Do I need a corded drill to mix thinset?

Question

I've been looking at tearing out my fiberglass shower, installing Kerdi, and re-tiling the whole thing. During my research into this project, I've come across quite a few forums that have members typing in all caps about not mixing thinset with a cordless drill because the motor will burn out. Is this true? Even for small batches? My shower is only 3' W x 3' D x 6' H.

I've got an older DeWalt 14.4V drill that's on it's way to retirement (its batteries aren't holding a charge well), as well as a new Milwaukee M12 lithium ion 12V drill and an M12 Fuel 1/4" impact driver. Is one of those sufficient or should I go buy a cheap HF corded drill or check Craigslist to add to my growing collection of tools-that-rotate-things?

Answer 1

First of all, I have to say that with the volume of work you have you can just mix the thinset by hand. I once had to install about 2.7 square meters of tiling and mixed several small batches of thinset with a spattle - no problems at all, I wasted much more time on applying the thinset and installing the tiles evenly. Totally not worth risking the drill.

Next, you should not use any drill for mixing unless its manual says it's suitable for mixing or that it has overload protection that slows the drill down in case of overload. Drills explicitly suitable for mixing are typically professional drills with very low RPM (500-700 RPM) and so very high torque. The "HF corded drill" you reference is nothing near that. Drills with overload protection are typically professional cordless drills with smart electronics that monitors all the parts for overheating and reduces the output power in case of overload. The Milwaukee M12 you have likely has the right type of overload protection (that's the impression I have from reading the online specs of the drill) and so you likely could use it for this purpose.

Answer 2

1) The issue is not so much the total amount of work the drill will need to perform over the course of your project. The issue is more with the load you will be putting on the drill at any given moment. Chucking a small stirrer will (likely) let the drill operate within it's design specs. Chucking a larger stirrer will (likely) force the drill to operate outside it's design specs.

2) For any power tool, if it starts to overheat, then it is best to stop and assess the situation. Unfortunately, there is no answer to what temperature constitutes the threshold for overheating.

3) For any power tool, if the rpm drops significantly when put under load, then it is best to stop and assess the situation. Unfortunately, there is no answer to what rpm drop constitutes an overload.

4) For either overheating or rpm-drop, the inadequacy could be with the tool or could be with the power supply, for example an extension cord whose gauge and length are too small/long for the task.

5) Given that, I suggest going ahead with your existing drills. If you encounter warming or rpm-drop, stop, let it cool, and switch to a smaller stirrer perhaps by cutting off some of the 'paddle'.

2, 3, 4 apply to any tool/project.

I wonder if a variable speed 1/2" router would work?

Answer 3

Mixing thinset by hand while remodeling a small shower with Kerdi and new tile wasn't a physically taxing process for me, but YMMV.

By the way, the John Bridge forums were the most helpful resource that I found during my research and remodeling job.

Answer 4

I use my cordless Makita to mix thinset with a small paddle. I get through one mixing per battery - batteries are 3 years old.

The method I use if I am doing a full bag is about 6 inches of water and slowly pour the powder in. When it gets anywhere near oatmeal consistency, more water. Then I pour more powder. Repeat 1-2 more times. Once all powder is in I am mainly mixing the top 10-12 inches. I take a putty knife and scoop the bottom every 45 secs of stirring. I also stir in reverse and forward almost equal.

Others may have their own method but I found that stirring the very bottom with a paddle is useless. Basically you push down the powder not mix it. Rolling the powder up with a putty knife is a little messy but saves 5-10 mins of mixing. Also when I am using my drill I am hardly ever pegging it. I want it going at a medium pace and I am moving the paddle around the bucket randomly.