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Technical Note (National Research Council of Canada. Division of Building Research), 1967-05-01
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Gypsum Board Application - A Survey of Practices in the Ottawa Area
Birtch, T. H.
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DIVISION OF BUILDING RESEARCH
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No.
487
LIMITED DISTRIBUTION
PREPARED BY T. H. Birtch CHECKED BY H.B.D. APPROVED BY R. F. L.
May 1967
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PREPARED FOR
SUBJECT
LIMITED DISTRIBUTION
Gypsu:m Board Application - A Survey of Practices in the Ottawa Area
As a result of inquiries received by the Division regarding current practices in the installation of gypsu:m board (drywall), a survey was undertaken in the Ottawa area of five of the larger house builders' operations. In addition, two application contractors were interviewed and one of the Co:mpliance Inspectors at Central Mortgage and Housing Corporation, Ottawa Branch Office, was contacted for his views and co:m:ments on practices and on difficulties that co:me to the attention of the CMHC Branch Office.
A su:m:mary of gypsu:m board installation practice s is given in Table 1. The survey showed that:
(1) none of the five builders uses screws to apply the sheets; (2) all use blued ringed nails and double nailing technique;
this technique e:mploys two nails placed about 2 inches apart and spaced at 12-inch centres on each inter-:mediate fastening to ensure that the sheet is held tightly ｡ｧ｡ｩｮｾｴ the fra:ming;
(3) all use 1/2-inch thick gypsu:m board, even where 3/8-inch is per:mitted;
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-(4) all but one are furring the under side of joists prior to application of the sheets;'
(5) only one contractor is furring under the trusses prior to application of the sheets;
(6) only one uses back blocking at the ceiling joints (i.e. small pieces of gypsum board applied with an adhesive to reinforce the back of ceiling joints that run at right angles to the supports).
The most common problem reported in both wall and ceiling installations is nail popping. The problem can be minimized by using dry lumber, but none of the builders contacted could be certain of overcoming the problem with normal application using ringed nails. Another but less frequent problem is the shadow formed by vertical wall joints. A method used by one applicator to control this problem is to find a stud recessed slightly more than adjacent studs and to use it as the joining stud for the sheets. The resulting depression is filled by joint cement so that the surface of the joint is even with the remainder of the wall.
Nail popping in the ceiling is most evident in the sheets adjacent to the walls. This may be explained as follows. When the ceiling framing supporting the gypsum board shrinks, a gap is normally left between the sheet and the wood member. Shrinkage of the wall plates, however, causes the ceiling supports to be lowered; the wall sheets that are butted snugly to the ceiling sheets keep the latter pressed tightly against the framing. This permits the nails to project down, causing nails to pop near the restraining wall sheets. One contractor using furring c1aim.s to have overcome this problem by placing the first row of furring about 5 inches from the walls. Another contractor, not using furring, does not nail the ceiling sheets to the ceiling supports at the wall, but depends upon the wall sheets for support at this location. The flexibility of this floating corner is said to eliminate the nail popping problem near the walls.
Ridging at the joints was not reported as a significant problem. It occurs in isolated instances, but less frequently now than in the past. Application of joint cement in well-heated and
ventilated houses and the use of thin layers of cement seem to have reduced the problem.
One builder reported a problem of sagging between supports on the ceiling when using 3/8-inch material. This sagging had been considerably reduced with the liZ-inch board. In addition, this builder recommends application of the sheet immediately after the vapour barrier has been applied and at a reasonably warm temperature.
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Another problem encountered in ceilings is shadows at the joints. Under certain lighting conditions, even slight imperfections at the joints are quite noticeable. This can be partially overcome
by installing sheets so that the light from the window is parallel to the long joints and by keeping the end joints as close as possible to the window. The best solution seems to be to spray the ceiling with a stippling coat. This method was used by all builders contacted. This is not applicable in kitchens and bathrooms, however, since these are not permitted to be stippled.
The following summarizes the specific points brought out in discussions with the various people interviewed.
(1) Ensure that no insulation is tucked under the nailing edge of the vapour barrier.
(2) Ensure that all framing members are straight, solid and reasonably dry and installed to provide an even bearing surface.
(3) Where possible order sheets to reach full length of room to be covered.
(4) Do not attempt to apply gypsum board or tape when temperatures are too low.
(5) Use blued ringed nails that penetrate not more than 3/4 inch into the supports.
(6) Use double nailing method as described previously in this Note.
(7) Use sheets at least 1/2 inch thick.
(8) Where a butt joint has to be made on walls, its location should be determined on the basis of the most suitable stud rather than on the length of the sheets.
(9) Install sheets on ceiling so that long joints are parallel to the light from the window and end joints are as close as possible to the source of natural light. (10) Use a proved type of joint filler.
(11) Apply sheets in a manner such that joints above openings do not occur in line with the sides of the opening. (12) Apply exterior cladding that requires considerable
nailing before the wallboard.
(13) Screws are considered too costly in the competitive house market, even though they are reported to reduce popping.
(14) Strip laminating using adhesives gives very satisfactory results, but the method is uneconomical.
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-(IS) Most contractors seem to be accepting some nail pops as inevitable and treat the repair of such pops as part of their normal operation, but they never
repair such defects more than once.
(16) Applicators believe that there is too much "bounce" to I by Z strapping and sugge st that I by 4 should be the minimum.
(17) Joint tapes should not overlap at junctions between intersection joints.
In general, it was reported that the application of liZ-inch sheet rather than 3/8-inch combined with the use of blued
ringed nails, double nailing and stippled ceilings has greatly re-duced complaints with regard to gypsum board finish.
!
TABLE I
GYPSUM BOARD PRACTICES IN HOUSE CONSTRUCTION (from a survey in the Ottawa area)
t
inch Dry Furring Furring WallBuilder on on Double Only (single Back Screws Trusses Joists Nailing application) Blocking
A X X X X X B X X C X X X D X X X E X X X Total Number 1 4 5 5 1 Nil
NOTE: It was reported that there is only one contractor in the Ottawa area using screws for wallboard application. It was also reported that he will revert to ring nails when his present supply of screws is exhausted •
