces sary to determine per centage of CO