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Old 07-31-2015, 10:53 AM   #1
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do you have to tape joints?


Is the tape only for strength ? Can you just fill it with mud and sand it down?

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Old 07-31-2015, 12:24 PM   #2
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I will defer to a drywall expert but if you don't tape you get cracks I believe...
The question is not whether to tape or not the question is whether to paper tape or fiberglass tape.
Now bring on the experts in drywall.

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Old 07-31-2015, 01:05 PM   #3
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Quote:
Originally Posted by begal View Post
Is the tape only for strength ? Can you just fill it with mud and sand it down?
You can do that, but all the seams will crack. That's why you tape and put 3 coats of compound on the seams.
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Old 07-31-2015, 01:17 PM   #4
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ok makes sense. But what if you put a bead of PL construction glue in there first, then filled in with drywall compound?
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Old 07-31-2015, 01:45 PM   #5
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Quote:
Originally Posted by begal View Post
ok makes sense. But what if you put a bead of PL construction glue in there first, then filled in with drywall compound?
Tape is cheap and only adds a couple minutes to the job. You only tape once.
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Old 07-31-2015, 02:34 PM   #6
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Quote:
Originally Posted by begal View Post
ok makes sense. But what if you put a bead of PL construction glue in there first, then filled in with drywall compound?
Try it and let us know. I'm betting it will crack. It will also take longer and cost more.

If you are applying the drywall compound anyway it doesn't add any time to apply tape at the same time.
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Old 07-31-2015, 10:28 PM   #7
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Begal:

You need to understand drywall:

Drywall is surprisingly strong and rigid considering what it's made of. The reason for that is entirely due to the fact that paper is very strong in tension. Fold up a sheet of paper until it's only an inch or so wide and try pulling it apart until it breaks. You'll find that very hard to do.

So, the reason drywall is surprisingly strong and rigid considering what it's made of, is that for drywall to bend, the paper on either side of the drywall has to stretch, and paper is very strong in tension. The strength of the paper prevents it from stretching, and that's what makes drywall so resistant to bending (considering what it's made of).

The weak link in the chain comes at the drywall joints. At the joints, you have to add paper to carry the tension across the joint if the drywall wants to bend. That's the whole reason for taping the drywall joints; to carry any tension across the joint so that the joint compound doesn't have to stretch, and therefore break. Drywall joint compound is actually fairly weak in tension, so you need that paper (or fiberglass) in it to carry any tension.

Exactly the same thing is done to make "reinforced" concrete stronger than regular concrete. In a "reinforced" concrete slab, there will be steel rebars embedded in the concrete an inch or two from each side. So, for the reinforced concrete slab to bend, then the steel rebars on one side or the other have to stretch. Steel is very strong in tension, and it's the resistance of those steel rebars to stretching that prevents the reinforced concrete slab from bending and therefore breaking. Were it not for the steel rebars in a reinforced concrete slab, the concrete would bend and break relatively easily. Where you see steel rebar placed only in the MIDDLE of a concrete slab, such as a driveway, then the purpose of the rebar is not to prevent the slab from bending, but only to hole it together if and when it cracks.

Now, imagine you have a reinforced concrete slab, but you were to somehow cut through the steel rebars on both sides of the slab. Now, if the concrete slab wants to bend, that's the spot where it will break. That's essentially what you have at a drywall joint; a break in the material that's preventing the drywall from bending. Taping a drywall joint is similar to welding steel rebars across the cut to reconnect the rebar on both sides of the cut. That re-establishes the strength of the reinforced concrete and make it work like it's supposed to.

Getting back to drywall:

What drywall companies recommend is that if you're going to use a fiberglass mesh tape on your joints, then your first coat of joint compound should be a "hot" mud, which means a joint compound with a chemical set to it that kicks in after a certain length of time. Synko makes chemical set drywall joint compounds that kick in after 30, 60, and 90 minutes, and I'm sure other chemical set times are available from other producers. It's the chemicals that cause that chemical set that result in the joint compound setting up stronger than regular joint compounds. Since fiberglass mesh joint tape is a little weaker in tension that regular paper drywall tape, you need the extra strength of a chemical set joint compound on the first coat to compensate for the weaker tape.

If you're using paper tape, (and if you're new to finishing drywall joints, you're probably going to find that to be an extremely frustrating experience) then you should use a "regular" or "Taping" joint compound for your first coat.

In each case, after the first coat you can use a "Finish" or "Topping" joint compound or an "All Purpose" joint compound if you wish.

Joint compounds actually come in three flavours;
1. "Regular" or "Taping"
2. "Finish" or "Topping", and
3. "All Purpose"

The difference between these is really in how much glue there is in them. The more glue, the better the joint compound sticks to the drywall, but the harder it dries and the harder it is to sand smooth. "Regular" joint compound has the most glue in it, so you would use that for your first coat so that it sticks to the drywall really well, and you probably won't be sanding much of that first coat. "Finish" joint compound has the least glue in it, so that it sands down fast and easy. "All Purpose" is half way in between Regular and Finish, and it's popular with drywall contractors who are doing drywall repairs so that they only have to carry around and use one kind of joint compound instead of two.

If you want to "soup up" your drywall joints, don't start caulking with a construction adhesive because your strength is entirely in the wrong place. You want the strength to be in the same plane as the face paper of the surrounding drywall. However, regardless of whether you use paper or fiberglass tape, that strength is a small fraction of an inch below being flush with the surrounding drywall face paper. Still, you can "soup up" your drywall joints if you're using fiberglass mesh by painting over the mesh with white wood glue diluted with water to make it into a paintable consistency. As the glue dries, it will bond the fiberglass mesh to the drywall paper, making for a stronger bond between the two, and that makes for a stronger joint. If you use a 3 inch paint roller to do the painting, that work goes very quickly. Try to paint the mesh on each side of the joint so as to prevent plugging up the holes in the mesh near the middle. You want your joint compound to be able to go through that mesh and fill the gap between the sheets of drywall.

Anyhow, people that are proficient at using paper tape to finish drywall joints will crap on fiberglass mesh tape. But, from a DIY'ers perspective, fiberglass mesh tape makes finishing drywall joints a breeze, and if you use a "hot mud" for your first application of joint compound, you should achieve the same joint strength as a properly finished paper joint.
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Old 08-01-2015, 11:28 AM   #8
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Also look into FibaFuse tape Lowe's is starting to carry it. Not to be confused with FibaTape it is a much better tape and a lot easier to use on the joints. Just my opinion but anything is better than the mesh.
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Old 08-01-2015, 12:27 PM   #9
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Quote:
Originally Posted by begal View Post
ok makes sense. But what if you put a bead of PL construction glue in there first, then filled in with drywall compound?

I once had a contractor repair a ceiling crack (that they had caused) and he used construction adhesive instead of caulk. He was quite proud of it.

Ask me if that cracked....

(Caulk, used properly--not as a catchall solution for bad construction--is flexible, and designed to be part of a movement joint.)

Making the joint rigid won't stop the movement, it just translates it slightly, very slightly. (The construction adhesive just crumbled out of the joint as the gypsum around it broke down. I ended up with the same, only much wider crack.)
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Old 08-01-2015, 02:54 PM   #10
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Quote:
Originally Posted by begal View Post
Is the tape only for strength ? Can you just fill it with mud and sand it down?
No, mostly for appearance. Per manufacturer of drywall, you are required to fill 1/8" and smaller gaps at joints with air-drying or chem. set. Larger gaps require chemical set only. It has to air-tight to meet minimum code requirements (and stay that way)- check with local AHJ. Shear-wall doesn't require taping joints as the racking resistance of a wall is by using 4' wide panels. Paper tape is better at hiding seismic hairline cracks than mesh tape which shows surface finish flaking and buckling under testing. Ask Inspector for acceptable alternatives to taping... Sound prevention may require it but fire prevention doesn't- unless Type X board- or similar for more than basic 15 minute rating.

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Old 08-01-2015, 08:13 PM   #11
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Begal asked: Is the tape only for strength? Can you just fill the joint with compound and sand it down?

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Originally Posted by Gary in WA View Post
No, mostly for appearance.
-Gary
Huh?

I'm presuming that you mean that untaped joints would detract from the appearance of the wall if and when they crack.

I couldn't see how an untaped joint would look any different (initially at least) than a taped joint.
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Old 08-01-2015, 09:44 PM   #12
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Use some water to dilute the bedding coat of tape to the consistency close to that of sour cream. Makes things WAY easier. Ron
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Old 08-02-2015, 04:57 PM   #13
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If you don't use tape it will crack. The reason the edges are tapered is so when the are tapped and mudded the taper fills in and you have a flat surface.
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Old 08-03-2015, 03:27 PM   #14
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Code doesn't require the tape if all edges have wood backing behind them- and others I said. You can just fill the tapered edges to meet code for the required 1/2" thickness (15 min. fire). But, why not tape if you have to fill it anyway... you could use square edge board and not fill edges or fasteners with anything, and still meet code- if one likes that look...lol. IMO, hot mud won't crack without tape as I have used it many times on plaster wall repairs, 40 years ago- no cracks yet.

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Old 08-03-2015, 03:30 PM   #15
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Quote:
Originally Posted by ront02769 View Post
Use some water to dilute the bedding coat of tape to the consistency close to that of sour cream. Makes things WAY easier. Ron

I was researching just the other day and read this, (maybe too easy; lol);http://www.durabilityanddesign.com/b...iew&blogID=108

Gary

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