fillers, epoxies and caulks, chinkings
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Lisa



Joined: 09 Feb 2007
Posts: 8
Location: Tenafly, NJ

PostPosted: Wed Feb 14, 2007 3:02 pm    Post subject: fillers, epoxies and caulks, chinkings Reply with quote

In restoring siding, weatherproofing and getting ready to paint, there are a number of different places on our house where bridges need to be made between wood. Can I pick everyone's brains out there for ideas?

At places where clapboard meets trim, what is an appropriate caulk to use? The carpenters that are here doing reconstruction of details sing the praises of polyurethane roofer's caulk as being able to last "forever" as it doesn't ever truly cure. Is that true? And is that a good thing, or is a little too permanent and irreversible? What is the best way to span gaps that are larger than the manufacturer of a caulk recommends? Will foam backer rod last?

We have detailed moldings at the rakes which have loosened up over the years. They probably still need to move a lot. What is the best way to handle gaps, some up to perhaps 1/2", which will need to stay really flexible?

After removing three layers of superimposed siding, we discovered sheathing on the gable ends with paint ghosts of half timbering that correspond to the original designs for this house. We will be putting things back the way they were. The sheathing is very thick tongue and groove. Some joints remain fairly tight, but there are gaps between other boards of up to 1/2inch. I did a small section that won't be too visible from below with the polyurethane caulks, but it tended to cup when placed over too large a gap. Epoxies might glue the whole thing together in a very scary way. I've been told that the glazing putties won't handle large gaps. What can I use? Was the intent orginally to try to make a smooth canvas for the timbering, or to see the joints in the sheathing?

John, I've been plowing through your archived video conferences and am finding them very helpful. A conference on this subject would be very useful to me.

Thanks much,
Lisa
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johnleeke
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Joined: 20 Aug 2004
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Location: Portland, Maine, USA

PostPosted: Wed Feb 14, 2007 7:21 pm    Post subject: Reply with quote

Quote:
At places where clapboard meets trim, what is an appropriate caulk to use?


Once again, pick the method first, then the material.


Figure 16. A designed joint is used to seal the top joint of the base board using backer rod and high-performance sealant.

One of our standard treatments, the "Designed Joint" for joints 1/16" to 1" wide, is scrape to clean the sides of the joint down to bare sound wood, prime the wood, install backer rod, apply one-part polyurethane sealant (100-200% elongation) We can get this treatment to work in joints up to 1" wide.

See page 23 & Figures 16, 17, 18, of the Practical Restoration Report, Exterior Woodwork Details for specific sealant and backer rod product recommendations:

http://www.historichomeworks.com/hhw/reports/reports.htm#Woodwork

Quote:
The carpenters that are here doing reconstruction of details sing the praises of polyurethane roofer's caulk as being able to last "forever"


First of all, NOTHING is FOREVER. If this is just an "expression" then they should know better than to use this "expression" around people would might be impressed.

No sealant joint can be trusted to perform for longer than 3 years, and may last for 5-8 years or (rarely) longer. This means that after three years you must check the seal and renew it if needed, and plan on replacing it all every 10 or 12 years--that is if you actually want it to keep the water out of the joint, and not just look like it is keeping the water out but really letting a little if it in and then keeping it in there to rot out out the wood. If you cannot easily get to a joint for this routine maintenance then methods other than a sealant should be used deal with the open joint.

Quote:
...polyurethane roofer's caulk...doesn't ever truly cure. Is that true?


Now, I don't want to sound like a "know-it-all", BUT it really gets my goat when tradespeople "talk" when they don't "know." This statement indicates to me one of two things:

1. The carpenters have selected a polyurethane caulk that is so poorly manufactured that is does not cure, or

2. The carpenters do not really understand how polyurethane sealant cures, or do not know how to accurately think about and use the term "cure."

(3. possibly, they do know and you just didn't "get" what they were saying.)

The process of "curing" is a chemical reaction that changes the sealant from a sticky paste to a rubbery solid. Most all polyurethane sealant products will surely cure completely. It could be they mean that it has a final cured characteristic of a certain "softness," "rubbery-ness." "Stretchy" would be a better way to think of it. One measure of this characteristic is the "percentage of elongation," how far it will stretch and then return to its original shape. For exterior woodwork joints 100-200% elongation is about right. Best quality sealants will have the percentge of elongation marked right on the tube or in its technical sheet.

Quote:
What is the best way to span gaps that are larger than the manufacturer of a caulk recommends?


There are many treatment for this situation: rebuild the woodworking detail for a smaller joint, flashing, "board stretching," etc.

Quote:
Will foam backer rod last?


Definitely, it only has to last a few hours or days. Foam backer rod has done its entire job just as soon as the sealant cures, usually within a few hours or days of application. Its entire purpose is to act as a form to hold the sealant in place and give the back side of the sealant a certain concave shape until it cures.

Quote:
We have detailed moldings at the rakes which have loosened up over the years. They probably still need to move a lot. What is the best way to handle gaps, some up to perhaps 1/2", which will need to stay really flexible?


I couldn't say without knowing the exact details. Keep in mind that some gaps are a good thing.

Quote:

A conference on this subject would be very useful to me.


I've shot video on all this from the barn painting project and hope to get some of it posted at the Reports from the Field. Watch for it there. Maybe at a conference after that.

Quote:
John, I've been plowing through your archived video conferences and am finding them very helpful.


Well, you plow the videos, I've got to go plow some snow....

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