TrueDEK® Classic Foundations

Here are the most frequently asked questions about the TrueDEK® Classic Foundations. If you find that you still have questions after reading through these, contact us and we can help!

What do I use to bond tile to the shower foundation?

Use a quality brand of modified thinset mortar mix. Before installing tile, TrueDEK foundations must be coated with Tank/10 waterproofing compound, which improves the bond between the foundation and the modified thinset mortar, and provides an anti-fracture membrane to protect grout and tile from minor movement in the underlayment that may otherwise cause a crack or fissure in the tile layer. Waterproofing must be completely dry before applying modified thinset mortar.

Can I get a TrueDEK Classic foundation with a centered drain hole?

You can trim the edges of a TrueDEK foundation so that the drain hole ends up in the center, but in their original format, all TrueDEK Classic foundations have an off-center drain hole. An off-center drain hole allows an installer to rotate the foundation so the drain hole misses a joist or some other obstacle.

Why is my TrueDEK Classic flexing when I lay it on the joists?

Chances are, the blocking you installed to support the drain hole is too close to the hole, so that the reinforcement ring on the underside of the foundation is preventing the foundation from sitting on the joists properly. If you look at the underside of the foundation you’ll see there is a strengthening ring and a squarish-shaped reinforcement area around the drain hole. If the ring or reinforcement area rests on blocking or a joist or some other support, it can prevent the shower foundation from seating properly. As screws are driven around the perimeter of the base, the area around the drain hole will remain raised, resulting in flex when a person steps on the base. This error must be corrected before tiling the shower; if not corrected, grout is likely to crack, tile may pop loose, and water may run away from the drain.

If joists or blocking are uneven, or there are high or low spots on the top edges of joists or blocking, this can also cause flex. You want to achieve even support along every joist, and from joist to joist, while assuring that the foundation is level.

A Classic foundation that is seated evenly on joists and blocking may flex a little, but once it’s fastened and bonded to the framing structure it becomes very rigid, just like plywood subfloor does when it’s installed on joists.

Do I need to support all edges of the TrueDEK Classic foundation?

Yes, all edges of a TrueDEK Classic must be supported, as well as the adjacent subfloor edges. Additionally, the drain area requires support. We recommend 2x stock for all support blocking, and make sure the blocking supports the edges by 1″ or more.

How level does a TrueDEK Classic foundation have to be when it’s installed?

The simple answer is, it must be level. The bubble has to be centered on a spirit level, and you want to check for level all around the perimeter and across the base from end to end and side to side. TrueDEK foundations offer plenty of pitch to speed water to the drain, but every degree that’s lost to an out-of-level installation diminishes drainage performance.

Do I have to use ARC waterproofing supplies, or can I use different products?

Some waterproofing products will not bond well to the plastic foundation. The waterproofing products ARC carries have proven to work over thousands of installations, and we stand behind them. Using other products may work, but you’ll have to experiment to build the confidence you’ll want to have before laying the tile. Whatever you use has to do the job for the long haul.

Can I finish a TrueDEK Classic foundation with any tile I want?

Yes, you can, within the limitations of a tile product’s specs and TCNA guidelines. The point load rating on a Classic foundation is 4,000 pounds-force/sq. inch, so it can handle even the smallest mosaic tile, pebble, and glass coverings, as well as any typical wheelchair or shower chair use. We recommend mosaic tile (1½” or smaller) because they can be installed without cuts within the shower foundation area; bigger tile has to be cut at the pitch intersections.

Can I get a TrueDEK Classic with the drain hole in the center?

The off-center drain hole is an advantage because it helps the installer avoid an obstacle by rotating the foundation two or four ways, depending on whether it’s a square or rectangular model. For example, when you set the TrueDEK into position the drain hole may sit directly over a joist, but by turning the foundation you may avoid this conflict. All Classic foundations have off-center drain holes.

Do I need to tape the joints around a shadow box, niche, or built in bench?

Leaving joints uncovered allows more opportunity for water to penetrate your framing structure. In the long run it pays to embed tape over every joint. You’ll never regret it. Remember, most tile and stone are impervious to water, but grout is not.

Can I remodel a TrueDEK shower?

Absolutely. One of the great things about aTrueDEK foundation is that you can remove the original tile or stone, then redo the waterproofing and cover with new tile or stone of your choice. Be sure to repair any damage to the fiber cement board underlayment on the floor or walls before reapplying waterproofing materials.

Is building a wet room expensive?

Great question. Any installation will depend on many factors, including the size and complexity of the room, the time and materials it takes to apply the waterproofing materials, and most significantly, the type of tile or other wall covering you choose. Wet room walls must be covered with some type of waterproof material like tile, stone, or sheets of acrylic, fiberglass, quartz or the like, and as you might guess, the cost of these materials varies widely.

Why would I consider a wet room?

A wet room provides several key improvements over an un-waterproofed bathroom. First, no water can penetrate to the subfloor, preventing rot, mold, and mildew from developing. Second, water cannot leak into rooms below. Third, shower spray can splash into the room and bathers can step out of the shower without having to dry off beforehand. Fourth, washing down the entire room for cleaning is easy and you’ll never worry about water getting into the framing. Fifth, a wet room can expand the maneuvering area beyond the shower, which can be a real advantage for people with disabilities or physical limitations. Sixth, wet room designs can make a small to medium size bathroom feel much more spacious.

What is a wet room?

A wet room is basically an entire bathroom that has been waterproofed. So, in addition to the shower area, the floor throughout the bathroom is waterproofed along with the walls to a height of about 3″ to 4″. All seams and joints in the floor, as well as the floor to wall joints and wall corners, are covered with embedded reinforcement tape.

Can I install two TrueDEK foundations next to each other to make a large shower?

This has been a good solution for some situations. You’ll have to plan for two drains, and two drainage areas with a slight ridge in the middle.

Can I use silicone caulk for installing the drain in my TrueDEK shower?

Yes, but we don’t recommend it unless you are very neat about it. Nothing bonds to cured silicone, so if any is exposed in places you intend to apply waterproofing, you’ll end up with a problem–be sure no silicone is squeezed into areas that need to be waterproofed. If you do use silicone you can clean up squeeze-out (before it cures) with WD-40 or similar products.

My foundation is installed and seems to flex in the middle. What gives?

Chances are, the reinforcement ring around the underside of the drain hole is hung up on a joist or blocking. If you look at the underside of a TrueDEK Classic you’ll see that there is a squarish-shaped reinforcement area around the drain hole. This reinforcement area isn’t flush with the ribbing or bottom surface on the rest of base. If the reinforcement area rests on blocking or a joist or some other support, it prevents the base from seating properly.

Another possibility is that the joists and blocking are uneven or there are high and low spots in the framing. You want even support, level support throughout the framing below a shower base.

Why would I use a TrueDEK on concrete?

Since concrete is so hard it is often believed it is waterproof. Not so. Concrete acts much like a sponge, absorbing and holding onto water over time. In a shower, water can get into concrete by soaking through grout (tile may be impervious to water, but grout isn’t), leaking around the edges of the shower base, or seeping into cracks in the concrete that develop as the material ages. Many showers were made using a vinyl liner under a packed mud (concrete) bed, with a custom pitched surface for drainage. Unfortunately, over time water often collects between the concrete and the vinyl liner, creating a filthy, mold-ridden mess. Eventually the concrete crumbles, and these showers became unusable. Thousands of them are being removed from homes, hospitals, and other facilities every year. Installing an ARC shower on concrete provides an impervious surface, covers any cracks that may occur in the concrete, diminishes the potential for mold and mildew growth in the concrete, and delivers consistent, precisely-controlled pitch planes for perfect drainage performance and predictable tiling results.

How do I install a TrueDEK Classic in a concrete floor?

You have a couple of options, though as always, we prefer installations that provide zero-threshold entry into the shower. You can remove concrete to a depth of 1⅛″ in the area where the base will go. We do this with a concrete-cutting saw and blade, first cutting along an outline of the foundation, then making scoring cuts about 1″ apart inside the perimeter cuts. We remove the remaining waste with a hammer drill and chisel. Use thinset mortar to bond the base into the recess. Alternatively, you can install the base on top of the concrete and build up the surrounding floor to end up with a level entry into the shower.

Can I use a TrueDEK Classic for other applications?

Sure, if properly installed and capable of supporting the weight you plan to set on it. A Classic makes a great dog-washing platform, and we’ve heard of them being installed as a catch basin in a floor under a washing machine. Anywhere you need a drain should be a candidate.

Do I need to support the edges of a foundation that don’t rest on joists?

Setting a TrueDEK on joists requires care and is a critical part of the installation. The entire perimeter of a base must be supported. Additionally, the drain area requires support. Use 2x stock for all support blocking, and make sure all edges are supported by at least 1½” of material. All adjacent subfloor edges also require support.

Where do I set a level to check my TrueDEK installation?

The perimeter of each foundation has a flat area for resting a level. If you have cut away a flat area, use the crest of the edge to set a level. Because of the importance of leveling a TrueDEK, consider using several levels to test your installation: a torpedo level for checking the edges, a longer carpenter’s level for going edge to edge, and a bulls-eye level for spot checks, like around the drain hole.

Can I drill into a TrueDEK?

Yes. In fact, if you cut a Classic you will want to drill new countersunk pilot holes for fastening it to the joists or other foundation material. Also, if for some reason you need to secure the base in a spot where there isn’t a pre-bored screw hole, simply drill a countersunk pilot hole into the field and drive a screw.

What type of screws do I use to fasten the foundation?

We recommend #9 or #10 flathead screws that are 2″ to 2½” long. We do suggest using coated screws as a bit of insurance against corrosion due to the wet environment. Pick a screw that is appropriate for the substructure beneath the shower foundation–wood screws for fastening to joists and Tapcon-style screws for concrete.

Do I need to drive a screw into every hole in the base?

You don’t have to, though most installers do. There are a lot of holes, and they are there for convenience. Driving screws holds the foundation in position while the adhesive cures. Once the adhesive cures there is little need for the screws.

Can I install the foundation on a subfloor?

You can do this and it will be fine. Be sure you cut a hole for the drain that is large enough for the reinforcement ring. Failing to do so will cause the ring to catch on the subfloor and prevent the base from seating properly.

Can I get a foundation in a size that’s not shown in the catalog?

Sorry, no. We carry the full line of foundations, though we hasten to add that the size of the base does not limit the size of a shower. There are techniques for floating slope beyond a TrueDEK to enlarge the shower–see our Extend the Pitch instructions.