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Author Topic: Bottom of sills (slightly) rotted - need some pointers  (Read 374 times)

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Offline bogart_bogesley

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Bottom of sills (slightly) rotted - need some pointers
« on: August 15, 2017, 09:05:42 pm »
I'm in the process of building a small post and beam house and I'm using 8x8s for the sills (excessive but I like the look).  At this point the frame is up and I have a metal roof on the structure.  The 8x8s are laid around the perimeter of the concrete slab between the posts.  I'm using rolled asphalt (mineral surfaced roll roofing) as a damp proof course between the concrete and sills (as suggested by Rob Roy in his timberframing book).  Throughbolts fasten the sills to the concrete (concrete has drop-in anchors embedded in it).

My issue is that some water found its way into the bottoms of the sills.  This happened because I originally fastened the reinforced poly that protects the structure from the elements to the sills (poly was sandwiched between 1x3s and then these were screwed into the outside of the sills).  This worked fine for quite some time, but at some point water started finding a way in.  It eventually dawned on me that I could just hang the poly and those 1x3s over the of the edge of the slab and weigh them down with cinderblocks and that's what I'm doing now.

But back when I noticed the sills were getting wet, I thought everything would dry if I just left the sills exposed to the open air and sun for a week or two (we had several particularly dry ones in a row).  Well months later I had to temporarily remove one of the sills and I found that the sills were not only damp but some decay had started.   I pulled up all of the sills and used an electric planer to remove everything that looked like rot (darker color, smelled bad).  For the most part it was just the very bottom layer of the sill--didn't even have to remove more than a sixteenth of an inch before I got back to wood that looked to be of the normal light color.  In a few spots around the through-bolt holes the dark stuff had penetrated a bit deeper but I removed all of that with a router.  Then I replaced all of the rolled asphalt with new stuff and left the sills out in the sun (bottom side up) to dry for a week.

So I'm just wondering what I should do at this point.  Should I just put the sills back and make sure they don't get wet this time?  Should I treat the sills with something before putting them back?  Or is it too risky to even continue using these as sills--should I completely replace them?

Thanks in advance for your responses.

By the way, one of my biggest regrets with this project is not letting the poly and 1x3s overhang the concrete slab from the very start.  I can't tell you how much time I've wasted trying to patch holes and prevent water intrusion around the perimeter.  I just didn't think weighing it down with some cinder blocks would be sufficient to withstand the crazy wind storms we've been having ... but so far everything is holding up.

Offline BigZ La

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Re: Bottom of sills (slightly) rotted - need some pointers
« Reply #1 on: August 15, 2017, 11:22:28 pm »
I would treat the sills with copper coat before reinstalling them. It won't hurt anything, won't cost a whole bunch.

Offline Don P

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Re: Bottom of sills (slightly) rotted - need some pointers
« Reply #2 on: August 16, 2017, 06:51:46 am »
In that same vein I was thinking of BoraCare or a Solubor/glycol mix.

Offline bogart_bogesley

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Re: Bottom of sills (slightly) rotted - need some pointers
« Reply #3 on: August 18, 2017, 10:41:15 pm »
Thanks for the replies and pointers.  I was hoping to use copper coat but the manufacturer didn't seem to think it would be a good idea to use it indoors.  I looked into BoraCare and other boric acid based treatments but after looking at the prices I ended up making my own .  The wood seems to have taken it up just fine