Concrete expansion joints allow expansion with temperature & humidity changes. This is important to prevent water/ice from shortening the life of your concrete driveway or walkway. If you are selling, this is important for curbside appeal.
This will prevent moisture from getting under your concrete sections: this is basic erosion.
The list of everything you need appears at the bottom.
How to replace driveway joint sealant:
1. Remove what is loose from the old joint.
Use a utility knife to remove old material and clean any residue that you can. You may need to use a chisel or go nuclear with a variable speed angle grinder with a cutting/masonry disc. Don’t use high-speed grinders: they will melt the old sealant. Be sure to use the safety guard and cut-resistant gloves (linked below). More fingers are lost with these cutting wheels than with saws.
You may need to dig down an inch to the foam backer foam ‘rod’ or whatever is in there. Acetone may help dissolve synthetics if there are any. Usually, it’s just old wood.
For the bits of old seal that will not come out, leave it. If it is still tight against the slab, that is what you want. Use a shop vac with a small crevice tool to get maximum suction and get all the loose bits out. Water pressure works too, but then you have to let it totally dry which could take several summer days.
2. Insert backing rod’
Before you shoot in the sealant, insert a closed-cell foam backer rod in between the joints. Avoid plywood: it’s not nearly as good as foam. This product is ¾ inch but you can get them in any size. This is also very inexpensive. This is made from low-density polyethylene foam that will fill most of the joint, and you’ll use less sealant. Get the size that is about 1/8 inch larger than your joint. If the joint is too big, braid 3 smaller rods together.
Push it down below the level of your driveway surface about ¼ inch. This gives you plenty of room for a good sealant layer. You don’t want it too thick or too thin.
3. Watch the weather forecast.
The sealer cannot be applied below 40°F (4°C). Pick a moderate day for best results, with no rain expected for another full day. Don’t drive on it for 5 days because it takes that long to cure, and that is for a moderate summer day.
4. Optional: sealant primer
I recommend highly the Silka products and really nothing else. Silka is the construction standard and they make products for all types of building materials from homes to high-rises.
Silka tells me that a primer is not absolutely necessary, but will always improve the bond between the concrete and the sealant. It’s the only product on this page that could be described as ‘expensive’, but a pint will last you a lifetime of sealant changes. You’ll need a small brush as well.
5. Prepare the tube of sealant
For the Silka sealant, I recommend buying several smaller size tubes of sealant: unless you have a larger size caulk gun. Most homeowners don’t need a gun bigger than the 10-11 oz. size. This size tube is much more commonly used in other projects: glue, caulk, etc. I’m a professional painter and I never have owned a large gun.
Go with the best: Sikaflex Pro. It stays flexible and is really sticky.
Cut the nozzle at an angle and use a long skinny poker to break the seal. I explained all this in my post about how to load caulk guns. Experiment with the size of the opening: you don’t want it too small. Have some disposable rags handy. Acetone is the solvent for what you get on your hands. Gloves are smart.
6. Let the goodness flow
Shoot in the Sikaflex sealant. Remember, it’s self-levelling, so no need to smoosh as you do with caulk. When it dries, it’s watertight and you’re ready to apply whatever driveway paint or sealant you like on your concrete.
Below is the full list of materials you’ll need to do this job.
For other concrete treatments start with these posts (they lead to all my posts on concrete):
If you have an old sealant (e.g. clear waterproofing), have a look at concrete prep for stain or sealant/paint.
The other post is if you plan to prep for stain or paint concrete in any condition.
The Applachian Mountians were once as big as the Rockies today. Erosion at work.
- Utility knife and spare blades
- Rags and acetone (in most nail polish remover)
- Cut-resistant gloves
- Variable speed angle grinder with a high-quality cutting disc
- Sikaflex self-levelling sealant
- Sikaflex foam backing rod
- Caulking gun for 10-11 ounce tubes
Any comments? Please feel free below.