Publisher’s version / Version de l'éditeur:
Technical Note (National Research Council of Canada. Division of Building
Research), 1965-09-01
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Painting a Wooden House in Ottawa
Latta, J. K.
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NRC Publications Record / Notice d'Archives des publications de CNRC:
https://nrc-publications.canada.ca/eng/view/object/?id=ff26f535-f312-49d6-b165-af5be183d5c2 https://publications-cnrc.canada.ca/fra/voir/objet/?id=ff26f535-f312-49d6-b165-af5be183d5c2DIVISION OF BUILDING RESEARCH
NATIONAL RESEARCH COUNCIL OF CANADA
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No.
458
NOTlE
PREPARED BY
J. K. Latta CHECKED BY CRC APPROVED BY NBH
PREPARED FOR Inquiry and record purpose s
DATE September 1965
SUBJECT
PAINTING A WOODEN HOUSE IN OTTAWA
A large number of Canadian houses are made of wood and have external cladding that is painted. This paint is usually applied for
decorative purposes although it is often thought to be necessary to preserve the wood. The considerable number of old unpainted wooden houses still in sound condition suggests that it may be mainly the aesthetic qualities of a house that are affected by the coat of paint.
Probably the most prevalent defect that develops in the paint coats applied to houses in the Ottawa area is peeling. This often occurs more rapidly after repainting than with the first painting when the house is built. Cases are known where it has occurred in less than twelve months after the house had been repainted. Although no detailed survey has been carried out, it would appear that a three -year life between paint jobs must be considered to be good. It was decided, therefore, on a purely personal basis, that when the house under study required repainting a record should be kept of the operation, and the subsequent performance of the paint noted for comparison with other house s.
The house had been painted by the previous owners during the
summer of 1960 with a conventional oil base paint. By the summer of 1963, widespread paint peeling made repainting essential. It was decided that a
satisfactory job would not be obtained by scraping, spot priming and repainting over the old paint, and that it was necessary to remove all the old paint down to bare wood and repaint with a prime coat and at least one top coat.
".
2
-The old paint was removed by means of a rotary mechanical rasp, except for some small areas where it was burned off with a blow torch. When all the paint had been removed, the wood was sanded lightly by hand, using a coarse sandpaper, to remove any fuzz and whiskers. This left the surface reasonably smooth, but with an open texture to which it was judged that the paint would adhere well. Following the hand sanding, all knots and nailheads were sealed with shellac.
At various times throughout the job, the moisture content of the wood was measured. This was done to check that the wood was dry enough to be painted and also to examine the changes following rain. It was not, however, a routine check carried out at allｴｩｾｳ immediately before applying paint.
The reasons for paint peeling are not clearly established, and it cannot be claimed with certainty that one type of paint will perform better than another in this re spect, although there are indications that alkyd paints may do so. Nevertheless, it was decided to use a latex paint, since, for a do-it-yourself job such as this one, the ease of cleanup with water was an important factor. Also, a satisfactory colour was not available in an alkyd paint. One prime coat and two top coats were applied over the prepared surfaces. The paint supplier had stated that only one top coat would be necessary over the tinted prime coat, but as it was found that the first top coat was covering much more than the recommended 400
sq f t lgal the second coat was applied.
A neighbouring house of the same type of construction was repainted with latex paint at the same time, but was hand scraped only, before being primed all over and then given two top coats. The relative performance of the two paint jobs to date is summarized below, as are the time and cost of the work on the first house.
,
3-PERFORMANCE
Both houses were painted during August and September 1963.
Principal house:
June 1965 No visible deterioration other than for some slight staining over a few knots.
Neighbouring house:
TIME
May 1964
June 1965
Considerable peeling in several locations, but particularly around the windows.
Further deterioration with large areas around the windows and also peeling badly elsewhere. These areas were scraped down and repainted at this time.
Removing old paint, rubbing down and sealing knots 74-1/2 man -hour s Applying prime and both top coats of paint 60 man-hours
COST
Materials
Rental and purchase of equipment Labour at $2. OO/hr Total
