This section is from the book "The Gardener's Monthly And Horticulturist V24", by Thomas Meehan. See also: Four-Season Harvest: Organic Vegetables from Your Home Garden All Year Long.
Some one in a recent number of the Monthly advises to glaze without lapping the glass. Before any one acts on that advice, he had best test its soundness by experimenting a little. When rebuilding our greenhouses here in 187S, I gave the "no lap" plan a careful trial by glazing in that way a section of a twenty-foot house, having an angle of about thirty five degrees. We first tried it by showering over the glass with a hose, and found that it leaked like a sieve. Not quite satisfied with the hose test, we waited until a heavy rain fell, which showed nearly the same result; the roof leaked on that part where the glass had not been lapped so as to be destructive to anything growing underneath. Were it pos sible that the glass could be cut so that when butted together the junction would be perfect, then that plan would certainly be the best; but that would be next to impossible. In the trial we made the glass was selected with the greatest care, yet in many places the point of a penknife could be run between the panes where they were joined together; consequently that even at the steep angle we used it on, the leakage was such as to show that the practice was a bad one in any place where water falls on the greenhouse roof.
We find no better plan in glazing than that now almost universally in use of bedding the glass in a thin layer of putty and tacking down tight with good-sized glazier's points, using no putty on the top, but instead, painting thickly with white lead. The laps should never exceed one quarter of an inch, and often an eighth of an inch is deemed sufficient.