"am i crazy to think about making my own foam backer board using dow blue foam?"

Yes.

Agree with Joe. Don't try to reinvent the wheel when moisture damage is the result of doing it incorrectly. If funds are tight, choose a lower cost method of waterproofing.

Why try to "make your own" when you can just buy the real deal?

The stuff for showers is made out of cement.

"The stuff for showers is made out of cement."

Except for the stuff made out of foam.

Thank you MongoCT for reading my post and answering it. I hear you about not being a mad scientist but can you please read my rationale for considering it?

1) kerdi and usg shower bases are unfaced foam and requires unmodified thinset and their membrane fabric to make it waterproof. laticrete and wedi shower bases come with waterproofing already applied.

2) The major brands offer their own foam backer boards with their fabric membrane applied except for wedi ( covered with fiberglass and thinset/cement).

*Their selling point is that its lightweight and waterproof*

3) For installation of foam backer boards, kerdi/usg/wedi/laticrete specify using a urethane caulking or their brand caulking for seams, change in planes and penetration sites OR thinset and fabric OR mesh and waterproof paint.

4) Their waterproof membrane fabric can be applied to a variety of backer boards to make the shower walls waterproof.

*Their selling point is its cheaper than their foam boards and makes a variety of backer boards truly waterproof*

5) If kerdi and usg unfaced/bare foam shower base + waterproof membrane fabric with unmodified thinset equals a waterproof shower base, why can't a same high density rigid foam board + their waterproof membrane fabric with unmodified thinset equal waterproof shower walls too?

* kerdi/usg shower unfaced foam base + waterproof membrane/thinset = waterproof*

* same rigid unfaced foam board + waterproof membrane/thinset = waterproof?*

* installation/material cost and time would be the same as using a cement based backerboard + waterproof membrane/thinset = waterproof*

I'm not certain how to answer your question, because I don't know what your motivation is.

The title of your post was about making foam backer board for shower walls. I could replicate their product with membrane, foam and contact cement, thinset, urethane adhesive, etc. I know I could fabricate a look-a-like product. And it might actually work. Or it might not.

I'd certainly do a couple of tests to see if my adhesive of choice will adhere to the factory surface of the foam, or if I needed to texture it a bit. And to make sure my adhesive of choice doesn't react with the foam in a negative way.

But I doubt if I'd save money while doing so, as I can buy membraned foam board for less than the cost of the membrane, adhesive, and naked foam.

Now you're including the foam trays?

I haven't used a Kerdi Tray in years. Probably 15 years or so. I do know that it had a dimpled texture to it. I don't recall if the surface of the foam was treated in any other way to accept thinset.

If you think you can replicate a sloped foam tray and the flanged drain, and have THAT be durable? Again, you could. Or it might delaminate in one way or another after enduring foot traffic. As to fabricating a Kerdi tray, you could source the parts for less than the cost of one. But now you're having to do shaping, fabrication, surface texturing, etc. Again, maybe you can do it. But that'll eat hours of time. So if the motivation is to save time, you probably won't. If it's to save money, you probably will. If it's to make a product that's equal or better to a manufactured tray? That I don't know. Your home made tray might work, it might not.

However, I recommend blowing off the foam tray and just using sloped deck mud. Then membrane over the mud. Fairly easy. Amazingly inexpensive. It'd be a lot faster than fabricating a foam tray. It'd be Inexpensive. And in case I didn't mention it, it'd be inexpensive. On top of that, you'd save money. (Hint)

The caulking. Are you looking to not use urethane adhesive/sealant between the panels? The manufacturers recommend it because...their massive R&D departments figured it's a step on the path to a successful installation. If you're making your foam panels out of the same material, wouldn't you want to follow their lead? If not, no worries. They're your panels.

Again it comes down to motivation. WHY do you want to do this?

I doubt if you could make a better, more consistent product.

You might be able to make a product that will stand the test of time.

You might be able to make foam wall board for equivalent or less money.

You can probably make a foam tray for less money. But you won't save on labor. Can you make one of equivalent quality, or one that will be as durable? It all depends on how good you are at shaping and surfacing foam.

If you really really want to do it? Just to do it? Then do it. That can be motivation enough.

If you simply want foam for thermal insulation or sound deadening? I've foamed walls with rigid foam panels. Then applied cement board over the foam, then applied a membrane to the cement board and tiled on the membrane.

I got foam. I got a surface applied membrane. I did it using accepted methods.

If you proceed, certainly keep me updated on this thread. Take process and progress pics and post. I'm intrigued by stuff like this.

Hi MondoCT,

Yes, I plan to make a sloped mud deck with thinset adhered membrane fabric and drain ( same manufacturer) for the shower base. I should of clarified, my bad.

I brought up the kerdi/usg unfaced foam shower floor + waterproof membrane/thinset to question why the same couldn't be done for shower walls too- unfaced rigid foam boards + waterproof fabric/thinset.

JB site wedi rep confirms the Dow blue foam core in the Wedi boards is the same Dow blue foam in their panel insulator/exterior sheathing.

Caulking- Yes, I plan to use specified urethane caulking to foam board for installation- to all sides, changes of plane and screw sites. like the wedi/kerdi videos.

Thinset/fabric membrane and mesh/liquid membrane were alternatives offered by the waterproofing systems.

Motivation- WHY do i want to do this?

super lightweight/clean/easy to cut foam tile backerboard + thinset applied waterproof fabric = waterproof shower wall.

VS

super heavy/dusty/hard to cut cement backerboard + thinset applied waterproof fabric = waterproof shower wall.

The difference is if you use one already made by a manufacturer, and something goes wrong, you have a factory warranty to fall back on. If you make your own, you're ON your own.

I'll add this then:

Durock? It's an approved substrate for any of the surface applied membranes. Sure it generates dust when cut with a power saw or angle grinder. But if you score and snap with a blade? It's pretty clean. It is heavy when compared to foam...but you'll be installing a half-dozen sheets max.

Foam board? Sure, it's even lighter in weight. Here's all I recommend. Find the foam you want to use. Choose a membrane, example, Hydroban sheet membrane. Then call Laticrete's tech department and ask what thinset/adhesive they recommend for adhering their membrane to the EPS/XPS/foam of your choice. If you get a solid answer, by all means move onward with the project! If not, repeat for each foam/membrane/adhesive combo you can think of.

Honestly, and again...I'm a guy who thoroughly appreciates the DIYer mentality...I built my own houses, boats, kayaks, canoes, airplane, swimming pool, I've drilled my own wells for water, I've done a couple of frame off car resto's...all solo. Trust me, I embrace the DIYer mentality.

But showers? Here, on this forum, I do worry about compromised showers. Because houses are the most valuable investment most people on these forums will ever make, and water damage from a shower can just muck things up in tremendous fashion.

Plus, it's near impossible to properly repair a shower short of tearing it out and rebuilding it.

If your primary concern is weight and dust? Then I'll wave the bugger flag. And I'm waving it in an attempt to help you out.

Just buy USG foam board and be done with it. Hydroban sheet is maybe $1.25 a foot? Kerdi about $2. Foam board? Maybe .40 cents. Adhesive? Who knows. Best case, you're saving yourself $1 a sqft by trying to make your own versus buying USG's product.

For a shower of your size, that's maybe $75 you're saving. On an expenditure of how much for the entire shower? It's a fairly small percentage.

Again...I THOROUGHLY embrace the DIY spirit. But with you being motivated by weight and dust? I'd spend the extra $75 to get the USG foam board. Lightweight. No dust. And you KNOW it's going to work. Plus you'll avoid the pain of having to lug a heavy and dusty bag of thinset home and the pain of trying to thinset or adhere the membrane of your choice to the foam of your choice with the adhesive of your choice on your own.

Just my opinion.

Worth the price paid.

Good luck!! Seriously. Whichever way to proceed, I'd love to hear how things turn out.

thank you for your replies, really:)

dropping the diy foam board route and will check out finpan propanel and jm goboard. these two brands are lower priced compared to usg/laticrete and the rest plus i can get them locally. hd pro desk can order the usg foam board for $40/ 3x5 board and can't seem to find laticrete hydroban boards anywhere locally.

with a regular 3x5 cement board nearly 50% of my weight, i'm grateful foam backer boards exist. i never considered tackling a project like this before learning about foam boards.... i gotta save my strength for lugging up my dry mud mix and tiles, though it'll be neatly divided into 25 lbs portions :)

i made a 4x4" box with some leftover polyiso board. i'll see how water tight it is for the heck of it. next week, i'm making a small plywood base with low wall using the rest the polyiso board for my mock up/practice mud bed.

any opinion or experience with finpan propanel or jm goboard?

"i made a 4x4" box with some leftover polyiso board. i'll see how water tight it is for the heck of it."

Polyiso is a closed cell foam, as long as you seal the joints the foam itself will hold water even without a membrane.

"any opinion or experience with finpan propanel or jm goboard?"

Never used either of the two.

I wouldn't risk making that myself. Too much can happen if there's any places where it's not sealed well enough, etc. There are probably other places where you can cut expenses, but the shower backer board should not be one of these.

I have a tub shower installed in 48 yrs ago with 4"x4" tile surround using 1/2" white xps foam backer. The tile is perfect to this day. They also put XPS under tile baseboard and it is solid with perfect grout. I pulled off some baseboard to install a door and the adhesive stuck so good I tore the XPS to get it off. The adhesive looks like 100% coverage very thin layer of white hard thinset. Not a single grout defect or crack in shower or baseboard and never regrouted. Since XPS is waterproof this seems like the Kerdi-board of the 60s. Today I'm DIY installing a 4'x10' walkin shower and can't find anyone who sells Kerdiboard except Home Depot 1/2"x32"x48". I found this post looking for what adhesive to use if I use 15psi 1" Dow blue board for backer. I'm thinking 2" barbed roof deck insulation washers and Tapcons to the concrete wall, silicone sealed and fabric taped joints, thinset adhesive, 18"x18" porcelain tile. I wonder if I should Redguard the lower 6'?

Did anyone jere talking about it, ever wnd up using the Dow bluefiamm board fir their showers?

Get in touch with Paul at https://builtwithfoam.com/product/rectangular-shower-bases/ He can build anything you need....

Cement board is not that bad to work with, just do that

@mrose1233, cement board will still need waterproofing of some sort.