Painting Advice and Premium Products from Experienced Professionals.
Caulking Tips and Advice
Courtesy of Sashco Sealants
The purpose of caulk (note: higher performing caulks are called "sealants") is to seal joints or cracks from the intrusion of water, air (either hot or cold), dust, pollution, insects and noise. Caulk can also serve the merely aesthetic purpose of dressing up or finishing off an otherwise rough -appearing joint. To properly serve these purposes, the caulk must stay in place - without cracking - for an extended period of time, and it can only do so if it maintains good adhesion to both sides of the joint and can easily flex with whatever movement occurs in the joint being sealed.

Understanding the job a sealant does is best understood by comparing its definition to that of an adhesive. Sealants are used to seal joints that move, and adhesives are used to prevent joints from moving. The following describes the basics of how to use caulking to get the most value out of the product, as well as your precious time and effort. By following the guidelines below you will greatly reduce the risk of failure and greatly increase the chances of achieving a sound, durable and attractive seal for many years to come.

The Four Keys:

1. Watch the Weather

Weather can effect the joint size and surface

Best caulking temperature; 50º-90ºF

Too cold – the surface will contract and the joints will expand – a frosty surface means poor adhesion

Too hot – joint will contract – a hot surface can cause blistering

A. 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: 1) The size of the joint at the time of caulking; 2) The contaminants on the surfaces of the joint; 3) The ability of the caulk to "wet" the surfaces of the joint for good adhesion; 4) The ability of the caulk to properly cure and develop its ideal physical properties; etc. (Note: Obviously, weather is of little concern when caulking inside a temperature-controlled house!)

B. 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. (Note: 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.)

C. Weather Extremes:
It is never good practice to apply caulk in very cold or very hot weather.
Here's why:
1) 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.

2) 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 (i.e., Sashco's Lexel) or reactive sealants (i.e., silicone).

3) 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.

2. Prepare the Surfaces and the Joint for Sealing

Clean out the old caulk

Clean the surface of all dirt, paint, oil, etc.

Use foam backer rod for joints 1/4" wide or wider

Use primer for joints under heavy stress

A. Removal and Cleaning:
Good surface and joint preparation is the real beginning of a professional and long-lasting caulking job, whether replacing old caulk or sealing a new joint for the first time. By using a putty knife, painter's 5-in-1 tool or other similar tool, remove all of the old caulk in the joint. A heat gun can be used to soften old caulk and loose paint to make removal easier, or 3M Indoor / Outdoor caulk-remover can also help remove all types of old caulk. The surface needs to be completely free from old caulk, peeling paint, weathered wood fibers, grease, oil, wax, dirt, rust, frost, moisture, etc. A wire brush works well to remove contaminants, and a drill-mounted wire wheel is often the best answer for cleaning dirty, unsound concrete. To remove some contaminants (like oil or grease) it may be necessary to wipe the joint down with a solvent-laden rag (letting the solvent completely evaporate before caulking). Remember, the best caulk in the world won't work if it is applied to a dirty or unsound surface.

B. Backer Rod:
If the joint or crack to be sealed is 1/4" wide or wider, it is best to install foam backer rod in the joint - to the proper depth - before applying the caulk.

The reasons are:

1) It saves money. Backer rod is generally cheaper than a good quality caulking compound, and most of the joint can be filled with the backer rod before the actual sealant is installed.

2) It provides the means to form an "hourglass" cross-sectional shape to the bead of sealant. This geometric shape allows the sealant to handle the inevitable joint movement much more easily than any other configuration. (The reason: Large surface areas of adhesion are established at the sides of the joint, while a relatively thin cross-section of sealant is left in the center of the joint to allow for easy flexing – see "flexible")

3) It provides a "bond-breaking" surface at the rear of the joint or crack that prevents the sealant from establishing three-point adhesion (see "two-point adhesion" - which, if allowed to occur, can lead to early failure.

5) It allows for additional pressure to be applied to the sealant during the "tooling" process, which further favors more sealant being forced into intimate contact with the sides of the joint for better adhesion.

Note: Backer Rod is easily installed in joints by simply pressing the material into the recess to a depth that will allow the thickness of the sealant to be approximately 1/2 that of the width of the joint. It can be installed just by pressing it into place with a finger or an appropriately sized tool. If you are using closed-cell backer rod, it is important to avoid damaging the surface of the rod (such as with holes or nicks) because wherever such damage occurs there is a risk of "out-gassing" from the backer rod and forming blisters in the sealant. (Note: Open-cell backer rod does not have this problem, but it has a much greater tendency to absorb water and hold it - with potentially very negative effects on the sealant - if the integrity of the sealant is breached at a later date.) Then, masking tape can be applied to both sides of the joint before caulking to prevent smearing on the exposed surfaces adjacent to the joint.

C. Primers:
If the joint or crack is in an area that will be subjected to particularly difficult stress, such as continual water submersion at the bottom of a swimming pool, it is important to use a primer before caulking. Primers are supplied by commercial caulking distributors for such special applications (look under "caulking" in your yellow pages).

3. Use the "Best" Sealant for the Job

Ease of application and clean up

Speed of cure

Check with manufacturer for performance information

Solvent-based for joints you can't clean

A. Best Performing Sealants:
The definition of "best" may be dictated by different circumstances. But, generally, the best performing sealants are those with great elasticity and great adhesion. The following attributes could also become factors for you as you consider what is "best" for a particular job: a) Speed of sealant cure; b) Paintability; c) Ease of application; d) Ease of clean-up; e) Odor and health effects of working with the sealant; f) Cost (especially when the total project life-cycle cost is considered); g) Shrinkage of the sealant; h) Toughness (or abrasion resistance); i) Chemical resistance; j) Heat or cold resistance; k) Ability of the sealant to adhere to the surface it is applied to, but not damage it.

B. Performance Information:
It is not enough to know the type of chemistry of a sealant to know whether it is the "best." Some "100% Acrylic" caulks can perform much worse than other "100% Acrylic" caulks. (The same can be said for "siliconized acrylic latex caulks" and other types of sealants.) Check with the manufacturer to get actual performance information. Cured physical samples - supplied by some manufacturers - are also a good indicator of performance, especially if you can compare them to other cured samples of candidate sealants. Be sure to understand the difference between the terms; elastic and flexible.

C. Surfaces With Poor Adhesion:
Sometimes circumstances prevent cleaning the joint surfaces as much as would normally be needed for good performance. In such cases, the "best" sealant to use could be a solvent-based product (like Sashco's Lexel) that has the ability - because of the solvents in the formula - to partially self-clean the surfaces of the joint with the solvents present for better adhesion.

D. What About Abrasive Areas:
Where abrasion of the sealant will occur - like on a sidewalk or driveway - the best type of sealant is likely to be the one that is toughest (even if it is not the most elastic). This type of situation is usually best handled by a polyurethane sealant. Yet, where abrasion of the sealant is a problem on the interior of a home - around a bath tub where abrasive cleansers are used - a toughened acrylic latex sealant will usually be an excellent choice.

4. Apply the Sealant Properly

Cut nozzle at 45º angle

Put tube in a caulking gun

Pull, don't push, caulk along joint

Fill joint making contact on both surfaces

Apply 2-3 feet of caulk at a time

Tool the caulk for good adhesion

A. Cutting The Nozzle:
Embossed markings are located on each tapered caulk cartridge nozzle that correspond to the size of the bead that can be dispensed when the nozzle is cut at each marking. By cutting the nozzle at different measurements, you can form a caulking bead to match your joint size. It' s easy! Just cut the nozzle at a 45o angle, place it in a caulking gun, and you're ready to begin (except that most cartridges have an internal foil patch at the base of the nozzle that needs to be punctured with a nail).

B. Getting Started:
Before you actually start to caulk, do some test caulking on a newspaper or paper towel to get a better feel for how the product dispenses. It is especially important to get the feel for keeping the caulking gun moving smoothly as you complete one stroke of the trigger and begin the next stroke. (Note: It is far better to pull the caulk tube nozzle along the joint than to push it. Pulling it allows the nozzle to smoothly slide over any obstructions on the surfaces being caulked; while pushing usually leads to more hang-ups and sudden stops (with attendant "blobs" of caulk occurring). Once you've run a few inches or feet of caulk and have a good sense of what to expect, then start your first caulking effort on a part of the house that is relatively out of the way and unnoticed. Then, by the time you get to those portions of the house that are more conspicuous, you will have developed a good level of skill and your results will show it. (Keep in mind: If you "mess up" a section of a bead, you can scrape it out right away and start over.)

C. Applying A Bead of Caulk:
As you apply the sealant, hold the caulking gun at a 45º angle parallel to the joint being filled. Orient the nozzle opening so that it forces sealant into intimate contact with the joint surfaces. As you finish applying each bead of sealant, relieve the pressure inside the tube by releasing the trigger and pulling back on the rod to stop the flow of caulk. (Releasing the trigger alone will not stop the caulk from flowing out of the nozzle.) Apply only about 2-3 feet of caulk bead at a time so that you will have enough time to get it "tooled" before it begins to "skin" over (which then makes tooling difficult or impossible).

The Art of Tooling:
"Tooling" the bead ensures good adhesion and a good look. "Tooling" is the process of gliding over the entire length of the applied bead of caulk in order to smooth it out and further force the thick caulk into enough intimate surface contact to establish good adhesion. (Remember, caulk is made not to flow; so, tooling is critical to force it into good contact with the substrate.) Tooling can be done with a finger (covered with a latex glove, wetted with some water or solvent, or just bare - depending on the caulk used), or with various tools (like a spoon, shaped piece of wood or a foam paint brush). It is important to avoid scraping an excessive amount of caulk out of the joint during tooling to avoid starving the joint for sealant and wasting a lot of caulk. Keep rags handy to clean up any mishaps, and clean up any problem areas right away since it is much more difficult to clean up dried caulk later. If masking tape is used along the sides of the joint, make sure the tape is removed immediately after tooling is complete (before the caulk skins over) so that it will pull away cleanly and leave a smooth, even line.

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