How different acrylic tubs are made


By far the largest proportion of acrylic tubs are built using vacuum forming.  This constitutes using a mold to form the shell of the tub.  Depending on the method of construction, one or two molds will be employed.
The forming of the tub shells occur when a heated flat sheet of acrylic is attached over the mold.  All of the air is sucked out of the mold and the acrylic sheet takes the shape of the mold.  Varying options as noted below are used to further enhance the quality of the product.

Single Skin Acrylic Tubs

This description would signify that the tub has only one vacuum formed acrylic shell.  This would be the inside shell which would come into contact with the water.  To strengthen the single shell, the manufacturer would typically add fiberglass and resin to the outside of the shell.  For additional strength, some form of board would normally be added to the base of the tub and it would be coated with fiberglass and resin to remain firmly in place.
To finish the exterior, the manufacturer will generally apply a gel coat.  This will look a little bumpy, but some manufacturers like this finish as it can be made to resemble an unfinished cast iron surface.
This exterior surface would then be painted to a color of choice to finish.
Tubs built like this generally tend to be the most lightweight of acrylic tubs.  It would be highly recommended to attach this tub to the floor as it can be relatively easily moved during use.

Double Skin Acrylic Tubs

This would signify that two acrylic shells are used in the production of this tub.  One would be vacuum formed for the inside of the tub and another for the outside.  In most cases, two or three layers of fiberglass would be added to these shells using resin to strengthen them.  In some cases, no further additions will be made.  The inside shell will then be turned over and resin or a resin/powdered stone mix will be poured over this outside of the inner shell.  The outer shell will then be fitted over the inner shell and they will be compressed together, giving the appearance of a single molded unit.

 The differences in Double Skin tub production are many.

·        Probably the most important is the thickness of the original flat acrylic sheet being used.  If it is too thin, it can lead to imperfections and waviness during forming and make the tub almost impossible to repair if scratched or damaged during many years of use.

·        Another extremely important point would be the base of the tub.  Without proper reinforcement on the base, the tub would be inclined to creak and give a little when entered.

·        How the tub is finished is also extremely important.  Some manufacturers don’t worry too much about this and tubs will be shipped with uneven drain and overflow holes as well as inconsistent body thickness.  When you run your fingers under the edge of the tub, it should be smooth and consistent with no scratching of your fingers, the same should apply to the overflow and drain holes.

·        The polishing of the acrylic shells needs to show consistency.  Forming marks from the mold on the acrylic can give the appearance of small scratches on the surface.  These can easily be polished away, but it is a job that is better done at the factory than in the home.

·        Mold maintenance also plays a hugely important part.  Without proper and continuous preventative maintenance on the molds, the drain holes can become unbalanced and low areas can form of the base and rounded edges of the tub floors which will cause water retention after draining.

·        To offer improved heat retention, some manufacturers will use a thin aluminum barrier and leave an air gap to avoid heat transfer from the inner shell to the outer shell.

This double skin acrylic tub is also relatively lightweight and it is highly recommended that all tubs are attached to the floor.