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Unread 04-12-2021, 04:31 PM   #1
chrismar
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3 season room, adhesive on subfloor

Hi, I'm in the process of demoing worn laminate flooring, and stapled and glued Luan over existing 3/4” OSB subfloor 16” OC 2x10 spanning 12’3” (just slightly better than L/360 by the calculator.) The subfloor is sound, with only a couple squeaks, and I'm going to screw it down to the joists extensively.

This is a "3 season" room in a rural northern Minnesota climate (no major humidity issue but can be cold obviously.) No existing AC or heat in this room.

Planning on screwing 5/8" plywood over the OSB (per the usual fastening schedule 6"/8") and then modified thinset Ditra heat, heat cable and then Ardex Liquid Backer board SLC to 1/4" per there specifications to encapsulate the wires, to then lay down an engineered hardwood. The heat cable will be used to take the edge off the floor in winter when barefoot and provide a slight improvement to the cold to make it more like a 3 season room than the 1 season room it is now. (It's the main way to our back yard to let the dog out, etc.) The SLC is spec'd to go over Ditra Heat with no primer for this specific purpose, poured to go 1/4" over the top of the mat per Ardex. (I know the Ditra is not strictly necessary but makes running the wire easier and may help keep the SLC isolated more in the even of temperature swings.)

My main question at this point, is about the large amount of adhesive left over the subfloor. The subfloor itself is level and flat, but the adhesive makes is quite bumpy. I have a lot of staples to remove.

I assume it is essential to remove the adhesive between the OSB subfloor/plywood interface? Any other strategies? Any recommendations about the best way to do so (I assume a drum sander and deal with the dust nightmare. Not a lot of tool rentals around these parts so I'm probably buying something.)

Thanks for your advice!
Chris
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Unread 04-12-2021, 04:39 PM   #2
chrismar
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(Should I add that I’m planning on using close cell phone below the joists in the open crawlspace for insulation and vapor barrier.)
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Unread 04-12-2021, 08:32 PM   #3
cx
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Welcome, Chris.

If you don't add that geographic location to your User Profile the information will be lost before we leave this page.

I'm glad to see you recognize that you really need a second layer of subflooring for your tile installation. The tile installation substrate manufacturers base their subflooring requirements upon new material, in near-perfect condition, and near perfectly installed. You have none of those conditions. You could probably do quite well with a second layer of nominal 1/2" exterior glue plywood if final height is at all critical.

You need to get that existing subflooring flat enough for near 100 percent contact with the second layer. Depending upon the glue residue, a drum sander might work or it might just clog up prematurely. I'd recommend you use a mechanical scraper first to remove as much as you can. From your photos I'm not entirely sure you can salvage that one at all, but perhaps I'm not viewing it properly.

The staples are always a problem to remove and sometimes you can do as well just driving them flush to the wood surface.
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I’m planning on using close cell phone below the joists in the open crawlspace for insulation and vapor barrier
I know you young people try to do everything with your cell phones, but I've gotta question that one.

My opinion; worth price charged.
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Unread 04-12-2021, 10:35 PM   #4
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CX, I'll translate since I'm probably in between aged, considering you and the OP:

"Close Cell Phone" = "Closed Cell Foam" when typed on an Apple dumbphone; which is why I have a native Android phone, one with which I can actually control the spellcheck.
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Unread 04-13-2021, 06:12 AM   #5
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How many square feet is this project?

I think I'd have to at least consider removing the OSB and replacing it with new plywood. The lumber costs might be the only thing to hold me back, but when I see that much work in the future, I have to wonder if it's worth it, trying to remove all that glue over OSB.
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Unread 04-13-2021, 10:39 PM   #6
chrismar
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160 sq. ft. Thanks for all the advice! I pulled the staples from 1/3rd of the subfloor and was thinking about putting a grinder or my orbital sander to it after I get off the rest. The adhesive is actually very solid (despite that one photo) and doesn’t really chip without taking the OSB with it, so I would have to abrade it somehow.

I assume I would just cut the OSB around the inside of the bottom plate and re-screw new 3/4” plywood

(and yeah, closed cell foam)
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Unread 04-14-2021, 06:16 AM   #7
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I did something similar yesterday. Took up carpet to find linoleum, started to scrap or it off and thought what a can of worms I have opened, I should have not touched it and just put laminate over top. But that is the theme in this house, a floor on top of a floor, and they didn't let me down in this room( I am hoping that it is the whole main level). There was a layer of partical board between the sub floor and the linoleum. I think it was less than chipping away.

In your case you could fix any crowns or dips in the floor of you take up the osb

Black stuff is tar paper,
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Unread 04-14-2021, 07:46 AM   #8
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Ugh, that doesn't look like any fun, at all, Shawn.
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Unread 04-14-2021, 03:21 PM   #9
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Dan, It went pretty good once I got past the edges, I took up the dining room and kitchen this morning, it was like frosted mini wheats, apparently it had gotten wet once or twice. I will post those pictures to my thread about my flip house so I don't highjack this thread

A toe kick saw works really well for situation you are in, harbor freight sells one for less than a $100.00 and it will get you right next to the wall. Then you sister on to the 2x for something to screw your subfloor to at the bottom plate
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Unread 06-07-2021, 05:23 PM   #10
chrismar
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Ditra coverage question

Ok I got the glue up with a lot of chipping, sanding and abraiding, and filled in a couple small gouges with plastic wood. Got it completely flat. Then rescrewed the OSB and then screwed down exp.1 3/4" plywood as spec'd and screwed to the OSB properly per your advice. Thanks. Turned out great. No squeeks, flat.

I hired a pro to put down the Ditra Heat mat, and I just had a question about a coverage concern. In some areas, I can see the gray thinset through the Ditra, but this is only about 20% of the mat it seems. Should I be worried that there is a coverage issue? It was just laid today so I don't want to go pulling on it. I wasn't there for the job so I don't know if coverage was checked at any point.

The guys are total pros and have done beautiful work for me in the past, but I don't know how much Schluter they do (previous jobs were on mud and CBB.)

Thanks!
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Unread 06-08-2021, 08:52 AM   #11
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I don't think being able to "see" the mortar through the mat is necessarily indicative of proper bonding of Ditra Heat mat, Chris, certainly wasn't when I installed mine.
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