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I am in the midst of a custom shower project. I am building a shower pan using the "traditional method" which is a concrete pre-slope, then a PVC membrane, then a top mortar bed, and finally tile.

The top mortar bed on my shower pan dried today. Turns out I really am not good at smoothing concrete. I can't lay tile on this. The slope is fine, but there are some dips and humps and a few divots in the pan. The curb is OK but there are a few uneven spots that I need to deal with.

I've been relying on Floor Elf's website and e-book. The author does a good job describing the right way to do the job. However he is an experienced tile man and I think has glossed over some details that I think I need.

How can I smooth this out?

If I have to redo the top bed I will, but I would like to avoid that entirely. I hesitate to use more bedding mortar as I found that difficult to work with the first time. I feel like I need a 'wetter' mortar. Can I use floor levelling compound? Can I use thinset to fill the low spots in then more thinset to stick the tile?

My technique sucks. How can I improve and get a smooth finish?

How can I maintain the multi-direction slope from the four walls to the offset drain? Sloping along one plane isn't too hard but maintaining a slope along two planes has proven tricky.

How can I lay out a smooth frame or reference line for mortar work?

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Apply thinset to low spots and ride off high spots with a straightedge to even the floor. A shower floor is not something you want to do over a hard mud surface. The preferred method is to pull your mud and lay your tile fresh, allowing you to use a beating block (4x6 inch is more than enough) using the block and riding at an angle to the tile beat the floor flat.

The biggest mistake pre-floating the mud is that the drain can be an issue if you cut your mud too high in relation. I should note that over fresh screed you want your thinset very wet as too stiff will pull up patches of mud if you pull a tile. If you do have to pull a tile when fresh, slide it while using a lifting motion.

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Tile setters use an abrasive called a rub stone: enter image description here

But you could probably use a sanding block. After making it as flat as you can, apply a layer of thin-set mortar. Before doing this, read up on techniques for using thin-set.

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    The stones are easily available, cheap, and effective. A sanding block would be an exercise in futility, IMHO. – Ecnerwal Nov 2 '14 at 22:04
  • An angle grinder with a diamond coated cup wheel will make short work out of that. If you don't have one, they are a little more than $200. Probably not worth it if you plan to use it once. – Jason Hutchinson Mar 18 '15 at 17:02

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