Watch the Weather

It's important to keep the weather in mind when you are planning on caulking outside. The best conditions include temperatures between 50-90 degrees F. When the contact area is too cold, the surface will contract and the joints will expand. Yet temperatures that are too hot will cause the joint to contract and can even cause blistering.

Weather Affects Performance: Often, insufficient attention is paid to how the weather at or near the time of application can affect the long-term performance of caulks and sealants. Weather can affect:

• The size of the joint at the time of caulking;
• The contaminants on the surfaces of the joint;
• The ability of the caulk to "wet" the surfaces of the joint for good adhesion;
• The ability of the caulk to properly cure and develop its ideal physical properties. (Note: Obviously, weather is of little concern when caulking inside a temperature-controlled house!)

Ideal Weather Conditions: Plan your caulking efforts for the most ideal weather possible - which is between 50ºF (and rising) and 90ºF, and when precipitation is not a potential problem. If wet weather has immediately preceded a period of ideal weather, it may be necessary to let 1-3 days of the ideal weather pass to allow the surfaces to be caulked to dry out or warm up adequately. Similarly, avoid applying sealants - even in ideal weather - if the weather is expected to turn bad shortly after application.

Weather Extremes: It is never good practice to apply caulk in very cold or very hot weather.

Here's why:

If a sealant is applied at either extreme, the size of the joint being sealed will be at either its widest (when cold contracts the substrates) or at it narrowest (when heat expands the substrates). Then, if sealant is applied at either temperature (and joint-width) extreme, it will then undergo the greatest possible stress over time as the temperature travels to the opposite extreme. By applying caulk to a joint in the middle of the typical temperature range expected for your area, you will minimize the overall stress applied to the caulk as a result of thermal changes.

In extremely cold weather there is always a chance that micro-crystals of ice may be present on the surfaces of the joint, and this difficult-to-detect frost could lead to poor adhesion and failure - even for solvent-based sealants such as silicone.

In high heat (especially in intense, direct sunlight), there is an increased risk that whatever solvents (or volatile liquids) are a part of the sealant's formula could evaporate too rapidly and cause blistering or bubbling of the sealant - even at the bond-line, which could impair adhesion.

Courtesy of Sashco Sealants.