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Caulking is a process used to seal the seams in wooden boats or ships, and riveted iron or steel ships, in order to make them watertight. The same term also refers to the application of flexible sealing compounds to close up crevices in structures against water,  air, dust, insects, or as a component in fire stopping.

Caulk (calk) can refer either to the caulking substance or to the process of applying it. Caulking as a term has spread to the building trade, meaning the activity of closing up joints and gaps in buildings. The function of caulking is to provide thermal insulation, control water penetration and noise mitigation.

This is mostly done with ready-mixed construction chemicals sold as caulk such as silicone, polyurethane, polysulfide, sylil-terminated-polyether or polyurethane and acrylic sealant.  Unlike construction caulk, which is applied where no building movement is expected, a sealant is made of elastomeric materials that typically allow movement of 25% to 50% of the width of the joint.  Silicone sealants form a durable, water-tight seal, but are not typically paintable.  Some silicone sealants are made to be paintable with certain types of paint such as water or oil-based paints.  Other sealants are paintable.

One-component sealants are commonly sold in cartridges which are loaded into a pistol-like caulking gun (opening at the side) or barrel gun (opening at the end) for application. During the tool-working time, which varies by chemistry, the bead can be pressed into the joint so that it can bond with the materials on both sides, and also be smoothed.  The time it takes for a chemical sealant to become a rubber is known as the curing time and varies by temperature and humidity.  Issues of technique that may not be obvious to first-time users:

  • The nozzle must be chopped short to match the intended      size of the bead. If the opening in the nozzle is too small, the bead is      liable to bunch and is difficult to keep even.
  • Common tools are a pointing tool, shaped wood, wet      finger or a spoon. Detergent should not be added to the moisture for      tooling since it may drip onto the bond surface causing a loss of      adhesion.
  • For neat work, the worker may apply painter's masking      tape beforehand, taping off the areas on each side of the joint to catch      any surplus, and remove the tape again before the tooling time has      expired.
  • To prevent three-sided adhesion or to avoid sag in      wide, deep joints, a backer rod     made of plastic foam can be pressed into the gap before caulking.

Backer rod can also be used to fill cracks in sidewalks, and masonry before caulking.  It is composed of a foam roll that is generally about 1/4 inch to 1 1/2 inch thick.  The material is stuffed into the cracks to be sealed and then caulked over.

Caulk is great a material that can help you do it all. Aside from sealing cracks and filling in any gaps or joints you have inside or outside of your home, caulk is also used to help waterproof and weatherproof homes. It is easy to use and very durable.  Considering that caulk is a multi-purpose wonder material for your home, it is even better to know that it is relatively inexpensive to buy. 

Using Caulk
Caulk can be used on practically any surface, including: 

  • Bathtubs 
  • Tiles 
  • Plumbing Fixtures 
  • Siding 
  • Moldings 
  • Skylights, window panes and windows 
  • Door frames 
  • Baseboards 
  • Flashing 
  • Foundations 
  • Concrete and mortar 
  • Blacktop and roofing 
  • Baseboards 
  • Plaster walls 
  • Air conditioners 
  • Gutters and downspouts 
  • Fireplaces and wood burning stoves 

It is important to remember, though, that there are different types of caulks.  Some may be more suited to the project and surface that you are doing than others. Also, keep in mind that, while acrylic caulks are slightly easier to use, they often deteriorate with exposure to water. If you plan to caulk an area that is exposed to water, then use a solvent-based caulk. 

Caulking a baseboard
Caulking a baseboard

Easy as Pie

It doesn’t matter if you’re a novice or a pro, caulking really is quite simple to do.  That is because caulk is almost always applied in the same way, so you don’t need to learn any fancy, new techniques each time you want to use it.
You can buy caulk in either a squeeze tube or as a cartridge. Be aware, though, that if you buy a cartridge, you will also need to buy a caulking gun. Whenever you plan to do some caulking, make sure you have these items nearby: 

  • Paper towels 
  • Bucket of water 
  • Mild cleaner or rubbing alcohol 
  • Sponge 
  • Caulk smoother 
  • Utility knife 

Before You Get Started

No matter what you are caulking, always make sure that the surface of your project is clean.  A clean surface will help the caulk adhere better. 

  1. Remove any dust or dirt from your surface with warm water. Never use soap. 
  2. Remove any leftover caulk that may be lingering on your project's surface. New caulk may not adhere properly to the old caulk. If you’re using a utility knife to do this, be careful not to scratch the surface. If there is any residue left, use a mild household cleaner or rubbing alcohol to remove what is left.
  3. Also, be sure to remove any mildew from the area using a cleaner specially formulated for mildew. 

Remember, caulk doesn’t last forever!  There should be an expiration date on the package. If not, then throw out any unused caulk after one or two years.  If you’re not sure that your caulk is still good, then give it a test run on a non-porous surface.  Does the caulk stick? Is it coming out smoothly?  Does it set within the appropriate amount of time?  If the answer is yes to all three questions, then your caulk is still good. 

Caulking Time!

If you’ve never caulked before, it may be a good idea to give yourself a test run first. Just use last week’s newspaper to get a feel for what you’ll be doing. Once you’re ready to put theory into practice, then follow these simple steps! 

  1. Cut the nozzle of the caulk cartridge. Because it is a tapered nozzle, the closer to the actual cartridge or tube you cut, the wider the opening will be.  Most nozzles come with markings on them. So, if the crack you are filling is about a ½", then just follow the guidelines on the nozzle.  Always cut at a 45° angle. If you are using a cartridge, then place it in the caulking gun. 
  2. Always apply caulk holding the tube or gun at a 45° angle.  Use even pressure to squeeze the tube or trigger. 
  3. As the caulk comes out of the nozzle, slowly move the tube or gun along the surface to be filled or sealed. Always go at an even pace. Your caulk should be able to fill the entire area where you are applying it. If it doesn’t, you may need to cut a larger opening in the nozzle.  But remember, it’s better to apply too little caulk and add more afterwards than to apply too much. 
  4. Once you have applied all of your caulk, use a caulk smoother to even out the finish. If you don’t have a caulk smoother, then just wet your finger or a popsicle stick to smooth out the bead of caulk. 
  5. When you are done applying all of your caulk, give it time to thoroughly set. It should indicate on the package how much time is required for the caulk to set.  If you plan to paint over the caulk, it is important that the caulk has completely set before you start painting. 

#1 Tip: If you’re caulking around your bathtub, do it right. Fill the tub with water before you start. Tubs tend to sink ever so slightly when they are full. So, when you caulk an empty tub, you may not apply enough caulk to compensate for the sinking. Which means you’ll end up with cracked caulk the next time someone takes a bath.

# 2 Tip: When smoothing your caulking with your finger, dip your finger into a small amount of little baby oil, begin smoothing. Then as you begin to feel a slight drag on your finger tip, clean your finger, re-dip into baby oil and continue. 

Remember, less is more.