A crack in your acrylic bathtub means you won't be able to take a bath or a shower without water running through the damaged area. This can end up damaging the subfloor or even causing a leak on the floor below. Follow these directions to repair your cracked acrylic bathtub.
Step 1 - Eliminate Flexing
If you have a crack in your acrylic bathtub, the first step is to stop the tub surface from flexing because excessive movement will lead to the crack reappearing or further cracks forming. To do this, check the entire surface of the tub and find the area where the surface is flexing. You will need to drill 0.25-inch holes through the area surrounding the crack, with a couple of extra holes adjacent to the length of the crack. Take care not to drill past the cavity and through the other side of the tub.
Inject the holes with insulating foam. For best results, use a 2-part foam that dries instantly so you can proceed without waiting for it to dry. This foam will pad out any cavities between the interior and exterior surfaces of the tub and make them more stable. Some insulation foams are toxic to breathe in, so check the list of ingredients and wear protective clothing (face mask, gloves, safety goggles) while using them, especially if you have a history of breathing or skin condition issues.
Step 2 - Halt the Crack
Now that you have stabilized the cavities of the acrylic bathtub, you will need to stop the crack from lengthening or reappearing after you’ve worked on it. You can do this by a technique called “stop drilling.” At each end of the crack, drill a 0.25-inch hole. It’s vital that you do this. If not, the crack will reappear later even though a repair has taken place.
Step 3 - Fill the Crack
To fill the crack, never use an epoxy filler. Instead, use a 2-part polyester filler and mix it according to the instructions on the tin. Apply the filler to the crack with a clean rubber spreader until the crack has been completely filled, including the stop-drill holes. Allow the filler to dry completely before you proceed.
Step 4 - Sand the Filler
Once the filler has dried fully, sand it down with very light sandpaper. Use progressive grits of paper; start at P320 and finish with P800. Rub lightly until the surface of the filler is even with the rest of the acrylic bathtub. When you’re happy with the repair, wipe the surface with denatured alcohol to prepare it for spraying.
Step 5 - Spray the Finish
To achieve the very best results on the finish, invest in a portable sprayer that’s designed for jobs such as this. You can find one at hardware stores.
Take your bathtub repair paint, which should be a color that matches your tub, and mix it thoroughly. Spray a light coat and allow it to dry before you add more coats. Keep adding coats as necessary until they form a suitable finish on the acrylic bathtub. Allow the paint to cure before you move on to the final stage.
Step 6 - Buff the Tub
To completely finish the tub, you will need to buff it with an auto polish urethane compound. This will give a harder finish and also feather the edges of the paint. Consequently the colors and repair will blend in completely with the rest of your acrylic bathtub. Just like with the insulation foam, if you have breathing problems or a skin condition then wear protective clothing while working with the compound. Urethane's generally not toxic to humans, but you can never be too careful.