Fiberglass Tub and Shower Crack/Hole Repairs

To properly repair cracks in fiberglass tubs and showers, it’s best to understand how they are manufactured. They are made in a mold, First thing sprayed in is the finish which is a thin coating of colored gelcoat. Next is chopped fiberglass and resin from a chopper gun. The thickest part is the floor area which varies from approximately 3/32″ to about 3/16″ inch thick. Next to give it support, strength and rigidity strips of 5/8″ to 3/4″ pressed board are laid out in the wet fiberglass. Behind that, they spray a thin coat of the fiberglass for 2 reasons; first as a moisture barrier and so the particle board doesn’t show.

These units fail when the floor is overloaded or it gets moisture into the particle board. Either way it allows the floor to flex (move) and the fiberglass tears or cracks. Once this happens the particle board get wet and it’s pretty much over with. If yours has a crack stand at a the crack and put your weight on it, it will flex or feel spongy. what this means is the boards are either broken loose or it is wet. Either way its strength is gone.

Easy cheap way that doesn’t fix it is to put a patch on top to cover the crack and try to support the failed area. Not only is it an ugly bump but it will crack around it and the moisture spreads through the board and a bigger area becomes spongy. Different companies call this repair several things the most creative I heard with a “MARINE REPAIR”.

Next repair is to try and support it from underneath by drilling a hole or two and injecting expanding foam through the hole. If the particle board didn’t get much moisture in it and the users are small (not heavy) people, I have seen this work for a couple years. Theirs two problems fist the wood products are wet this doesn’t fix that. Secondly there are no structural quality foams that you can spray through a hole.

How to repair cracks in fiberglass tubs and showers

  • You might wonder how do we know this? Because we tried fixing them these ways years ago. It only works temporarily at best.
  • This is how to fix these permanently.
  • This shower was being used the morning we repaired it and they started using it again the next morning.
  • Here it is when we arrived. taping up the crack stops more water from getting into it until we can fix it.

Meet Your New Best Friends

This after the tape is removed all the work area is cleaned and the floor is cut out. you can see the particle board under the fiberglass.
Once the fiberglass floor piece is removed all the particle board is removed with a hammer chisels and pry bars.
Once all the wood is removed it is filled with compacted mortar mix, filling the entire cavity under the floor with solid cement. The piece we cut out is cleaned up and floated back in wet mortar mix to exactly where it was when it was manufactured.
Once this sets up the cut joint and cracks are ground out and put back together and bonded with multiple layers of fiberglass. It gets sanded down so the floor is as it used to be. we match the color and re-glaze the repair area so everything matches.
Repairing it this way is permanent! When you step into it, it’s as solid as standing on your garage floor. We guarantee it will never have a collapsed floor again.


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