What Caulking Should I Use For Stucco? Cracks, Lath, Etc.

What Caulking Should I Use For Stucco?

There are tons of caulking choices out there nowadays and knowing which one to use for stucco is half the battle...

Right?

It is a very simple choice though when it comes down to which caulking you can use and the other question is what type of caulking for what part of the stucco process.

What Type of Caulking Can I Use?

There are two main types of caulking that are best for stucco applications and these are for repairing cracks and for using when lathing to seal up certain areas.

The two main types that are recommended by most people are an acrylic based caulking and a polyurethane based caulking. These both have different characteristics, which makes them suitable for different objectives.

  • An Acrylic Based Caulking: A caulking with an acrylic base (or acrylic/silicone base) is better suited for applications that are needed on the finish coat because it is easier to work with and blends into the stucco finish easily, using the correct tools and methods. This is the primary caulking that I like to use on hairline stucco cracks

  • A Polyurethane Based Caulking: Polyurethane based caulking is good for sealing up areas on the lath portion of the stucco process. Areas like windows, doors, where lath meets wood, etc. are better suited with a polyurethane based caulk.

    Polyurethane provides a better seal and is more watertight. The polyurethane also bonds very well to most materials without any adverse effects but is much thicker and harder to work with so it is not recommended to use for blending into the finish.

    It is sometimes used for larger, deeper cracks as a filler and sealer and then a different caulking is used on top to blend the finish in. This is not usually recommended by manufacturers (usually voids any warranties made) and you will want to make sure that the two caulking materials will bond to each other.

  • Silicone Caulking: Silicone is not really recommended because it is so hard to work with and cleanup is a much harder process. It doesn't stick to materials like a polyurethane will and it will not work well to blend into the stucco finish.

    Now, a silicone caulking will work and I have seen people use it but it is less effective than a polyurethane and really "sub-par" in comparison.

  • Rubberized Caulking: Rubberized caulking does have its purpose and can come in handy every now and then. The material that makes up the rubberized caulking sticks to the stucco paper very well and is usually used on areas that will see more water than normal.

  • Sanded Caulking: Sanded caulking is basically an acrylic based caulking that has a fine sand added to it so it matches the finished stucco a little better. Now it is important to note that the sand is indeed very fine and it is not going to be a perfect match for some of the more coarse finishes without a little work.

Where Can I Buy Caulking?

One of the best things about caulking is that it can be found almost anywhere and is usually in stock, no matter what type you are looking for. The big box hardware stores will usually have it and I have also had very good luck at my smaller, local hardware stores.

Home Depot and Lowes will carry polyurethane, acrylic and sanded caulking most of the time (from my experience). A stucco supply yard will also have caulking in stock most of the time and it will usually be an acrylic or polyurethane based caulking. Some companies will carry a sanded caulk as well but is more rare.

Which Types of Caulking Are Paintable:

This is a question that comes up a lot and the answer is surprising... all of the caulking is nowadays is usually paintable. Now most manufacturers these days make a caulking that is paintable and I can only assume that it is because it is much harder to sell one that can not be painted and is intended for specialty applications only.

You will want to read the tube though to make sure that it is indeed paintable as different manufacturers have different products. Some manufacturers recommend certain types of paints over others, mainly having to do with the base that is used for the paint.

The Caulking I Use For Stucco:

I wanted to recommend some caulking I use myself to give those of you out there that might still be a bit overwhelmed some more specific examples.

Acrylic Caulking: I have used the Alex Plus caulking (40 year) for many years now and really like how well it blends into the finished stucco.

This is an acrylic caulking with silicone added for extra water resistance, among other benefits.

Alex Plus Caulking

​It works best for stucco cracks and I even use it where stucco meets wood in less weather prone areas (lath) where the walls meet the roof sheathing, rafters, etc.

This stuff is super inexpensive and there is NOT a hardware store anywhere (I have found, anyways) that does not sell it.

​Polyurethane Caulking: There are two main polyurethane caulking brands I like and have used extensively and these are Sikaflex and Fortiflash brands. The Sikaflex can be found at Home Depot and is usually found down the cement aisle, rather than the caulking aisle. 

Polyurethane Caulking

I use the construction sealant they make but they also have a 1a formula that I heard works well too.

​Fortiflash also sells a polyurethane caulking I really like but I have not seen it at Home Depot or Lowes or any smaller hardware store. I will usually get these at my local stucco supplier. I do prefer the Sikaflex though because of the thicker consistency.

Sanded Caulking: I have used a couple of different sanded caulks that have worked well.

These are basically the same types of caulking, made up of the same ingredients for the most part and the base is usually acrylic.

Sanded Caulking

​Mor-Flexx is one brand that works good ​but I have also used mortar repair types of caulks with good success.

​Helpful Links:

Here are some links to some of the recommended caulking I use, which can be found nearly anywhere for the most part and should help you find the right caulking a lot easier.

Acrylic Caulking: (Link Here) Remember, the acrylic caulking is best used for crack repair or any other types of repairs that need to be done on the finished stucco surface, as it blends in easily and cleans up with water.

It can also be used for the lathing portion of the stucco process too and bonds pretty well to the black paper used to waterproof the substrate.

Polyurethane Caulking: The Polyurethane caulking is best used on the lathing portion of the stucco process and will bond to the stucco paper extremely well. Cleanup is difficult though and requires mineral spirits most of the time.

You can use it to seal up larger cracks in stucco too but remember that trying to get the caulking to smoothly blend into the existing finish will be a lot more difficult to do compared to using the acrylic caulking. Sikaflex and Fortiflash are the two polyurethane caulking products I have had good luck with.

Sanded Caulking: (Link Here) The sanded caulking is only used on finished stucco surfaces and nothing else. It works best on medium to rough stucco finishes and can be used on smoother finishes too but an acrylic will do a much better job of concealing the area since it has no aggregate mixed with it.

About the author

The Stucco Guy

My name is Ryan and I have been in the construction trades for many years now and I feel that there is a huge "knowledge gap" when it comes to particular trades.... like stucco. I hope you find the information here useful. Thanks for stopping by!

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