# Drywall/Mud - largest workable gaps and unevenness?



## alexz (Jul 4, 2006)

Hello all.

I'm working on my first drywall job. I have framed a new doorway through an existing wall and then built a closet-like area that will be the new home for my fridge (desperately need the space in the kitchen and sacrificed some space in the adjoining guest bedroom). When I was cutting through the existing drywall, I cut it flush with the studs so I could later nail up some pieces of 2 x 4 along them to be used as the drywall anchors (suggested by a friend of mine). This is an older house and the original drywall is mostly 3/4". Unfortunately, some of the original drywall has, gulp, variable thickness. Yes, in some places, a single piece of the sheet rock is 3/8" thick and in other areas 3/4" thick. So, obviously, installing the new drywall to be flush with the existing sheetrock will be a bit of a challenge. Luckily, this variability is only a few places. :thumbsup:

So I have two issues:

1) The existing drywall is 3/4" and the thickest drywall I could find is 5/8". I also bought a bag of the spacers used in tiling jobs and have attached them to the 'nailing' studs to serve as shims. This appears to be working well - they seem to be the perfect thickness. Sound like a good idea to you? I couldn't find any 'drywall shims' at home depot or lowes and don't have time to wait for an order to come in.

2) The variable thickness. How much of a 'jump' of thickness from the original sheetrock to the newly adjoining sheetrock can be aesthetically concealed with tape and mud? I know that the whole purpose of mudding is to conceal gaps and uneven transitions, but how much can I get away with? Also, a friend who's done some drywall work has suggested that I use a belt sander to sand down the thicker pieces. Will this make the drywall difficult to prime and paint?:confused1:

Thanks for taking the time to read this and respond.

Alex


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## redline (Mar 5, 2006)

alexz said:


> Hello all.
> 
> This is an older house and the original drywall is mostly 3/4". Unfortunately, some of the original drywall has, gulp, variable thickness. Yes, in some places, a single piece of the sheet rock is 3/8" thick and in other areas 3/4" thick. So, obviously, installing the new drywall to be flush with the existing sheetrock will be a bit of a challenge. Luckily, this variability is only a few places. :thumbsup:
> 
> ...


Do you mean that the older surface is plaster and lath?


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## alexz (Jul 4, 2006)

*No, the older surface is some sort of sheet-rock or drywall*

I was surprised to find out that this house that was built in 1950 has no plaster walls. A good find :thumbsup:, as I hear that dealing with plaster/lath is a pain in the butt!

But yes, at least one panel of the original drywall/sheetrock is in fact variable in thickness. 

Alex


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## joasis (May 28, 2006)

The very nature of the manufacturing process of drywall makes it impossible to have a true "variable" thickness. I also have never personally seen 3/4 inch rock, nor did a quick check reveal any past manufacturing. If you see that much variance, undoubtedly, you are seeing a lot of mudded 3/8 or 1/2 inch board. 

I have seen some plastered walls that were not plaster, per say, but similar to mud, and placed on cardboard backing...maybe you have that rarity?


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## AtlanticWBConst. (May 12, 2006)

strange house...very strange...:huh:


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## alexz (Jul 4, 2006)

Thanks for replying guys. The wall material is now even more of a mystery to me. 

But the question still remains. How much of a gap and unevenness can be 'feathered' with mud and well concealed?


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## AtlanticWBConst. (May 12, 2006)

A good taper can cover anything in regards to wall imperfections.

It will just take more coats to do it, rather than the standard 3 coats used in new construction.


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## hvacdude (Aug 19, 2006)

hi alexz.

i've seen that thick brown paper backing sheetrock before. as for the variable thickness--- could be a defect or it may have been stored in such a way that created that problem. who knows?

if you get your mud up to 1/4 inch, its getting to thick.
read the directions ALWAYS, on the brand of mud you buy. i like READYCOAT it dos'nt seen to crack as easly and you can get a job done in a day-- with small jobs. i really don't like that brand at home depot. but thats me.

wish ya luck


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## joasis (May 28, 2006)

I thought of something, and maybe a few other drywall guys may offer opinions about it, but I have seen drywall mud thinned and the fiberglass cut in....may be the way acttually get it where you need it, since standard mud over 1/4 inch is very prone to cracking.


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## AtlanticWBConst. (May 12, 2006)

Joasis,

Actually the mud cracks when:
It's put on so thick that there is more moisture content in it. As it dries, it cracks from the moisture coming out of it (evaporating). This happens more so, when you have thick coats and the compound is dried at an accelerated rate. (i.e. - heat source) 
We just fill in the cracks on the next coat and make sure that another coat goes on over that. I can't see where a layer of mesh tape is going to help it not to crack since it is about moisture, not about strength.

That is just my 'personal opinion' based on what I have worked with. I have never tried, what you are suggesting...


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## joasis (May 28, 2006)

I was thinking about loose fibers cut into the mud, and I agree with why and how the heavier coats of mud crack. IMO heavier applications of mud will not be sound a few years later, from many of the "patches" and :repairs" I have seen. I personally would not do heavy build coats of mud,...to me it would be easier to correct the original problem, but I am sure there are times when it may be the only way.


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## d.janvrin (Oct 20, 2006)

It Might be plaster over 3/8 sheetrock ive seen it used in basements and hallways. Why I dont Know9 Maybe $$$ Maybe lighter) But Have seen it, Have Matched It,.
Before I d Put Tile shims between stud and rock, Id buy lattice stock (Or Rip flat stock)and shim Complete stud *FLAT and EVEN* . If you use Tile shims :no: (Many Uneven pcs) The screw WILL eventualy POP :yes: or show . Sheetrock Has to be Tight And Solid to its Frame !!!!


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## troubleseeker (Sep 25, 2006)

Never seen or even heard of 3/4 inch drywall. Maybe 5/8 with a skim coat of mud? I would rip thin wood lath from 2x4 (rip on the flat so they are 1 1/2 wide) and stick them over the studs with adhesive rather than the dot effect you're going to get from tile spacers. Except in cases of small areas that can be completely bridged with a wide tapeing knife, you are not going to be able to thicken the shallow pieces so they can't be seen when light shines across them. What you can build up is really determined by how flat your expectations are for 
the finished product. Whatever you do, use thin coats or it will crack.

Any one who tells you to belt sand drywall is not a "friend". Once you get through the paper, you will never get a decent paint job on it.


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