OSB sub-floor smooth or rough side up?


Old 06-29-12, 03:43 PM
Thread Starter
Join Date: Jun 2012
Location: USA
Posts: 4
Received 0 Votes on 0 Posts
OSB sub-floor smooth or rough side up?

Hey gang,

Renovating a bathroom. I have cut and fitted an 3/4" OSB subfloor, with the shiny side up. I plan to put down an electric radiant floor mat, then Ditra, then the tile. My question is will the shiny side hold the thinset?

If not I'll have to buy two new pieces and use the existing pieces as a template. The bathroom is trapezoidal in shape, and the pieces are not symetrical in the slightest.

Old 06-30-12, 07:14 PM
Temporarily Suspended
Join Date: Jul 2008
Location: NY
Posts: 10,982
Received 0 Votes on 0 Posts
Some of them are stamped, up or out.
Old 07-25-12, 07:40 AM
Join Date: Dec 2003
Location: USA
Posts: 994
Received 0 Votes on 0 Posts
OSB is not appropriate for a subfloor. Especially in a bathroom.
Old 07-25-12, 07:58 AM
ray2047's Avatar
Join Date: Mar 2006
Location: USA
Posts: 33,582
Received 13 Votes on 11 Posts
Wait till the water gets too it and it is so mushy you have to remove it with a spoon. I know they use it on roofs but the one leaky roof I encountered with OSB my hand went right through where the water had leaked. Years ago I have seen the effect of water on a similar product, particle board, in a bath room. Totally disintegrated.
Old 07-25-12, 09:41 AM
Join Date: Dec 2005
Location: USA
Posts: 3,185
Received 1 Vote on 1 Post
Just like plywood there are differing grades of OSB. Use the correct OSB and you won't have a problem. Schluter says on hteir website that OSB is a suitable subfloor for Ditra.

I've never used OSB under Ditra but I would not hesitate. I have no idea though about what side up. Try an e-mail to the thinset manufacturer or to Schluter customer service.
Old 07-25-12, 03:08 PM
chandler's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Dec 2005
Location: USA
Posts: 39,965
Received 6 Votes on 6 Posts
Rough side up, mainly for footing. It is imprinted on the sheet anyway. Always use a proper subflooring material such as Advantech. Although it is an OSB material it has an impregnation that wards off water damage. Nonetheless, your Ditra installation should take care of it all, and as Wayne says, they approve OSB.
Old 07-30-12, 09:00 PM
Join Date: Mar 2009
Location: WA
Posts: 1,165
Received 0 Votes on 0 Posts
Joist spacing plays a big role....... initial application; https://docs.google.com/viewer?a=v&q...Nl0Ggpec6X2jug

Tile... may want to stiffen the floor a bit; from the "search" here; http://www.doityourself.com/forum/fl...-subfloor.html


Thread Tools
Search this Thread
Ask a Question
Question Title:
Your question will be posted in: