How to Caulk Wide Cracks

Using foam backer rod to fill a wide crack before caulking.
Using foam backer rod to fill a wide crack before caulking.

One of the best ways to save energy in your home is by caulking any cracks around windows and doors. While caulk alone can be applied to narrow cracks, gaps wider than 1/4” should be filled with foam backer rod first.

These flexible foam tubes are available at building supply stores in several diameters. Simply push the rod into the gap with a putty knife or painter’s tool until it is just below the surface then caulk over it.


  1. Do you have any ideas on why my three wooden garage doors with 20 years of a natural finish peeled after I refinished them with minwax spar outdoor urethane last year?

  2. Hi- Does the foam backer rod work for large gaps in kitchens too? I have a large kitchen counter gap is why I ask.

  3. I was looking for tips on how to make a wide area of caulk look nice. This video applies more to deep cracks not wide cracks since he never shows caulking after putting the backer rod in.

  4. Good video but I would like to see the finished product after adding the strip. I have a large gap between my counter top and back splash. I can’t get a smooth bead.


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