Shim spacing at front of shower base

[Skrider]

Hi,

I'm putting in a bathroom in the basement that's roughed in. The shower is in the corner and needs to be shimmed. The base is fibreglass.

How close do I need to place the shims? There is a high spot in the middle and both corners at the front have to be shimmed leaving just the middle third touching the concrete. If I just shim the outside corners is there any chance of the front lip cracking?

Thanks!

 

[Jadnashua]

If the whole thing is not supported, it is likely to flex and create stress cracks and it's often really hard to keep the walls to the pan sealed if things are moving around. Instead of shims, consider piles of something like deck mud or Structolite. THen, set the pan down into the stuff and ensure it is perfectly level as you squish the stuff down. The piles will spread out and provide support. Leave it alone for the stuff to cure, then continue.

 

[Sponsor]

 

[Skrider]

How long does this take to set up? I had screwed on the drain with plumbers putty and then glued down the drain. I can unscrew the drain and lift off the base.

Do I need place it all along the front lip where the low spots were or are you also saying to put piles under neath the rest of the base?

Thanks for the help!

 

[Skrider]

If this is mixed right it should have a dry consistency and not ooze. So i can just press down on the base to get it to level? How much in behind should be filled?

 

[Skrider]

I put a thin backer board so the mortar would be able to slide away and then laid a bed just higher than level. Set the base in, leveled it up and packed the mortar from the front some more. I scraped away the excess and now it's setting up. It seems level so hopefully it's good.

Thanks for the advice!

 

[Jadnashua]

You really want the entire base to be supported and not just the edges. WHen you stand in there, if not supported, the fiberglass (or acrylic, or whatever) can flex, and eventually fail from fatigue.

 

[Skrider]

Well...crap. You said it the first time and I guess I heard the answer I was looking for! The walls are still open. I could still access the under side from the side.

You're suggestion then would be to fill the entire void? I could still mix mortar and push it underneath from the side.

 

[Skrider]

Thanks for your patience. This project is taking a lot longer than I expected.

 

[Jadnashua]

Probably the most critical location in the pan is near the drain...any flex there will eventually cause the pan to crack and could cause the drain to leak beforehand. IOW, while the edges are important, many of these pans really need full support. Not seeing yours, I do not know exactly how it was constructed, but if there are a lot of voids and it is not supported well, you'll likely have issues down the road.

In your bare feet, walk around on it...have someone also watching, see if you can detect any movement. If you can, fix it now. Pushing stuff in from the edges is not likely to get all the way to the middle.

 

[Skrider]

The base seems solid. It's reinforced with fiberglass and something like cement.

I checked on the stuff that I did have under the lip and it just seemed to crumble away...and the base hasn't even had anyone stand in it yet!

So back to square one. I'll pull the base and get enough to fill the hole thing. I worry about it getting stuck on a mound of the mud. The base is 4x3' and about 2" from the floor. If I build it up that much will I be able to squish it done until it's level and low enough to connect to the drain?

I see now other posts about it crumbling and comments that it needs to be packed. If I pack it before hand will it be to hard to level? If I just have the bottom played (2x4's) of the surrounding walls will that be enough of a form?

 

[Reach4]

From what I have seen posted, I think you want little mounds or piles that are maybe up to twice as high as would be needed to touch the base, but spread out so that the piles cover maybe 25% to 40% or so of the area. That way the piles will have a place to squish down to. In the case of a tub, they recommend putting water in the tub during the curing. I don't know what you would do for a shower base.

They often put a piece of plastic sheet over the mortar piles to not adhere to the tub in case the tub needs to be replaced later.

https://terrylove.com/forums/index....d-for-one-piece-maax-fiberglass-shower.59860/ should be useful, but I would not use plaster of paris. I would probably make my piles smaller and more regular.

I have never done this.

 

[Skrider]

Ok. So in placing the mounds higher than the compacted height, will that be enough compacting of the mortar to give it strength?

 

[Jadnashua]

Deck mud is like wet beach sand until it cures. It does need some thickness to hold together, though. To prevent the plywood from sucking too much moisture out of it, put some plastic down on the subfloor first. Without seeing the underside of the pan, it's hard to say what would work best.

 

[MikeKenmore]

hope you don't mind if i jump into this thread with a similar question, so here goes.

I'm installing a kohler archer tub (acrylic). it has 4 wood block feet embedded into the acrylic at about 1/3 and 2/3 of it's length. i shimmed those up with simpson tie plates (http://www.homedepot.com/p/Simpson-Strong-Tie-1-13-16-in-x-5-in-Tie-Plate-TP15/100375260) to get the tub level. this results in about a 1/4" gap along the apron at one end, no gap at the other end. i am tempted to just use more simpson tie plates to more or less provide continuous support (max 4" gaps).

good idea or bad idea? see photo. i would obviously push these under the tub to be flush with the apron.

also, I've seen a few vids where they spray a bunch of spray foam underneath the tub (which is set to level) and then fill the tub with water so it stays level. you'd probably never be able to remove the tub again without destroying the subfloor.

or, could you use thinset as your material for piles?

 

[Jadnashua]

Thinset, when applied thicker than design (typically, no more than 1/4", but there are some designed to thicker applications), will shrink and crack, so not a good use of that material in this application.

I'd first stand in the tub when all of the four feet are tight on the floor, and see if you notice any deflection anywhere. If you do, I'd use the same technique and use piles of deck mud (or structolite) underneath it to get it level. The piles will spread out when you press down to get things level, and then just let it cure at least overnight. As to the apron, somewhat depends on what you're putting on the floor for finish. If you're dealing with tile, then you'd need at least the 1/4" cbu with thinset under it, then the tile, and it would hide any gap. A few shims and I'd be happy. Typically, the tub would have ledger board(s) to support the long edge, and with the bottom fully supported, it should be fine. Deck mud isn't really sticky like concrete or thinset - it's mostly sand with enough cement in it to hold it together - when mixed, it's like wet beach sand...grab a handful, squeeze and it should hold together with no excess water dripping out. You'd want plastic on the floor to prevent the wood from sucking moisture out of it before it could cure, and you could, but it typically won't stick much, put another layer on top of it. This will retain the moisture and let the cement cure for maximum strength as the water gets incorporated into the cement chemically - excess will eventually dry out, but most of it when mixed properly actually goes into the cement to cure it.