Believe me, I’ve scoured the net and other than a post I found elsewhere from 2006 (and not very much info), couldn’t find any ideas on this.
I have a five year old house with a treated sill plate on a gasket, on a block wall. Originally just faceless batts in the joist bays but no apparent moisture issues.
Looking around recently I noticed that the tip of one of my anchor bolts has a ton of surface rust. This is a bolt in a bay I had foamed last year but had NOT covered that bolt fully. I then looked around at the other bolts in my basement, ones totally uncovered and those still mostly covered by batts (I only foamed in about 3/4 of the basement).
What I’ve found is that there is a little surface rust on the washers of these bolts where they contact the sill plate (all washers). The nuts are all shiny, even on the more rusted bolt, but the washers have surface rust where they contact the plate and the bolts above the nuts all have a little (it’s mild in most cases). The worst obviously being the first one I saw, though others that are uncovered are doing much better.
It occurs to me this is occurring because the bolts, sitting in masonry, are basically pillars of coldness as they hook up with sub-freezing concrete blocks. The inside warm air comes in contact with these cold metal masses and it must be condensing and rusting, even though these are presumably properly galvanized (I certainly hope anyway!) bolts.
I’m going to spray Great Stuff over all of these, which should help keep them cold and limit condensation.
Is this a common problem?
Sorry not pic at this time, I could add later if anybody cares, though.
Replies
It is common
but not a real problem of any consequence. Not really a fastener that needs to ever be removed so the surface rust doe little harm.
It's a hex nut (not square) and all look clean. I'll definitely do my best to get a pic later of both the very mildly surface rusted ones and the one in worse shape.
AFAIK some houses were built without any anchor bolts at all in the past.
Build was first half of 2005 so I'm assuming the newer more corrosive formula.
Here are two examples. The one without any foam around it had only batting around it so I pulled that away. The other one near the foam has been exposed like this for about a year, though I found some others semi-covered with foam that were in good shape, so there appears no rhyme or reason. The one near the foam is a tiny bit less rusted than another one I found but couldn't get a good picture of.
I really have no idea how these were a year back because I didn't pay any attention. You can see on the foam-bolt pic that there is rust on the foam. However, it's in the shape of the threads, so I wonder if they shrunk away from it and it had been there a year ago, I don't know.
Anyway, seems quite a heavy surface rust for a 5 year old bolt, doesn't it? Basement is kept at 50% RH year round.
For the more rusted bolt I took the nut off and its washer (I flipped it over so the part where it contacts the wood could be seen). Both are zinc coated (this is weaker than hot dip galvanization). Although I tightened this bolt last year with a 3/4" wrench (and thus it is a 1/2" bolt), it loosened very easily with simply my finger, no pressure whatsoever. It seems that although the bolt is rusting the nut is not rusting as quickly, so they are not rusting together.
In any case, apparently this ACQ lumber is really nasty on anchor bolts. Hot dip galvanized or stainless steel should be used, which is not. However, the international building standards appear, as of 2006, to be ok with regular steel bolts in this scenario if they are at least 1/2" thick, presumably because it would just take so darn long to rust through that they're ok with that.
Probably what I'll do is just foam these up to protect from interior, warm air and forget about it.
You were right, that is pretty heavy rust for 5 years. I have steel outside (under cover) for 20 years with less rust.
Like Dan said, though, long way to go to rust through.
Before you seal them all up forever, I'd simply blob a bunch of old motor oil (or new) over the ones you can get to easily.
I'd almost bet that when the house was built there were a few good rains before the roof was on???
I don't think 'shiny' nuts = galvanized. Once you seal an object like that, there should be no continued rusting. Condensation is airborne moisture that hits a cold surface, so if the surface has no air surrounding it (to speak of), then there shouldn't be condensation. That is one of the basic rules of insulating ... fill cavities to prevent the potential for condensation on surfaces.
Probably a good idea, but I'm about to seal up much of the basement with wall and ceiling drywall ;)