Drywall mud and tape question

#1

Hi all

This is probably a super dumb question but is bugging me so I'm going to chase it down.

It relates to drywall (gyprock for me!) joins.

If I read it correctly, the "How to drywall and caulk? Step Sequence...." sticky post by Knightfly on the former John Sayers forum indicates that:

1. around the floor, ceiling, corners we leave a gap and caulk after pushing in backer rod
2. where there are butt joints between sheets we leave a gap and caulk the gap after pushing in backer rod
3. where the sheets meet and both have recessed edges we push the sheets tight and tap and mud

The last one is the one that confuses me.

I get that where the drywall meets different material or meets another face that runs at a different angle ie ceiling, corner that this has the potential to be a weak point for movement so we use a flexible joining solution (an appropriate caulk) but its unclear to me why we rely on a very thin layer of potentially brittle mud to cover the very small gap between recessed sheets.

What am I missing - have I misunderstood the instructions, has practice changed since this post was penned or is there another good reason we rely on mud and tape on "recessed joins"??

Sorry if this has been answered elsewhere but I couldn't find a definitive answer in my searches.

Andrew

#2

when joining sheets - tape and mud - that's the reason drywall edges have the recess. so if doing two layer - one vertical and one horizontal, or simply staggering - mud and tape on the first layer - finish sufficient to allow the next layer to sit flush. the interior layer (let's assume its the finish surface) then finish to level 4-5 depending on whether or not you'll see it behind all the wall treatments and gear or not.
on joints - corners, wall-ceiling, and floor - stagger edges and use backer rod and caulk on each layer. on the floor side - they're generally just square to the floor and i layer of backer rod and caulk per drywall layer. then under baseboard, a layer of backer rod and caulk to finish.

#3

Thanks Glenn

I'm very happy to be using less caulk and more mud given the price difference

It just seems strange on the face of it that we use a potentially brittle product (mud) to cover the small gap between recessed sheets when we obsess (rightly!) about small gaps. (Stuart's chart showing TL loss from small gaps is burned on the back of my mind )

I was thinking about this last night while caulking and it did occur to me that the drywall wall probably moves more as a unit when you caulk all around it, you have the tape in there as well and then there's the staggering. (I'm doing two layers with green glue). I also wondered whether mud is denser than I thought it might be.

I trust your experience but my inquisitive nature finds it hard to let go of understanding the science of it all :geek:

Anyway...back to cutting, moving and hanging sheets.....and taking some pics for an overdue build post :oops:

Andrew

#4

the tape and mud - will seal it and as noted more normal for installation. unless your foundation or other structural bits are not stable, the wall should be fine with the mud. it where there may be flexing - e.g. corners then the caulk is best although you can then add a layer of tape or corner bead and mud to finish.

#5

Thanks Glenn
I'm fully committed to mud and tape for recessed joins - do you also do the same for butt joins?
I'm working to the assumption that because butt joint mud and tape leaves a raised area around the join its OK for layer 2 of a two layer wall but where you are doing 2 layers caulking might be better on butt joins on layer 1 to keep everything flat
Andrew

#6

Depends on how you align the sheets however butt joints happen and most times it's the magic of very wide feathering that makes it "flat". That said a bit of caulk there before just using mud can ensure it's stays sealed

#7

Thanks Glenn - its full steam ahead!

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