Historic House Wooden Post Repair
Q: While preparing to repaint my front porch, I discovered that the bottoms of the turned posts are badly rotten. Please tell me they can be saved.
A: Yes they can. I've restored countless porches over the years and I've yet to encounter a terminally ill turned post. If the damage is minimal, you can simply dig out the rotted wood and use an epoxy wood repair system such as Abatron (www.abatron.com) or SystemThree (www.systemthree.com) to fill in the gaps.
To assess the extent of the damage, drill a series of exploratory holes into the bottom of the post using a 1/4-in. drill bit. If the wood at the center of the post is as punky as it is on the edges, you'll have to replace the bottom of the post. How much you replace is up to you.
If the post is highly visible or if you're a perfectionist the can't miss approach is to cut the post at the point where the square base meets the turned center section and graft on a replacement base fashioned from a stable wood species such as vertical grain fir (pressure-treated wood is a poor choice because it tends to split, shrink, and warp). This repair can be done in place, but you will have to remove the railings, provide temporary support for the post, and make sure that the top of the post is securely attached to the beam, before you begin.
In most cases, serious damage from wood rot is confined to a few inches at the bottom of a post; so for those situations where aesthetic considerations are a bit looser, or money is a lot tighter, I prefer to trim six or eight inches off the bottom of the post and replace only that section. It won't be an invisible repair, but there are ways to make it blend.
Start by marking the cut line on all four sides of the post, using a framing square as a guide. Then, transfer these dimensions to the block of wood that will be used for the patch (don't forget that the angle of the bottom edge must be beveled to match the sloping porch floor).
Use a reciprocating saw to cut the nails that fasten the bottom rails of the porch railings to the posts if it's not a hassle to work around the railings, they're best left in place. Before you cut the post, position a 2x4 and a light-duty jack beneath the porch beam and apply just enough pressure to take up the weight.
Cut the post using whichever type of saw you're most comfortable with I prefer a Japanese pull-saw. When making a technical cut such as this one, it's good practice to leave the line (i.e. cut slightly wide of the pencil line), and fine-tune the cut using a belt sander. Verify that the bottom of the post is perfectly flat before you put away the sander.
After cutting the replacement to size, and checking that it matches up perfectly with the existing post, you could install it as is, but if you do, you will eventually find an unsightly crack along the joint where the two sections come together.
I've never been able to eliminate this crack despite numerous experiments with a myriad of adhesives and fasteners so instead of hiding it, I highlight it by rounding the edges to make the joint appear to be decorative; A trim router equipped with a 3/16-in. roundover bit is an ideal tool for this procedure, but you can achieve comparable results with a sander.
Before installing a replacement block, I coat the end grain of the block as well as the post with an epoxy primer from West System (www.westsystem.com), and then I butter the top of the block with an adhesive that's created by adding a thickening agent to the primer. West System products are available in small quantities at many hardware stores and most marine supply houses. But if you'd prefer to avoid epoxies, you can treat the end grain with a wood preservative be sure to allow it to dry completely then use polyurethane caulk as the adhesive.
After slipping the buttered-block beneath the post, you need to check all sides with a straightedge to verify that the components are properly aligned, then lower the old post onto its new partner and wipe off the adhesive that squeezes out of the cracks. Clamp the two components together by "toe-nailing" a few 3-in. decking screws between the top piece and the bottom.
For maximum longevity, the newly repaired post must be primed and painted as soon as possible.
Tom O'Brien is a veteran restoration carpenter who writes frequently about construction practices and old houses.