Concrete bathtubs are beautiful, stylish, and durable – but incredibly expensive. If you have a little DIY know-how, why not do it yourself and save the money for the rest of your remodeling?
It’s possible to make a concretebathtub yourself. However, you’ll have to build a frame, prevent air bubbles, and properly seal it to make it watertight. This does mean pouring your own concrete bathtub will take a bit more time and skill, but the results can be very worth it.
Main Topics
3 Major Types of Concrete Bathtubs
If you’re planning to build or buy a concrete bathtub, it’s important to decide what kind of tub you want. While you can make any tub out of concrete, the following three are the most common.
Freestanding
Freestanding concrete tubs are ideal for placing on the floor, against a wall, or in the middle of the room. These tubs may or may not have feet. For example, the simplest designs are simple rectangles that sit on the floor. These are sturdy, easy to cast, and require little molding. You can also buy a bathtub mold with legs or attach metal legs to your concrete mold. However, this will be incredibly difficult as concrete is heavy and difficult to move.
Deck Tub
A deck tub either drops into a deck and frame or features a lip and extension or “deck” on at least one side. Decks can fully surround the tub or can extend off to one side. Often, they function as a “table” for storing shampoo and other toiletries. However, you can make very large or surround decks – suitable for anything from candles to using as seating.
Sunken Tub
A sunken tub fits into a hole in the floor, offering a step-down entrance. This kind of tub is very accessible for seniors. It’s also very popular for people who like to sit in the tub to relax, as it gives you a better view of the room. Sunken tubs also offer more access to hidden plumbing, making them a top choice for anyone who wants to install a whirlpool or bubble bath.
Estimated Cost to Build Your Own Concrete Bathtub
The cost to build your own concrete bathtub depends on size, location, finishing materials, and shape. For example, it’s relatively easy and cost-effective to build a freestanding rectangular tub. If you want a round tub or an oval one, building the frame will be more complex. You’ll also likely need a pre-made mold, which will increase costs.
Assuming you want a simple, rectangular concrete bathtub, you can make the following cost estimation.
$15-$35 per sheet of plywood, with 4+ needed
$12-$15 per 16’ of 2×4” #2 lumber, with 80-150 feet or more needed
$5-$30 for silicone
$80-$150 for the drain and plumbing
$30-$2,000 for the faucet
$5-$10 for screws
$5+ for sandpaper
$25-$300 for sealant
$5-$20 in supplies such as gloves, paper towels, soap, etc.
$5-$25 per bag of high strength concrete such as Quickrete without gravel. You’ll need at least 2 80 lb. Bags. However, you’ll need 6 or more if you’re casting a large deck or steps in or out of the tub.
$20-$50 for mold release
The price variations lie in the fact that there are significant differences in faucets and fittings you could choose. Similarly, you could choose a basic sealant to impregnate the concrete and make it watertight. Or, you could choose a rock lacquer or something else expensive from a specialty shop.
There are also plenty of optional costs. For example, you could spend $20+ on pigment to dye concrete. You might decide to invest in a bathtub mold which might require a custom build. That could cost you several hundred dollars. Or, you could invest in tools to make the concrete smoother – such as concrete shakers, clamps, and seals.
Essentially, casting your own concrete tub will save you money – but it might not save you as much as you’d like, unless you already have the tools and materials lying around.
Importantly, if you want a round or oval tub, you need a concrete mold. Concrete molds also help to ensure the shape is more uniform and that the inside of the tub is smooth. Worst-case scenario, you can buy casting rubber in bulk and cast your own from an existing tub. However, this will likely cost a considerable sum, as casting rubber typically costs $30-$100 per 5 gallons, and you’ll need 10 or more gallons. Alternatively, you could steam and bend wood to shape your form. However, most DIY-ers will find this to be a significant undertaking without professional equipment.
Things You Will Need
Assuming you want to pour the simplest possible tub yourself, you’ll need the following list. However, if you choose to buy a plastic mold, you can skip the mold list.
For the Frame:
80-100 feet of 2×4” boards
4 sheets of 8×4’ plywood
A box of No. 9, 2 ½ inch Phillips’s head screws (hardened steel)
A power drill
A circular saw or table saw
1 ¼ inch Forstner bit or Spade or Paddle bit
A 1 ¼ length of PVC pipe
2-4 tubes of silicone and a caulking gun
Mold release spray / Silicone / Vaseline
Optional for the Frame:
U-Clamps or Frame Clamps
A bathtub mold instead of the inner plywood
Casting rubber
For the Tub:
Concrete – Calculate out the total volume based on the dimensions of your tub
Sealant
Finish
Drains and other fixtures
Optional for the Tub
Concrete setting equipment such as concrete shakers and vibrators
How to Make a Concrete Bathtub: 9 Steps to Follow
For this tutorial, we’ll assume you want a simple tub installed away from the wall. If you want to build this into the wall, you’ll have to build the frame against the wall, reinforce the wall section you’re attaching the tub to, and go from there.
We’ll calculate for a rectangle with a 6” deck against the wall and a 4” deck on either end. The walls will be straight, with no customization such as a slanted headrest or steps. You can always add these first. However, we strongly recommend practicing with casting concrete before moving to the tub. You’ll have to cast in-situ or on site, because you can’t move the tub afterwards. That means you get one chance to get it right.
Build the Frame
Measure out the space you want in the tub. Calculate the size you want based on your space, and figure out how the tub best fits in. Then, get started building your frame.
The idea here is to build a “box within a box” mold. This means you’ll create a larger box for the outside of the tub plus any deck for the tub first.
Measure the full length and width of the tub, including the deck. So, if you want a 72” long tub with a 4” deck on either end, your total length is 80”. Then, if you want a 30” wide tub with a 6” deck on one side and a 3” deck on the other, your total width is 38’. Most concrete is not easily cast at less than 2” thick. Plus, the thicker you make the walls, the more durable they’ll be. We’re also assuming that you’re casting directly into the floor – which means you don’t need a bottom panel. If that isn’t the case, you might want to use a two-part mold made by a professional, as moving concrete forms can cause them to crack.
You’ll have to add half an inch to your mold measurements for the plywood.
Measure and cut your 2x4s. In this case, we’ll go with 3 vertical supports and corner supports for the frame. You’ll need the following lengths of wood:
6 x 42.5”
6x 72.5”
You’ll also need vertical supports. In this case, let’s assume you want the tub to be 24” high. You need an additional. 1” of clearance to ensure you have space to put the interior mold in. Drill everything together, so that you have 3 rectangles, and then attach them to the vertical supports, with the vertical supports on the outside. You need one at each corner.
From there, you can easily cut your plywood and attach it to the inside of the frame.
For the inside frame, repeat the step, but with the frame on the inside of the “box”. You’ll want to detract your deck from the total measurements when cutting the wood. Make sure you detract an additional ½ inch from the 2×4 measurements as well, so that your frame is the right size. Finally, cut a top for your inner mold and attack it, from the inside. Then, you can simply suspend the frame over the other using two 2×4” s which are the width of the total frame. You also want to attach them to the rest of the frame, so that the concrete does not push the frame up.
Drill the Plumbing
Figure out where your plumbing should be and drill the holes. You want to vacuum afterwards to ensure there is no dust. Then, insert a throwaway pipe into the hold and cap both ends. You should also drill holes for plumbing fixtures and use a pipe to fill the holes. The necessary size depends on which plumbing you choose – so it may be ideal to select fixtures first. However, in most cases, you’ll need 2x holes for bolts, 1 ¼ inch holes in the tub wall for the faucet, a 1 ¼ inch spillover hole, and any other lines you might find to be necessary.
Make sure you plan these out carefully because you can’t change them after the fact.
Seal the Frame
It’s crucial to completely clean and seal your frame before pouring concrete. This prevents some imperfections. It also ensures you can get the mold out. Sealing will take two steps. The first is to seal holes and cracks.
Caulk every corner facing the concrete to smooth out the seams. Here, it’s important to get these as smooth as possible, especially on the inner mold. Take the frame out and flip it closed side up so you can easily apply the silicone. Use a wet rag and soap to smooth the silicone and don’t leave a mess. Unfortunately, leftover drops will show up in the concrete.
Impregnate the wood frame. You can do this with commercially available mold release formulated for wood and concrete. Many people also prefer to use heavy coatings of oil or lard. We’d recommend the mold release unless you’re on a budget. In this case, use a heavy spray of oil and allow the wood to soak for at least half an hour. Always spray on more oil before putting the concrete in. Make sure you apply mold release to your pipes to ensure that they will come out as well.
Eventually, the more you coat your mold, the fewer problems you’ll have getting the mold out. But, you also want to ensure the mold release does not mess up the finish on the concrete, so apply it smoothly.
Mix the Concrete
The finer and heavier your concrete, the better it is for tubs. For the best results, choose an extra strong, heavy concrete. However, a basic concrete available as Quickrete will likely do. Here, it’s extremely important to ensure you have a fine mix with no gravel.
Mix the concrete according to the instructions. Plus, it’s always better to overshoot calculations and mix it all upfront. Having too much concrete is significantly better than not having enough, because staggered drying layers will ruin your tub.
Pour the Concrete
Pour the concrete as quickly as possible. Use a concrete pump or have several people help you to fill the mold. The faster you fill it, the more evenly it will settle, the less layering problems you will have, and the fewer problems you’ll have with air bubbles.
Here, it’s extremely important to work the concrete to get rid of air bubbles. Vibrate the mold, use your hands to shake the concrete under the bottom mold, or use a concrete vibrator. It doesn’t hurt to do all three. The more you shake and move the concrete, the more likely it is to settle properly, without air bubbles or missing pockets. Use a trowel to smooth the concrete at the top.
Wait
Most concrete needs 3-5 days to cure. The damper and more humid it is, the longer you should wait. Do not rush this process as it will make or break your cast. Keep in mind that the concrete at the bottom of the mold has almost no air so it will take significant time to cure.
You can spend this time smoothing the concrete on the top once it’s started to dry. Use a damp rag to wipe it level, so that you spend less time sanding later.
Remove the Frame
Start taking the screws out on one side of the outer frame. Pull the outer frame off. Then, see if you can pull back the plywood panel. It may be quite stuck. Check to make sure everything is completely dry and uniform in color. If it’s not completely dry, put the frame back on and wait.
Otherwise, continue taking the frame apart. Remove the inside frame first, as pulling plywood away from the inside frame will create some stress on the outside. Pull the plumbing pipes out. Work your way around the outside of the tub and remove the last of the frame.
Wait and allow the tub to air dry some more.
Sand It
Smoothing and sanding your tub can take a lot of work. Depending on what you want and how it’s been cast, this could take days, or it could take longer. You likely want to use very thin layers of cement to smooth out any visible air bubbles or holes. You’ll also want to take a large grain sandpaper to smooth out obvious bumps and imperfections. Eventually, you’ll want to take finer grained sandpaper to the whole thing. Unfortunately, most of the sanding should be done by hand. However, you can use a machine polisher with a fine grain sandpaper if you know how to sand concrete.
Seal, Polish, and Finish
The final step to building your concrete tub is to seal and finish the tub. That means using a professional sealant. These range from basic concrete sealants (look for clear) to patterned and enameled sealants. Apply your sealant of choice in thin layers, according to the directions on the package. In most cases, you’ll need multiple layers to ensure it’s fully sealed.
Frequently Asked Questions
Building a custom concrete tub is a lot of work. You likely run into a lot of problems. And, sanding and finishing require work. Here are some of our frequently asked questions to help.
Are Custom Concrete Tubs Expensive?
Yes. If you buy a concrete tub, you can expect to pay $500-$3,000 per tub. On the other hand, if you have it poured for you, to measure, you can expect that to double or even triple. Plus, if you need a custom mold and measurements, you might spend as much as $6-10,000 on your custom tub if you have a professional do it for you. If you choose to do it yourself, the costs will be much lower. However, a lot of things can go wrong so it’s important to figure out concrete casting, to ensure your mold is smooth, and to take steps to source a good concrete mix and sealant.
How Heavy is a Concrete Bathtub?
That heavily depends on the density of the concrete. Low-density concrete weighs about 4,000 lbs. per cubic yard. In most cases, you’ll use about a quarter of that for your tub. A high-density concrete, which creates a smoother finish and requires less sanding, can weigh up to 4 or more times that.
Are Soaking Tubs Worth It?
That depends on what you want from your home and your lifestyle. Soaking tubs are an investment. Some people find them worthwhile, others do not. However, they can add to the value of your home as well, which means you may recoup some of the investment if you choose to sell.
Next Steps
Installing a concrete tub requires patience, skill, and quite a bit of dirty work. You’ll also invest quite a bit of money for something that might not work out the first time. The good news is, if your tub cracks of fails, you can always take it out and try a new one. But, if you use good concrete, cure it properly, and shake it during the initial pour, it should be sturdy enough to last a lifetime.
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