I noticed a crack in the bottom of my tub, and noticed that it flexed when I stepped near it.

I called in 2 companies to give me an estimate on repair. The first, proposed a more or less straightforward fiberglass repair: laying down a new full sheet of fiberglass on the bottom of the tub and then a partial re-coating.

The second proposed a more expensive option that seems more long-term, but is much more radical. They proposed cutting out the entire bottom of the tub and then pouring in new concrete to create a new support for the tub bottom. Then, they would re-attach the tub bottom with fiberglass repair materials and do a partial re-coating.

This second method, while radical, seems to address the root issue. However, in trolling the home repair areas of the internet, I do not find mention of this method. That makes me insecure. It is also double the price of the first approach.

Is anyone familiar with this 2nd approach? What are the pros and cons?

  • fibre glass tubs are realtively cheap. repairing a fibre glass tub properly can cost more than a new one. when i say propely i mean glossed,no visible crack,etc. You can do a DIY job by buying fibreglass/epoxy premix at any autobody shop - apply it yu self. sand it down- tada. $5 fix.. looks like rubbish. or just patch it up on the underside- but the crack could cut you if it sharp..Prices vary from company to copmapny, but you can get good ones in a builders depot for not to much. – Piotr Kula Aug 30 '11 at 12:51
  • Yeah, I did some fiberglass repair a few years back and am enough of a klutz to know I want a pro to fix this. A new tub will cost $3-4K installed. A basic patch and re-coat, $450. The more radical repair solution, $900. I am OK with $900 vs. $4k, but I want to be sure the method is sound. I'd hate to have it done and then a few months later have to spend the money to have the whole thing replaced. – BJ Safdie Aug 30 '11 at 13:58
  • Yea- I know what you mean. The thing like in all the answers you need to see why it cracked. So you have to remove it and make sure you have support in this area it cracked. Then get some repair guy maybe. – Piotr Kula Aug 30 '11 at 19:52

I'm not familiar with the second approach but, as you say, it would address the root issue of the tray flexing when in use and should prevent the problem recurring. It also does seem to be rather radical.

The main drawback I can see is that you are causing more "damage" to the tray and therefore increasing the risk of the repair failing.

I'd ask the company if you can contact (or be contacted by) someone else who's had this done so you can ask them what they thought of the procedure. Ideally you'd be able to see the end result and check out for yourself before proceeding. If the firm is reputable they should have no problem with this. In fact refusing this would be a sign that the firm wasn't as reliable as they made out.


The second contractor is correct in that the root cause needs to be addressed. The root cause is either that the tub was never supported in the first place, or that the supports were made of wood and rotted out due to moisture under the tub.

In addition to what Chris said, price a new fiberglass tub versus the repair. Removing the old tub might prove to be a better solution than the hassle of laying new fiberglass and trying to get it to match. Just remember that a new tub will need to be supported somehow underneath, or it too will crack.

A few questions I'd have is if the tub is on the first or second floor of the house, what kind of subfloor there is (is it wood underneath, or is it a concrete slab, i.e. basement, condo, or slab-on-grade foundation?), and if you'd experienced any water leaks below it.

  • The subfloor is wood. This is a duplex, one-story condo with a crawl space underneath. One side of the bath abuts the other unit in the duplex. I am pretty sure that the back long wall of the shower and other end of the tub are against the exterior walls. I had an inspection done a few months back and there was no sign of leakage. I need to get under there and check again, as I just noticed these cracks. – BJ Safdie Aug 30 '11 at 13:49
  • In a duplex/condo, they probably did not support the tub correctly -- things that are hidden in multifamily construction often get neglected, sadly. I would probably not pour concrete on top of wood... I would probably just make sure that the tub, when the bottom is replaced, is adequately supported with more wood. If it's not supported, you'll hear a sickening 'crunch' any time you walk in the tub. Ask me how I know... – Karl Katzke Aug 30 '11 at 17:30

I always recommend first that homeowners replace cracked tubs/showers. But, as that is a costly option, there is the second option. To the left or right of the tub/shower is a room that backs up to the bathroom. Go in that room, cut out a two foot by two foot section of drywall on the wall that the tub/shower is attached to. Used a razor knife, not a drywall blade (never know what might be back there you don't want to cut). Find the studs, and cut there. This will make your life easier for when you have to replace the drywall. Now, fill the tub halfway with water. Take a can of of "large gap" spray filler and squirt a few streams under the tub where it is not touching the subfloor. Wait a couple of minutes, let it expand, and repeat till the spray filler has become a cushion around the bottom of the tub. Now let it dry overnight. In the morning, let the water out of the tub. The reason for the water in the tub was so that the spray foam did not raise your tub up. Take a fiberglass repair kit and repair the crack. Now, replace the cut out drywall. This solution will fix the crack, and keep it from happening again. And it should only cost about $80 instead of $300 to $700 for a new shower enclosure.

  • Surely this only works if there is a room that adjoins the bathroom on the same wall as the shower/bath. – ChrisF Aug 30 '11 at 8:45
  • See my comment above, coming through another wall is not really an option. – BJ Safdie Aug 30 '11 at 13:53

There are several options for repairing a cracked bathtub floor. First would depend on the size of the crack. Minor cracks and spider cracking can be repaired with a fiberglass bathtub repair kit. Larger cracks up to 16 inches can be repaired with a bathtub inlay kit.

The fiberglass inlay option is a permanent repair solution for most bathtub floor cracks on fiberglass, acrylic and plastic pvc bathtubs including major cracks at a cost of $135 for the inlay kit. In both cases the bathtub floor would require extra support by either adding structural support under the tub or the addition of expanding foam injected in the space between the bathtub floor and existing floor of the bathroom.


Personally, I would replace this tub; Tubs are cheap, relatively speaking, and if you have a large crack that's flexing, it may indicate impending failures elsewhere in the tub (part of the tub already couldn't handle the stresses).

The major problem with replacing a tub in an existing home is getting it out, and the new one in. Bathroom doors are generally on the narrow side, and hallways also trending toward the narrow. Between the two you may find that cutting up the old tub is the easiest way to get it out, but that's usually not an option for your brand-new tub.

Also, most bathtubs have tile backsplashes and/or shower areas. You will need to remove the first course or two of tiles above the level of the tub, so the new tub's backsplash can be put in behind the tile. The tile, if properly installed, will not come off in one piece, and most contractors won't even try unless instructed by you (at significantly higher job cost). If that tile isn't something very generic like white squares, you may end up having to tear out and retile a significant portion of the shower stall. That can be more expensive than the cost of the new tub itself.


I have done over eight major repairs all with excellent results, including one where a 15 x 12 inch section had broken right out. Support the tub by going through the drywall in the room adjacent to the tub, prefer non plumbing end. Use spray foam is the easiest. I use a backing board as a guide for the foam so I can spray against backing board. Use a hand grinder or belt sander to bevel fibreglass around crack until each side of the crack is about 1.5-2inches wide. Fibreglass with at least 3 layers of mesh. When dry sand flat and smooth. Then buy an inlay kit $85 from Lowes that matches tub color. Easy to apply. If the repair is wider than inlay, color mix final coat with a colorant, cheapest at a marine store $12. The repair is permanent. It has 3 steps to resolve problem. 1.Support the tub bottom. 2. Fibreglass mesh in a ground out hole that is bevelled. 3. Finish with an inlay. You will be proud on how the tub looks when finished no one will be able to tell.


I would avoid the second option. Concrete is porous and would absorb moisture which would then transfer to the wood structure of the house. Plus you would need to check building codes in your area to see if this is even allowed.


Cut a hole under the tub in the flooring underneath around where the crack in the tub is then patch crack from underneath then reinforce the tub underneath with 2x4 by scabbing in the 2x4 between the floor joists to support the underside of the tub then patch up hole you cut out to access the tub with and then go back up to the tub and now patch up the other side of the tub let dry sand and paint it the color that matches your tub hope you figure it out good luck

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