Why choose concrete spacers and bar supports over those made of plastic?

Plastic spacers and bar supports

Plastic spacers and bar supports do not bond well with concrete. When the concrete is poured into the form, a small gap is created between it and the plastic. Plastic has a coefficient of thermal expansion and contraction 10 to 15 times that of concrete, and when subjected to temperature variations, the plastic continues to expand and contract at that higher coefficient. At high temperatures, plastic can even melt. The result is a separation between the spacers and the poured concrete, creating a free passage for corrosive agents to reach the steel reinforcement from the exterior of the concrete product. This will cause the steel – and eventually the concrete – to corrode.
If steam curing is applied to the concrete, the heat in the curing process causes the plastic to expand while the concrete is relatively fresh and weak. After reaching the maximum curing temperature and volume expansion of the plastic, the temperature is held at this level until the concrete reaches the desired strength. After curing, the subsequent lower temperatures cause the plastic to contract, and a gap remains at the interface between the plastic and concrete.
Plastic spacer are also subject to corrosion when they come into contact with chlorides and chemicals, where concrete has a much higher resistance.

Concrete spacers and bar supports

Concrete spacers and bar supports are made of the same material as the poured concrete, so thermal expansion and contraction are equal. And because they are the same material, the concrete and spacers will bond. No gaps!
Concrete spacers and bar supports help maintain material integrity and uniformity of the concrete, and provide a cover over the reinforcement that protects against corrosion.

Concrete spacers with a plastic MoClip or MoStek.

What about Molenaar’s concrete spacers with a plastic MoClip or MoStek? Does the plastic MoClip or MoStek in the concrete spacer have a negative effect on material integrity? Does it weaken the corrosion protective cover over the reinforcement? The answer is no!
The plastic MoClip or MoStek is placed on the top of the spacer and does not come into contact with the surface of the concrete product. The plastic MoClip or MoStek is embedded only 5 mm into the spacer, which maintains the material integrity at the product’s surface. The plastic in the MoClip or MoStek is used only for easily attaching to and holding the reinforcement, leaving the concrete part to do the work of the spacer.