What is the best sealant to use?
There are many good choices, yet there are some products on the market that are not very good.
To start with, let's talk about caulk and sealants in terms of chemistry.
Caulking is a generic term referring to a liquid or paste that is used to seal a gap between two parts with the intent of making the joint waterproof. The chemistry of sealants vary, here are some general terms to understand.
Sovlent Base sealants start as a liquid and then dry through evaporation. The solvent component helps them stick to dirty surfaces, however as they continue to dry over time, they can become brittle, shrink, and crack. Solvent Base sealants can be sometimes be identified by their ingredients which can include Toluene, Xylene, Naphtha, and Petroleum Distillates.
Water Base or Latex Base also turn solid by drying and can be cleaned up with soap and water . While easy to use and effective in light duty applications, we generally don't reccomend Water Based products to be used on RV's, which are subject to extreme weather and chemical expose.
In comparison, Reactive Chemistry sealants go through curing process as they change from a liquid to solid. Most of the RV products are 1-part with the curing from a liquid to a solid initiated by moisture in the air or on the surface of the part. The Super Glue you buy at the store is a "moisture curing" chemical, and the Silicone, Urethane, and Modified Silane sealants cure the same way.
We prefer the Reactive Chemistry products and will discuss these in greater detail.
Silicone
Silicone is a high-performance, 1-part, moisture cure sealnat that has the potential to outlast and outseal traditional products. It does not shrink and dry out. It has a high-gloss finish and is available in clear. The downsides include not being paintable, the fact that nothing else will stick to silicone so you will always have to use silicone, and they are subject to peeling when featheredged.
Urethane
Sikaflex makes a line of 1-part urethane sealants that have great for durability and adhesive strength. The downsides include a matte finish and they can become dingy as the surface holds dirt.
Modified Silanes and other hybrid products are advanced polymer-based sealants that combine the best properties of both silicone and polyurethane to deliver superior performance, however not recommended for continous water exposure and are higher priced.
What is butyl tape?
Butyl tape is a pliable putty filler with a high solvent (butyl) content. These tapes are typically used under window frames and trim strips. They have moderate adhesive quality though are prone to drying out and shrinking. Installed correctly they have the potential to provide a good seal, however they should be combined with a bead of sealant.
How can i tell if my caulking is good?
Visual cues are missing caulk, cracks, dried gaskets, staining, etc. The best way to test for leaks is by performing a "blower door test".
Can I just run a bead of caulk over the original caulking?
Like most maintenance work, preparation is the key to a good job. Removing the old sealant and cleaning the aged sealants from the parts is key. Preparation generally takes the most effort and time, and like painting, the application of the caulk is the last step. In many instances the seal or gasket is behind a door or window requiring removal of the object to replace the seal.
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