Polysulfide VS. Polyurethane

What Sealant Do You Need?
by Don Casey

In every Marine Center you will find an array of different sealants and caulks sufficient to make your head spin. With so many choices, how do you know which one you need?

It is not as difficult as you might think. Virtually all modern marine sealants fall into one of just three types, each with specific characteristics that make it the best choice for some jobs and unsuitable for others. Selecting the right sealant is essentially a matter of identifying the materials you are wanting to seal–specifically if any component is plastic–and of determining the likelihood of ever needing to separate these components.

If neither component is plastic and if you want to preserve your ability to disassemble the joint, use polysulfide.

Polysulfide is the most versatile of marine sealants. It is a synthetic rubber with excellent adhesive characteristics, and you can use it for almost everything. As a bedding compound it allows for movements associated with stress and temperature change, yet maintains the integrity of the seal by gripping tenaciously to both surfaces. It is also an excellent caulking compound since it can be sanded after it cures and it takes paint well.

However, the solvents in polysulfide sealant attack some plastics, causing them to harden and split. Specifically, you must not use polysulfide to bed plastic windshields or plastic portlights–either acrylic (Plexiglas) or polycarbonate (Lexan). Don’t use it to bed plastic deck fittings either, including plastic portlight frames. Plastic marine fittings are typically ABS or PVC, and polysulfide will attack both. If you know that the plastic fitting is made of epoxy, nylon, or Delrin, you can safely bed it with polysulfide. Below-the waterline through-hull fittings are in this group, but when there is any doubt, select an alternative sealant.

Polysulfide adheres well to teak (a special primer improves adhesion), and is unaffected by harsh teak cleaners, making it the best choice for bedding teak rails and trim. The black caulking between the planks of a teak deck is invariably polysulfide. For this application, a two-part poly-sulfide gives the best results. Polysulfide is the slowest curing of the three sealant types, often taking a week or more to reach full cure. Because it will adhere to almost anything, polysulfide has a maddening propensity to get on everything, so neatness is called for in using this sealant. Polysulfide sealants will have polysulfide printed on the package, or sometimes Thiokol–the trademark for the polymer that is the main ingredient of all polysulfide sealants regardless of manufacturer.

If you want the two components to be joined together permanently, use polyurethane.

Think of polyurethane as an adhesive rather than a sealant. Its grip is so tenacious that its bond should be thought of as permanent. If there seems to be any likelihood that you will need to separate the two parts later, do not use polyurethane to seal them.

Polyurethane is the best sealant for the hull-to-deck joint. It is also a good choice for through-hull fittings and for rubrails and toerails, but not if rails are raw teak because some teak cleaners soften it. Like polysulfide, polyurethane should not be used on most plastics–acrylic, polycarbonate, PVC, or ABS. The cure time for polyurethane is generally shorter than polysulfide, but still may be up to a week.

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DIY do it yourself? “FREE ESTIMATES”

There are numerous blogs on the internet that explain how to do DIY expansion joint replacement. We have rarely read one that was accurate. Often, the author misses the details crucial to longevity of the sealant. Preparation is the key which bloggers rarely touch on. We have found that bloggers seem more interested in providing a compelling story to drive website traffic than they are in telling “the entire story”. Bloggers claim it is simple to insert backer rod and apply sealant with a caulking gun without any real experience performing this task. Each project we do is unique and requires its own set of obstacles to overcome. Just bending over or working down on your knees on concrete is hard work, not to mention bloody knuckles from scraping the concrete while trying to remove old sealant or wood.

Grinding or power washing the interior joint wall is critical for sealant longevity. Dust must then be removed from the joint by compressed air and the joint must be completely dry. Backer rod is next to impossible to find at your local hardware store and when you find it, it is generally found to be too small. An average expansion joint ranges from ¾” to 1” in width and 4” deep. Mastic Masters carries 9 different backer rod sizes to accommodate the variety of joint sizes due to movement. This is also why prefabricated expansion joint products don’t work. If they do go in snug, they soon will settle down when the expansion joint contracts.  Prefabricated expansion joints are required by the ACI (American Concrete Institute) to use a lubricant sealant to hold the filler in place and provide 100% water tight seal. See TrimGasket for more details as to the deficiency of pre-fabricated expansion joint fillers.

A consumer can buy a 29oz Tube of Sikaflex SL concrete grey sealant, with no other options in colors, at Home Depot, Lowes or Wal-Mart for about $12.98 a Tube. The package claims you get 12ft at 3/8 bead, meaning you get 3/8 width and 3/8 depth per Tube @ 12ft.  As such, if you had a 1” joint, you would need ½” depth of sealant.
Therefore, you would need 3 Tubes to cover 12 ft of 1×1/2 expansion joint costing you $38.94 plus tax for just 12ft  or  $3.25 a ft. plus tax. This does not even cover the cost of backer rod or any other tools required to complete this project. Mastic Masters charges far less for the same work (taxes included) with a two year warranty and we come to you. We offer 80 color choices to match your concrete. What are you waiting for?

Joint Sealing is a necessity, not a luxury! Joint sealing is specified in every commercial expansion joint in every major city world wide. Your home and property should not be the exception. Sealing joints protect people and property from erosion, staining, trip hazards, pest invasions, splinters and it simply just looks better.

Sustainability is Concrete Repair!


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Why Sealing is NEEDED?

ACI 504R-90

The introduction of joints creates openings which must be sealed in order to prevent passage of gases, liquids or other unwanted substances into or through the openings.

In buildings, to protect the occupants and the contents, it is important to prevent intrusion of wind and rain. In tanks, most canals, pipes and dams, joints must be sealed to prevent the contents from being lost. Moreover, in most structures exposed to the weather the concrete itself must be protected against the possibility of damage from freezing and thawing, wetting and drying, leaching or erosion caused by any concentrated or excessive influx of water at joints. Foreign solid matter, including ice, must be prevented from collecting in open joints; otherwise, the joints cannot close freely later. Should this happen, high stresses may be generated and damage to the concrete may occur. In industrial floors, the concrete at the edges of joints often needs the protection of a filler or sealant between armored faces capable of preventing damage from impact of concentrated loads such as steel-wheeled traffic. In recent years, concern over the spread of flames, smoke and toxic fumes has made the fire resistance of joint sealing systems a consideration, especially in high-rise buildings. The specific function of sealants is to prevent the intrusion of liquids (sometimes under pressure), solids or gases, and to protect the concrete against damage. In certain applications secondary functions are to improve thermal and acoustical installations, damp vibrations or prevent unwanted matter from collecting in crevices. Sealants must often perform their prime function, while subject to repeated contractions and expansions as the joint opens and closes and while exposed to heat, cold, moisture, sunlight, and sometimes, aggressive chemicals.


HOA approved and recommended

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