Epoxy Coating on OSB to prevent nail pull out??

[woodtech]

Good day!
I recently saw an application of a marine epoxy coating to strengthen a historic brick wall. That was in Europe.

I'm tempted to use this technique on a cedar shake roof. The roof is built of 1/2" OSB sheating with No:1 heavy shakes installed over the sheating using 2" No. 6 shake nails.

The nails penetrate the OSB all the way through, protruding about 1/2".

What would happen if we used some kind of epoxy coating to brush over the protruding nails, inside the roof structure and create a surface bond between the OSB and Nails? That way strengthening the design with comparatively little expense.

Any comments/suggestions would be great.

Thanks
Pete

 

[sundale]

Placing a marine epoxy coating over a historic brick wall is a horrible idea. A brick wall wants to "breath" and placing an impervious barrier like that will cause condensation within the brick and mortar as moisture migrates from the building interior to the exterior and is blocked. I would think it likely to see this epoxy spalling off the wall after a few freeze/thaw cycles...

An epoxy coating such as you suggest for your OSB sheathing would do very little to increase the withdrawal capacity of the nail. I would expect that there would be minimal bond of the epoxy to the protruding nail head. I specify a ring shank or spiral shank nail for the anchorage of the OSB to the trusses/rafters. The anchorage of the shingles to the sheathing is per Code and/or per the manufacturer

Why do you need more withdrawal capacity?

 

[Ron]

woodtech...as with sundale, not sure why you need extra pullout resistance. Besides, if you do, since you're using 2" long nails going through presumably 1/2" or 5/8" OSB, just bend the nails over. Since they should be all in lines, it wouldn't be that difficult to devise a bending device to bend multiple nails at a time. The epoxy will slightly increase the pullout resistance, but only if the exposed nail is heavily coated. Coating anything other than the nail shank is a waste of epoxy. It would be quicker to bend the nails individually than to coat each with epoxy. Yes, you could spray the entire underside of the OSB with epoxy and coat the nails in the process, but you probably have 0.1% or less nail surface area as compared to wood surface area

Further, most of the time in shingle and shake applications, the failure is not in "pullout" but "pullover" where the material around the nailhead fails and the nail stays in place as the material flies away.

 

[RARWOOD]

I had thouht at one time the N.D.S. allowed for an increase in withdrawal value if the nails were "clinched" (bent over). I look through my N.D.S.'s back to 1982 and could not find a provision for increasing the load.

Maybe I am remembering it from Don Breyers or SlideRuleEra's book (when he writes one).

There is discussion of clinching in the Forest Product Lab's "Wood Handbook" and the 1997 Commentary for the N.D.S

 

[unclesyd]

sundale,
There are several projects in San Francisco that used Epoxy/Fiberglass on very old unenforced masonry walls for Earthquake resistance. The coating was done mainly on the lower part of the wall and around penetrations.

The example in the program was the Woolen Mills Buildings.

 

[sundale]

I am sure that an impervious exterior coating can be done well if proper steps are taken, like to place a vapor barrier on the inside face of the wall. The importance of a seismic retrofit also would outweigh water damage concerns.

This being said, I have seen many old brick walls (in Denver) damaged by freeze/thaw spalling due to Harry Homeowner applications of impervious paint.

This is off topic, but here's a link. BIA has a wonderful web site.

http://www.bia.org/html/frmset_thnt.htm

 

[RARWOOD]

I was thinking about this problem this morining, and just wondered if you could squirt a dap of construction adhesive on the nail shank. I would think that if you used an adhesive that will bond to wood and metal that you could increase the pull out resistance.

 

[PEinc]

I think that the adhesive would be pushed off as the nail penetrates into the wood.

 

[unclesyd]

Look around on this site for ideas about using a Pal nut, push on nut or washer on each nail. I don't believe the nail will pull out if there is one of these on the back side. They make all sizes.

Just thought about this and am going to use it in my shop, especially at the corners.

http://www.thefastenerwarehouse.com/page/page/568857.htm

 

[woodtech]

Thanks for the advice.
I just had a lingering concern about the OSB sheating and its ability to hold a nail. It has not been tested for Cedar Shake applications ( as per the Cedar Shake and Shingle Bureau.) They only tested Plywood. It should be OK with OSB as it is widely used for Shakes as far as I can see. So I was looking for a fast and inexpensive way to strengthen the application.

 

[Ron]

woodtech...OSB can achieve the same span ratings and structural properties as plywood. It is much more susceptible to water damage, tends to deflect a bit more than plywood under load, and is dimensionally less stable than plywood, but all in all, it works for roof sheathing.