[Expert advice] Acrylic sealant. The basics

Acrylic sealants started to appear in the USA and Europe in the late 1970s. No exact date of their "birth" was recorded: they were the result of the evolution of acrylic fillers, as manufacturers gradually changed the formulation of fillers and gave them more and more of the properties of a sealant.

Acrylic sealants are made on the basis of a water dispersion of an acrylic or an acrylic-styrene polymer. The properties of the resulting sealant depend largely on the quality of that base. A sealant also contains a mineral filler (most often ground calcium carbonate), a thickener, a plasticizer, a biocide and a coloring pigment (if the sealant is colored).

How do acrylic sealants cure?
They cure as the water they contain evaporates, that is, by drying. Clearly, the drier the air and the higher the temperature, the faster curing goes. This is what makes acrylic sealants different from silicone, polyurethane and hybrid ones, which, on the contrary, take up moisture from the air in order to cure and polymerize faster the higher the humidity is.

Benefits of acrylic sealants

• Environmentally safe and odorless. Since only water evaporates from an acrylic sealant as it hardens, it gives off no odor and has no harmful effect on the environment.
• Paintable. Unlike silicone sealants, almost all acrylic ones can be painted with any type of paint once dry. Some of them, however, are not paintable, so check this property before you buy.
• Range of colors. Any combination of coloring pigments can easily be added to an acrylic sealant during production to obtain any color required.
• Vapor permeability. This property matters particularly when sealing window units. An acrylic sealant lets water vapor through, so condensation does not build up inside the joint. Not all acrylic sealants are equally vapor permeable, by the way, so when choosing a material for sealing window units it is better to check this figure separately.
• Compatibility. An acrylic sealant is compatible with all building materials, does not react with them and has good adhesion to both smooth and porous materials.
• Low price. An acrylic sealant costs roughly one and a half times less than a silicone one.

Drawbacks of acrylic sealants

• Not resistant to prolonged contact with water. Acrylic sealants should not be used in joints that are permanently in contact with water: they will simply be washed out of such joints over time.
• Low elasticity. Acrylic sealants belong to the plasto-elastic class, that is, they do not fully recover their original shape after deformation. They are therefore not recommended for sealing joints with a lot of movement.

Applications of acrylic sealants. Where are they used?

• Sealants for exterior work. Used mainly for sealing joints in log houses and in precast concrete panel buildings. They have increased resistance to low temperatures and to UV light.
• General purpose sealants for interior work. Used for filling cracks in walls, for fitting and sealing baseboards and other trim, and for filling tile joints. They are also used for installing doors and windows (if they meet the vapor permeability standards).
• Sealants for parquet and laminate. Used for filling joints in parquet and laminate floors and for repairing and restoring wooden furniture. Unlike general purpose ones they have higher wear resistance and can be sanded once dry; they are also often made in a wide range of wood-tone colors.

Can acrylic sealants be applied to a damp surface?
Yes. Unlike silicone sealants, acrylic ones can be applied to a damp but not to a wet surface. A surface counts as damp if it does not shine after being wetted with water. If it does shine, there is too much water on it and the surface is wet.

Freeze resistance of acrylic sealants.
Once cured, acrylic sealants have a minimum service temperature of about -60°C. During transport and application, however, many of them must not be frozen: the water they contain would freeze and the acrylic dispersion would break down. To prevent this, manufacturers add ethylene glycol to the sealant, which keeps the water from freezing at sub-zero temperatures. Such a sealant may be frozen during transport and storage, and it is sealants of this kind that are called freeze/thaw stable. Details of the temperatures at which a particular acrylic sealant may be transported, stored and applied are given on the packaging and in its technical documentation.