Siding Caulk: Everything You Need to Know

When it comes to home improvement, caulk is one of the best secret weapons a homeowner can possess. Used throughout the interior and exterior of homes to fill gaps or cracks, caulk is an incredible, flexible acrylic that can prevent air or moisture from getting in just about anywhere. Using caulk on exterior siding is a relatively straightforward process, but there are several things to think about before you go shooting your caulking gun across your entire home. Here we outline some siding caulk basics, including when to use (and when not to use) caulk, the best materials and colors of caulk for your particular home, and a few DIY tips and tricks to help you get started.

When to Use Caulk on Exterior Siding

Siding caulk can be used on several different areas of your exterior siding to help prevent water damage and moisture buildup. Some of the most commonly caulked areas of siding include both corners and crevices, as well as some butt-joints and window and door trim boards. When deciding how to use caulk on your siding, however, it is generally more important to consider where you should not use it. If overused or incorrectly placed, siding caulk can cause more damage to your exterior than good.

It is generally not a good idea to use caulking on wood siding. As homeowners with this kind of siding know, wood naturally expands and contracts with fluctuations in temperature and precipitation. Placing caulk over large portions of wood siding prohibits the natural movement of the wooden panels and can cause extensive damage to the exterior of your home.

Many professionals, like those at James Hardie, also agree that you should not use caulk on fiber cement siding unless there is no metal flashing underneath. Flashing acts as a waterproofing layer for this type of siding, and caulking will prevent the flashing from doing its job.

As far as trim boards are concerned, you should not caulk around these areas if they sit on top of the surface of your siding. Doing so would prohibit air circulation and cause a damp environment with the potential for mold buildup and prohibit the movement of siding and trim materials.

Finally, you should refrain from caulking the bottoms of horizontal siding sheets or the edges of the tongue and groove panels. The layering of siding panels acts as a natural waterproofing that will allow precipitation to fall off naturally, so caulking would stop the normal movement and function of your panels.

Choosing the Right Caulk for Your Siding

When searching for the right kind of caulk for your exterior siding, quality is obviously important — as with any home improvement project, cheaper does not always mean better. In addition, there are several other factors to keep in mind when choosing the right caulk for your siding:

Material

Siding caulk comes in a variety of acrylic materials, including latex, silicone, butyl rubber, or a mixture of these ingredients. All of these materials have different properties and are meant to be used for specific home improvement situations. You can read more about the various caulk materials at Repair Home.

Butyl-rubber is sometimes recommended for exterior siding since it’s a specialty outdoor caulk that can withstand changes in temperature and repeated exposure to the elements, but you can choose any exterior caulk that will bond to your siding—just make sure to read the labels and spot-check on an unseen portion of your siding to make sure.

Color

It is possible, and for some homeowners preferable, to color-match your caulk to your siding. Some siding companies stock bespoke caulks in pre-matched colors that will go perfectly with your siding (like James Hardie’s ColorPlus color matching scheme).

While it is ultimately up to you to determine what color to opt for, we would recommend choosing something inconspicuous in a shade slightly lighter than your siding — avoid white unless your siding is white. Remember that your caulk color and siding won’t match exactly since caulk and siding are made from two different materials with different consistencies.

DIY Caulking Tips and Tricks

If, after reading up on the whats and whens of siding caulk, you decide to complete this home improvement task on your own, there are a few things you should keep in mind. First, we recommend investing in a large, good quality caulking gun. There are cheaper and smaller options are out there, but we find that these will usually cost you more in the long run with cleanup since they are messier and require more frequent refilling.

During the caulking process, it is essential that you have a cloth or towel ready to mop up and smooth and excess product before it sets on your siding and makes a large and tough-to-clean mess. Remember where not to use caulk, since this is just about as important as knowing where to use it if you want to avoid larger home improvement bills and more frequent repairs in the future. And if you feel this job is out of your depth and personal expertise, you can always give yourself peace of mind and simply bring in a professional to complete the job for you!