Replacing a Sill

QUESTION: I have a 1870 double Cape with balloon framing (where studs could go from the basement roof-line). I removed the fascia boards covering the sill on the outside of the north side, and found that I could shove a screwdriver 2 inches into the sill plate, which is a 10-by-10 inch beam, which means the outer 2 inches of the sill is rotted out. Does this mean that I should replace the sill? I also have a brick wall of sorts on the inside of the sill. Where it goes up, I don't know how high it is. Is that brick wall supporting a wall? The brick wall is covering the sill, so I cannot check the inside of the sill for decay. Could I put 2 inches of gravel on the earthen floor of the basement to try to allow water to drain properly?

ANSWER: Let's start at the end. There is no need to put gravel on the earthen floor, but if you do not walk around that basement much, you can put plastic sheets down to keep water vapor from coming up. And ventilate the basement in the summer. In fact, you could put a concrete floor over that sheet plastic. As for the decayed sill on the outside, I think that water for behind those fascia boards and remained longer because it was on the north, shady side and caused the decay. But never fear, if you can keep that sill dry it is likely that it will decay no further. You can douse it with bleach that will help kill the decay organisms. Then make sure the siding and fascia boards keep water away from the sill. And if there are 2 inches of decay on the outside of sill, you still have 8 inches of solid wood to help hold up the house. This may go against all conventional thinking, but it can and does work. That brick on the outside of the sill is probably built with the bricks on their narrow sides, and are mortared to act as a vapor barrier. It is called brick nogging. You could also have the sills replaced at least on the north side but this is an expensive operation and may be (repeat, may be) unnecessary.

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QUESTION
I need help replacing the sill at the back of my house, which is more than 125 years old and has a rock-and-mortar foundation. Some of the mortar has decayed and fallen out. Can I safely replace the sill without fear of the rocks shifting? Also, what is the safest way to fix the foundation? Some people have told me to clean out the old mortar and blow new cement in; some said to take down the whole wall and have a new one poured. Which is better?

ANSWER
Let’s start with the foundation. Most stone foundations will stay intact with or without mortar. Yours is made of field stone, perhaps with granite blocks on the very top, where the foundation is exposed to the outdoors. Such foundations are often very wide, 12 to 20 inches or so, with stones carefully stacked so they do not move.

Mortar is mainly used to seal the cracks and joints and make the walls air-and water-tight and to keep out rodents and other vermin. Such stone walls can stand without mortar.

You can re-point, which means to chip out the old mortar to a depth of a least 1 inch, deeper ideally, and as wide as the joint. Then, dampen the joints and insert mortar.

 Wet the joints before installing the mortar to help keep the mortar to help keep the mortar from drying out too fast, and press the mortar in very tightly. As for replacing the rotted sill, this is structural, so you have to hire an engineer or architect to either show you ho s it is done or to do it for you.

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