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Repair Decayed Lower Jamb Joint

Posted: February 24th, 2012, 4:19 pm
by johnleeke
Peter Carroll asks:
What is an acceptable practice for attaching a sill when the tenon at the base of the jamb(s) are rotted? Is it acceptable to wedge the new sill to the sub-sill, then secure new sill to the sub-sill with deck screws through pre-drilled, recessed pilot holes. Is it acceptable to treat the tenon or, what is left of it, on the jamb with wood hardener the epoxy, then proceed as you described. Feel something is needed here to address what is frequently found when replacing a sill.

We need to set the standard for this right now.

Both of those methods sound possible to me. I sometimes I take the traditional approach and rebuild the end of the jamb by splicing on a new piece of wood with the appropriate shape to match the jamb and re-create the joint. Sometimes I take the contemporary approach and rebuild the end of the jamb and the joint with wood-epoxy repair methods, using fiberglas rods to provide the structural strength needed. I've refined both methods over the past 4 decades, and have some of each still performing well after 25 years.

What is your favorite repair method for this damage? (Click "post reply" to let us know)

If you want to submit your method for consideration as a standard, learn how here:

Re: Repair Decayed Lower Jamb Joint

Posted: March 1st, 2012, 2:05 am
by Martin Muller
When the bottom of the jamb is severely decayed I typically resort to a wood block inside the pocket space, screwed to the sill.
The jamb is then fastened to the same block (recessed screws through the jamb above the decayed area), securing the sill and jamb to one another. Then the decayed bottom of the jamb is treated with consolidant and missing wood replicated with wood putty epoxy.

Re: Repair Decayed Lower Jamb Joint

Posted: March 4th, 2012, 2:04 pm
by sschoberg
This is one of the areas that most of us need to be guided through. Is it really ok to do a quick and easy repair in this area when we're spending so much effort in restoring the sashes? Shouldn't we make as much an effort on doing jambs restorations as we do the sashes? A quick answer is, if the customer can afford it then certainly. But in reality it would be difficult for me to tell my typical customer that I must remove his/her whole window in order to restore or replace one or both of the jamb sides, not to mention asking them to pay the extra cost to do so.

Most times it may be OK to make the customer aware of the extra work needed, and give them the option of us doing the complete thing or just doing the repair with the block of wood and a couple of screws. We try to avoid putting any screws in what we repair. but we have done it.

Sometimes and depending on the general condition and quality of the house construction we may do more harm in removing the whole window to do the poper repairing of a jambs problem such as described here.

I would think making the customer aware of the problem and giving them the different levels of options to address the needed repairs and documenting what was decided and completed on each particular window.

I think what becoming obvious is the documentation of what has been done to each window will serve the structure and owner and subsequint owners in the best manner. Maybe helping the homeowner establish a structural history of repairs should be part of our education of our customers. A special part of the standards could give guidlines for doing this. I like this idea and I think it can be used to help our customers in choosing us as their professional of choice for restoring their windows.

Re: Repair Decayed Lower Jamb Joint

Posted: March 5th, 2012, 3:29 pm
by johnleeke

Next drawing assignment:

Read through the discussion above, on jamb end repairs:


We need an illustration for the traditional method of rebuilding the end of the jamb by splicing on a new piece of wood with the appropriate shape to match the jamb and re-create the joint. I have done this repair method with the jamb still in place and with the sill still in and with the sill removed.

You might have done this method too and have photos of it. If not, could you do three quick sketches showing this repair. 1. jamb in the wall that is rotted out at the lower joint, 2. jamb end cut back to sound wood and prepared for a stepped splice, with new piece to splice in. 3. completed repair. Just make these as quick sketches to serve this discussion; then later, after comments, you may refine them into drawings for publication.

Re: Repair Decayed Lower Jamb Joint

Posted: March 6th, 2012, 2:24 pm
by oculus
Ok John,
Here are the quick sketches. These are not finish drawing quality. They are for discussion only.
This approach is how I do it. I know that there are various ways to do this so I would like some discussion about the technique that should be in the standards document. For instance, there is a conservation firm out here on the west coast that doesn't want to see any metal fastners in the repair junction. I however use stainless steel screws driven through the back. So please comment so that we have a consensus.

Re: Repair Decayed Lower Jamb Joint

Posted: March 6th, 2012, 2:25 pm
by oculus
step 2

Re: Repair Decayed Lower Jamb Joint

Posted: March 6th, 2012, 2:26 pm
by oculus
step 3

Re: Repair Decayed Lower Jamb Joint

Posted: March 6th, 2012, 3:18 pm
by johnleeke
Amy, the sketches are great!

I usually make the lap "zig zag" the other way, so the open face of the lap is to the outside and easier to shape. This way both shoulders of the lap can be made from the outside (I usually use a Fein sander with a wood saw blade, or if no power is available I just carve the shoulders and the face of the joint with sharp chisels.) All this can be done from the outside with the jamb still in place.

If there is limited access to the back of the jamb, I will put the screws in from the front temporarily, and then take the screws out from the front after the adhesive has cured and fill the screw holes. I do the "shank hole/pilot hole" routine for the screws, so the screws clamp the face of the lap joint together in a positive way.

My method of fitting the new part in place is to put a couple of 4" screws into the outer face of it to act as temporary handles.

Re: Repair Decayed Lower Jamb Joint

Posted: March 6th, 2012, 4:05 pm
by oculus
If you "zig-zag" the other way isn't it easier for water to penetrate into the joint?

Re: Repair Decayed Lower Jamb Joint

Posted: March 6th, 2012, 5:13 pm
by johnleeke
>>If you "zig-zag" the other way isn't it easier for water to penetrate into the joint?<<

I see your point, but the upper shoulder can still slope down to the outer weathering surface.

I guess some water could get into the lap joint by seeping into the joint between the edge of the jamb and the edge of exterior casing. The lap joint is filled with adhesive, but I guess the joint could still work loose and open up. To prevent the two sides of the lap joint from working against each other I match the orientation of the growth rings in the new part with the rings of the old part, so they expand and shrink in the same direction with changes in moisture content.

I've got some of these in place for nearly 40 years and still holding up. I'd guess it would be good as long as it's kept painted plus 10 or 20 years. I've seen two or three old repairs like this lapped to the outside 80 to 100 years ago, these joints were lapped to the outside, and fastened with steel box nails, nothing inside the joints, two had paint still covering the joints, one never had any paint, all holding up just fine. (on a barn here in Maine)

After the splice repair is all done the surfaces of the jamb, plus the joint with the casing could be treated with a paintable water-repellant that would tend to keep water out of the joint, but that would shift this into the contemporary type. Well, I guess this is already in the contemporary type because I use a modern adhesive developed after 1940.

Before 1940, they might have put lead paste in the joint and screwed it, leaving the screws in place. I have seen that in lap splices on other exterior woodwork. In boat work I have seen pine tar and rosin used in laps. But, I have not done it myself. I've always used the best contemporary adhesive I've known about, through the 1970s it was resourcinol, they I shifted to epoxies during the 80s and since.