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Posted by MiamiCuse on February 6, 2008, 7:59 pm
>> I am remodeling this 35 year old house and throughout the house the walls
>> are made of a double layer of gypsum board as the layer underneath and a
>> layer of plaster / cement material on top. Total thickness is about
>> 3/4".
>>
>> http://i173.photobucket.com/albums/w67/143house/P1010626.jpg
>>
>> This presents a problem in matching new wall with existing. If I use the
>> standard 3/8" or 1/2" wall board it will not match. I could use them in
>> areas where I torn down the entire wall from end to end, but in other
>> areas
>> I have to match the existing thickness. I guess I have three options:
>>
>> (1) Use one layer of 3/4" sheetrock and try to match it, or
>> (2) Use two layers of 3/8" sheetrock, or
>> (3) Furr out wall a bit to use one layer 3/8" wall board
>>
>> Not sure which one is the most convenient and economical.
>>
>> Also, electricians, plumbers, window installers have worked on the house
>> and
>> there are numerous places I need to make a patch but the patching is
>> impossible since the cuts are done in an irregular fashion. See pic:
>>
>> http://i173.photobucket.com/albums/w67/143house/P1010625.jpg
>>
>> I try to cut them on a straight line and it's hopeless. Can't use a
>> recipricating saw because of the concrete layer underneath. Tried a
>> angle
>> grinder and there were so much dust I could not stand it. Any advise?
>
> Yep. Don't let your tradesmen cut nasty holes for you to patch. You
> should cut the openings or have the tradesmen cut straight lines.
I tried to tell them to cut straight lines but they never listen to me.
They told me this is not regular sheetrock so they had to pound it out.
>
> A reciprocating saw will work just fine, you'll just go through a lot
> of blades. Most reciprocating saws accept the blade in a reversed
> position (teeth are facing up instead of down when the saw is held
> horizontally). Reversing the blade allows you to have a much lower
> angle of attack which is necessary since you don't have blade
> clearance behind the drywall. Tape the vacuum hose to the end of the
> saw so it will pick up most of the finer dust as you cut.
I am getting a lot of kicks when the saw blade hits the concrete wall right
behind it. It's not working this way I have to think about a different
approach.
>
> As an alternative, it's easier to cut complicated outlines in the new
> drywall than trying to cut into the existing wall. You'll have to
> clean up the edges of the cutouts, but you can use scribe cutting
> techniques to cut any sort of outline to follow the contours of the
> cutout. You mark the scribe line on the new drywall patch with a
> compass and cut to the line with a drywall keyhole saw. It goes
> fairly quickly and will cut way down on the amount of dust you'd be
> blowing around cutting the drywall with a power tool.
>
> I attach scrap plywood blocking behind the drywall so it's fastened on
> both sides of the cutout every foot or so (the blocking ends up
> looking like a ladder running up inside a long cutout). Then you can
> attach your drywall, or cardboard/plywood shims, to the blocking. I
> prefer to have the cutout repair drywall sit just a bit lower than the
> original wall surface as it makes taping easier. You'll end up
> bridging over the entire cutout and it's better to have one smooth,
> gradual bump, than to have bumps on either side of the cutout from the
> tape.
>
> I would not use a single layer of 3/8" drywall. 5/8" should work
> nicely. If the existing wall surface is flat and true, you could shim
> that out a bit with some cardboard to you won't need as much joint
> compound. Standard fiberglass mesh tape would be a poor choice for
> your repair. It's noticeably thicker than paper joint tape and the
> loose ends end up requiring more compound to cover them (and you can't
> sand them), so the bump ends up being bigger. Either use paper tape,
> or something like Tuffglass tape (TKO Coatings) - that's a flat woven
> tape that is much thinner than standard fiberglass tape.
>
> R
>
RicodJour thanks I think I may try to fur out the wall to flush with
existing surface instead of using thicker or double sheets. This will make
future repair easier, I think...it's good to know about Tuffglass tape I
will need it where I am matching new to old walls.
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