"a practical hands-on
   guide to bathroom

Shower Base Installation
General information:                                                                                                                            

It is very wise to install the base on a sound surface.  If necessary, replace the wood subfloor (or the bad portions of it) before base installation.  It doesn't have to be "pretty", but is has to be structurally sound and level. 

It's also
extremely important that your base is level when you install it.  That will affect water draining and shower door installation.  It's good idea to "dry lay" the base first to see if it will fit your area.

Shower bases normally have "ribs" underneath to give them strength to minimize flexing (flexing is
bad - it will eventually break the caulk joints or cause the shower base to crack);  however, I suggest also using expanding foam or mortar underneath the base to give it a firm feel.  Expanding foam and mortar will harden overnight.  If you use mortar, I suggest you install a plastic membrane to keep the moisture from entering the subfloor.  This procedure
will prevent the base from flexing or squeaking when someone stands on the

The shower base should be leveled and then screwed thru the lip (flange) into the three walls with flat stainless steel or brass screws to secure the base to the walls and keep it level (the screw holes thru the flange should be predrilled to prevent cracking). I always recommend screws instead of nails in bathroom work because screws usually have better holding-power and if you make a mistake you can remove them with ease.  If you're installing a cultured marble base, DO NOT screw into the lip since this may create a stress crack, but be certain to set the base in mortar for stability.

The base drain is normally connected to a 2" PVC pipe and a rubber donut with a trap below.  Base manufacturers enclose instructions for installation.  Normally, a rubber donut is pressed outside the pipe into the drain.  Rubber donuts may be a challenge to install - if you put liquid soap on the PVC and the donut, it will help in setting them in place properly.  Be careful not to misalign the trap below the base (in the room below) so there will be the correct pitch in the drain line.  Incorrect pitch may cause poor drainage or allow sewer gases to enter the house.  When working with the old abs (black) plastic pipe, keep in mind it is subject to
  cracking and it's best if you replace it.  If you do have abs pipe and you don't replace it, a
mission band (rubber
coupling with metal bands) is required to connect the abs pipe to PVC pipe.  Also, make certain the drain pipe does not come in direct contact with the wood subfloor since this may cause a squeaking noise when someone enters the shower (a problem almost impossible to fix except to tear out the shower)

When installing a shower base in place of a bathtub, keep in mind that a 2" drain is required extending to the plumbing stack.