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How To Install A Fiberglass Bathtub | In-depth Guide

9 Easy Steps To Know How To Install A Fiberglass Bathtub

After a long tiring day at work, your bathroom tub is where you can relax while taking a hot bath. So it is mandatory to choose the right kind for the perfect pleasure. But the main key to having a perfect-looking tub depends fully on the installation process that you need to pay attention to. This installation can be done perfectly by a professional or you can do it on your own if running on a budget. 

To install a fiberglass bathtub make sure the subfloor is level, choose the right tub for installation, do the measurements, install a stringer, connect all the drain plumbing, place the tub in place, and attach the tub flange to the studs with roofing nails, and lastly finish off the wall with drywall and paint. 

Installing a bathtub doesn’t have to stress if you hire the right person or gather all the things and information that you need. If you are also installing your bathtub then we would recommend you to take a look at this article because you can learn all the small details that you need to finish your installation in one place. 

What Is A Fiberglass Bathtub? 

Fiberglass products for shower walls or tubs are made of fiberglass and resin and are no different than a cast on a broken arm or a vintage corvette. It is lighter-weight and pretty economical. These bathtubs are made of multi-layer systems starting with a gel coat and then building it up with fiberglass resin. 

They look vibrant, have a classy finish, and are very easy to maintain. Fiberglass bathtubs can be installed in many ways and they come in different shapes, colors and sizes. Even if they are prone to chipping you can fix it easily. 

Acrylic Vs Fibreglass Bathtub 

Qualities Acrylic Fiberglass 
MaterialIt is a poured resin product that is poured into a mold into the size and shape of the panels or the tub that is going to be producedFiberglass bathtubs or any other products are made of Fiberglass and resin
Weight Heavier by nature. More insulative in propertiesLighter in weight
Cost efficiency Can be very expensive More economical 
Expansion The way acrylic products are made makes them non-porous. Meaning they will not expand or shrink due to any temperature change Fiberglass is like cast iron.  It expands when comes in contact with hot water and shrinks with cold water
Life spanAs they remain in their shape they  have a long lifespanFiber products are prone to chipping or cracking so they don’t survive a long way

Porcelain Vs Acrylic Bathtub

SturdinessIt is a multi-layer porcelain product that is less sturdy than AcrylicA good quality acrylic bath with a thick baseboard is pretty solid
Heaviness They are much heavier and thicker than AcrylicAcrylic is much lighter than Porcelain
RetentionPorcelain products can expand or shrink due to the change in heat so they have less retentionIt has much better heat retention as it does not expand or shrink
Cost Very expensive Less expensive than Porcelain
Production Porcelain products go through a very extensive production process and take much time to complete so they are more expensiveAcrylic tubs are much easier to to to produce and take less effort to they are pretty cost-effective 
Lifespan As they are easier to change their shape due to temperature so the products are more prone to chipping or cracking and have less lifespanMuch more durable and have a long lifespan
Maintenance Needs a specific type of porcelain-based cleanser to clean and need great maintenance as wellClean with regular cleanser or detergent. But still takes great maintenance 
Style Add a more classic vibe to your bathroom Add a more modern touch to your bathroom

Acrylic Vs Ceramic Tub

When it comes to bathtubs acrylic and ceramic are pretty common and popular choices for bathrooms. They are both budget-friendly so if you are looking for a new tub for your bathroom you can choose from any of these types. Though they look pretty identical they have many differences when it comes to material and other qualities. 

Acrylic Tubs

These tubs are made of solid sheets of materials like petrochemicals, resin, stabilizers, fillers, dye, etc which makes its products heavier and sturdier. As are non-porous they do not expand or shrink when poured into hot or cold water. This quality makes acrylic products more durable and long-lasting. They do not crack or chip that easily. They are much lighter than ceramic or Fiberglass as well. 

Acrylic bathtubs add a modern touch to your bathroom and are easier to match up with the decor. They are pretty economical and have great resale value. As they come in different shapes and sizes you can almost install them in any way. They hold on to water temperature longer than any other material. 

Ceramic Tubs 

They are produced by forming multiple layers of ceramic tiles and clay compressed with extreme heat and pressure. So they take a long time to form their ultimate shape. They are pretty common to find in the stores and because they come in pretty cheap people with budgets like them more. 

But unlike acrylic, they do not hold onto the heat for long and are pretty easy to break or crack after several years of usage. So if you are looking for a long-term commitment then these are not right for you. They come in classic or modern or in any other style which makes them versatile.

They also require great maintenance and many other additional maintenances as well because if they crack it is not easy to repair them. Ceramic tubs are heavier than acrylic tubs because of the way they are made. 

Acrylic Tub Vs Cast Iron

Cast iron tub is usually made of enameled steel which is essentially a flimsy version with a much thinner enamel coating. But they are still pretty tough and can last many years. On the other hand, the most common alternative to Fiberglass bathtub material is acrylic. These tubs are made with vacuum-formed acrylic sheets reinforced with fiberglass, resin, and other materials. 


If installed correctly a good quality acrylic bath with a thick baseboard is pretty solid. But if you can afford a German super steel bath is rock solid. So when it comes to sturdiness steel without a doubt is the winner. 


If you like having a hot bath, remember that although steel will warm up the bath quickly it is a conductor. So it will take the heat out of the water. Acrylic on the other hand is a sort of plastic that is an insulator. So it won’t take the heat out of the water. 


If you buy an acrylic bath from a good quality manufacturer that uses lucite cast acrylic any sort of scratch on the bath can easily be removed with a little bit of toothpaste. Cast iron has an enamel coating that is baked in a kiln and has the hard-wearing properties of glass. Although cast iron can chip or rust you can fix it too. 


Cheap acrylic baths can turn yellowish after years of use. But if you buy acrylic baths UV stabilized this is much less of a worry. Cast iron, on the other hand, will not discolor.


Acrylic products are made of chemicals and plastic which is not eco-friendly overall. But cast iron can be 100% recycled and are eco friendly. 


A good quality cast iron bath is typically more eco than a good quality acrylic bath. But either way, you need to avoid lowering costs because it may make you spend more additional expenses in the long run. 

9 Easy Steps To Know How To Install A Fiberglass Bathtub

Fiberglass bathtubs are pretty easy to install and you don’t even need to hire a professional if you have general knowledge about the process which you can also learn from the steps we explained down below:

Step 1: Turning Off The Water Supply

Before removing the old tub, shut off the water supply. If your bathroom does not have a separate cutoff valve, then you’ll need to turn off the water to the entire house. Open any lower-level valve to relieve any remaining pressure in the lines. 

Step 2: Removing The Drain And Overflow

Tub drains have a stopper that unscrews, providing access to the drain flange at the bottom of the tub. Use the screwdriver to detach and release the waste and overflow valve cover that will be on the side of the tub. Remove the tub spout as well. 

Step 3: Gaining Access To The Drain

You’ll need to get access to the underside of the tub, either from behind the wall or through the ceiling below the bathroom. Use channel lock pliers to disconnect the pipes below the T where the drain and the overflow valve meet. 

Step 4: Separating The Tub From The Wall

You’ll need to cut out a section of drywall approximately 6-inches above the tub on each of the three sides. Use a straightedge to mark and cut the wall with a dry saw to remove the section. Now you can remove the screws attaching the tub to the walls. Cutaway any caulk between the tub and the floor with a utility knife. 

Step 5: Removing The Tub

Use some extra hands for this part. Lift the front edge of the tub to force a couple of 1x4s underneath. Now slide the tub out of the alcove. Remove any old stringer left on the walls. Clean the area well for the new tub installation.

Step 6: Measurements

Measure the width and depth of your alcove. Mostly it should be 5 feet long and 30 to 32 inches wide. Make sure to check the drain sides so you can buy a right or left drain tub. If you are using a customized one then you’ll need to relocate the entire setting. Make sure the subfloor is level or make it level. Keep the new tub packaged until you are finally installing it. 

As you need to mark the studs, place the tub in place to mark it at first then mark the studs again for the stringer. 

Step 7: Stringer And Drain Installation 

Cut a 2×4 according to your measurement and screw it onto the studs. Now install the drain of your tub using plumbers putty on the flange and screw it down. To connect the overflow valve, place the rubber gasket on the elbow and position it behind the tub and attach the cover plate to the overflow elbow and gasket.

Connect the overflow and drain pipe with a T. Now install the drain strainer onto the flange. 

Step 8: Hooking Up The Drain

Carefully place the tub in a place where the flange should rest on the stringer. Make sure all the plumbings inside and outside are aligned. Now tighten all the connections nicely. Now attach the tub with nails with the studs. 

Step 9: Last Finishing

With the tub in place, finish up the wall with drywall and paint. Install the new baseboard or sound walls that came with the new tub and finish your installation. Lastly, reattach the spout in place. 

How To Install A Freestanding Fiberglass Tub | 3 Simple Steps

Installing a freestanding tub is pretty easy and it saves a lot of extra expense that otherwise would be needed on other kinds of installations. Free Standing fiberglass tubs are lightweight and come pretty cheap. So let’s take a look at the whole installing processing in detail:

Step 1

Two people must be used to move or lift the tub. Position the tub at its desired final location and trace its contour with a pencil. Ensure the floor drain and trap are pre-installed and compliant with your local regulations. 

Step 2

Use a throw rug to protect the tub. All bathtubs usually come with a pre-installed drain. For installation, it is recommended to use an adjustable P-trap. If the p-trap has a pipe-to-pipe connection use the supplied pipe adapter. Use PVC cement to join ta pipe connections. But if it has a lock nut connection, installation using a standard PVC P-trap is done similarly.

Step 3

Test the installation for leaks by filling up and emptying the tub. The tub should be flushed to the floor for maximum stability. Use silicone to seal the contour of the tub and leave it to dry for 24- hours. For hot and cold supply lines, the position and sizing of the holes for your chosen faucet should be following the faucet instruction manual.

How To Install A Fiberglass Tub On A Concrete Floor

  • Measure the width and depth of your alcove. Most bathtubs are five feet in length and either 30 or 32 inches wide and they come in two different configurations. As you face the alcove if the drain opening is on the left you’ll need to purchase a left drain tub. Check the subfloor if it’s level and if needed use a leveling compound to even out the surface.
  • Many tubs have a sound deadening and leveling pad on the outside and this needs to rest fully on the subfloor. Set the tub onto the skids and slide it into the place in the alcove. Check the tub if it’s level and uses shims to even it out. Take a pencil and mark all the studs for reference on all three sides. Now set the tub aside
  • Now it’s time to install the stringer. As you’ve already marked your studs you need to allow the height of it. Measure the distance of the reference line on each stud. This will serve the top edge of the stringer you’ll install
  • Cut a 2×4 according to the length of your tub and use deck screws to attach it to the studs on the new reference mark. Turn the tub on its side and install the drain according to the instructions. Use plumbers putty to attach the drain flange
  • To install the overflow valve, place the rubber gasket onto the overflow elbow. Then position it behind the tub. Attach the cover plate inside the tub to the overflow elbow and the gasket behind the tub. Connect the overflow and drain pipe with a T fitting
  • Finally, install the drain strainer onto the flange. Carefully move the tub back into place. The flange should rest on the stringer. Make sure the drain and overflow plumbing coming out of the tub is aligned with the drain outlet in your bathroom
  • Connect the pipes and tighten them down. The top of the flange has to line up with the reference marks you established. Join the tub flange to the studs with roofing nails. With the tub in place, finish off the wall with a water-resistant green board and paint. Reinstall the baseboard to finish molding around and in front of the tub. Finally, reinstall the tub and the installation is complete

How To Install A Tub Surround To Studs 

Prepare the alcove by stripping the walls to bare studs. The floor must be level and cleaned properly. Cut the hole in the subfloor according to the printed installation instructions that came with your tub. 

Next measure, mark, and install the firings strip. Place one end of the firing strip securely against the back wall. Then using the pre-printed guide, mark the floor at both ends and in the center. Now lay the firings strip in place aligning the front edge of the strip with your marks on the floor. Screw the firing strip in place. Now you are ready to install.

Carefully set the bottom edge of the tub spring on the floor so it is resting against the front edge of the firings strip. Then lean the tub back until it is sitting on the floor. Then gently press against one corner of the apron until it is securely sealed in Lyon’s lock. Then repeat the process in the other corner. Make sure the apron is sitting flush against the floor and the lock is visible at both ends. 

Now carefully peel off the protective layer from the flange. Secure the tub by screwing the nailing flange at every stud. Now your tub is installed and you can proceed with the rest of the wall installation. 

How To Install A Bathtub On A Concrete Floor

After you’ve taken out the old bathtub and the dray walls around it follow the steps down below to learn about the rest of the installation process on a concrete floor:

  • First, make sure the cutout for the drain is the proper size and is in the proper location. Make any adjustments if necessary
  • If you are installing the tub on a concrete floor you have made it level. There are two options to level your floor. You can pour a bed of mortar and then set the tub while the mortar is still wet or you can level the floor with more concrete
  • Once the floor is leveled go ahead and test-fit the tub. The tub should have solid contact with the ground on the entire surface. Once everything is checked it’s time to build the drain assembly. Start by installing the drain onto the tub and then the overflow drain. You can use a kit for solid assembly. You might need to cut the pipes to make them fit. 
  • Take some ABS glue to finish the drain assembly. Now you can place the tub to connect the drain lines with your tub and the mainline. Use silicone to attach the gasket. Now install the overflow drain. Use silicone to the drain flange and screw in the drain stop
  • You can pre-drill the tub flange to secure the tub to the studs. Now screw the tub all the way around. Check for any possible leaking and if there is no leak you can proceed with the Rey of the wall installation process 
  • Lastly, use chalk to seal the sides of the tub where it meets with the floor 

How To Install A Bathtub Without Access Underneath | 3 Easy Steps

When it comes to a freestanding tub there remains no excess underneath to do the plumbing. So what you need to do is set it up so that you and just drop the tub right down on top. If you’re on a concrete foundation or you’re in a space where you can’t get below underneath you need to follow our truck that we are about to explain to you.

Step 1

If you’re going to install one of these tubs you need to get a drain kit called Jacuzzi MZ 2000. It comes with a downspout and an extra part that you can set into the floor to set the pipe underneath. Cut the drain pipe according to the required measurement so the drain alignment kit flush fits with the floor. Dry fit the connections to check if the cut and measurement are perfect. 

Step 2

Use PVC glue to attach the pipe support on the floor and screw that down to hold it in place. Use a channel lock to pop the protector cover out. Use the plumber’s putty to assemble the drain assembly. Install the drain assembly on top of your tub as usual. Put the bottom gasket and lock the nut from underneath. 

Step 3

Lubricate the drain pipe below putting it onto the rubber protector. Now use some extra help to put the tub directly onto the plumbing assembly. You have to be very careful with this part so you don’t knock out the plumbing. Lastly, install the rough end at the back and install a spout of your liking. 

How To Install A Tub Surround Over The Existing Tub

Before installing your tub surround over the existing tub you will need to build a stud frame. The stud pocket should be plumb and square at the back and front corners. Refer to the roughing information on your installation guide for product-specific information. Once your stud frame is built and leveled and install your rough plumbing into the wall. 

Install the drainpipe as usual. Measure out support foot placement on the floor. Position a protective liner in the bath basin. Staple a felt pad to the subfloor to make contact with all of the support feet. 

Next, attach the metal support clips to the flange of the locations shown in your specific roughing information. Lift and position the bath on the sun frame and level your tub. If necessary, install the plastic attachment clips at all of the remaining stud locations. Shim under the support feet to level it out.

Now install the back wall and insert the tabs into the slots. Verify that the seal is installed undamaged and fully sealed. Measure and mark the faucet holes into the end wall and then drill holes into it. install the end walls and engage the pins in the slots. Make sure that the front edges are flush with no more than a 1/32-inch gap, starting at the bottom install screws through the dimples to secure the flanges to the.

Make sure the walls are nicely secured. Use shims if needed. Install the faucet and the rest of the accessories and seal where they contact the wall panels. Next, cover the framing with a water-resistant wall bond and then install the finish wall material. When you’re done painting apply a 100% silicone sealant when the unit contacts the finished wall.

3 Steps To Know How To Install A One-piece Tub Surround 

In a one-piece tub surrounding the wall panels are attached to the tub making it one single piece. These kinds of tubs have to be brought in and installed before the walls and you need to start with the plumbing first. If your subfloor is made of concrete make sure it is level or use mortar to level the subfloor because that is the key to a successful tub installation. Let’s learn how to install them:

Step 1 

You might need to purchase a drain kit according to the tub settings. First place the tub setting into place to mark the feet, do all the measurements, and dry-fit the drain connections to see the alignments. When you are done mapping out glue the drain connectors using adhesive. 

Step 2

Now use a plumber putty on the backside of the flange and place in it the drain hole and press downwards and tighten it. Remove the excess putty from the sides. Use a channel lock to screw the drain stopper. Install the overflow valve the same way. 

Step 3

If your tub feet do not sit flat then use shims to level it out so it does not move. Use a 2×4 as a stringer to attach at the backside of the tub. Now screw in all the tub wall flanges with the studs. Use challah or silicone on the tub sides to make it waterproof. 

Note: The whole process of one-piece tub installation is similar to a three-piece tub installation. The only difference is here you can attach the whole thing at a time and not in pieces. 

How To Install A 3-piece Tub Surround | 5 Easy Steps

When installing a 3-piece or 3-wall tub surround the tub should be installed at first and the whole process we’ve mentioned earlier. After you screwed the tub flange and applied sealant on the sides the installation process of the wall begins. 

Step 1 

When you complete the installation of the tub you’re now ready to install the walls. Check the walls to ensure they are square and level. Now set the back wall in place making sure it rests flush against the tub. Bring the bottom of the wall out a few inches so it leans against the studs as you retrieve the left wall panel. 

Step 2

Set the left wall in place, washing it between the studs and the rear wall to ensure a tight corner seal. Realest the process with the right wall. With the walls in placemark each stud along the top of the wall. Now remove all three wall panels and set them aside temporarily. Be careful that the back wall does not fall when both side walls are removed.

Step 3

Next starting just below the marks apply a generous bead of adhesive along the length of each stud. Carefully peel back the protective film from the edge of each wall. Be sure to peel back the film from the bottom edge as well. Leave the remaining protective film in place until the installation is complete. 

Step 4

Carefully replace each wall panel: first the back then the left and then the right. Once the walls are in place make sure that all seams are flush and tight. Then press firmly on each panel along the length of every stud to assure a firm bond with the adhesive. Double-check both corners to assure that the seam is tight and smooth. 

Step 5

Now starting with the front vertical flange, screw the end walls to the stud at the pre-marked holes. Screw the wall’s snug button not over tighten the screws. Then screw the top of each wall at every stud. Once the drywall finishing is complete remove the protective film from the walls and tub. This completes the installation of your 3-piece tub surround. 

Final Verdict

For a dream bathroom, a perfect bathtub matters the most as you will be resting while taking a bath. So you must pay attention to the whole process from choosing the right kind of bathtub, installing it perfectly, doing regular maintenance, and fixing any problems as it arises.

Frequently Asked Questions (FAQ)

Can I Install A Tub By Myself?

Yes, you can. But if you don’t have any previous tub installation experience then it can be very tricky for you. But don’t be discouraged already. Just do extensive research on the process, choose the right tub, select your desired installation process, collect all the needed tools first, and check all the steps before starting the next so you don’t make any mistakes and have to start all over again. 

Do You Have To Put Mortar Under The Tub?

If you are installing your tub on concrete or the floor is not even then you can use mortar to make the surface even. Use a level to check the sides and keep leveling the subfloor. If your subfloor is not even then you can chip the tub easily or it will make squeaky noises whenever you’ll step on it. Moreover, your drain assembly will not be perfect or might leak if the floor is not leveled perfectly. 

Do You Need Mortar Under An Acrylic Tub?

It is a good idea to use mortar under an acrylic tub because it will even out the subfloor and secure the tub in place. Make sure that once you have laid out the mortar bed you must place the tub over the wet mortar to fix it in place making the mortar level out on its own. 

What Is The Difference Between An Acrylic Tub And A Fiberglass Tub?    

Acrylic and Fiberglass bathtubs are somewhat similar in style and appearance. But they do have a huge difference when it comes to quality and longevity. Both the types are mainly made of plastic but their production technique is what makes them different. 

Fiberglass for shower walls or tubs is made of several layers of fiberglass and resin. It is lighter than fiberglass and economical. On the other hand, is a poured resin product mixed with other chemicals that are poured into a mold to the size and shape of the tub or panel. Acrylic tubs are heavier and more expensive but last longer than fiberglass. 

Do You Have To Put Mortar Under The Tub?

Applying mortar under the tub is not always necessary. If you have an uneven subfloor or the subfloor is made of concrete then you can use mortar to fix it. But if you have a freestanding tub 

How Do You Install A Bathtub Step By Step?

To install a bathtub you need to make the subfloor fully level, then dry fix all the drain pipes to measure their sizes,  carefully place the tub in place, connect all the drain connections, attach the drain stopper, screw the tub flange, install the surrounding walls and lastly paint if needed.

Can You Install Your Bathtub?

Yes! With the right tub, tools, plumbing knowledge, and some extra tease arch you can install your bathtub. 

How Many Layers Of Fiberglass Do I Need For A Tub?

There is a minimum requirement of two layers to make a Fiberglass tub but three will be better. But make sure you spend much time on the preparation, compression, heating process, etc to make the tub stronger. 

What Do You Put Under A Fiberglass Tub?

Usually, to support any kind of bathtub there is a support system like a mortar bed or plaster or a layer of durable product that can be fitted. You can also use plywood or shims underneath but that will be very tricky to fit in all the corners. Some people also prefer to use spray foam underneath to get all the tight spaces that are almost impossible to reach. 

What Do You Put Under A Bathtub For Support?

There are many options to support a bathtub from underneath like a mortar bed, paster, silicone, plywood, shims, spray foam, etc. The choice is yours and you need to be careful with this process because the support depends on how you installed the tub, what is the material, how much space you have underneath if the support is good enough to hold the weight, etc. 

How Hard Is It To Install A Bathtub?

Nothing is hard if you have proper guidance and knowledge about it. So if you are installing your bathtub on your own make sure to do thorough research on the procedure before making any move. Also choosing the right bathtub matters a lot. So overall it is not that hard to install a bathtub and you can use some extra help while doing it. 

What Do I Need To Install A Bathtub?

The first thing you need to install a bathtub is a bathtub that is perfect for you and your family, a good-quality drain kit that will last for years, a drilling machine, nuts, screws, silicone, spray foam, skids, some 2x4s, paint, etc.

How Do You Attach A Stud To A Bathtub?

Prepare the alcove, level the floor, install the firing strip, place the tub in place, install the drain kit, secure the tub to the studs by screwing the pre-drilled hole, and nail the flange at every stud. Now your tub is attached with all the studs and you can proceed with the rest of the installation. 

Can You Use Spray Foam Under The Tub?

Yes, you can. In fIta better way to create a support system underneath the tub to prevent chipping or cracking. And this will also fill up any tight space that you usually could not reach. 

Can You Put A New Tub Over An Old One?

Yes, you can about it. But you may require some new plumbing, cleaning, repairing, and supporting for the new tub to fit perfectly. 

Should I Put Drywall Behind The Tub Surround?

It is not recommended at all. Because over time the drywall will soak up moisture and will get ruined. But if you are installing your bathroom in a new place that was not supposed to be a bathroom you can cover the walls with drywall but makes sure the walls do not catch the water.