seamless installations on wood subfloors
INSTALLING CONCRETE AND TERRAZZO OVER WOOD SUBFLOORS
Polished concrete, seamless overlays and terrazzo are becoming extremely popular options for flooring. Most contractors and home owners feel like these hard surfaces are not available to them when working with plywood subfloors. With advancements in cementitious technologies over the last 10 years, terrazzo, polished concrete and other seamless floors are now possible without compromise in quality when going over plywood subfloors. Ceramic tile has been installed successfully over wood floors for years, manufacturers specify systems to facilitate tile installations that come with warranties, these are not yet available for seamless terrazzo and concrete installations, however they can be done without cracking with proper care and consideration.
The first thing to consider is the framing of the floor system and how stable it is. If the floor is not supported with adequate joist sizing or spacing, the best installations will fail. New construction codes are adequate, it is when considering renovations, or do it yourself jobs, when problems can come up. Weight is not usually a problem with thin section terrazzo or polished concrete floors as they are comparable to large format tiles. A 3/4” t&g plywood layer is usually the minimum sheeting needed over the joists. In some cases a second layer of 1/2” screwed and glued down is recommended.
If the wood floor is not flat and there are dips and high points, some sanding/ filling my be necessary to ensure the problems do not get compounded and telegraphed through to the finish. In most cases, it is best to start with a flat floor, rather than try to make it up with the concrete or terrazzo layer. Level and flat are two different things, in most cases it is flat that is most important. It is essential that any paint, sealer, oil or anything that will act as a bond break is sanded off the wood.
Uncoupled membranes protect solid surface materials because they allow a small degree of movement differential between the substrate and floor covering. Now a universal standard with tile installations, these systems can now be part of the cracking puzzle when considering finished concrete and terrazzo floors. Uncoupling membranes absorb any substrate movement, and eliminate the transfer of stress to the layer above, ultimately preventing cracks. In addition to providing uncoupling, they can also serve as a waterproofing layer that protects moisture-sensitive substrates, such as plywood or OSB (oriented strand board), as well as provide heavy load distribution to ensure the finished floor remains durable.
Divider strips are used to do just as their name suggests… provide an aesthetic transition between surfaces. By separating the different terrazzo mixes, design freedom is further extended.
The primary function divider strips offer is to control cracking in your terrazzo flooring topping. Instead of cracking in the panel or design of the flooring, the topping will crack along the divider strip joint.
Available in zinc alloy, aluminum or plastic, divider strips can be specified in custom sizes and shapes,
Honoring control joints
Not all areas can be mitigated with uncoupled membranes alone. Structural columns and load bearing beams sometimes need divider strips to follow their orientation. Seamless floors are great, but not when they have a massive crack in the middle. Integrating columns, load bearing beams, control joints and thresholds into your concrete and terrazzo floor plan is critical to long term performance and crack control.
UHPC SUB LAYER
In extreme situations where a client wants concrete or terrazzo floors, but the sub floor is in really pour condition a UHPC sub layer can be installed. Ultra High Performance concrete such as Ductal by Lafarge can be installed over the wood sub floor and then topped with a decorative layer. Ductal utilizes a massive amount of fibre and finely divided cementitious materials to achieve up to 2900 psi flexural strength.
Surfaces over wood sub floors
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