All mortar curb vs. wood curb

[Beagle]

My local tile store recommended building an all mortar curb similar to the rough sketch I attached. They claimed that wood in the curb will eventually swell or shrink causing cracks. However all the pictures and descriptions I've seen online and in these forums use wood for the curb base.

Is my tile store wrong or can wood cause problems later?

- Pete

[davem]

The only thing that would make wood swell would be water. If you build the curb right, the wood should never see a drop.

I think a *very* small amount of shrinkage would be ok due to the construction of a curb. Once the mud is tiled it forms a very strong structure that can support itself. If the wood inside moves away just slightly the mud/tile structure would stay put.

Besides, the curb in that picture looks like it'd be hard to build!

[Beagle]

Thanks for the response. The store claims you nail a 2x6 to the front of the shower leaving a gap between the liner and the 2x6. You tuck the mortar down the front and build it up. Then you remove the 2x6 later as the mortar sets up.

I was reading some older threads and see that John prefers using a 2x4 set on end with thick mortar around the board. Sounds like that would be a good compromise.

- Pete

[e3]

AS DRAWN WOULD NOT MEET PLBG. CODES IN MOST PARTS OF THE COUNTRY. MEMBRANE SHOULD TERMINATE AT OUTSIDE EDGE OF CURB. THREE 2X4 ARE USED ALL THE TIME AND AS SAID SHOULD NERVER SEE WATER IF DONE RIGHT. NEW IN THE TCA HANDBOOK FOR 2005 WILL BE PRE-MADE CURBS LIKE "PRO FORM" SEE LINK

[John Bridge]

Hi Pete,

For years I built curbs out of bricks, pieces of concrete blocks and other masonry rubble, but I've never tried to build one our of mortar only. As Eric said, you need to wrap the liner over the top of something. And what if your front form warped from the moisture? You come back in the next day and the front of your curb is bowed out.

[Scooter]

I don't think mortar alone would be very strong. Concrete perhaps, but not mortar.

If you use Kiln Dried Fir there will be no shrinkage. You are correct that if you use wet, green, or PT wood, there will be significant shrikage.

I am a carpenter, not a tile guy, OK, so here is why, with apologies to John, why you want to put the 2x4 flat, not on edge.

There is a species of wood in furniture making called Quarter-Sawn Oak. If you look at the end the grain goes up and down. Flat sawn Oak the grain goes side to side. Got it? All the really nice furnture uses QS species, and the best flooring is also QS. It doesn't shrink, nor expand as much. Here is why:

Wood expands and contracts along those grain lines. So a flat sawn 2x4 gets wider as the seasons change, because the grain goes side to side. OK? A Quarter Sawn 2x4 gets fatter as the seasons change, because the grain goes up and down. So, typically, QS wood is more stable.

If you buy Verticle Grain Kiln Dried Doug Fir, it is QS. There will be less expansion and it is a very very stable wood.

So while 99% of my framing for any house is stupid wet and cheap 2x4's, I like to hand select Verticle Grain Kiln Dried Fir for certain areas: Walls that are going to get tiled, curbs, and exposed areas in living rooms, not hidden by cabinets and doors.

This is my two cents worth.

[John Bridge]

I put the stinkin' 2 by 4 on edge because I want the curb to be narrow.

A single 2 by 4 on edge, even if it does shrink or try to bend, will not bend a curb that has 3/4 in. of reinforced mortar and tile on both sides of it. No sweat.

We are not worried about shrinking so much as we are swelling. Keep water away from your lumber, and you're in good shape.

[HI]

Toss out the liner go with a concrete curb it will least forever
and waterproof using a liquid and mambrane once you use this you will never go back to a Pasc again!

[cx]

HI, you gotta help me a little here.

What brand of liquid membrane are you recommending for these shower pan applications?

I ask because I don't know of any manufacturer of such trowel-on/roll-on/paint-on products that recommend their product for such application. But I'll take an education anytime.

[tileguytodd]

Actually,C-Cure's Pro Red is being spec'd by architects for commercial applications as a trowel applied surface membrane for slab on grade and below grade applications.
It has not to my knowledge been used as an above grade membrane in any commercial applications although i dont see any specific reason why it wouldnt work using proper methods and the same precautions you would use with any liner material.

Architect specifications for specific projects i have read called for the following.
A clamping membrane with a minimum 1 1/4" depth Preslope of Tilecrete or similar with trowel applied Pro Red 963 membrane and fiberglass cloth reinforcing at all wall floor junctures and at drain out 9" Minimum.( each coat had a specific minimum thickness in mills of which escapes me at present)Curb is trowelled, wrapped with fabric completely.This is allowed to dry and a second coat is troweled over this and allowed to dry.
Clamping section of drain is then attached and final slope completed.

It seems to me a rather lengthy process unless you have a number of them to do like in a hospital/nursing home/Motel etc or at the very least other area's to be tiled.
Lets count the trips shall we

Paintable Trowelable Membrane
1st day-Preslope(needs to be dry before 1st coat)
2nd-1st coat(apply with trowel and apply cloth where required)
3rd-2nd coat((may not be dry under certain conditions)
4th or 5th day-Final slope
5th or 6th day-finally ready for tile!!( i would go broke quickly doing a few jobs like this.

Summary-4 days minimum to prep for tile with this method

Standard PVC or CPE Pan Liner
1st day- curb prep,preslope,(go to Lunch)install liner and concrete board.Tape CBU.
2nd day-Install final slope and finish curb.Install wall tile.
3rd day -Grout wall tile.Install floor tile and Curb with accelerated morter.Go to lunch. grout floor tile and install any remaining fixtures or handicap bars.

Summary-Even getting ambushed with having to shim walls add nailers etc this method will require 4 days maximum for most household showers to be fully completed

Kind of a no brainer from a business point of view.
Now if you like working lots of partial days and being a Part timer,well, there ya go

[Dan48]

Go to the liberry on this site and read the john Bridge article on building curbs. It is very very good and clear.

[e3]

and Todd--you didn't even count the number of day's needed before a water test can be done...then if you happen to have a leak that needs to be patched you need to wait x numbers of days before you can water test again...Had a contractor tell me it once took him over 30 days to get a gang shower to pass the 24 hr. test..5-7 day's to cure in-between patches...

[K_Tile]

Todd & Eric
Lat 9235 also has a 7 day wait period before flood testing. All my commercial jobs receive Nobleseal or Noble TS.