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TRADITIONAL CONCRETE vs. SYNTHETIC STUCCO PLASTERING

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Man new building products are now distributed here in Costa Rica these days and with every new product, the manufacturer's installation recommendations vary. Purchasing these new and sometimes high-tech construction products is simple, the challenge is finding experienced tradesmen to properly complete the installation according to the new recommended guidelines rather than the old methods most of the local workers have grown up with.

 

To the average homeowner, a stucco coating is a term applied to various methods of plasterwork, both exterior and interior. The most common use is to refer to plaster or cement used for the external coating of buildings. If the exterior sheathing and/or plastering methods fail and humidity is allowed to enter the interior wall cavity of a dwelling, the exterior sheathing will need to be replaced. Additionally, removal and replacement of interior finishes such as drywall, finish carpentry, paint and floor coverings will need to be completed. Mold remediation in the wall cavity structure is also another consideration depending on how much moisture was allowed to enter the dwelling. These are all expensive finish items to repair or replace.

 

More than likely, the purchaser/owner is responsible for the additional costs. Just ask anyone who has ever owned a unit in an established condominium project in the real world.

 

Traditional Concrete Stucco consists of a mixture of cement or lime, sand and water, applied in one or more coats on metal lathe and rough masonry over framed structures and has been used for decades. Traditional three coat stucco has a long history that is well accepted and defined in the Model Building Codes.

 

Traditional Concrete Stucco facts:

1. A Moisture Barrier is required on top of moisture sensitive substrates such as wood, gypsum, etc.

2. Three coats or layers with a total thickness of 3/4 of an inch or more; Scratch Coat, Brown Coat and Finish Coat.

3. Metal Accessories; Casing Beads or Stops or Grounds, Weep Screeds, Corner Aids, and 4. Control Joints or Expansion joints at 144 square feet.

5. Flashings are required as a part of weatherproofing the system.

6. Vulnerable to excessive cracking depending on the humidity during the curing process.

 

Synthetic Stucco is a newer stucco system that is very similar to traditional stucco but with some advantages. It provides design flexibility, durability and moisture management. It can also be finished in a variety of ways including premixed colored cement stucco finish coats, elastomeric coatings and paints or even acrylic textured finishes. Each synthetic stucco system is a proprietary mix of Portland cement, polymers, fiber reinforcement and secret ingredients.

 

Synthetic Stucco Coatings use additives such as acrylic resins or polymers. The most common type is that which is applied to EIFS - exterior insulation and finish systems. EIFS has been used for a little over thirty years in the USA and Europe and combines exterior finish system durability with good thermal insulation and a variety of textures and colors.

 

Synthetic Stucco facts:

1. A Moisture Barrier is required on top of moisture sensitive substrates such as wood, gypsum, Styrofoam, EIFS, etc.

2. Synthetic Stucco is applied in coats with a total thickness of 3/8" to 1/2", applying a brown or base coat and a finish coats depending on the desired texture.

3. Metal Accessories - Casing Beads or Stops or Grounds, Weep Screeds, Corner Aids, and Control Joints and Expansion joints at 144 square feet, window and door corners and per architectural details.

4. Flashings are required as part of weatherproofing the system.

5. Vulnerable to cracking. Although, if mixed and installed properly, the proprietary mixes are very effective at minimizing cracking.

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Most cracks that occur in exterior and interior stucco walls here in Costa Rica are usually the result of inexperienced tradesmen using the wrong materials and/or application procedures.

 

Additionally, the application procedures vary from product to product so this adds to the problem. Using the wrong materials and/or improper application procedures, can result in unsightly cracking, peeling or flaking of the plastered stucco walls and soffits in construction projects.

 

There are three basic kinds of cracks in plastered traditional concrete and synthetic sheathing products such as DensGlass and the difference is very important to understand.

 

1. Larger cracks that are not even from side to side - in other words, if you run your hand across the crack, and one side of the crack feels higher than the other side - This kind of crack means that something structural has failed or settled and may be a serious problem that should not be ignored. Common causes are inadequate structural support, foundation shifts or earthquakes. Probably the most important concern in construction projects where synthetic sheathing has been installed on exterior walls is the possible infiltration of water into the wall cavity where excess moisture could cause mold and affect the interior installations.

 

2. Little fine cracks that are even on both sides of the crack - that is, when you run your hand across the crack the surface feels smooth - This crack is fairly common in the construction that I have inspected here in Costa Rica. It is caused by traditional cement plaster drying too fast, and you will especially see it on walls that have been exposed to sun while drying. To properly dry concrete, you should keep it wet - as in spraying the newly plastered walls with water - for at least seven days depending on the climate. If this is done, there will be fewer if any cracks. These cracks are not a result of structural damage and can be covered up by using silicone type products manufactured by the local paint companies for this purpose. This type of cracking rarely causes interior moisture problems.

 

3. Lots of cracks that vary in width and are close together and usually curved in a group on walls - These are caused by poorly mixed concrete that contain too much or too little water or a mixture where contamination such as dirt or bad water entered during preparation. This same appearance can be the result of improper coatings being applied to inadequate synthetic sheathing.

 

For value and peace of mind you should consult with an experienced builder who understands which building products are best suited for the type of structure specified. A qualified builder also needs to know the proper installation procedures for the selected materials and he should have sufficient command of Spanish in order to train and instruct the local tradesmen how to install the products according to the manufacturer's recommendations.

 

In the case of exterior stucco coatings, the plaster product needs to be not only compatible with the exterior sheathing chosen and aesthetically compatible with your architectural design but also one that is 100% waterproof, sealing the interior walls form the outside elements. A good product that is waterproof is not only cost-effective in the short term, but in the long term, prevents costly maintenance expense caused by moisture, salt penetration and mold.

 

The sheathing materials and plaster coatings I recommend have been selected because they have been proven to be able to withstand the intense UV rays and seismic movements here in Costa Rica.

 

I train and instruct the tradesmen I work with to apply the exterior coatings according to the following four step application process which meets or exceeds most manufacturer's recommendations.

 

1. Install fiber mesh or metal lath to the sheathing product.

2. Apply base coat for strength and adhesion.

3. Apply top coat for waterproofing and abrasion resistance.

4. Apply final texture coat to create the desired stucco appearance.

 

Most often, depending on the exterior sheathing product used, if it is toweled over polypropylene fiber mesh or expanded metal lath in three coats it will last for many years. The mesh and lath give strength and quality-control of application, and the plaster coatings provide an aesthetically pleasing water proof barrier that won't crack or de-laminate.

 

Here in Costa Rica the tradesmen are accustomed to installing the mesh only over the joints where the sheathing panels meet in order to save time and material costs.

 

Some condo purchasers in Costa Rica have found out the hard way that the exterior plastering products and installation procedures used on projects here have not bonded to the exterior sheathing properly nor have they repelled moisture nor prevented water intrusion into the wall cavity. The failure of the buildings exterior coatings and lack of flashing on windows and doors permitted moisture intrusion inside the walls which has caused the metal structure to rust as well as damaged the interior finishes. All of this damage has occurred within the first year of ownership so the future repairs will only become more frequent and costly to the owners.

 

There are permanent solutions to correct the problems rather than just temporarily repair the cracks. But you will need to hire an unbiased, and knowledgeable builder who understands the building system and knows the proper materials and application procedures that need to be used to permanently seal and waterproof the exterior walls.

 

If you discover cracks in the exterior stucco walls of housing that you are considering purchasing in Costa Rica save yourself time and money by hiring an experienced builder to conduct an inspection of the potential problem areas prior to closing. Damage caused by water intrusion into the wall cavity usually requires extensive interior remodeling and potential mold remediation. Remember, here in Costa Rica if it seems too good to be true it probably is. So don't get pressured into purchasing housing that seems like a great deal but will end up costing you a lot more to repair than you anticipated.

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Hello, I am in Costa Rica right now. I am from the US. I have been applying synthetic stucco in the US for almost 30 years. I have been to countless classes on its application. I am one of the good ones. If there is anything I can do to help, just let me know. My email is stuccodavid@hotmaillcom.  I don't have any of my tools with me but it wouldn't take much to get them.  

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