Basement wall cracks are somewhat common and you don't always need to panic when you see them. But, is there a concern with cracks that are wide enough that they can allow termites to infest your home?
I just attended a conference of pest control companies and what they were talking about was that cracks that are less than 1/64th of an inch (that's really small) can allow termites and carpenter ants in. They crawl into these cracks because they like dark and moist and they are looking for something to eat and the silt plate right there. This can cause a lot of damage to your home overtime.
Termite tunnel on stone foundation
The pest control industry recommends that these cracks get fixed to help stop these critters from getting in. A tell-tale sign is a trail of hardened wood dust, this is a sign of termite problems.
Most of the time the calls we get are because these cracks are leaking water. During this winter season you also have cold air coming right through. Also, you can get Radon coming in as well. If you are at the stage where you are selling your house these cracks can cause problems in the sale. For sellers and buyers, when the home appraisers come in the report of cracks in the foundation can hold up the whole sale.
There are three things in life you can be sure of: death, taxes, and if you have concrete it is going to crack, you just don't know when or where.
With basement floor cracks, oftentimes they crack because concrete is like a piece of raw spaghetti, if you have any movement at all it is going to break. If I ask you to only crack a piece of raw spaghetti part way, it is next to impossible. You have the soil under the concrete that is settling, you may have footings and those settle too, which can cause cracks.
Not only do you have settling issues but heavy equipment going down the street or earthquakes (there was one felt in Gardner, MA a few days ago) can also cause cracking. Blasting can cause cracks, or when the concrete is poured it can have too much water, too much wind going on over it, or it can dry too quickly. Oftentimes when they pour concrete floors, by code they are supposed to put a vapor barrier or plastic down. They poke holes in that plastic so the water can penetrate more quickly. This can speed up the time that it takes concrete to cure which can also cause cracking.
You may notice in big box stores, some garages, or even in sidewalks that made with concrete that there are lines every so often. These are expansion joints, or basically controlled cracks. These often help concrete from cracking; not a guarantee, but they help. But, in residential construction they don't often put these expansion joints in.
Those are some of the reasons that concrete cracks in basement floors. But, while cracks are unsightly and can cause homeowners concern, most often they are not structural issue. But, basement floor cracks do let a lot of cold air and organic odors up, they also let moisture and radon up. Also, if you want to sell your house, buyers get nervous about basement cracks.
To repair a crack we have to clean it out and sometimes we have to put a specialty sand or gravel down to where the ground is under the concrete because there can be a 3" gap between the soil and the concrete because that material has compacted over-time. So we bring the sand up to the bottom of the floor and then we put a hybrid 2-part epoxy material or a urethane type material into it which actually welds the concrete together and helps stop the moisture, air, or odors from coming in; and it looks a lot better too.
Just recently in Cambridge, MA, there was water coming into the home from around a new water pipe. The water company dug out in front of the house a little bit. Once you dig you disturb the soil which has been getting compacted for what could be around 100 years or for as few as five years. Either way, the rain compacts the soil which helps keep the water from coming into your home. But utility companies put fluffy soil on top of a pipe or conduit and they don't compact it at all. Then in the basement, they will use hydraulic cement, put it around the pipe and call it finished.
Hydraulic cement is to be used in an emergency to try to stop water, but it doesn't expand or contract. Soil and stones move because of the freezing cycle in Massachusetts. That's why we have so much water coming in around water pipes, electrical conduits, irrigation cable, and other wall penetrations. We see this all the time.
If a utility company is digging down into the yard to install a pipe that is going to run through the wall, and they don't compact the soil, that soil can even act as a sponge and pull the water right to the wall. If the utility company has not done a good job to seal it, that is where the problem lies.
To fix this, we'll work from the inside. We will clean out in between the stones and hydraulic cement that they put in. We use oakum, which is like rope. We'll soak that in a polymer resin material and work it into the foundation. That will expand and we then put a specialty mortar over that. These materials will expand and move with the stones and soil, but it will always stop the water.