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How to Fabricate an Airstream/RV Shower Pan with No Mortar - Part 1

April 29th, 2017 by Chris Taulborg

I've scoured the internet trying to find ways to fabricate a shower pan/liner that would be ideal for Airstreams/RVs/Schoolies but haven't been able to find anything suitable for our situation - so I decided to come up with my own way.

The Challenge

Building a shower pan isn't the most complicated task, in a residential setting. There are many ways to accomplish it - for example a pitched slope mortar bed over subfloor, then PVC shower liner/membrane on top of that, then another layer of mortar, and then finally tile:

Photo/information from finehomebuilding.com

However, as you may or may not know, installing a mortar shower base in your airstream, schoolie, or RV isn't a viable option because of both weight and rigidity - driving down a bumpy highway will turn that meticulously crafted mortar base to crumbling dust in short order.

So what are your options? You can:

  1. Hope that you didn't foolishly throw away your original shower surround (like we did) and/or that it's repairable.
  2. Hope that you can find one used or new for purchase for under $2000 or that you're lucky enough to not have an-oddly sized side bath setup that makes it impossible to locate a replacement.
  3. Hope that you can find a local bodyshop/fiberglass fabricator make a new liner for you (for a basic pan you're looking at least $1000 or more), or be willing to learn the art of fiberglass fabrication yourself (and spend a decent amount of cash and huge amount time getting the tools and skills you need to make this happen).
  4. Leave your camper parked permanently and go ahead with an all-mortar base.

The Solution

None of the above were viable options for us. That left me with one route - come up with another way. After thinking about it for several weeks now, I believe I have come up with a great way to build a mortar-free, pitched slope shower pan that will have two layers of waterproofing.

If you get stuck or want to discuss, feel free to contact me - I'd be happy to share any information I can.

The Tools and Materials You Will Need

If you are an airstream/RV owner, the tools and materials you will most likely need for for this, 99% of which you can get at your local Home Depot/Lowes, are the following:

Step 1: Cut Your Plywood Base

The guide assumes you have already built out a suitable support structure on which your shower pan will rest. In my case I used pieces of 1/2" Baltic birch plywood screwed together. After your structure is in place, measure out the dimensions of your floor and cut out your 1/2" birch/marine grade plywood to this dimension. This will serve as the "subfloor" for your shower pan that your drain will rest on.

Step 2: Cut a Hole for Your Shower Drain

Dry fit your u-trap and drain into your plumbing system. Carefully measure the position of where your drain will be relative to the floor, and mark it on your plywood base. Measure the rough hole size for your drain and drill a pilot hole. Use your jigsaw to cut out the the hole.

Step 3: Use Your Shims to build Pitch/Slope and Cut Second 1/2" Plywood Sheet

Set your drain in place. Grab your composite/wood shims and stack two on top of each other so they add up to about 1/2" thickness. Spiral these out from your drain to make a slope. Template this shape onto a second piece of 1/2" Baltic birch/marine grade plywood cut to the same dimensions as your sub floor. Use your jigsaw to cut out this shape and set in place.

Repeat the shim process again, doubling up if desired/necessary depending on your overall shower floor dimensions; don't worry about gluing or cutting these outer shims yet.

You can now start to see how this will shake out, looking at it from the side shows a perfect slope towards the drain:

Step 4: Glue

Liberally apply wood glue between the layers of plywood and under the wood/composite shims. Do not worry about cutting your shims that are hanging off the edges, it will be easier to cut them all at once when everything is secured and dried. I used construction adhesive to join together my composite shims due to the ridged structure. 

Step 5: Spray Foam the Voids

This step is really optional, but I decided to go for it since I was doing all this work as it is. Simply spray in the foam between the larger voids and wait for it to cure.

Step 5: Trim the Overhanging Shims

Trim off the overhanging shims using a hacksaw or jigsaw, and trim your foam with a razor knife.

Step 6: Install Drain

Set your shower pan in place. Dry fit your drain assembly and make sure everything lines up correctly. Cut a section of ABS pipe to size as needed to cover the gap between your u-trap and the bottom of your flange, adding in your 1.5" to 2" reducer/couple to make the transition between your 1.5" ABS pipe and the 2" drain. Double check everything, then use the Oatey ABS Cement to bond everything together and hold for thirty seconds while the cement sets.

Step 7: Install PVC Shower Liner

This is the first step in waterproofing. First, cut your PVC liner to size, adding about 3-4" inches all around and a little more for the "curb"/entrance area of the shower. Then, cut your 1/4" plywood sheet to the same dimension as the shower pan, and mark and cut a hole for the top piece of the shower drain flange assembly. Install the PVC liner directly to the platform you just built. The below video shows this process well, with the obvious difference of subbing out the mortar base with the wood base you just built:

I used construction adhesive under the PVC liner to attach it securely to the wood. Immediately proceed to step 6.

Step 8: Install 1/4" plywood tile base

Attach the top portion of the drain flange assembly and secure in place (see video above for how to do this). Next, add some construction adhesive or 100% silicon liberally on top of the liner in a zigzag fashion. Next, place your 1/2" plywood on top of the liner/glue:

Check your pitch, which should be spot on because it should still follow the contour you've established throughout. To ensure everything stays tight to the pitch/slope, use weights/water-laded buckets/anything heavy to set on top while everything cures:

Up Next: Flexible Water Proof Membrane and Tile

The next post will provides details on the second phase of the shower pan/waterproofing process, which involves the application of the water proofing membrane (AVM 750 Paste/Fabric Mesh). This will go directly on the plywood structure, and once cured will form a flexible water proof membrane that you can apply thinset and tile directly on.

If you get stuck or want to discuss, feel free to contact me - I'd be happy to share any information I can.


Posted in the category Renovation.


Natasha R Snodgrass
1 year, 2 months ago
Looks good! Where did you purchase the AVM 750 Paste/Fabric Mesh? I’ve looked online and can not find it. Thanks!
ChrisNatasha R Snodgrass
4 weeks, 1 day ago
Looks like you can buy it here: https://www.sunshinesupply.com/750PsteYllw1galUnt
David Watterson
1 year, 11 months ago
I am anxiously awaiting your next post. Great post so far... I've looked everywhere on how to build a shower pan for my camp trailer from scratch and yours is the first I've found to be what I am looking for. Really interested to see what type of tile you use and what type of grout (silicone?) Are you familiar with http://flextile.com?
ChrisDavid Watterson
4 weeks, 1 day ago
More details in part two!
2 years, 5 days ago
I love this idea. Is there a part two yet for the shower install? I am very interested as I am converting a closet into a wet bath for my classic camper. The space is a weird shape and this seems to be the best option/solution for me because shower pans are not sold to fit my space. Also, I am having a hard time understanding how step 8 works. It seems like 1/2 inch plywood would be too rigid to adhere to the pitch of the shims underneath without pulling loose. Is it just glue holding it in place? Also, you mention applying tile next, won't the mortar between the tile crack? Or are you planning on using something else? Looking forward to hearing your response and seeing part 2. Would love to see video!
4 weeks, 1 day ago
Part two is posted! The top most sheet of plywood is 1/4", not 1/2" which would be to rigid for sure. Yes, a liberal amount of glue/construction adhesive is holding it together.
2 years, 2 weeks ago
Hey- would really like to know how the finished product turned out- also if I may ask what you plan/did use for the shower walls? I'm scratching my head about what to use (my bathroom is basically the same layout as yours just flipped). I've thought maybe FRP but the joints just worry me so much about leaking from movement...any ideas would be awesome :)
4 weeks, 1 day ago
We were really happy with how the shower came out, and we had zero leaks the entire time we were out on the road! The only issue we ran into later on was with our tile installation – we didn’t put enough “mortar” and grout under the tile, and several of them started to peel up, which turned into a game of whack-a-mole after the second year. This was purely cosmetic, as the tiles were purely a decorative function and it was completely water proof under them, but still something that annoyed me – so on the last year out, while at an RV park I ended up scraping off all the tile, going to home depot and buying the same tiles (which were still available!), and redid it with a much more liberal base of flexible mortar/adhesive, and it held up fantastic after that.
2 years, 2 weeks ago
Any chance you'll be doing the post anytime soon? I've been waiting a year. ;-)
4 weeks, 1 day ago
Yes, it is now posted!
2 years, 1 month ago
the bathroom was already pulled out of our vintage airstream. great stuff. thank you
4 weeks, 1 day ago
Thank you for the comment!

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