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.
