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Muntin Rib Repair

Posted: Tue Apr 08, 2014 2:52 pm
by johnleeke
Muntin Rib Repair

Update: 9/1/14, see red notes for updates

See the book for more details and photos of each step: Save America’s Windows, page 52, 2013, second edition

Condition to be Treated: Split, broken or weathered and worn out muntin rib.

Description: These thin fragile strips between the glazing dadoes are easily damaged or weakened by decay. A rib that is split but still intact can sometimes be glued back in place. If the rib is decayed or missing, replace it with one sawn from wood. If a joint is made at the end of a rib repair, a butt joint can be used if epoxy adhesive is used; a scarf against water flow is critical if other adhesives are used. There are two ways to attach the rib to the muntin: Butt (with a flush butt joint, steel pins and adhesive; or Groove (with the rib set in a groove with adhesive). The groove may work better if the rib is less than 3/16” thick.

Typical Procedure:
New First Step: 1. If using a groove, scribe along the sides of the rib with a razor knife to the desired depth of the groove before removing damaged rib. This prevents tear along the shoulders of the groove and serves as a visual depth guide.
2. Trim away damaged rib flush with glazing rabbet shoulder.
3. If using a groove, carve the groove between the scribed lines with a narrow sharp chisel.
4. Make enough rib stock for all rib repairs. Match the thickness of the adjacent ribs.
5. Cut and fit the new rib.
New joint design: Form a "V-scarf" joint where the new rib meets the old rib. See the replay of the April 5th video conference for details:
6. If using a groove, glue rib in place and temporarily fasten twice or every 10" with tape or string wrapped around the rib and muntin. Allow adhesive to fully cure, then remove the tape.
7. If using a butt, use tiny stainless steel brads, pre-drill the rib with the brad, or spin them into place with a brad-spinner. Apply adhesive under the bottom edge of the rib, then set the brads 1/8" below the surface and fill with glazing putty. Allow adhesive to fully cure.
8. Trim the face of the rib flush with surrounding ribs or face of stile or rail. Clean any excess adhesive out of glazing rabbets.

Wood, match wood of sash, very straight-grained
Adhesive, weather proof Type 1 (such as TiteBond III), or epoxy formulated as a wood adhesive
Brads, galvanized steel or stainless steel, if needed
Tape, blue painter's tape, if needed
Cotton string, reusable and more sustainable than disposable one-time-use tape

Wide chisel, to trim ribs, sharp
Narrow chisel, same width as ribs or slightly narrower, sharp
Table saw, to cut rib stock
Nail set
Small finish plane, sharp
Electric drill
Nail spinner, to set brads (Vermont American #16621, UPC: 4532516621 5)
Diagonal cutters, to trim brads to length

Quality of Results:

Best Work: Rib matches originals in width and height. Face of rib is flush with face of surrounding sash parts. No adhesive buildup outside of joints. No adhesive at free joints. Rib is aligned square and true with surrounding parts.

Inadequate Work: Rib is tilted out of square. Gaps in the joints between the rib and neighboring parts. Rib is not the same thickness and width as original ribs.

Re: Muntin Rib Repair

Posted: Tue Apr 08, 2014 3:08 pm
by johnleeke
See the full replay of the April 5th video conference for more details: ... 45:28&fb=0

Or, go here:
and scroll down to find a compete "table of contents" to the replay.

In this video conference we repaired sash muntin ribs, with two methods:

--Modern Method, gluing a broken rib back in place with specially mixed epoxy adhesive, and

--Traditional Method, repairing a split and missing rib with new wood, setting the new rib in a groove and attaching it to the old rib with a V-scarf joint, and brads to hold it to the muntin. I've seen rib-in-a-groove-and-brads method used as a repair done over a century ago that was still performing well, so I think it is a valid method, even without modern or traditional adhesives. Of course, an adhesive could be added with this method, which might help keep moisture out of the joint.

Linda Kucera helped me design the new (to me) V-scarf joint, which is a combination of the "V profile" on a vertical joint that I have been using for years, and the sloped or "scarf" joint used by several of the window preservation specialists, including Linda. I like the V-scarf joint and will continue to use it as my standard "best work" joint, although other joint designs may take less time and cost less to implement.

I have always used epoxy materials for adhesive with the modern method. Linda and Andy Roeper describe the "type two" and poly-urethane hot melt adhesives they use for this repair method. The hot melt adhesive is Titebond's "HiPURformer(tm) Advanced Bonding System." Andy says this system gives him a quick 1 to 3 minute set time, just hold the part with your fingers (no fastening or taping needed), and 24 hour full strength cure time. Andy, which specific adhesive do you use with this system?

Here are sources for specific tools and materials mentioned in this video conference:

Nail Spinner
Mfg. Info.: ... m?CID=4229
Supplier: your local Ace Hardware store, if not in stock they should be able to order it

Wire Brads: your local hardware store

Cut Brads:
Tremont, Fine Cut Headless Brad Standard
Mfg. Info. & Supplier: ... 4&mv_pc=14


In the conference Linda mentioned she used "type two" glue, and I mentioned that "type three" could be used for this sort of repair. There may be some confusion about types of glue, at least in my mind there is!). There are specific glue products to consider and a generic way to refer to the different types of glue.

The Titebond(r) brand has three different products: Titebond Original (not water resistant, for interior use only), Titebond II Premium (water resistant, for interior or exterior use), Titebond III Ultimate (water-proof, highly resistant to water). These are polyvinyl acetate adhesives.

Polyvinyl acetate adhesives for use with wood, are of three types based on their water-resistance at these performance levels: Type 1 for wet-use, Type 2 for intermediate use, and Type 3 for dry use. So, it could be confusing to say "type three" because it could mean, in this generic sense the least water-resistant (Type 3), and in the specific product sense (Titebond III) the most water-resistant.

So, if you want the most water-resistant Titebond glue, use Titebond III. Here is a Titebond rep describing their glues and their various characteristics:

The gap-filling adhesive, I mixed in the video conference with Abatron's LiquidWood and WoodEpox products ( ... onkit.html) has the disadvantages of the time it takes to mix it up (about 5 to 7 minutes) and the hefty cost of the materials. It has the advantage of 35 years of proven performance in this specific use based on my own personal experience and side-by-side field testing with other adhesives.

Titebond's "HiPURformer(tm) Advanced Bonding System." Andy says this system gives him a quick 1 to 3 minute set time, just hold the part with your fingers (no taping needed), and 24 hour full strength cure time. There are several "flavors" of adhesive in this system. Andy, which specific adhesive do you use with this system?
Manufacturer's info: