Mortar to set bath tub?

Is there a specific type of mortar to set a bath tub?

anything that is mostly sand.

Thanks. Should I get it from HD?

Nothing with small gravels in the mix; that will cause the mortar pack to break up over the years and cause creaking when you step into the tub.

I set my tub using quickrete mortar last weekend. I can't say how it will hold up in the future, but it feels very solid. I used a fairly stiff mix. I set the tub and then put some weight in it to keep it from rising. Seems good so far.

Here's how I did it on a wooden floor.....just used quickcrete mortar mix....

I just did this yesterday. Used Quikrete 1102 Mortar Mix. Good stuff, worked great. If the tub has mounting feet, use construction adhesive on the bottom of those also.

Overflow pipe.

Randy, I noticed in your picture that you have the overflow/drain already set in place. Then are you just dropping in the tub? Im no expert, but in all the books I have seen they show that this is installed on the tub, then the tub abd drain are all dropped into place. Your way seems a bit easier for restricted spaces. Is this how you did this? Im curious because I will have to do this in the next week or so, and this seems like a good alternative. Any drawbacks to doing it this way? Also, I see you have plasic under the mortar, Is this to keep the wood from drying out the mortar? So I guess the mortar doesnt bond to the floor, but just supports the tub? I have a Kohler tub with feet and they say to use mortar bed. Should I also use adhesive under the four feet? The tub doesnt have a nailing flange.

If mortar (well, any concrete product) dries too fast, it loses strength - it needs to cure, which is a chemical change which actually incorporates the water into the structure. The plastic underneath stops the wood from pulling moisture out of the mix, allowing the concrete to cure and attain its full strength.