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 TB 55-1900-201-45/1
2-14. Plywood Construction. In general, the replacement of a portion of a panel of plywood is not acceptable. How-
ever, in the case of a small damaged area between frames, a flush patch backed by a butt block may be used. Small
surface defects may be repaired using commercial fillers (epoxy, putty, etc.). In allowing this type of re- pair, the wood
must be decay free and all damaged wood removed. Quick repairs of this type are satisfactory where basic strength has
not been affected. The danger lies in covering up progressive defects; such decay which grow worse under the repair
material.
2-15. Framing Repair.
a. Damage to one or more scattered or isolated frames can be repaired by the use of sister frames, though it is
preferred that the frame be replaced if practicable. Damage to more than two adjacent frames shall not be repaired with
sister frames.
b. The preferred type of sister frame is one of equal or greater size than the damaged one and as long as possi-
ble. This frame shall be fastened to the planking and the other structure with fastenings at least equal in size and num-
ber to those of the damaged member.
c. Where structural or machinery interference or other reasons prevent the fitting of a long sister frame, well tied
into the other structure, a shorter "partial sister" may be fitted as a temporary repair. This should extend as far as is
practicable on both sides of the damage and shall be securely fastened to the damaged frame by through bolting or
equivalent means as well as to the planking and other structure.
d. A sister frame shall not be used as a repair for decayed frames. The decayed wood will eventually "seed" the
sound wood with decay spores in spite of any attempts to prevent it by the use of wood preservatives or to isolate the
new wood with sealing compounds. When extensive decay is present in a frame, the only permanent repair is to replace
it and any adjacent wood affected.
2-16. Decayed Frame Heads. Heads of frames under the covering boards often become decayed. With sawn frames,
this can be corrected by re- placing the upper futtock. If the futtock is long or the frame is in one piece, it can often be
cropped off well below the rot (at least two feet) and a piece spliced in using a glued and screwed scarf joint of proper
dimensions. Repairs to more than two adjacent damaged frame heads will not be made by short cropping but shall be
made by renewing the frames or replacing the damaged sections by scarfing and then sistering the frame.
2-17. Use of Fiberglass Reinforced Plastic.
a. Glassing an unsound structure as a way of restoring strength is a temporary repair. This is especially true of
glassing planking or other areas which tend to work or "come and go". The laminate has
2-15
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