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How to Seal Cracks and Gaps in Concrete

How to Fix and Repair Cracks in Concrete

Cracks in concrete can be fixed by using a polyurethane joint sealant called Vulkem. The Vulkem comes in two different styles – Semi-Self Leveling (SSL) or Non-Sag (NS) . If these are cracks that are in a driveway, sidewalk, steps, garage or basement floor, these products are best suitable. 

You do not want to add a cementitious product to a crack. During season changes, the concrete can shift, and it will just break out the hard cementitious product that was put in place, possibly causing worse cracking. The Vulkem is a flexible joint sealant designed for this. If the crack you are fixing is completely horizontal, then the Vulkem 45SSL will be best. Be sure to use the Kool Rod backer rod in place before dispensing out of the tube. 

If there is any slope to where you are repairing the crack, then you need to use the Vulkem 116. It is a thicker material, and it will not run like the self-leveling. This can also be used with an Kool rod backer rod. If you are fixing a crack that has a water repair in a wall, you will need to use a 3-step product called Krystol PlugKrystol Grout, and then Krystol T1. Or the crack pack injection kit.

Once you determine the best product to use for your job, the materials can be gunned out using a caulking gun, the semi self level will level itself out, where the Non sag will require a bit more work smoothing out each crack with your finger. This is something the average home owner can do, there is no need to hire a professional for this job.

How to Seal the Gap Between Siding & Concrete

Vulkem is a concrete sealant for filling gaps in siding and the cracks in concrete. For areas that need to be filled with siding, the vulkem would work, however you may be able to use a product more cost effective such as a Pl Premium. Vulkem has a good adhesion to most construction materials such as concrete, precast concrete panels, wood, PVC joinery, and aluminum. It is available in a non-sag version or a semi-self leveling. Its very easy to apply as most homeowners already have a caulking gun kicking around. 

The Non sag comes in a 300ml cartridge and is applied with a regular small caulking gun. The Non-Sag version must be smoothed out; This can be done by using a putty knife or your finger, just make sure if you use your finger that you have a bucket of water with dish soap nearby - this helps when it sticks to your fingers.

The Vulkem 116 can be used horizontally or vertically. The Vulkem SSL is a self-leveling material and can only be applied to flat, horizontal surfaces. You must use a back rod in the gaps prior to the Vulkem 45 SSL as this allows the self-leveling material to stop and not just run down the entire gap. Be sure that the backer rod fits snug but not too tight. Usually, you want it slightly larger than the gap. 

Backer rod can be used for the Non sag sealant as well but is usually only needed for the wider gaps to ensure it is not applied too thick; It will not cure properly if it is applied too thick. Another product that can be used to seal small cracks in concrete or hairline cracks is Matchcrete Clear. This product is also great for decorative crack sealing because it is clear.

How to Repair Cracks in a Concrete Basement Floor or a Concrete Garage Floor

Cracks in a basement floor can be repaired by using a few different products. This will depend on how wide the crack is and if there is a water issue or not. 

Ask yourself the following questions: Is it a hairline crack or a wider crack? Is there water coming up into the crack? Are you putting anything on the floor afterwards, like a coating, stain, sealer, or overlay? 

Polyurethane sealants cannot be covered up with any type of coating or overlay. Why? The material gasses off and won’t allow anything to stick to it. If a crack or spall is needed to be repaired and covered up with an overlay or coating, you would require a material called Roadware 10-minute concrete mender. This product can only be used indoors and is black in color. 

If you are repairing a hairline crack in a polished basement floor, you will want to use Matchcrete clear. This can be polished after it’s cured, and it is clear in colour so it is aesthetically pleasing. 

For wider cracks that will not be coated and that you simply just want to fill, a polyurethane can be used. This material comes in two forms Vulkem 45 SSL (Semi-Self-leveling) and Vulkem 116 (Non-Sag). If you plan to use the self-leveling, you will need a backer rod. This gives the Polyurethane something to sit on so it doesn’t run down the entire depth of the crack; If it’s applied too thick, the material wont cure properly. Backer rod can also be used with the non- sag but is more common and required for the self-levelling. 

If you are having water issues coming up through the floor, you will need to do some major grinding and cutting work. This can be done by channelling out the crack 1.5" wide and 1" deep. You will need to make the channel into a rectangle shape, not into a "V" shape. 

The three products that are needed are Krystol Plug, Krystol Repair Grout, and Krystol T1. Remember to take caution when mixing these materials up. Start with a very small amount as
the setup time is about 1-2 minutes. The colder the water, the better. We suggest having a few ice cubes floating in the water to ensure that it’s cold. 

The first step (if it has running water) is to plug it with the Krystol Plug - you want this to be no thicker than 1/2". Dampen the surface and press the plug tightly in the channel until it’s set up. It should only take a few minutes. Complete this until the entire channel is filled 1/2" thick. Next, you will need to mix up the Krystol Repair Grout; Again, this sets up very fast, so cold water with ice cubes is best. This material will be used to fill the rest of the channel (the other 1/2"). 

Prior to pressing into the channel, the surface should be damp with water (saturated-surface- dry or SSD – this means wet, with no standing water). Press the Krystol Grout into the channel and hold it in place until it sets. The Krystol T1 is a protective coating that crystalizes the pours of the concrete, creating a permanent waterproof barrier. The area needs to be SSD prior to this application as well; Mix up the T1 in a small clean pail and spread it overtop of the cracked area, at least 12" on either side of the gap. 

After about 6-24 hours you can wet cure; This helps retain any moisture. Keep it covered with a tarp or poly and continue this process for 3 days. Once it’s set hard it is complete. 

These techniques can be used for a basement floor or wall with water issues. If using 10-minute mender on a garage floor, make sure it is covered afterwards with an overlay or a decorative coating. This material oxidizes in the sun and is meant for interior applications only. A garage is one of those grey areas where it can be considered Interior or Exterior. 

Do Concrete Expansion Joints Need to be Sealed? 

Yes, concrete expansion joints need to be sealed. They can be sealed with a flexible sealant such as the Vulkem 116 or Vulkm 45SSL

Use the (Non-sag) if the concrete slab has any slope to it. If it doesn’t have any slope you can use the (Semi-Self-leveling).

Products we recommend, available at (ALL WILL HAVE LINKS ATTACHED) 

- Vulkem 116 (Non-sag)

- Vulkem 45 SSL (Semi Self-leveling)

- Kool Rod

- Krystol Leak Repair System (Krystol Grout & Krystol Plug) 

- Krystol T1 & T2 Waterproofing System 

- Roadware 10-Minute Concrete Mender

- Roadware Matchcrete Clear