I want to build a custom bath tub

Due to my bathroom size and shape I need to Custom make a tub . How many layers and what oz would be suggested for a tub cast over foam? Thanks in advance. I feel like this is the best place to get advice from professors.

 

Most of the strength will be from outside, but you need enough strength inside to deal with say a knee of a 300# person or someone dropping something hard into the tub.

If it were barebones, Alaska cabin, I'd say about 2x12oz outside, support the tub every 16" on the bottom with a vertical section. Inside, I'd want a minimum of 2 layers of 6 oz woven. If you must seam, seam at the edges.

For a nicer version, I'd go to 1708 on each side, two layers.

Some of this depends on the edges.

The outside edge will need to have a 90 or it'll bend bad with only a couple layers of 6 oz.

So, as with all things here, a napkin sketch might be important for best answers

 

This is my basic sketch of framework

 

You need to have support all the way across the bottom; 16-18" oc depends on laminate plan..a center stringer also not a terrible idea

 

If you have a proper subfloor, the simplest procedure is to build it up in layers of pink insulation foam, like contour lines on a map. Glue the layers with polyurethane, spread with a notched trowel. Make sure the drain is in place before you begin, in the right location and height. And make doubly sure it doesn't leak, because you aren't getting at it after.
When you're done stacking, time to shape. This process is how SUPs and surfboards are made, so I'd suggest checking one of the numerous diy websites for tips.
Since your foam is bearing directly on the subfloor you won't need any framing, but your layup should be fairly substantial.
That's my boat guy suggestion.
My residential carpenter advice is not to do it. If you have an odd space that won't fit a tub, put in a shower stall instead. It will be a lot more useful, and look a lot better. A handmade tub will, unless you're a true craftsman, reduce the resale value of the home. A well made shower with good tile work design will increase the resale value of the space.

 

I have modified existing fiberglass tubs to fit undersized rooms, it’s much easier/cheaper than building a tub from scratch.
That said, if I did have to build one from fiberglass, I’d make a throwaway male mold, probably from plaster, so the tubs inside surface could be smooth gelcoat.
Modern brush/roll on waterproofing membranes make ceramic tile tubs a possibility too, and are adaptable to almost any configuration or size requirements.

 

My width is 44 inchs but my problem is drain placement. I'm sure I could modify tub . And move drain . I have done fiber glass for golf carts and came out pretty good.

 

The pink poly can be for the crossmembers and support, but it will delam as a tub material. You need to use marine foam for the tub.

 

Thank you so very much. I knew this was the place to go for right info.

 

The pink poly is actually not great for crossmembers on further. I don't like to make DC mad here, but the more I think about it....the pink poly can delam from a heavy person entering the tub even as a crossmember. Stick with timbers and bond the tub to them.

 

You won't make me mad. After all, I think he should build a walk in shower.

 

The foam used should be pretty rigid, one heel can carry full body weight in a very small area.
I bought a PVC shower stall that had a foam eggcrate under the floor for a support grid, it lasted until my 250# BIL
visited, was cracked all over in a week. I wondered if hot water had weakened the plastic?

 

Most folks spray foam under those if they experienced using them before..

 

Manufacturer should have used a thicker layup. World is full of idiots who cheap out inthe wrong place. Glass and resin are not the expensive part of a premade shower stall.