Addendum to discussion about bonding agents

 

 

The more I learn about the uses of glues the more I am finding how tricky they can be. We discussed in the last installment of the proper uses of different types of glue. Some glues are strictly admixtures and some are particularly suited for the receiving surface. Problems typically arise with respect to weather and moisture retention. We discussed last time that acrylic admixtures should slow the set time down thereby making the cement material denser. This is not the case when it is hot. However, in temperatures over about 85 degrees F we find that the modified material spikes with the introduction of acrylic. That is, the material will set the mix more quickly when it is hot. With respect to PVA and EVA surface preparations we are finding some of the same inconsistencies. As plasterers and support personnel, we constantly look for new ways to improve the outcome of our products and finishes. I was recently on a job in Santa Barbara where the plasterer was re-scrubbing an existing Santa Barbara Finish (smooth) parameter wall. Since a smooth coat was already on the wall (unpainted) the plastering contractor felt it prudent to glue the wall before scratching in the first coat of smooth stucco. As it was a warm sunny day the glue appeared dry and the scratch coat was applied. As the crew doubled back over blisters began to appear. All the discussions that I have had about blisters are there is too much moisture in the material and the second coat breaks the set and bond of the first coat. What I have found since is that judging the readiness of the first coat when there is glue on the wall is tricky. It appears dry but in reality the glue is holding moisture on the inside of the first coat. Some plasterers always wait over night following the application of glue to make sure it is completely dry. These bonders all re-emulsify as the wet mud is introduced over the top. The difference is that a PVA will continue to re- emulsify for up to a week (or more depending on weather) and an EVA will only re-emulsify for 72 hours. The distinction is important and, at the same time, very tricky. The weight of the stucco can pull itself off the wall if the glue re-emulsifies following application. So we want the glue to “wet up” as we apply the stucco to insure a chemical bond, but we want it to cure before an appreciable amount of moisture is introduced. Another problem is when a bonding agent is put on the wall it will again hold moisture. This time it is after both coats of smooth (Santa Barbara Finish) is applied and the material has had its final “hard trowling”. The material looks great but since there is moisture present it continues to cure over night and the moisture naturally wicks out and hydrates. This leaves “checking” in these areas. This is also known as “spider web cracking,” “crazing,” or “shrinkage cracks.” Some of these are considered normal and part of the finish as it is virtually impossible to eliminate these small cracks.

 

Consider also that if there is suction (as with the aforementioned re-stucco of an existing smooth wall) should we use glue? In this case we are eliminating the suction bond in lieu of a chemical bond. I have always been partial to a suction bond whenever we can get it. As I interviewed more mechanics about this issue I noticed that some have found (receiving surface type) bonding agents to be tricky enough to quit using them. These guys have gone to using a polymer modified base coat similar to Basex to base out the wall. This is a way to introduce a polymer modified cement coating to bond to the existing wall and still have suction and key to bond the finish coat.  

 

When I discuss polymer modified cements, base coats and glues, I usually find myself voicing one of my favorite adages: “for every solution comes its own set of problems; we just hope the solution is better than the problems they bring!”  We are all “big boys” when it comes to plastering and construction and know that we picked a trade that is very difficult. We get blamed for every crack and imperfection in the finish coat and sometimes have no answers why. As we try to elevate the industry by using new products and techniques we have to remind ourselves that it is worth the effort. At least we are out there trying. Who knows? Maybe we will find a cementitious finish that someday will have all the functionality we want with none of the present problems. Until then, let’s just keep thinking!

Shuttle Endeavor Stages Flyover of Local Stucco Business

 

To commemorate the 50^th anniversary of Merlex Stucco of Orange, NASA today staged a flyover of the Space Shuttle Endeavor over the Merlex facility.  Although no Merlex products were used on the Shuttle, President Nick Brown says “we have some terrific Venetian plaster finishes that go on real thin and would have really classed up the cockpit.”  Crossing over the Merlex plant at approximately 12:30 pm today, the Shuttle approached from the North, flew over Knott’s Berry Farm and Disneyland, across the Santa Ana River to the east, and then banked right toward its ultimate destination, LAX.  Often quoted as saying “It’s not rocket science” when talking about stucco, the Merlex team welcomes any future involvement with the U.S. space program.

Real Stucco vs. Synthetic Stucco

Many people are confused by what the difference is between real cement based stucco and synthetic stucco. In the 1970’s we started hearing about stucco that didn’t crack and had more color consistency than the stucco we were using. Then the word EIFS (Exterior Insulation Finish System) was thrown around and the confusion really started. EIFS is for energy efficiency using foam boards or other products to achieve better insulation values and is a whole other discussion. Much can be learned on line regarding EIFS Systems. One of the problems is that we have so many names for synthetic stucco such as; Acrylic Stucco, Synthetic Stucco, Plaster Finish, and manufacturer names such as; MX Acrylic, Dryvit, Sto, Synergy, Thoro etc. Here is the difference:

Synthetic Stucco is made from acrylic resins and is very similar to paint. They have an aggregate added to replicate the look of stucco without some of the inherent problems of real cement stucco. Different size sands are used to achieve different finishes as traditional stucco uses different size aggregates. Once on the wall it would be difficult for anyone to tell the difference between Acrylic Stucco and a painted cement stucco wall. The key here is painted. It is fairly easy to tell the difference between real and synthetic, if not painted. Even though the products are supposed to be similar when they are installed they are worlds apart in physical make up and functionality. Real Stucco uses natural materials and is cement and lime based. Synthetic stucco is acrylic resin based using no cement or lime. The similarity is the sand or aggregate used. The functional aspect is also important. Synthetic stucco stops water from coming into the wall and are either characterized as water proof or at least water resistant. Cement Stucco typically dries hard enough to keep water out but the idea is not to necessarily keep water out of the stucco. More importantly it can penetrate the stucco and then naturally wick out and dry by being highly vapor permeable. Synthetic Stucco can keep and hold moisture if it can find a way in. This is usually through the windows, doors, or roof lines. Because of water related issues the manufacturers have tried to use co-polymer resins that have more vapor permeability than earlier synthetic stuccoes. Cement Stucco is very rigid and is susceptible to cracking. This has been by far the number one problem associated with stucco.  Cracks are caused by many variables all related to movement and can be read about in earlier Blogs or on line. Stucco also tends to dry differentially by how long the moisture stays in the wall. Cement Stucco typically is darker if it dries slowly and lighter if it dries quickly. In hot, dry, or windy conditions the entire building can be lighter in color than intended; conversely in cloudy, moist, or wet conditions the entire building can be darker than intended. In addition, walls can dry differently just based on shading. The north side of the house can dry darker than the south side. Even shading from plank, trees, or other structures can telegraph on to a wall and cause discoloration.   Synthetic Stucco was introduced to solve these problems and for the most part they did. Since Synthetic Stucco is a lot like paint it dries more evenly. Because of the nature of the resin it moves more than cement stucco and is not as susceptible to cracking. Keep in mind nowhere did I say “solve or eliminate” the problems. Problems and their manifestation are all a result of degrees - how much movement, how much water intrusion. The other question was of course cost. Price was always the motivation of using traditional cement stucco. It is relatively inexpensive. Synthetic Stucco changed that and made the cost significantly higher. Still, when stacked up against other claddings, both these materials are still very affordable. So let’s go through and recap these products:

Synthetic Stucco

1.       Made of Co-polymer Resin

2.       Uses sand or other aggregate to achieve the look of Cement Stucco

3.       Resistant to water

4.       Crack resistant

5.       Color fast

6.       Comes  wet in pails

7.       Spread with an acrylic trowel

8.       More appropriate for dark colors

9.       Able to have smooth to very heavy textures

10.   More expensive than cement stucco

11.   Can be used over brown coat or in EIFS (Exterior Insulation Finish System)

Traditional Cement Stucco

1.       Made of Cement and Lime

2.       Uses different size sand to achieve different finishes

3.       Highly vapor permeable

4.       Comes dry in bags

5.       Spread with steel trowels and floats

6.       More of a “natural look”

7.       Less expensive

8.       Can be used over brown coat, continuous insulation systems, base and mesh.

As you can see there are more differences than first meet the eye when making a decision which product to use. Cost is a factor and how the materials function and ultimately look are certainly things that need to be addressed. Do your research, look at the budget, and make the right decision based on your design needs and expectations of all involved.

SEALERS FOR CEMENTITIOUS SURFACES

MERLEX STUCCO NOMINATED FOR MOST SUSTAINABLE EXTERIOR FINISH ON             GREEN THINKER NETWORK 



There are many sealers on the market. Most are to protect the surface from water or moisture intrusion. There are sealers that are designed to enhance the beauty of the surface or add gloss or a “wet look”. Sealers can be categorized as surface or penetrating. Surface sealers are usually silicone based and last from as little as a few months to a few years. The reason is that silicone is a larger molecule and therefore sits closer to the surface. Since UV light is what attacks these sealers then the larger molecule silicones will break down first. Penetrating sealers are usually silane and or siloxane based. This is a smaller molecule and therefore penetrates further into the surface before forming the hydrophobic barrier.  Silicones are usually less expensive than silanes so how long you want the sealer to last is important question. The substrate is the next most important variable. How porous is the material? This will determine how deep a penetrating sealer will go. This is a two edged sword, the material will last longer as it penetrates deeper but it won’t seal the surface from staining. The primary function of a good penetrating sealer is to keep moisture out of the wall cavity. This is where the water can do the most damage. It can find a way into our homes damaging drywall and carpet but what we don’t see is usually worse. Degradation of wood framing, damaging electrical outlets and shorts and growing of molds are just a few examples of damage water can do as it enters the wall space. We must be aware however; that penetrants are just that, they will not protect the surface from staining unless built up to the surface with subsequent coats.  The proper way to put on penetrating sealers is to make sure that new concrete, masonry or stucco is cured and “thirsty” enough to accept the chemical. Since the chemical is now carried by water this is pretty easy to test. The literature usually says to wait the initial 28 day cure period before application. The problem with this is that your wall can get badly stained in 28 days. My advice is to gauge the weather against how dry or “thirsty” your substrate is and then make your own decision as to when to apply the sealer. These sealers need to form a barrier so there needs to be enough material put on to make that barrier. This usually means we put on a “flood coat” and then brush off any excess material. From a chemical engineering perspective the exact proper way is to apply a very light “fog coat” of material to “open the capillaries” of the wall. Then come back immediately and flood the surface to insure the wall accepts as much material as possible. Most often people just use a pump up “bug sprayer” and fill the wall with material until it runs and then back roll or brush off the excess. There is a very important caveat here though, when it is hot dry or windy and when doing flat surfaces it is critical to get the right amount of sealer on. If there is too much material and the substrate cannot accept the chemical and it will be deposited on the surface. This will result in a residual sticky material left on the surface to catch dirt, leaves, foot prints or whatever blows by. So try to do the job in the morning before the sun is too hot and don’t use these sealers when it is windy for this reason and you won’t get an even application. If you find that there is residual material left on any surface you can cut it off with a solvent. Paint thinner or any other solvent can be put on a rag and cut the material off the surface. Don’t worry, the rest of the material will still be in the wall as long as you don’t let the solvent penetrate. Just use it to wipe off the excess chemical without having it drip off the rag. It will evaporate very quickly and be gone leaving your sealer intact. Remember to cover all windows and frames as these penetrants can etch glass. Please read all the safety instructions before use. Think about the material you are putting the sealer on. Is it a flashed brick with very little suction? Then the material will go in very slowly or not at all. Very porous products like a Concrete Masonry Unit (concrete block) are very porous and will therefore use a lot of product. Merlex makes a penetrating sealer call Micro-Seal II that is less expensive than any other penetrating sealers I have found. It is a great product and is warranted for 10 years!  The literature will show how much sealer will cover different materials. Logic dictates that the more “open” the surface the more material will go in and the further it will go in. The less “open” the substrate the less the material will go in and will therefore go further in terms of coverage. You can use these products on brick, block, stone, concrete, stucco or any other cementitious substrate. I have found over the years that silicones are used because people don’t know about silanes. Why would you use a sealer that will last 3 years at best when you can use penetrants lasting 10 years? The price difference is not that much. I guess if it is model complex of homes or a case where a year of protection is fine then the less expensive silicone will fill the bill. I talk mostly to homeowners that are doing their own homes and want maximum protection for the longest period. Go with a good penetrating sealer and take all the precautions talked about here and you will protect your surfaces without having to reapply every few years.