How It Works

Trim-A-Slab Product Info

Trim-A-Slab is a replacement for rotted and old wood typically found between slabs in driveways and sidewalks. This wood was used during the slab construction, and is part of the ‘formwork’ used to define the size and shape of the slab. Once the cement had cured, it remained to accommodate movement of the slab as it is heated in summer and cooled in winter. This wood then functions as an ‘expansion joint’, but not very well.

The problem is that what makes good formwork does not necessarily make a good expansion joint. The elements conspire to attack and destroy the wood, even if it was a rot resistant variety or pressure-treated to resist rot. Moisture allows bacteria to attack and break it down, movements open gaps which allow dirt and roots in, and eventually, the formwork looks a lot more like potting soil than wood.

Unless treated with weed-killers, your driveway can easily look like the one pictured below. Of course, chemical weed-killers are also undesirable, as driveways are almost always very close to storm drains. The best way to keep chemicals out of your local watershed and fisheries is not to use them at all.

Driveway with Trim-A-Slab

driveway with trim-a-slab

how it looks on a driveway

Driveway with Wooden Expansion Joints

wooden expansion joints

wooden expansion joints


Cost Comparison

When it comes to expansion joint repair, there are a few options to consider. You can replace the wood with new wood, replace it with caulk, or replace it with a filler strip. Of these options, wood is clearly the worst. It is the hardest to fit back into the space, and there is no easy way to secure it. Any warping tending to lift it out of the joint will create a protruding trip hazard. All the same problems explained above with new wood remain as well, so weeds will establish themselves in the cracks, and in a few years the process will have to be repeated.

The next thing to consider is the caulk-like repair. This method has more than a few issues as well. The material will fill the void space completely, which is good, but any subsequent caulk shrinkage or movement of the slab to open the joint will pull the caulk from the concrete and create a vertical crack. This crack then fills with dirt, debris, and finally weeds. The caulk-like fillers simply don’t have enough compliance (which is pure stretching) to fill an expanding gap.

These materials also must be installed with some planning and skill. The depth of the evacuated joint must be closely controlled in order to be able to correctly estimate the amount of stuff needed to fill the joint. This can be done by back-filling the joint with sand, or by installing a filler strip (backer rod) which is pushed down to the desired depth. The filler strip is fairly easy to use, but the finished expansion joint is actually poorly supported, and can collapse down into the joint over time or due to foot or wheeled traffic. Lastly, the caulk-based repairs are a viscous sticky liquid which must cure. This means it must be installed carefully, and in a controlled manner to get a nice end product. The following instructions are from a tube of name-brand concrete and mortar filler and sealant:

Apply in temperatures over 40 F
Do not apply when rain or freezing temperatures are forecast
Joint should not exceed 1/2 wide by 1/2 deep
Allow to cure for 24 hours before direct exposure to water
Completely dry in 7-14 days
These are a lot of restrictions, and in addition, if your driveway is sloped, the material will run downhill, and may be difficult to keep where you want it.

problem caulk

The best method is to re-fill the gap with a ‘compliant filler strip’; Trim-A-Slab. A compliant strip, which is compressed when installed, is able to expand back to a larger size when the slabs move away from each other. Neither wood nor caulk fillers can do this. The more compliant the strip, the greater the range of motion that the joint can have without becoming loose and allowing dirt and weeds to accumulate. Trim-A-Slab is very compliant, so much so that it takes only 4 sizes to fill gaps from 3/8″ wide (about half the diameter of a dime) all the way up to 1 and 5/8″ wide. This compliance also makes Trim-A-Slab incredibly easy to install. Most of the time, it can be installed by hand.

The table below summarizes the cost, as well as some of the other factors which should be considered when deciding on a repair for your expansion joints.


As you can see, Trim-A-Slab is a clear choice for families that lack time, tools, skill, and wish to save some money on a simple DIY project. Trim-A-Slab installs fast, about a foot per minute. A typical 2 car driveway with 100 ft of expansion joints is done in about an hour and a half. It will take about 37 tubes of caulk to do the same job! How many squeezes of the caulk gun is that?

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