Typically I encourage people to follow the manufacturer’s instructions. Especially when the company has clear, detailed, and easy to understand instructions. But when it comes to both Ditra Heat and
Ditra Heat TB [edit: now called Ditra-Heat Duo] there are two things that I just don’t feel are good ideas.
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This post deals with the installation of Ditra Heat mats only and not the heating wire.
So what are the two things you want to avoid when installing Ditra Heat mats?
Pre-fill the waffles. Always.
I feel strongly about this. Now the Ditra Heat Handbook doesn’t specifically tell you to not pre-fill the waffles. However, it does tell you to start setting the tile right over the mat. Also, the photos show the tile being set right over the orange heat mats. This is not a good idea, in my opinion.
First of all, what does pre-filling the waffles mean? This is where you skim coat thinset mortar over the top of the heat mat. You do this with the flat side of your trowel. Then you let it dry before installing the tile. This skim coat layer helps to protect the wires below. This is important for two reasons.
- It helps to protect the wires from the teeth of your trowel when combing the mortar.
- If you have to pick a tile back up after it’s been set (during installation) you won’t drag the wires out with it. The wire can stick to the underside of the tile. You can prevent this by pre-filling the waffles.
An additional benefit of prefilling Ditra mats is being able to snap chalk lines and actually being able to read them.
Don’t install tile the same day over the Ditra Heat mat
Schluter says this is ok. Again, I think this is a bad idea. As mentioned, when you have to pick a tile up and re-install it (you will have to do this- more than once) the suction of the tile can pull up the Ditra mat causing it to break the bond to the plywood.
My advice: install the Ditra Heat mat one day and install the electric heat wire a different day. Then skim coat the wires with thinset and let that dry. You have enough to do just installing the tile properly. You don’t need additional challenges or things going wrong.