Can someone explain why wood in contact with concrete causes rot?

[Nick Gromicko]

I'm not arguing as to whether or not the contact should be protected... I'm asking where the moisture comes from. Anyone who has inspected rustic homes has seen the ends of wood girders or joists that are in contact with stone walls (remember, stone does not have left over moisture from the curing process) all rotted out.

David is correct that those situations that are closer to the ground (like in a crawl space) are worse... but why? Where is the moisture coming from if not from the curing process and not from wicking up moisture from grade?

[Marcel R. Cyr]

We should not be advocates of having lumber bear on any masonry, concrete, nor stone foundations in todays World of Science as we know it today.

Any lumber in contact with whatever material that is susceptable to moisture intrussion by wicking or cohesion should be treated for moisture protection.

Even structural steel beams and miscellaneous metals wether painted or not should have treated wood if it is in contact.

Marcel

[dcook1]

Originally Posted by gromicko

I'm not arguing as to whether or not the contact should be protected... I'm asking where the moisture comes from. Anyone who has inspected rustic homes has seen the ends of wood girders or joists that are in contact with stone walls (remember, stone does not have left over moisture from the curing process) all rotted out.

David is correct that those situations that are closer to the ground (like in a crawl space) are worse... but why? Where is the moisture coming from if not from the curing process and not from wicking up moisture from grade?

Sometimes with older houses the grading does not direct the water away from the foundation. This moisture is part of what is wicked into the foundation wall. While the stone may not contain moisture, the mortar will, especially the old lime based mortar. It will pull vast amounts of moisture.
Also old stone wall can absorb water from the weather if not protected well.

[Marcel R. Cyr]

[quote=gromicko]I'm not arguing as to whether or not the contact should be protected... I'm asking where the moisture comes from. Anyone who has inspected rustic homes has seen the ends of wood girders or joists that are in contact with stone walls (remember, stone does not have left over moisture from the curing process) all rotted out.
quote]

Moisture Vapor Diffusion and Ventilation Deficiencies.


Marcel

[Nick Gromicko]

You are getting close. I'll give you a hint...

A stone house has a stone fireplace in the middle. The girders and joists that hold up the second floor are rotted where they penetrate the exterior walls, but not where they penetrate the fireplace walls. The untreated wood is resting on bazillion year old stone so the moisture from curing isn't the reason for the rot. They are 8 feet off the ground so it isn't wicking up of moisture from grade that is the reason for the rot. And no water is coming in from outside, so outside moisture isn't the reason for the rot.

This is also seen in turn of the century city row homes where the ends of floor joists (sometimes 2 or more stories up from grade) resting on the inside row of brick on a 2 brick thick exterior wall are rotted while the ends of the floor joists resting on the interior brick walls are fine.

Where is the moisture that is causing the rot coming from and what is causing this moisture?

[Michael Larson]

Interior moisture laden air condensing on the cold brick surface near the wood causes the wood to wick this moisture up and eventuallly rot.

[Marcel R. Cyr]

Originally Posted by gromicko

You are getting close. I'll give you a hint...

A stone house has a stone fireplace in the middle. The girders and joists that hold up the second floor are rotted where they penetrate the exterior walls, but not where they penetrate the fireplace walls. The untreated wood is resting on bazillion year old stone so the moisture from curing isn't the reason for the rot. They are 8 feet off the ground so it isn't wicking up of moisture from grade that is the reason for the rot. And no water is coming in from outside, so outside moisture isn't the reason for the rot.

This is also seen in turn of the century city row homes where the ends of floor joists (sometimes 2 or more stories up from grade) resting on the inside row of brick on a 2 brick thick exterior wall are rotted while the ends of the floor joists resting on the interior brick walls are fine.

Where is the moisture that is causing the rot coming from and what is causing this moisture?

The reason that the ends of the wood joist are still high and dry would be explained as the surroundings in this case stone, is wicking the moisture out of the wood and keeping it dry. Under 19%.

If the rest of the framing is getting rotted, would logically be explained with the water vapor transmission from the surroundings. The humidity levels in a confined area such as a crawl space or basement, will and would create premature deterioration of the wood fibers with excessive moisture.

If I could explain this in French vocally, maybe it would go faster, but you would not follow the meanings. ha. ha.

Marcel
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[dcook1]

The stone on the exterior walls gets moisture from outside when it rains, and the moisture is being absorbed into the mortar.
An inner wall of double brick would also not get the moisture from the exterior and will stay dry and in better shape over the years.
The interior walls will do not get the moisture from outside and does not get wet.

[Nick Gromicko]

Michael basically got it. The reason inspectors often find rot at the point where untreated girders come in contact with walls is that most LOAD BEARING walls are also EXTERIOR walls and are therefore cold. Condensation builds up where the wall is thinest (like at a girder notch). The moisture doesn't come from wicking (which can't happen on a second floor) or curing (which can't happen with stone) but from indoor air condensing on a masonry wall at the spot where the wall and the indoor air temperatures are greatest in difference.

[Michael Larson]

Basically is good enough for me Nick.

[Nick Gromicko]

Curing of concrete produces such a small amount of water relative to what is needed to cause rot that an interior load bearing stud wall on a concrete slab with a vapor barrier underneath (to prevent wicking up of ground moisture) can have an untreated sole plate and no sill sealer of any type.

[Marcel R. Cyr]

Originally Posted by gromicko

Michael basically got it. The reason inspectors often find rot at the point where untreated girders come in contact with walls is that most LOAD BEARING walls are also EXTERIOR walls and are therefore cold. Condensation builds up where the wall is thinest (like at a girder notch). The moisture doesn't come from wicking (which can't happen on a second floor) or curing (which can't happen with stone) but from indoor air condensing on a masonry wall at the spot where the wall and the indoor air temperatures are greatest in difference.

I guess my French was not clear enough.

Sorry.

Marcel

[Michael Larson]

That may be but around here any floor plates or sill plates in contact with concrete are required to be treated wood.

[Nick Gromicko]

Here too. But sometimes code officials and inspectors get something in their head (concrete can't touch untreated wood) and can't get it out. I found an exemption in the Building Code that few know about:

Read page 2 of http://209.85.135.104/search?q=cache...lnk&cd=3&gl=us

[Brian C. Hoagland]

Because the density varies between different substances utilized in a homes construction so does the rate of energy absorption and radiation. Wood in contact with concrete will absorb moisture which condenses on the concrete whenever the temperature of the concrete drops below the dew point of the suurounding air.Inasmuch as the concrete is also in contact with the soil, (be it a hollow block, solid pour or stone foundation) the concrete is likely to be apt to cool faster than the surrounding air promoting condensation. Concrete also does have the ability to wick moisture, but I think condensation probably is a greater concern. Everything considered, if the building is really old and the wood is'nt rotted I'd say don't fix it if it ain't broke. But I'd hate to explain to an attorney in a court how even though I know direct contact is'nt permitted under codes I felt no reason to mention it in my report