How to Evaluate and Repair Block Foundation Cracks
In this weekly Q&A column, retired builder/building inspector Cam Allen answers readers’ home renovation questions. Have a question? Enter it in the form below.
It is no secret that numerous parts of Canada, such as Alberta, Montreal and Southwestern Ontario, are seeing excessive rainfall right now. I live in Southwestern Ontario and our IT tech owns a home with a block basement. For the first time that he can remember, this past week it saw measurable levels of water invasion.
If you are experiencing water invasion due to intense rainfall and have a block basement that lacks any manner of sump pump or water extraction system, see my column, Basements!!! They are often dark, damp, and a flood risk. How can we mitigate? It will guide you as to the systems available to help with this problem. This week we are going to look at what happens when excessive water and/or soil pressure affects the structural integrity of a block basement.
Some Background on Block Foundations and Cracks
First, a bit of history on block foundations. They have been around for a lot longer than most folks think. The Romans invented concrete but the actual uniform concrete block did not evolve until the mid 1800s after British Inventor Joe Aspidin invented Portland cement and then a company in Chicago G.A. Frear started mass production of concrete blocks similar to what we see today. Another gentleman by the name of Harmon Palmer invented a cast iron machine that quickened the process by adding hollow sections, making them lighter. Blocks today are stronger and lighter. The development of architectural blocks with decorative surfaces are now quite common.
The issues with cement blocks for a basement are well documented. They absorb water, they are affected directly by compaction of soil, both at the base of the wall and the density of the soil pressing against the wall. Today, poured concrete and ICF foundations make up over 90 percent of all foundations in new home construction.
The movement of a block foundation is the most common defect found. Minor vertical settlement cracks are usually not a structural issue unless they are seeing constant movement. Movement like a “step crack” in the blocks, commonly in the corners of a block foundation, is usually settlement over time and once monitored and confirmed for no movement, most are DIY repairable.
Get the Green Building Project Checklist
Use this handy checklist on your next project to keep track of all the ways you can make your home more energy-efficient and sustainable.
Horizontal cracks are a serious issue and need to be addressed. They indicate excessive pressure against the wall, commonly caused by saturated soil pushing inwards. This hydrostatic pressure can lead to a number of defects.
The three most common are pressure against the top of the block wall, causing the base blocks to tilt. This activity at the base block can also put soil pressure against the base and push the wall inward. The most common is a horizontal crack where the block wall bows or a crack develops along a large portion of the wall. This is often located one or two rows of blocks below the exterior soil level.
Is the Crack Active?
The first thing to do is establish if the crack is active. There are a couple of ways to investigate here. One way is to purchase a “crack monitor” One of the most well known is the Gilson Concrete Crack Monitor. This device attaches by way of adhesive across the crack, be it vertical or horizontal and provide documentation of any movement. They are available online in the $20–30 range.
One of the quickest and cheapest methods I have used is to clean off two spots on either side of the crack, take two dabs of urethane adhesive for concrete and a single strand from a pure bristle paintbrush and imbed this strand into the dabs of seal that you have put on either side of the crack. Do not use a synthetic paint brush strand, they are hollow and don’t attach as well.
After you have installed one or more crack monitors this will likely
take some time before you will see any results. Hopefully you don’t see any! If you find that the paintbrush bristle has broken or the monitor is showing continued movement, then the next step is to evaluate the actual movement along with the length of time it took to expose any movement in the block wall.
DIY Basement Repair
No matter what you find, corrections to the grades around your home and extensions on your eavestrough that discharge at least 6–8 feet from your home should be your first project. There are some DIY repairs you can do if the cracks are not moving and are directly related to overall settlement. Materials like hydraulic patching cement and epoxy injection will help to restore the integrity of the wall. If you use an epoxy injection, the crack must be dry. Epoxy injection has shown to be very effective for minor crack repairs.
If the crack monitor shows active movement, if the crack is anywhere from ⅛” to ¼” wide, the wall is exhibiting any manner of deflection or bowing then a professional foundation restoration contractor should be called. To establish if the wall is bowed take a straight 2×4, 8-foot long and a 4 foot level and hold against the wall. With the level resting up against the 2×4, establish level and then measure any distances that are present from the block wall to the 2×4. This check will provide you with a clear visual view as to the degree of bowing or deflection your basement wall has moved.
When to Call in a Contractor
Depending upon the severity, it is possible to re-establish the integrity of the wall without removing it or raising the house and replacing the basement, both of these are extremely expensive options. One method of restorative work done is where the soil around the home is dug down a couple of feet, strategically chosen spots located and the blocks are removed. Then #3 rebar fitted into the hollow openings in the blocks, then concrete pumped into the concrete blocks. I have seen carbon fibre strips attached to the rim joist, tightened like a strap to stabilize the wall as well as installing buttress sections made of blocks and anchored to the floor and wall by way of metal pins. Kevlar sheeting adhered to the block walls is yet another method.
My point here is there are a number of methods of which most are effective if applied professionally and done before the wall has a deflection of any kind over a ½” to an 1” of movement, depending upon the type of crack and its location.
Cracks in a block basement wall are not uncommon, what you have to understand is where the fine line is between settlement and activity in the wall and tend to any problems before they become a major repair.
Images from Depositphotos
Have a Home Renovation Question?
Write it down below and we’ll get back to you. All questions get answered – every week, we’ll select one for publication in the column.
