How to fill the gap between a concrete patio and house?

This article will discuss methods to fill the gap between your concrete patio and your house. Discussion on the purpose of this gap in your homes and how to install this gap is also presented in this article.

How to fill the gap between a concrete patio and house?

One way to fill the gap between your concrete patio and your house is through caulking this gap. Caulking involves using a material that will seal joints or seams to prevent leakage or for water to enter the concrete gaps transferring this absorbed water inside your homes.

Materials you need:

Step-by-step instruction:

Step 1: Determine any material that makes the gap more porous.

Old disintegrated asphalt saturated fiber boards can be the reason why the gap is more porous. 

Step 2: Clean the gap.

Remove any porous material other than the soil in the gap. You can use a flathead screwdriver to remove the fiberboars then vacuum the debris to ensure that the gap was cleaned.

Step 3: Determine the size of the gap.

Check first the size of the gap so thath you can determine the thickness of your bakker rod you need to install and the amount of sealant you need to use to seal the gap.

Step 4: Insert the backer rod.

Trim the backer rod as based on the size of the gap using the pair of scissors, then using your finger lay the backer rod into the gap. Set the rod ¼ inch lower than the surface of the concrete. You can further even out the backer by rolling the foam backer using a spline roller. Again, as a reminder, use the exact backer rod thath works best wth your sealant . This will ensure that you do not need to do the repair again.

Step 5: Apply the sealant

Apply the concrete crack sealant or a urethane caulk to the gap once the backer rod was properly paced. There are various options of sealant you can use depending on the appropriate purpose of sealing or what other issues you want to be solved by sealing the gap. For example, if you opt to have a waterproof concave lip look in between the patio and the wall of your house that’s why a concrete crack sealant applied with a caulk gun can be done.

Fill the gap at the farthest corner first and apply to the gap as based from the instructions in your sealant. Always mind the gap while applying the sealant and ensure to just apply enough sealant that can cover the backer rod and the space between your patio and the wall of the house. As soo as you identify the width of your sealant cover it with ⅛-inch layer of sand.

Step 6: Smoothen the sealant.

Using the back of a plastic spoon, you can smoothen the sealant along the gap. Clean the spoon with rag and mineral spirits when sealant sticks in the spoon. Doing so will ensure that the sealant is evenly leveled in the gap.

Step 7: Caulk narrow cracks.

Cracks of about ¼ inch wide or less can be caulked without uing backer rod. Just carefully draw the caulk gun down the crack then smoothen the sealant above the gap.

Step 8: Allow the sealant to cure.

Allow the sealant or tha caulk to dry and cure for about 24 hours. Once the sealant hardens, brush off the excess sand added and save it. Check the kind of finish you want for the job. There are different formulations of patio sealers you can actually use that can provide a different finished look to your paving slab. These includes the following:

  • Satin finish patio sealant
  • Gloss wet look finish patio sealant
  • Matt finish patio sealant
  • Color enhanced finish patio sealant.

Also, you can further add sand and adjust the amount based on the look you prefer.

Why is there a gap between your concrete patio and your house?

Gap in between your concrete patio or concrete steps and house is usually referred to as expansion joints. These expansion joints are put placed before the concrete is poured in your garden walkway, driveway, garage floor, basement floor and in between your concrete patio and your house or any other areas where a slab meent another slab.

The purpose of these expansion joints is to allow the two different slabs to freely expand and contract at varying weather conditions especially during hot weather conditions and prevent the gap to be a water drainage. Concrete or paving slab outside or located in your patio receives direct sunlight during summer and bakes it, while the slab inside your home sits in the shade. This indicates that the rate of expansion and contraction of two slabs is different, expansion is more prominent on the paving slab.

Therefore, it is important to fill the gap with a material that is flexible to absorb this motion. Furthermore, you need a material that will prevent precipitaion or absroption of water in between your patio slab and retaining wall during winter. Thus, using cement based to fill this gap like mortar and gravel is not an option because it will just crack and will allow absorption of water and drain this water inside your house.

Installing expansion joints in between concrete slabs

There are three methods you can use to create expansion joints for your concretes. The easiest way is to add expansion joints during pouring, slip an expansion joint material in between sections and position it along the edge of the form. Materials you can use are asphalt coated material, cork, plastic, or bakker rod. Make sure that the material extends to the full width and depth of the slab.

Second method is to use a joint trowel. when  pouring and troweling your concrete slab create a narrow space between slab sections using a joint trowel. The disadvantage of this method is it does not allow the expansion joint to extend completely on the entire thickness of the slab. Nonestheless, it creates enough space on top of the slab to allow the expansion and contraction. This method, therefore, is usually used for narrow concrete surfaces only such as sidewalks.

If the concrete slab was already poured and cured, an expansion joint can be added using a concrete saw. This third method will require a concrete saw to cut through your concrete slab. Mark the width and depth of your expansion joint then cut.


The gap between your concrete patio and house serves a purpose of maintaining the integrity of your home by allowing your slabs to have room for expansion and contraction at different weather conditions. With this purpose, appropriate material shoul be used to fill this gap to prevent damage in your concrete floor and walls and to prevent water absorption in your concrete.

There are several methods you can use to successfully install these expansion joints depending on the thickness of your slab and the stage of construction you want to install these joints.

For any questions and suggestions about this article, please feel free to submit your thoughts in the comment section below.

FAQs: Fill the Gap Between a Concrete Patio and House

What do you use to fill concrete expansion joints?

You can use foam backer rods to fill concrete expansion joints. This is a good alternative to self-leveling sealant. The diameter of the backer rod should be ⅛ inch larger than the width of the concrete expansion joint. Backer rods also ensure a watertight seal. This is effective especially if the rod sits underneath the concrete pad surface.

How often should you put expansion joints on concrete?

An equal distance of 24 to 30 times the slab thickness is the common valur for expansion joints space. For joint  spacing wider that 15 feet requires the use of load transfer devices such as dowel or diamond plates. The joints should also be placed that are square as possible with length to width ratio of 1.5 is to 1.

Why is the ground sinking around my house?

If the ground around your house is sinking there is a possibility that there are serious problems on your foundation. Other noticeable sign can also be observed to indicate that there are actually foundation problems. These signs include stuck windows, cracked bricks, house settling noises and drywall cracks.

How deep do you cut expansion joints in concrete?

Saw cuts should meet the structural engineering specifications usually the rule of thumb is to cut the joints ¼ to ⅓ of the slab thickness. Thus, for a 6-inch thick slab it requires 1.5 to 2 inches deep. If it is cut too shallow, cracking may occur but if it is cut deeper, the aggregate interlocking will ntot be enough to transfer loads.

Why do they cut lines in concrete?

Sidewalk lines or technically called contraction joints are the lines they cut in concrete for walkways. They do this to prevent random cracking in your concrete slab that may break them apart. Contraction joints should be cut in the fresh concrete before the concrete dries, otherwise it will be hard to cut through. With these lines cracks that formed in your concere can follow the path of the cotraction joints.


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