Ceramic Tile Advice Forums - John Bridge Ceramic Tile

Welcome to John Bridge / Tile Your World, the friendliest DIY Forum on the Internet


Advertiser Directory
JohnBridge.com Home
Buy John Bridge's Books

Go Back   Ceramic Tile Advice Forums - John Bridge Ceramic Tile > Tile & Stone Forums > Tile Forum/Advice Board

Sponsors


Reply
 
Thread Tools Search this Thread
Old 01-28-2010, 04:57 PM   #1
POBO6
Registered User
 
Join Date: Jan 2010
Posts: 8
Underlayments

Stumbled upon this forum - from what I've seen - looks excellent!

Been trying to pin down the proper subfloor in an existing home for 13" x 13" porcelain tile. I have 2 x 8 floor joists, spaced at 16" o.c., and the longest span is 13'. Currently there is a 1/2" thick plywood subfloor, overlaid with 1/2" particle board. I know the particle board has got to go (with some sweat labor, as it is nailed through the 1/2" subfloor into the joists). After removing the particle board, can i get by with adding a layer of 1/2" plywood, or do I really need to go with 3/4" ply to make it 1 1/4" overall? If I need to go 3/4 on top of 1/2, will OSB do the trick (trying to cut costs and yet be sensible) My plan is to use ditra & Schluter web says OSB is acceptable if it's 3/4".

Also, I originally was going to use my nail gun and shoot the new layer down into the joists but if i read right, this would be a mistake? If I am forced to screw down only to the subfloor, what spacing should I use for screwing - hopefully not a zillion screws like hardiboard. Also, do I use PL glue between the two layers?

I've read so much here & there that my head is spinning, and could use someone to set me straight . Many thanks!
__________________
Paul

Last edited by POBO6; 01-28-2010 at 05:15 PM.
POBO6 is offline   Reply With Quote
Sponsored Links
Old 01-28-2010, 05:42 PM   #2
HotinOKC
Registered User
 
HotinOKC's Avatar
 
Join Date: Dec 2007
Location: Moore, Oklahoma
Posts: 1,202
Without even running your #'s through the calculator, your joists are not strong enough for ceramic/porcelain tile. Do you have access to these joists to sister them?
__________________
Mark


Support our Troops!
http://www.dav.org
HotinOKC is offline   Reply With Quote
Old 01-28-2010, 05:45 PM   #3
Kman
Moderator
 
Kman's Avatar
 
Join Date: Nov 2006
Location: NW Arkansas, Ozark Mountains
Posts: 8,885
Your initial problem here is that your joists are over-spanned. You can fix this by either sistering all the joists that run under the tile installation, or building a support somewhere under there to cut the span to 11' or less. After that problem is fixed, you can move on to the subfloor.

Since that 1/2" ply is so thin, if you can't take it out, I would just ignore that it's there and go over it with 3/4". OSB would work, but plywood would be better since you would effectively have only one layer there. Trying to screw into the 1/2" would probably result in some screw jacking and stripping. If at all possible, I would take out the 1/2" and save yourself the trouble.

Be best to use some 2 1/2 or 3" screws directly into the joists. They'll hold much better than nails.
__________________
Kevin

The top ten reasons to procrastinate:

1.
Kman is offline   Reply With Quote
Old 01-28-2010, 06:38 PM   #4
jadnashua
Veteran DIYer- Schluterville Graduate

STAR Senior Contributor

 
Join Date: Jul 2004
Location: Nashua, NH
Posts: 11,727
You will end up with problems if you try to use PL construction adhesive between the two sheets. What you want is 100% contact between them so there is no possibility of tenting or flex...you won't get that with some beads of adhesive. If you really wanted glue there, you'd need full-spread wood glue like Titebond II or III.

With all of the nails or staples between the particle board you are tearing out, the original layer of ply won't be all that structurally sound.

If it were in good shape, the second layer would normally be offset and only anchored to the first sheet, not into the joists. As noted, it might end up being cleaner to cut it out as well. You may need to install some blocking to support the edges, since the original layer probably goes under the walls, and the joists probably won't be able to be hit with the new layer.
__________________
Jim DeBruycker
Not a pro, multiple Schluter Workshops (Schluterville and 2013 and 2014 at Schluter Headquarters), Mapei Training 2014, Laticrete Workshop 2014, Custom Building Products Workshop 2015, and Longtime Forum Participant.
jadnashua is online now   Reply With Quote
Old 01-28-2010, 08:43 PM   #5
POBO6
Registered User
 
Join Date: Jan 2010
Posts: 8
ok - thanks for the replies. I went down the basement to do a double check of what I had for bearing walls. In the kitchen and hallway areas, I appear to be fine as far as span is concerned... The area below the entryway is a finished room (sheet rock ceiling), but I know has blocking (bridging) between the joists - surely that helps stiffen up the joists? I will go with 3/4", screwed into joists as per kman's suggestion. (leaning towards osb for everything but the entryway area) As far as the original 1/2" ply's condition, I will determine, after I rip up the particle board.

If you can open up pdf files, attached is a floor plan, and you will see what I am working with. Thanks again, and I am always open to suggestions!
Attached Images
File Type: pdf tile floor Model (1).pdf (64.6 KB, 220 views)
__________________
Paul
POBO6 is offline   Reply With Quote
Old 01-28-2010, 09:18 PM   #6
Brian in San Diego
AC Specialist -- Schluterville Graduate
 
Brian in San Diego's Avatar
 
Join Date: Oct 2005
Location: San Diego, CA (Northwest part of the city)
Posts: 10,767
Quote:
Originally Posted by Paul
The area below the entryway is a finished room (sheet rock ceiling), but I know has blocking (bridging) between the joists - surely that helps stiffen up the joists?
Actually bridging, blocking and/or cross-bracing between joists does absolutely nothing to stiffen the joists. It only helps to prevent the joist from twisting. The only way to get a subfloor up to the correct deflection is by shortening the span, sistering the joists or adding additional joists to reduce the distance between joists.

Brian
__________________
Brian
If that doesn't work, I'll always think it should have.
Brian in San Diego is offline   Reply With Quote
Old 01-29-2010, 09:34 PM   #7
POBO6
Registered User
 
Join Date: Jan 2010
Posts: 8
So, if I "sister" up the joists in the entry way, I will have to do it from the main floor level. With the existing 2 x 8 joists, is it mandatory that I use 2 x 8's alongside, or will nailing a 2 x 6 alongside suffice to reduce deflection?
__________________
Paul
POBO6 is offline   Reply With Quote
Old 01-30-2010, 08:31 AM   #8
Brian in San Diego
AC Specialist -- Schluterville Graduate
 
Brian in San Diego's Avatar
 
Join Date: Oct 2005
Location: San Diego, CA (Northwest part of the city)
Posts: 10,767
Paul,

If you sister the joists in that area then the deflection goes to L/442 from L/221 if I am reading your drawing correctly (2x8s, 16" OC with 13.5" unsupported span). The sisters have to cover the middle 2/3 of the span so the sisters need to be at least 9' long and be centered in the middle of the span. It would be better to use 2x8s but you could use 2x6s but this would increase the deflection. You really don't have a whole lot of wiggle room in that sistering is only going to get you slightly over (10%) the required deflection.

I would recommend you do some searching on here about sistering joists. It isn't just nailing them together. Most people talk about construction adhesive, drilling holes and lag bolting them together in a staggered pattern. I have never done it before but just toe nailing the sister in is not going to do what you need to have done.

Brian
__________________
Brian
If that doesn't work, I'll always think it should have.
Brian in San Diego is offline   Reply With Quote
Old 01-30-2010, 10:29 AM   #9
POBO6
Registered User
 
Join Date: Jan 2010
Posts: 8
Brian, thank you for the reply. Looks like I will plan to gut the subfloor in the entryway & sister up the joists w/ 9' 2 x 8's per your suggestion, but if I have no obstacles, I just may instead add full joists in between, for 8" o.c. joist spacing.

One quick question - in the hallway, I plan on putting tile, which is a max of 3'-4" out from the bearing wall underneath. How does that figure into the deflection range? The bathroom will not be done at this time, but everything else shown will be.
__________________
Paul
POBO6 is offline   Reply With Quote
Old 01-30-2010, 10:47 AM   #10
Brian in San Diego
AC Specialist -- Schluterville Graduate
 
Brian in San Diego's Avatar
 
Join Date: Oct 2005
Location: San Diego, CA (Northwest part of the city)
Posts: 10,767
Paul,

Sistering would be the better option. The Deflecto doesn't allow the entry of 8" OC but the deflection for 10" OC yields L/353 which for all intents and purposes would work since the tool is a little conservative. If you want to get the best beefiness for the buck sistering would be the way to go.

If you are talking about the little alcove in the upper left of your drawing (nice drawing by the way) I would go for it. Maybe not the correct response but I wouldn't go to all the trouble of trying to sister for that little area.

Brian
__________________
Brian
If that doesn't work, I'll always think it should have.
Brian in San Diego is offline   Reply With Quote
Reply

Stonetooling.com   Tile-Assn.com   National Gypsum Permabase


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
underlayments between tiles and concrete slab Lukasz Tile Forum/Advice Board 8 10-21-2006 08:33 AM
help with Underlayments for Marble/ granite mahesh Tile Forum/Advice Board 13 09-08-2006 05:43 PM
underlayments? im confused.. b_ross Tile Forum/Advice Board 1 11-05-2005 08:51 AM
underlayments for marble scott anthony Professionals' Hangout 4 07-22-2005 08:03 PM
Underlayments - Ditra, CBU Bud Cline Reference Liberry :-) 1 03-24-2002 01:16 PM


All times are GMT -6. The time now is 04:31 PM.


Sponsors

Powered by vBulletin® Version 3.7.4
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
Copyright 2014 John Bridge & Associates, LLC