I'm laying 16" ceramic floor tile on hardibacker board. What size notch trowel would work best?

I'd use 1/2" x 1/2" square notch for floor tiles that large.

There are a lot of charts (http://www.tileandstonetips.com/trowels.html) on the web that can help guide you as well.

Thanks,
Json

I have had good results with a 1/4x1/4 trowel but then again I don't own a 1/2x1/2 trowel so Schwim may be correct too. The main things to check is lay your tile, tamp it down, lay a few more and then pull up one tile. Check to see how much contact you have been making with the tile. Anything less than 90% signals time for a larger trowel.

I have had good results with a 1/4x1/4 trowel but then again I don't own a 1/2x1/2 trowel so Schwim may be correct too. The main things to check is lay your tile, tamp it down, lay a few more and then pull up one tile. Check to see how much contact you have been making with the tile. Anything less than 90% signals time for a larger trowel.

I don't own either, I did check out a web site and they recommended 1/2" also. If they have a 3/8", I might buy one of each. Thanks

They are fairly cheap, around $9 but get one with a nice wooden handle if you are going to do much work. I have not laid 16" in a few years but do tins of 13" and 12" with a 1/4x1/4 trowel every week. Remember to pull a tile to test the amount of contact you are getting.