How Do I Fix Cracks in a Tub Enclosure?

Written by chris stevenson
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How Do I Fix Cracks in a Tub Enclosure?
You can gain access to the underside of a tub if you have a crawlspace. ( Images)

Tub enclosures endure a lot of foot traffic, moisture and sometimes dry rot or mould. Tub enclosure panels can split at the seams and leak water onto the bathroom floor. Bathtubs made of fibreglass or acrylic have a tendency to flex over time with repeated weight shifting, which can lead to spider cracks on top of the surface or extended, deep cracks in the flooring. Rather than replace the entire tub or enclosure seams and panels, a homeowner can use some basic steps and products to complete a crack repair.

Initial Cleaning

Mix a solution of dish washing liquid and warm water in a bucket. Clean the tub and enclosure with a cleaning brush and rinse thoroughly with plenty of water. If there is mildew or mould, use a cap-full of bleach in the bucket, then rinse thoroughly. Dry the tub and enclosure with terrycloth towels.

Caulk Removal

Examine the condition of the caulking around the panel seams for loose and deteriorating caulking material or silicone sealer. Use an X-acto knife or sharp screwdriver to remove rotten and loosened caulk or sealer until you reach solid material which adheres to the surface. The seams will include the tile areas that meet flush with the tub's top edges, as well as the aluminium frame where it joins to the acrylic or fibreglass panels. If the panel frames have screws instead of rivets, use a screwdriver to tighten them.

Small Surface Cracks -- Spider Webs

For small spider web surface cracks, use heavy, 80-grit sandpaper to sand down the small stress cracks, then sand over the area again with a 320-grit sandpaper. Wipe away residue with a towel. Use some epoxy resin, either for fibreglass or acrylic material, and a small paintbrush to apply several layers of resin over the spiderweb crack. Sand lightly between coats with the 320-grit sandpaper. Use an epoxy resin kit that has a pigment (colour) that matches the colour of your tub, if possible.

Injection Foam

If you have deep cracks in the base edges of the tub, you will need to obtain some polyurethane foam in a spray can. Use a drill to drill several holes along the length and sides of the crack. The drill bit must be thick enough to allow the foam nozzle to reach down inside the holes. Once you have drilled the holes, push the foam nozzle down inside each crack and discharge the can until the foam begins to raise up through the open drill holes. The foam will expand dramatically, serving as a solid backing that will support weight underneath the tub.

Deep Crack Preparation

Use a Dremel tool and a cone bit to grind a bevel in the crack along its entire length. Achieve an angle of 45 degrees or less to give you a larger surface area for adhesion. Sand the crack with 80-grit sandpaper, using a cross-hatch motion, then do the same with the lighter 320-grit sandpaper. Sand past the crack on all sides to provide an extra area for adhesion. Wipe away the residue with a towel.

Crack Repair

Obtain an epoxy resin fibreglass kit. Read the instructions for the proper mixture of the catalyst and resin. Use scissors to cut strips of the kit fibreglass that will cover and overlap the crack. Mix the epoxy resin in a small, plastic cup. Use a paintbrush to apply resin to one side of the fibreglass patch and to the crack area, overlapping the margin. Press the patch down onto the tub surface and paint a thick coat of resin over it. Let it dry, according to the directions. Use 320-grit sandpaper on a sanding block to sand the surface down until it is nearly flush.

Multiple Patches

If the kit recommends multiple patches, cut the extra patches progressively smaller and apply them one at a time over the preceding patch, stacking them. Brush resin over the lower patch and the underside of the top patch each time you apply one. Sand with the 320-grit sandpaper after allowing each patch to dry. This will create a small, dome-shaped patch. Use a sanding block and 320-grit sandpaper to sand down the entire patch until nearly flush with the surface.


If your fibreglass patch repair kit comes with pigment options, mix the correct colour in the resin and paint over the sanded crack. You can purchase fibreglass tub paint separately and use it to paint over the cracked area. You may also elect to repaint the entire tub with a different colour or the original stock colour.

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