what is a shim in slab foundation repair

What is a Shim Used for In Slab Foundation Repair? (Definition, Types)

You’ve heard or seen the word “shim” referenced in discussions or articles about foundation repair. It’s one of those words you have never come across and you don’t really know what it means. Rather than continuing to pretend like you know about this word, you’ve decided to look it up. Bravo for following up on your curiosity.

Anchor Foundation Repair Bryan College Station

At Anchor Foundation Repair, we try not to use terminology that everyday folks don’t understand, but sometimes it happens unintentionally because we say this stuff in our sleep. I’ve bought more than 80,000 pounds of shims so far in my life so I can for sure tell you what shims are and how we use them in the foundation repair world.

This article will define shims, explore different types of shims, and explain how they are used in the foundation repair industry with a focus on slab-on-grade foundation repairs. So let’s *shimmy* on into the next section and check it out. (sorry, it had to be done . . . but now that it’s over with, I promise not to use the word shimmy again . . .)

What Is the Definition of a Shim?

holding shims

Shims are used a lot in construction and not just for foundation repair. First, let’s just look at the general definition of a shim, and then we’ll narrow it down to foundation repair specifics. 

According to yourdictionary.com, there are a variety of meanings and interpretations for the word shim. Here is a collection of the most relevant definitions that apply to the construction world.

  • A thin, usually wedge-shaped piece of wood, metal, or stone typically inserted under some part so as to level it or make it flush with another part.
  • A thin, often tapered piece of material, such as wood, stone, or metal, used to fill gaps, make something level, or adjust something to fit properly.
  • A thin piece of material, sometimes tapered, used for alignment or support.
  • To fill in, level, or adjust by using shims or a shim.
  • To adjust something by using shims.

In case you didn’t notice from the list above, a shim can be a thing (noun) as well as a thing you do (verb). Essentially, you shim your house with shims. Isn’t that shim-tastic? Oh look, now I’ve made it into an adjective . . . sort of . . . 

Here are the keywords that I think we should focus on out of all that stuff up there:

barrel o'shims used in slab foundation repair
  • Thin
  • Inserted into or under some part
  • To level it
  • Fill gaps
  • Adjust
  • Fit properly
  • Align
  • Support

So now I’ll make my own super-definition:

A shim is a thin piece of material used to make slight adjustments between home elements, including foundations. Shims are inserted between larger parts to fill gaps, level, adjust, and make things fit properly while maximizing alignment and support.

What Is the Purpose of a Shim?

Well, my shim-tastic (trademark pending) super-definition above included the *what is* question and the *what is the purpose* question all in one. But just in case you missed it . . .

shims in slab foundation repair

The purpose of a shim is to fill gaps, level, adjust, and make things fit properly between larger home elements while also maximizing alignment and support. In the world of foundation repair, those are all purposes that shims serve during the repair process.

The “ larger home elements” that shims are placed between in slab foundation repair are the pilings or piers, or other underpinning support on the bottom side and the underside of your slab foundation on top. All the shims are inserted in between those two elements. We’ll include a picture somewhere around here.

What Types of Shims are Used in Foundation Repair?

There’s foundation repair for slab homes and there’s foundation repair for crawlspace homes. Many people will tend to think of the tapered wooden shim if they have heard of the word shim before at all, but that shim type is used on crawl space homes, not slab homes.

Tapered Wood Shims Are Used On Crawl Space Homes

Some of the above definitions talk about the shim being tapered or wedge-shaped. In foundation repair for block and base and pier and beam (crawl space foundation) homes, some of the needed shims are made of wood and tapered. Tapered wood shims are also used in trim carpentry and framing. 

Shims for Slab Foundation Homes

Since we are talking more specifically about shims for slab-on-grade foundation repair, we will narrow down our description of shims even further.

what is a shim and how is it used in foundation repair?

The first shims that we use are actually concrete blocks, but most people (and even us sometimes) don’t think of them as shims even though technically they are. A set of concrete blocks rests on each pier cap to begin bridging the gap between the pier and the underside of your slab. Then a series of smaller shims get used to continue filling the space. We will describe the process more in the following section.

The typical shims for slab foundations are small rectangular pieces shaped like a 3” by 5” note card. These shims will vary in thickness from ⅛” to ⅝” thick. Shims for slab foundation repair can be made of steel or plastic. Anchor uses steel shims, no plastic for us.

We have also heard of stainless steel shims, but that is not very common. Some people have inquired about stainless steel shims and we don’t use them because they are not readily available. The best type of shim to use in slab foundation repair is the one that your contractor can easily source in your local market.

We have been using the same reliable shim company forever and they manufacture these specialized parts out of the Houston area. Many other slab foundation repair companies in our region likely use the same product. Check out *The Shim Shop* online or on social media if ya feel like it.

How Are Shims Used In Foundation Repair?

Metal shims used in slab-on-grade foundation repair are installed in the following manner. There is a space to fill in between the pier cap and the bottom of your slab. What a foundation repair installer will do is this starting with two concrete block shims on either side of each jack: 

  1. Raise the home using jacks to the desired position
  2. Insert the thickest shim available that will fit into the space
  3. Continue inserting the thickest shim size on top until no more of that size will fit
  4. Then begin inserting the next thinnest shim size on top until no more can fit
  5. Then move to the next size down (if needed) to fill the space completely
  6. The last few shims will be pounded in with a sledgehammer
installing a shim in slab foundation repair

You end up with a neat stack of steel shims on either side of the jack that is supporting your home. Once the shims are all securely in place on top of every pier, the jacks are lowered and removed.

These metal shims are flat and strong and are designed to maximize the surface area supporting your home. Shims will get some cosmetic surface oxidation in the form of rust, but they will remain durable and not deteriorate or lose strength. In other words, they will last a very long time and a little rust won’t hurt them.

More About Our Foundation Repair Methods and Process

I’m just guessing here, but shims are kinda boring to most people. We don’t even get that excited about shims but they do help us do our job well so we are thankful that they are there for us and for our homeowners. Something we get a little more excited about is our drilled pier construction.

stack o shims for a slab foundation repair

At Anchor Foundation Repair, we have been inspecting and repairing foundations for 35+ years in Bryan, College Station, and other Brazos Valley communities like Navasota and Brenham. Our drilled bell-bottom pier design and construction is something much more unique in the foundation repair world than the shims that we use.

Most slab foundation repair companies use pressed pilings rather than drilled piers. Bell-bottom piers are harder to install and take more expertise and time to construct. Check out what makes drilled piers different (and superior in our opinion) compared to the *more popular/easier to install* option: What Is a Drilled Concrete Pier? Home Foundation Repair Spec Sheet.