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Old 11-08-2017, 10:35 AM   #16
ss3964spd
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Louie,

I sistered a whole mess of 2X10's in my home years ago, but did not have access from the top. That job was approximately zero fun.

Keep an eye out for crowns and cupping when you select your lumber, and again when you install it. Have some bar clamps on hand to draw new boards against old if you end up sistering.

I'll go out on a limb and say that no matter how careful you are with selecting lumber and installing it, the resulting floor won't be flat if you're using sawn lumber. Be prepared with an electric hand plane and a looong, very straight edge.

Dan
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Old 11-08-2017, 11:06 AM   #17
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Thanks Dan.
Excellent idea, ill purchase an electric planner today.
Wayne recommended i use Kiln dried joists... Home depot has 110 on hand near me... so ill be picking through all of them to find the best.

Food for thought, i came across a company in British Columbia that has a manufacturing plant in New england area... they are called structurelock.com
prefabricated metal cross bracing...customizable sizes. i think i might give them a try.
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Old 11-08-2017, 12:02 PM   #18
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For what it's worth Louie -

If I had to do my sistering project again I would A) do as CX mentioned and not fuss with the new sistered joists landing on either the sill or the beam - hold them off by an inch and B) I'd seriously consider ripping 1/4-1/2 inch off of each to give you some wiggle room, unless you don't care if they are flush with the bottom of the existing joists over that section that has no ceiling below.

Chances are your existing joints are not perfectly dimensioned from end to end. The new ones won't be either - mine certainly weren't. For instance, I assumed a sawn 2X10 would be 9.5" from end to end. They were not. Some were a little less, some a bit more. I fought almost each one.

Food for thought.
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Old 11-08-2017, 01:04 PM   #19
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Im expecting it to be a lot of work. Since ill be sistering my 2x8 with 2x10s, the bottom of the sister is going to be 2 inches longer than the original.

Im wondering if i should utilize the 2x10s as the top reference point ( make it 1 to 2 mm higher than the originals. if i cant match it perfectly.) that might make a better when screwing in the subfloor. i wont know if the original will be better than the new as far as it being true. i guess ill judge that on an individual bases as i sister one at a time. ill do my best to make any crown parts towards the center of the span.
im really thinking of just ripping out the 2x8s all together and drop in brand new 2x10s .
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Old 11-08-2017, 03:19 PM   #20
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If you're seriously considering removing the existing joists and replacing, Loui, there is no way I'd use dimension lumber for the job. You will do much better at flattening your subfloor if you'll use engineered joists instead.

That said, you're still not likely to get a subfloor meeting the tile industry standards for those 12x24-inch tiles. But you'll get a lot closer.

My opinion; worth price charged.
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Old 01-12-2018, 11:28 AM   #21
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Tongue and groove under Ditra

Hi Guys,
long story short ( after much work from my last post )
I am about to purchase plywood subfloor. but i have a few questions that i might be easier answered than searching and reading ( short on time)

Ditra manual states:
"recommended tongue and groove "
but it also recommends spacing ends 1/8 apart.
Question- if using tongue and grove, does that mean i still space the long ends 1/8 apart? or fit the tongue and groove side tightly? ( thought that was the point of tongue and groove)


Manual also states a minimum thickness of subfloor and underlayment depending on joist spacing tile used etc. ( im using porcelain 12x24).
Question- My joist spacing is 12 OC. I planned on using 3/4 ( or thicker if they have it) for subfloor. do i need an underlayment over the subfloor? i didnt think i needed it.


Lastly-
it didnt state to use or not use exterior grade, plywood. unless "exposure 1" is exterior grade. ( probably could have googled that answer myself)

thanks guys. Ill send pics on my project development but ill put them on my other thread... man it has been a tough couple months of work to get to this point.
Louie
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Old 01-12-2018, 02:33 PM   #22
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I think this is the perfect time to use the deflectolator.
http://www.johnbridge.com/vbulletin/deflecto.pl

You can install ditra directly over the subfloor. Assuming it will support your finished product. Pretty sure that you will want t&g directly over the joist. The thicker the subfloor the better. Go with the 1-1/8 t&g if it will work for you.
Use modified thinset to adhere the ditra to the subfloor. I have been a fan of back buttering the ditra. But it's difficult to do with longer runs.



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Old 01-12-2018, 02:55 PM   #23
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Thank you Shady
Yes, when the project started, i used the deflecto guide.
I laid new joists.
double 2x10s 12oc on a 15 foot run.
I made the center joist a triple 2x10

I think the 1 1/8 t and g will be perfect. Do tightly but the t and g, or space that 1/8 inch apart?
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Old 01-12-2018, 04:10 PM   #24
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I would always do a t&g seam tight when directly on joist. Use a subfloor adhesive on those joist. I think it would be good to use the adhesive in the t&g also but not necessary. Use a high quality screw to attach the subfloor. Typical gold screws might be too brittle.

Someone will correct me. I think the 1/8th gap at the seams only applies for underlayments. Ie something that can or will move separately from the main structure.

Btw, Double 2x10s 12oc. I got to see a pic of that. Sounds like it will hold a Tank!

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Old 01-12-2018, 05:19 PM   #25
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well ill tell you.. this project is NOT easy... especially considering i never did anything like this before.. if you want to have a real laugh, my day job is auditing, and my night and weekend job is animal rescue... go figure.
anyways, so, the original joists were 2x8s 16oc. i originally posted questions in this thread here ( there are lots of original pics to see what it was like before)
http://www.johnbridge.com/vbulletin/...d.php?t=123973

once you guys informed me that what i had was not sufficient for tile, my plan was to sister the joists with 2x8s. then i said, heck, perhaps ill sister with 2x10s to make it even stronger. Well, it turned out after i started sistering, 50% of the original 2x8s were failing and had structural cracks. so i decided to take out all the original 2x8s, and i went all out and replaced with double 2x10s 12oc.. as i said, im not a carpenter... and for real, it was a a freakin pain not only leveling each joist, but matching up each joist when doubling them. i glued, bolted and nailed each set. that was a bitch. What made the real time consumer was that, sitting 2x10s on the main beam and sill, would have made the kitchen 2 inches higher than living room. and thats with out tile. So, i notched out each end 1.5 inches to fit over the main beam, and sill, to make it almost original height. I understand that notching them technically doesnt make them a 2x10 any more and is sort of frowned on today. but i suspect they will still be stronger than 2x8s. And being bolted together would be even stronger. notching out the edges 1/8th of an inch at a time to get the floor level was a nightmare. i used a digital level and each joist is at the most 0.05 to 0.10 off at the most. the wood was garbage and it was difficult finding good boards to work with at HD.

Now, to help with any twisting i used heavy structural corner brackets and bolted them to the ends of each joist, then to the main beam, and sill. ( pictures will show it.) i know its unconventional, but, surely it aint going to hurt anything. (but i guess that remains to be seen).
I went one step further, and made my center joist, where the island and kitchen table will be, a triple 2x10. man that was heavy to work with. im all alone and carrying a triple 2x10 through my living room, and walking along a joist was pretty hard. lol. but its in.

I took a picture of the other side of the kitchen, ( i knocked a wall down thats why it is a large area) and you will see THAT half still has the original 2x8s. I will be removing those and replacing those as well. Anyways, heres a few pictures... again hopefully its all overkill, and i didnt make any real mistakes. but, if so, ill correct them if needed..
in hind site, i worked hard to get each joist set perfect before glueing and bolting. using a clamp to bend each one to match the top. but now that i think of it, i only really needed just one joist top to touch the plywood. oh well.

thoughts?
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Old 01-12-2018, 07:02 PM   #26
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FOllow the instructions for the subflooring you select. Generally, on a straight, cut end, you want a small gap between sheets. That recommendation comes for new construction where the area could be exposed to the weather (say rainstorms) for a bit prior to it being closed in. The Plywood Association calls for actual underlayment to be installed without that gap (many do not agree, but hey, they make the stuff) AND to be installed only after the building is enclosed and within a day or so of covering it. The rationale is that the subflooring may be exposed to radical differences in moisture, but the underlayment is being installed near the completion of the building, and won't need that joint to account for those radical moisture changes. Some of the subflooring materials want you to get the T&G in tight, some don't. It depends on what you're using. Tight usually works because it tends to have at least some moisture in it from the mill, and will shrink very slightly once installed. But, it will also swell if the humidity gets high. Many of the grooves are engineered to account for that if installed per the instructions.

FWIW, notching the joists effectively makes them the strength of the thinnest section.
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Old 01-13-2018, 12:27 AM   #27
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Quote:
Originally Posted by Jim
FWIW, notching the joists effectively makes them the strength of the thinnest section.
It's not quite that bad when notching at the supports--the flexural stresses there are typically low, so the capacity of the notched area is typically adequate. The principal issue is that a sharp corner in the notch creates a stress concentration that could lead to crack formation. If the crack propagates into a more heavily loaded area that's not good. So the best practice is to make the notch like a long skinny trapezoid, so the depth of the section changes slowly along the length of the member.

Cheers, Wayne
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Old 01-13-2018, 09:14 AM   #28
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"So the best practice is to make the notch like a long skinny trapezoid, so the depth of the section changes slowly along the length of the member."

ah, i see, perhaps i will round the inside corners for a smooth transition.
Heres a thought, i seen types of "mending plates", would that be an added benefit if i were to place a mending plate vertically at the notched sections where it slips over the beam. More of a preventive measure vs a correction to a problem that doesnt exist.
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Old 01-13-2018, 03:01 PM   #29
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The vast majority of strength in a beam is the top and bottom of the thing. The middle is more to keep the top and bottom in place. Look at an I-beam or I-joist. A typical I-joist uses fairly thin plywood to hold the top and bottom in place - not particularly strong in itself, but it does hold the top and bottom in place quite well.
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Old 01-13-2018, 03:28 PM   #30
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Jim, that's correct, but you also have to consider the strength required at different places along the beam. The demand is greatest in the middle of the span, not as much at the ends. That's why the building code allows limited notching (on the compression side) in the end thirds of the span but no notching in the middle third. Notching on the tension side is only allowed at the supports.

Cheers, Wayne
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