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A Letter from Sandy
  Deember 2014

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Choosing the Right Exterior Caulk

If you prepare your home for winter by sealing out moisture and outside air with a high performance caulk, you'll not only reduce energy costs you'll prevent costly repairs from rotted wood and blistering paint.


Choosing the Right Exterior Caulk


Why Caulking is Important

If you prepare your home for winter by sealing out moisture and outside air with a high performance caulk, you'll not only reduce energy costs you'll prevent costly repairs from rotted wood and blistering paint. Proper caulking also will retard the growth of mold and mildew and it will reduce the number of insects and small creatures who visit your home looking for food, shelter and warmth. There are lots of good reasons to check the caulking around your home and make sure it's in good condition. If you find that re-caulking is needed, how do you find choose the right one when there are so many types of caulk to choose from?

Properties of Good Quality Caulk

All caulking material must have excellent adhesion properties so that it can be used with a variety of building materials, even under wet conditions. To maintain a watertight and airtight seal, it must also be flexible. It's also important that a caulk be able to maintain these properties over time or it can pull away from the surface and fail to do its job. A good quality caulking material must also be attractive and stay clean, even after years of service.

Questions to Ask

When you're choosing an exterior caulk, ask yourself these questions:

  • What surface(s) will it be applied to? Is a specialty caulk the best choice? For instance, choose a specialty caulk for brick and a 100% silicone caulk for your roof.
  • Do the caulked surfaces need to be painted? If so, don't use a 100% silicone caulk because it's not paintable.
  •  If the adjacent area can't be painted at all (such as where vents or flashing meet the roof), what color caulk would work best, or should you use a clear caulk?
  • How large are the gaps or cracks that need to be bridged?  Most caulks work best on cracks that are less than a quarter of an inch wide. If you do need to caulk a wider area, choose a specialty caulk formulated for this purpose or first fill part of the recessed area with an appropriate material.
  • Do you prefer a caulk that's user-friendly? Some caulks require mineral spirits to clean up, and some caulks such as high quality urethanes are very difficult to apply. If you require ease of use and water clean up, choose a siliconized latex caulk or a specialty caulk as appropriate.

Some Basic Types of Caulk



100% Silicone


This type of caulk adheres best and lasts the longest, but it sets up quickly and is more difficult to apply and correct mistakes, requires mineral spirits to clean up and can't be painted

. It's best for non-porous surfaces and has a shorter shelf life. Check the expiration date on the tube because if you use one that's outdated it won't cure and makes a mess.


Polyurethane Caulk


This type of caulk is the best for almost any application, but it can be difficult to use and requires mineral spirits to clean up. It can be painted.


Elastomeric Caulk


This type of caulk is an excellent choice for most porous surfaces because of its flexibility and adhesion properties, its ease of use and water clean up.


Latex Caulk


Although it tends to be less expensive, latex caulk will harden when exposed to the elements so its durability is questionable and it's not the best choice for exterior surfaces.


Siliconized Acrylic Caulk


The most popular caulk and easiest to use, this is a good choice for most applications.


Synthetic Rubber Caulk


Known for excellent adhesion, the ability to stretch and recover and for mildew resistance.

Butyl Caulk
There are numerous problems with butyl caulks. They're difficult to use, dry slowly, require solvent clean up and have a tendency to shrink excessively and harden and crack quite prematurely.

Within each category of caulk, look for one with a 50 year warranty. It's worthwhile to pay a little more for a better grade of caulk.

Areas to Check

Examine the following parts of your house to see if caulking may be needed:

  • Where the siding meets the foundation
  • Around air ducts or vents, heating or cooling equipment, openings for plumbing or wiring
  • Where window or door frames meet siding
  • Around skylights and the chimney
  • Where different types of building materials meet
  • Where wood, vinyl or aluminum siding forms corner joints

Some Words of Caution
Keep in mind that not every crack should be caulked. On older homes with lapped siding, don't automatically caulk the undersides of the boards as these houses need to breathe. Check with a contractor about the construction of your home to determine if it's appropriate. Also, some modern garage doors are designed to have panels that "float" and caulking might void the warranty. Investigate the construction of your particular doors to see if caulking is safe before you do it.

Doing the Work
Once you've chosen the right caulk, make sure that the surface you're applying it to is clean. If the old caulk has failed, scrape it out and wipe the area with a damp cloth to remove dirt or residue. Make sure the surface is clean and dry so that the new caulk will adhere properly. Weather conditions are important as a water-based sealant can't be used when it's wet outside and if it's too cold, a water-based caulk won't cure. Read the label. Check required drying time. Some caulks can be painted with a water-based paint within four hours, but you must wait twenty four hours to use an oil-based product, including a primer. Read the label. Sometimes the caulk will shrink, making a second application necessary. Read the label to determine how long you must wait to recaulk.

Prepare the tube for use by cutting the tip at a 45° angle. If you're using a water-based product, have a bucket of water and a cloth at hand. Apply the caulk in a continuous and even bead with no gaps. For the best appearance, lightly wet your index finger and smooth the bead.

Choosing the right caulk may not be an exciting topic, but it's one that's well worth knowing something about.

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