reversible decking design to minimise rot

How To Repair Decking

This article details the steps required to repair decking that has rotted. It is taken from an original article written by Steve Smith, and modified to reflect European construction and materials availability. A sister article exists that explains why decking rots, and how you can design decking to resist rot.  That article deals with how to build decking to be rot resistant, as it is very simple to double the life of decking by considering how decking rots during design and construction stages. If you have to repair decking that has rotted, then this article is for you.

Repair Decking – or Replace it

There comes a point at which restoration is no longer practical and replacement must be confronted. It is necessary to define the point at which restoration is impractical. This depends on the amount of strength which the joist may have lost and which practical repairs may be expected to return to the structure.
The following recommendations are based on over thirty years of such type repairs by our customers. We are neither architects nor professional engineers, and we take no responsibility whatsoever for these recommendations. We strongly urge that any structural repair be overseen by a licensed architect or structural engineer as appropriate, and done in full conformance with all building codes and existing regulations.

General Procedure for Repairing Decking

The overall restoration begins with the disassembly of the top of the deck. Each piece of wood which is to be restored is treated in the prescribed manner, and missing portions of wood replaced with filler. Upon reassembly, a high-adhesion synthetic rubber sealant or a layer of Bituthene® is used to fill all the spaces between planks and joists. This prevents the reoccurrence of the kind of deterioration which damaged the deck in the first place.
In many cases the owner values the aged, weathered appearance of the old deck. It is usually possible to maintain the same appearance by using the same deck planks, and with sufficient artistry in colour matching the filler to the old wood joists the repairs may not appear obvious even from below.
The following procedure is a rough guide for the experienced contractor or the talented amateur. Remember that every situation is different and there is no substitute for looking and seeing and understanding.


  1. If the deck planks are screwed down the screw must be removed from above. If the deck planks are nailed, the nails may be removed easily by striking the plank from below with a dead hammer. Once the deck and joist are slightly separated a wedge may be driven in (below) from the side, or the planks may lift up easily with the dead hammer. It is also often feasible to strike the plank from below, lifting it up a bit, and then hit it from above with the dead hammer. This should be done adjacent to the joist and usually results in the nail standing proud (above the plank). The nail may then be pulled out from above with an appropriate tool.
  2. Number the planks on the edge with a pencil to aid reassembly in the same order on the deck.
  3. Place the planks upside down on a few sawhorses. Using a wire brush, lightly scrub the area where the plank laid on the joist to remove the loose, badly deteriorated wood.
  4. Soak the entire bottom side of each plank with Clear Penetrating Epoxy Sealer. If it is important to preserve the weathered appearance of the deck then the planks should be turned over promptly (within perhaps 1/2 hour) and solvent-cleaned with Epoxy Clean-up Solvent and rags or paper towels to remove the CPES which has soaked through to the top side. If this is not done before the CPES cures there will be visible patches of epoxy on the top, which may take many months to weather away. It is important to remember that absolute perfection cannot be attained. Restoration is the art of approaching the original, but a sharp eye may see some evidence that repairs were done.
  5. Allow the deck planks to dry for at least 48 hours, with the bottom side up. This aids the evaporation of solvents and cure of the CPES.
  6. Using a wire brush, lightly scrub the top edges of the joists to remove the soft, badly deteriorated wood. Wood soft enough to be scrabbled away with the bare fingers should definitely be removed.
  7. Soak the top edge of each joist with CPES. Ensure that the wood is completely saturated. Where the nail holes show extensive and prolonged absorption it is usually desirable to ream out the deteriorated wood around each nail hole with a 1/2″ drill and then continue the impregnation process. Place something under the joist to catch the CPES runoff (for filtering and recycling) if desired.
  8. Allow at least 48 hours for the solvents to evaporate back out of the wood. In case of severe deterioration where deep impregnation has taken place, one to two weeks drying time may be necessary. As a general rule, when the impregnated areas no longer smell strongly the restoration procedure may be continued.
  9. Replace missing wood with Fill-It epoxy filler. This extremely high-quality filter does not shrink or absorb water. It was made originally for underwater repairs on boats. When cured (usually overnight) it may be sanded or shaped with normal woodworking tools.
  10. Sister any joists that may require it. Use substantially clear grain fir with few and small knots, if any. Use Smith’s Tropical Hardwood Epoxy (it will glue all woods) or 3M 4200 (softer, with better flexibility than 5200) as the glue and bedding sealant between sisters and the original members. Screws or ring-shank nails are preferable to plain nails. Nail or screw the sisters before the adhesive cures, and ensure their top edge is flush with the top edge of the original joist.
  11. When the sealant has cured use a sharp wood chisel or a serrated knife as appropriate to remove any excess rubber that may have squeezed out on the top edge.
  12. The deck planks are now ready to be replaced in their original numbered order. Drill suitable pilot holes for any screws or nails that will need to go into filler. Place each plank in its original position, drill the pilot holes, and then take up the plank. Lay a strip of Bituthene® on each joist where the plank rests. 3M 4200 may also be used. Replace the plank and drive the nail or screw through the plank, through the Bituthene® or wet sealant and into the joist. Boats are repaired in this manner and the life of the repair may be expected to exceed the life of the deck.

Assessing Decking Joist Degradation

Where the underside of deck planks shows deterioration to a depth of a quarter the plank thickness or less, then restoration should be feasible. When the top edge of the joist shows deterioration over the full width of the joist and to a depth of perhaps a half inch to an inch it should be feasible to restore the existing joists. When the top edge of the joist shows deterioration extending through no more than a quarter of the thickness of the joist it should be possible to restore the existing joist, but it will be necessary to sister a new structural member onto the existing joist.

Repairing Decking Joists – Sistering

Sistering, or the fastening of a new structural member in parallel with an existing weakened one, cannot be done in a piecemeal manner. The new wood and the old wood have different properties and will expand and contract differently. If the repairs are not symmetrical and distributed over the full width of the structure there will be bending, twisting or warping of the deck. Where a 2X12 has severe deterioration along the upper edge, an appropriate repair would have a 2 X 10 glued and screwed to the old 2 X 12 on EACH side, flush with the top edge. The structure is symmetrical side-to-side and therefore would not be expected to bend, twist or warp with age. The new joist strengthening members (sisters) would run the full length of the deck and extend into the adjoining structure if possible. Since the additional supporting structures span the full width of the deck, one would not expect the deck to bend or warp as is the case when only small pieces are sistered to a portion of a joist.

Special Materials Required to Repair Rotten Decking

Smiths Clear Penetrating Epoxy Sealer and Fill-It to repair rotten wood.

rotten wood repair kit epoxy resins fill-it cpes

Bituthene to seal gaps.

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