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FAQ

Answers to the Most Frequently Asked Questions

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What is the smallest tile size I can install over RPM?

You can install with mosaic tile as small as a 1/4″ x 1/4″.

Why would I use 5/16″ thick (RPM-330, V1) vs 1/2″ thick (RPM-500)? Is one stronger than the other?

Strength wise, they are about the same. It primarily depends on how thick you want your total substrate height to be. For example, if you are using a 3/8″ thick tile and are trying to join up with a 3/4″ hardwood flooring, then you would want to use the RPM-330 or RPM-V1 (5/16″), so the two surfaces would be level with each other. If you were using an 1/8″ thick mosaic tile, for example, and wanted the same results, you would want to use the RPM-500 (1/2″). However, if necessary you could float your cement leveler above the studs of the RPM to create whatever height was needed.

Can RPM be used in a shower application?

No, we do not recommend using RPM in a shower pan.

Is RPM an anti-fracture membrane over concrete?

Yes, RPM has been tested and received a “high performance” (the highest possible) classification for anti-fracture over concrete.

Can any brand of heat wire be used with RPM?

Yes, any brand of heat wire can be used with RPM, provided the wire is rated for under tile application. RPM is not rated for the type of wire that is specifically designed to be embedded into the middle of a concrete slab.

Why do I have to wait 28 days after the tile and grout has been installed before I can turn on my floor heat?

This could accelerate the cure time of the leveling product, tile thinset, and grout which could cause the cement products to lose some of their adhesive qualities and/or get shrinkage cracks in the grout.

Why do you recommend a 2nd sensor probe for the heat wire thermostat?

While this does not happen very often, every now and then the sensor probe may fail. The only way to fix this would be to remove tile and chisel into the underlayment cement (and hope you do not cut the heat wire) to install another probe. If you install two sensor probes at the same time and run both of them to the thermostat electrical box, hook one up and leave the other loose in the box. If one ever fails, just disconnect the failed one and hook up the new one and you are back in business.

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