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A coworker wants to remove a shower door and put up curtain and rod instead. His problem is that the tub and shower surround is a one piece fiberglass unit. He wants to know if there is a way to fill the holes that remain from the track removal attached to the tub and surround. He also wonders if there is some sort of resin kit with color matching or even some type of smooth or low rounded plugs that could be installed and painted to match tub color.
If the entire enclosure was in wretched shape I would suggest looking into a complete refinish job, which would repair the holes plus resurface the entire shebang. Mention this up front because your friend may find removal of the doors may produce more damage than expected. Besides the obvious holes in the sides of the enclosure, the bottom track for the doors is typically glued in place with caulk. It is not uncommon for the vertical end supports to also be caulked/glued in place. This extra caulking helps prevent leaks but makes removal of the shower door frame more of a chore and the chance of damaging the enclosure during removal is increased.
Extreme care must be taken to remove all visible caulk before attempting removal of the track. Use a thin flexible putty knife between the track and enclosure to break the caulk seal. Unfortunately, small pieces of the enclosure may rip off with the track regardless of the care used in its removal. If the track appears to be very firmly glued, the use of a heat gun to warm the track may soften the caulk enough for easier removal!
As far as masking the screw holes, your friend could purchase a matching adhesive caulk and smooth it into the holes with a damp finger. Some hardware and most home stores carry a variety of colored caulks that are used in plastic laminate countertop work. Since water contact will be minimal in the affected areas this type of caulk should stand up well.
There are also plastic caps (or covers) that mount onto screw heads. They are commonly used in assemble-yourself furniture and in other applications where an exposed screw head is unattractive. I have seen two types. One type of cover has a protrusion on the back that is pressed into the "cross" of a Phillip's head screw. The second is more sophisticated, utilizing a washer-like base that is held onto the surface by the screw. A matching cap snaps onto the base concealing the screw head and protecting it from moisture. This second type is the better of the two... the first type tends to fall off over time unless you glue it in place… a good use for either caulk or GOOP.
Either of these screw covers can be painted to match the enclosure with oil or latex paint, or left "au naturel".
Lubrication is a start, though I would have chosen a silicone lubricant instead. WD-40 isn't really a lubricant... it is a protectant that has some lubricating properties. First and foremost, the mechanical functioning of the door should be evaluated.
There are a couple of problems to look for. The first is the condition of the wheels, also called "rollers". Are they still round and smooth, or are they starting to look like the soles of an old pair of sneakers? Do they rotate easily without any wobble? If you notice either of these problems, remove the old rollers (most are held on with a screw) and take them to the hardware store to get a proper size match. The doors will have to be removed do this (more below).
The second problem could be in the adjustment of the door. When closed, the door should fit vertically against the side molding. If there is more than one rubber doorstop, it should make contact both of them. If it doesn't, there is a tendency for the door to lift out of the track when opened too "aggressively"!
The way to adjust the door depends on the design. Some doors have multiple holes for each roller... moving the roller to a "higher" hole lowers the door, etc. Others have the roller screws in a "slot" that allows finer adjustment. Before making any adjustments, look at the bottom track. Some doors run inside a U-shaped track... others (the so-called trackless doors) utilize a sliding mechanism. Be sure the sliding mechanism is disengaged before attempting to remove the doors for adjustment. Some have a lever... others use a simple screw-on clip. (Be careful not to break anything... it may be impossible to get a replacement part!)
Aggression! Leading me to the final possibility... that someone is being a little too violent with the doors. Sliding doors do not take well to banging and excessive force... they retaliate by jumping out of the track! Team up a maladjusted door with aggression and the only result can be home repair tragedy!
When you adjust each door, be sure to adjust it to the side it will be at when "closed". The correct closing position of the inner door is near the showerhead. The outer door should close further away from the showerhead. This will keep water from blowing through the gap between the doors. Having seen the staining and damage that can occur over the years, this is not a minor point!