Still having little luck finding definitive info on the cost/benefit of routine comb replacement. There seems to be some difference of opinion as to the propolis content of combs. I always thought that it was high, and therefore it puzzled me as to why we would want to remove combs if they were saturated with propolis. We are led to believe that the propolis coated woodenware is a good thing, but the old black combs are a bad one.

Hepburn writes:

While wax is the basic building material for the nest,
with continued use the combs become modified by the additions of silk and
propolis. Thus, much of the honeybee nest gradually changes from a single to
a composite material. Some of the material properties of the individual phases
of the honeybee nest have now been characterized, but their
possible contributions to the composite have remained unexplored.

HUBER (1814) suggested that white and yellow combs
differed mechanically and that propolis (not the source of yellowness), added
to wax, colours it darkly. Inasmuch as propolis is a common constituent in
dark combs, its properties are relevant to the discussion.

The fibre reinforcement of silk in the propolisbearing
brown comb was an order of magnitude stronger than white wax
alone ; the former considerably stronger than the latter at all of the assay
temperatures. On average, the breaking strain in the reinforced comb was
double that of white wax.

Intact brood comb is a planar isotropic silk-wax composite material in
which the silk acts as a fibre reinforcement that greatly improves the overall
mechanical properties of the comb.

THE COMBS OF HONEYBEES AS COMPOSITE MATERIALS
H.R. HEPBURN S.P. KURSTJENS

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