They were fabric covered, see the dicussion in PPRN and Airvector:
From Professional pilots Rumour Network
Join Date: Mar 2018
Location: Canada
Posts: 1
DC-3 and DC-4 Fabric Elevators etc...
I'm a former DC-3 and DC-4 captain for Millardair in Toronto and I saw this question about fabric control services and thought I'd help you out.
The elevators were heavy and lacked hydraulic assist thereby making control inputs heavy. In the DC-4 as an example, the fabric elevator combined
with a counter weight spring aided the pilot in pulling back on the yoke.
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1st Mar 2018, 22:00
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tonytales
Join Date: Aug 2001
Location: Ft. Collins, Colorado USA
Age: 87
Posts: 189
The DC-4/6/7 and Constellations all had fabric covered rudders. During heavy maintenance checks a fabric tester was used to determine if it had deteriorated. The dope that had been applied would dry and crack but a "rejuvenator" could be applied that softened it and extended its life. Aside from that we had very little trouble with fabric covering, at least in my experience.
Some of the radar Constellations had their center rudder which lived aft of the radome on top, fixed (deactivated) in place in place and metal covered. Apparently the two outboard fins and rudders were sufficient.
Fabric covered controls were definitely lighter than metal covered ones. The higher speed of turbine aircraft ended their use on transports.
From airvectors:
The wings had three spars, a dihedral, and were of tapered planform; each wing had a one-piece single-slotted flap inboard and an aileron outboard, with a trim tab on the right aileron. Tail flight controls were conventional, elevators and rudder, with the tailfin featuring a forward fin fillet and the rudder featuring a trim tab. Although the wing had all-metal flight control surfaces, the tail surfaces had metal frames with fabric covering. Most photos of C-54s show them to have leading-edge pneumatic de-icing boots, but some photos don't show the boots; it is unclear which production had them and which did not.
By the way, the KLM logo in the white part of the rudder was later forbidden by the Minister of the Interior, on the grounds, that you are not allowed to modify the Dutch flag..... So they moved it to the fin.