Swedish
Admiralty. The first tar and gravel roofs in Sweden were very
defective. The impregnation of the paper with a water-proofing liquid
had not been thought of, and the roofs were constructed by laying over
the rafters a boarding, upon which the unsaturated paper, the sides of
which lapped over the other, was fastened with short tacks. The
surface of the paper was next coated with heated pine tar to make it
waterproof. The thin layer of tar was soon destroyed by the weather,
so that the paper, swelled by the absorption of rain water, lost its
cohesiveness and was soon destroyed by the elements. This imperfect
method of roof covering found no great favor and was but seldom
employed.

In Germany the architect Gilly was first to become interested in tar
paper roofing, and recommended it in his architecture for the country.
Nevertheless the new style of roof covering was but little employed,
and was finally abandoned during the first year of the 19th century.
It was revived again in 1840, when people began to take a renewed
interest in tar paper roofs, the method of manufacturing an
impermeable paper being already so far perfected that the squares of
paper were dipped in tar until thoroughly saturated. The roof
constructed of these waterproof paper sheets proved itself to be a
durable covering, being unimpenetrable to atmospheric precipitations,
and soon several factories commenced manufacturing the paper. The
product was improved continually and its method of manufacture
perfected. The good qualities of tar paper roofs being recognized by
the public, they were gradually adopted. The costly pine tar was soon
replaced by the cheaper coal tar. Square sheets of paper were made at
first; they were dipped sufficiently long in ordinary heated coal tar,
until perfectly saturated. The excess of tar was then permitted to
drip off, and the sheets were dried in the air. The improvement of
passing them through rollers to get rid of the surplus tar was
reserved for a future time, when an enterprising manufacturer
commenced to make endless tar paper in place of sheets. Special
apparatus were constructed to impregnate these rolls with tar; they
were imperfect at first, but gradually improved to a high degree. Much
progress was also made in the construction of the roofs, and several
methods of covering were devised. The defects caused by the old method
of nailing the tar paper direct upon the roof boarding were corrected;
the conseq