# Fixing Diagonal Drywall Cracks?



## Nealtw (Jun 22, 2017)

Have you looked at ways to better support the floor and walls from below. 

I would question size and span of the floor joists.


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## Yodaman (Mar 9, 2015)

The cracks will need to be taped and coated with joint compound, then refinished.
But if these cracks still open and close seasonally, then the repair will be short lived.


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## SeniorSitizen (Sep 10, 2012)

Those diagonal cracks are caused by racking walls. Notice each is from a corner. That could have easily been prevented during construction but will be hell to correct now. Hopefully someone on this forum will have a solution.


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## Steve Sr (Mar 7, 2013)

Nealtw said:


> Have you looked at ways to better support the floor and walls from below.



I don't really think that this would be practical. I don't know if the house was built to code or not. I am assuming that it was but the code doesn't account for expansion and contraction of materials. 



For two of the cracks pictured I used a floor jack and installed supports at the edge of door frames. These had initial success but as the floor joists would expand (and lower) with humidity they would never quite return to their original position.





Nealtw said:


> I would question size and span of the floor joists.



I would too but I am not a structural engineer. I think that they should have put two longitudinal floor beams instead of just one. 



So does the code normally allow interior walls to be placed on top of the sub floor or should they be placed on top of floor joists? There has been no cracking issues on walls that run perpendicular to the floor joists


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## Steve Sr (Mar 7, 2013)

Yodaman said:


> The cracks will need to be taped and coated with joint compound, then refinished.
> But if these cracks still open and close seasonally, then the repair will be short lived.



I think that seasonal movement has been reduced significantly since the crawl was conditioned but don't believe it is zero. Besides you still have the unconditioned roof trusses which may move at the top of the walls where these cracks are.


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## Steve Sr (Mar 7, 2013)

SeniorSitizen said:


> Those diagonal cracks are caused by racking walls. Notice each is from a corner. That could have easily been prevented during construction but will be hell to correct now. Hopefully someone on this forum will have a solution.



What is a "racking wall"? I think that most of this was caused by the floor joists bending with changes in crawl humidity. Now that the crawl is sealed and conditioned the humidity runs in the 40-50% range year round.


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## SeniorSitizen (Sep 10, 2012)

Steve Sr said:


> What is a "racking wall"? I think that most of this was caused by the floor joists bending with changes in crawl humidity. Now that the crawl is sealed and conditioned the humidity runs in the 40-50% range year round.


Google explains racking much better than I could.:smile:


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## Nealtw (Jun 22, 2017)

Steve Sr said:


> I don't really think that this would be practical. I don't know if the house was built to code or not. I am assuming that it was but the code doesn't account for expansion and contraction of materials.
> 
> 
> 
> ...


 So the answer is no and you have decided that there is nothing to talk about but expansion and contraction. 

If you want to stop stuff from moving you do things that will stop them from moving.


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## Yodaman (Mar 9, 2015)

If you are running 40 - 50 RH all year, then you are in the sweet spot for whole house RH, and doing much better than most.

It is not uncommon to see a room partition sitting on a subfloor. But this assumes no load bearing. Look underneath and see if the subfloor has sagged. You could possibly add in cross blocking between the joists depending what else is in the cavity.

Regarding the HVAC, I would get some support under it to take the weight off the floor joists.

There is no magic trick for fixing drywall cracks. There are some rubberized spray coatings that may work on very small cracks, but you are beyond that now. Tape and mud is your friend.


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## 3onthetree (Dec 7, 2018)

Let's set the expansion and contraction from moisture talk aside. Now that these structural stress cracks are there, fluctuations in moisture will enlarge/reduce the gap in these cracks, but it is not the cause of them. 

Any crack going to an opening corner, especially diagonal, is a failure from carrying the forces down the wall. Not a failure in that it will fall down, but something is either inadequate in its support or it is moving to much. 

Enter the new HVAC hanging from the joists that were not originally designed for that point weight (and even vibrations from kicking on). I think you imply it is in the crawlspace hung from the floor joists. For a permanent fix, look at decoupling the unit from the floor. Then replace the drywall with sheets that form an "L" shape over the openings.


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## Steve Sr (Mar 7, 2013)

Yodaman said:


> If you are running 40 - 50 RH all year, then you are in the sweet spot for whole house RH, and doing much better than most.



These readings are for the crawl with a dedicated dehumidifier set to turn on at 50% but the main house doesn't run much different. It may run 45-55% in the muggiest part of the summer mainly because I keep the AC set at 78 during the day and 75 at night. Often the dew point is upper 60s to mid 70s during the summer.





Yodaman said:


> It is not uncommon to see a room partition sitting on a subfloor. But this assumes no load bearing. Look underneath and see if the subfloor has sagged. You could possibly add in cross blocking between the joists depending what else is in the cavity.



In the places that I have done some reinforcing I have noticed the subfloor sag. I have strategically reinforced between floor joists under door frames with some success but, being wood, the floor joists will still move a little.





Yodaman said:


> Regarding the HVAC, I would get some support under it to take the weight off the floor joists.



The total weight of the AHU and attached filter/ducting is only about 250# and is supported at 4 points on a 3' x 5' rectangle to the above joists. This isn't a whole lot of P/SF loading so while it may have been a contributing factor I think the crawl humidity at that time (un-conditioned crawl) was a bigger factor.




Yodaman said:


> There is no magic trick for fixing drywall cracks. There are some rubberized spray coatings that may work on very small cracks, but you are beyond that now. Tape and mud is your friend.



Any recommendation on the best tape and mud to use for this application? From my reading it looks like plain paper or something like Fibafuse might be applicable and not mesh.


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## Steve Sr (Mar 7, 2013)

3onthetree said:


> Let's set the expansion and contraction from moisture talk aside. Now that these structural stress cracks are there, fluctuations in moisture will enlarge/reduce the gap in these cracks, but it is not the cause of them.



Correct.





3onthetree said:


> Any crack going to an opening corner, especially diagonal, is a failure from carrying the forces down the wall. Not a failure in that it will fall down, but something is either inadequate in its support or it is moving to much.



I definitely agree. The main issue is interior walls on sub floor combined with a marginal floor joist system that probably barely met the existing code at the time. The house was built in 1980 at the very peak of stag-flation. I got a real deal when I was able to assume a 12.5% loan when the going mortgage rate was closer to 16%. Builders were cutting all the corners that they could.


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## SeniorSitizen (Sep 10, 2012)

Research Expansive Clay Soils ( vertisols ). What we see in your pics is common in some regions of TX with expansive clay soil.


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## Steve Sr (Mar 7, 2013)

SeniorSitizen said:


> Research Expansive Clay Soils ( vertisols ). What we see in your pics is common in some regions of TX with expansive clay soil.



Yes, we have clay soils here but it is Triassic clay, the yellow kind, that is hard as a rock. The majority of the footer of this house sit on a large chunk of this stuff. The map here:


https://geology.com/articles/soil/


shows that my area has little chance of having this expansive clay soil type.


I think that the biggest issue was borderline code construction standards when the house was built. For example the flooring joists sit directly on top of the foundation with no top plate. One side of the house has 2x8 floor joists (shorter side) while the longer side uses 2x10s. To make things line up they simply put a 2x2 under the 2x8s to bring that side up to level with the 2x10s. I could go on but I think you should get the picture.


Believe it or not this was one of the better built houses that I looked at!


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## Yodaman (Mar 9, 2015)

Steve Sr said:


> Any recommendation on the best tape and mud to use for this application? From my reading it looks like plain paper or something like Fibafuse might be applicable and not mesh.





Use general purpose green lid mud. The tape, I like Fibafuse for it's ease of use and non-lift. But plain old paper is stronger, and what I would use here.


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## jeffnc (Apr 1, 2011)

Steve Sr said:


> Any recommendation on the best tape and mud to use for this application? From my reading it looks like plain paper or something like Fibafuse might be applicable and not mesh.



Mesh tape is always going to be the weakest, all else being equal. I'm not sure which is stronger, paper or FibaFuse, but I think FibaFuse claims to be stronger. The strongest seam you can make will probably be FibaFuse with DuraBond, then coated with anything really (except DuraBond if you want to sand it!).


This is not a help to the OP I realize, but just to point out, this is often caused by drywall hangers taking shortcuts and installing their drywall. This page probably explains it better than I could.


http://www.renovation-headquarters.com/drywall-installation-openings.html


While that is a good description of the problem, I don't really agree that that is the best way to hang drywall around a door. I think the best way is to hang the drywall horizontally fully around the door opening, and then cut it in place, as shown in photo 2 here.


https://www.constructionprotips.com...ionals-share-their-drywall-installation-tips/


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## Steve Sr (Mar 7, 2013)

Yodaman said:


> Use general purpose green lid mud.



Are there any more specifics other than "Green Lid"? What I currently have is Dap wall board compound with a "red" lid. Do you know what the difference is between these two products?




Yodaman said:


> The tape, I like Fibafuse for it's ease of use and non-lift. But plain old paper is stronger, and what I would use here.




Fibafuze claims to be stronger than paper by their labeling so I am tempted to give it a try.


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## Steve Sr (Mar 7, 2013)

jeffnc said:


> Mesh tape is always going to be the weakest, all else being equal. I'm not sure which is stronger, paper or FibaFuse, but I think FibaFuse claims to be stronger. The strongest seam you can make will probably be FibaFuse with DuraBond, then coated with anything really (except DuraBond if you want to sand it!).



Any suggestions on where to find Durabond? The local big boxes don't have much of a selection if any. I guess they think that the casual DIYer can't handle setting compound (hot mud).


I was in the local Lowes today and also saw some interesting products - 



Dap Dynaflex Flexible Spackling
Dap Elastopatch Flexible Patching Compound


Are any of these (or anything like them) worth considering?


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## jeffnc (Apr 1, 2011)

Yodaman said:


> But plain old paper is stronger, and what I would use here.



Reference?


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## jeffnc (Apr 1, 2011)

Steve Sr said:


> Any suggestions on where to find Durabond? The local big boxes don't have much of a selection if any. I guess they think that the casual DIYer can't handle setting compound (hot mud).



I'm sure you can find EasySand, which is setting compound. Otherwise, a local building supply place or drywall supply place should have it. Otherwise, you should be able to order it off the Lowe's or Home Depot websites.





Steve Sr said:


> Dap Dynaflex Flexible Spackling
> Dap Elastopatch Flexible Patching Compound
> 
> 
> Are any of these (or anything like them) worth considering?



I would probably try an elastic caulk before those, although I haven't used those. Maybe something like DAP Extreme Stretch.


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## Yodaman (Mar 9, 2015)

Steve Sr said:


> Are there any more specifics other than "Green Lid"? What I currently have is Dap wall board compound with a "red" lid. Do you know what the difference is between these two products?


 I have never used the Dap product, have always tried to use green lid GP for taping and next coat.

But reading thru the Dap description, it reads similar to a medium or finish coat product due to it's easy sand characteristics. To make a product easy-sand, less adhesive is used. And in my mind the trade off is some strength.

Personally (IMHO) any stretchy type of quick fix compound sounds gimmicky. Your tape isn't going to stretch. Your paint isn't going to stretch. So what are you really gaining? 



Steve Sr said:


> Fibafuze claims to be stronger than paper by their labeling so I am tempted to give it a try.


I have no science or ref. on the strength between paper of Fibafuse.
Just 30 years exp. with paper and only a couple with fiber, but they are probably similar in strength. If you already have it, I would use it.
I would probably pass on the Dap though.


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## ClarenceBauer (Mar 4, 2005)

Yodaman said:


> I have never used the Dap product, have always tried to use green lid GP for taping and next coat.
> 
> But reading thru the Dap description, it reads similar to a medium or finish coat product due to it's easy sand characteristics. To make a product easy-sand, less adhesive is used. And in my mind the trade off is some strength.
> 
> ...


The DAP compound does NOT contain any CLAY. Used as a finish.
The Green Lid has CLAY added which along with the Mica would make the Green lid harder.
Something I would LIKE to know is Fiber Fuse tape approved for use with paper faced Gypsum board Systems. As it is Designed for use with Paperless Drywall Systems. Does the manufacture recommend it's use with paper Gypsum products?


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## jeffnc (Apr 1, 2011)

ClarenceBauer said:


> Something I would LIKE to know is Fiber Fuse tape approved for use with paper faced Gypsum board Systems. As it is Designed for use with Paperless Drywall Systems. Does the manufacture recommend it's use with paper Gypsum products?





It's called FibaFuse, and yes of course. It has a specialty use with paperless drywall, because it itself is paperless, so it cannot feed mold like paper tape can. That is usually the major reason for using paperless drywall. So it makes sense to use FibaFuse, which is made of fiberglass, with paperless drywall, which has a fiberglass surface. But aside from that specialty use, it is a general purpose drywall tape. (Some find it not as good for corners, and pros who use a standard taping knife to tape corners will find it cuts easily. I personally have no problem with using a corner knife, and it works well with a corner knife.)


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## jeffnc (Apr 1, 2011)

Steve Sr said:


> Are there any more specifics other than "Green Lid"? What I currently have is Dap wall board compound with a "red" lid. Do you know what the difference is between these two products?



Green lid refers specifically to USG Sheetrock brand All Purpose compound. It's a standard but I wish people didn't use that term because there are other manufacturers that make a similar product, and we really should be calling it "premixed all purpose". Your DAP product is called lightweight, so it's probably equivalent to USG Sheetrock Plus 3 lightweight compound. It is lighter as the name implies, but it's also not as strong and not the best one recommended for the first embedding coat. If your'e not going to use a setting compound, then All Purpose with paper or FibaFuse is the next strongest for the first coat. USG actually makes many, many joint compounds and some are actually stronger for the first coat than All Purpose, but that is by far the most popular and easily available one.


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## ClarenceBauer (Mar 4, 2005)

Order some crack monitoring gauges & place them over the existing cracks & monitor the movement over say 6 Months time period. The amount of movement after all the corrections that have been made may be very little & you will have a better idea of what type material could be used.


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## Steve Sr (Mar 7, 2013)

jeffnc said:


> I'm sure you can find EasySand, which is setting compound. Otherwise, a local building supply place or drywall supply place should have it. Otherwise, you should be able to order it off the Lowe's or Home Depot websites.



Thanks for everyone's suggestions. It looks like the Easy Sand is a lighter weight (i.e. less strong) version of Durabond. It looke like either of these would have to be ordered from one of the big boxes. Based on the discussion I would assume that I should use the Durabond for the initial coat since it would be stronger. Correct?


As for the second and third coats I'll probably use the all purpose Dap that I already have.


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## Steve Sr (Mar 7, 2013)

Next question... I already have a stiff 6" putty/taping knife and I am assuming that I would need a more flexible knife for the final coats. If you were to add a single flexible knife to your collection how long would it be? 6", 8" 10" 12"?


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## jeffnc (Apr 1, 2011)

Steve Sr said:


> Next question... I already have a stiff 6" putty/taping knife and I am assuming that I would need a more flexible knife for the final coats. If you were to add a single flexible knife to your collection how long would it be? 6", 8" 10" 12"?



You don't necessarily need another 6" knife. IMO you should have a small one like 3", a 6", and a 12". You can add 8" and 10" later if you find you're doing a lot. Technically you don't really need 8" or 10" since the 12" is wide enough to cover.


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## Yodaman (Mar 9, 2015)

I use a 4, 6, 12, and a inside corner trowel. I also use a rectangle mud pan when taping, and hawk for all other coats. I have 8's and 10's but never use them.


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## jeffnc (Apr 1, 2011)

Yodaman said:


> I use a 4, 6, 12, and a inside corner trowel.



Yes, I have a corner trowel too. I think all DIYers who do corners should have a corner trowel also. I know pros don't often use them, but that has more to do with how they do large jobs over 3 days (corners can be done in 2 coats), than how useful a corner trowel really is for getting clean corners. If you use FibaFuse for corners then a corner trowel is a virtual necessity.


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## Steve Sr (Mar 7, 2013)

jeffnc said:


> Yes, I have a corner trowel too. I think all DIYers who do corners should have a corner trowel also. I know pros don't often use them, but that has more to do with how they do large jobs over 3 days (corners can be done in 2 coats), than how useful a corner trowel really is for getting clean corners. If you use FibaFuse for corners then a corner trowel is a virtual necessity.



I'll keep the corner trowel in mind for the next project that I have that has inside corners. THe current project is limited to some 8"x8" patches, 24"x14" washer outlet box repair and the 3 cracks originally pictured.


BTW, I did find some Durabond at a local drywall house. I guess that it is not used that much for new construction or the big boxes would carry it.


I never did get any comments on Durabond for embedding the tape followed by all purpose for the top coats. Is this a solid plan?


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## jeffnc (Apr 1, 2011)

Steve Sr said:


> I never did get any comments on Durabond for embedding the tape followed by all purpose for the top coats. Is this a solid plan?



Sure. You just want to make sure you apply the paper and first coat in such a way as to not have to sand into the Durabond or paper. As long as your sander only touches All Purpose compound it will be fine.


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## Steve Sr (Mar 7, 2013)

Continuing the saga... I got the durabond and Fibafuse tape on all of the areas that needed it. My main objective was to fill the cracks, embed the Fibafuse with as little buildup as possible. I think that I succeeded. In the process I found that nothing was flat including the existing walls! UGGGGH! After the Durabond was dry I did a light scraping and sanding to get rid of any high spots.

I am now on to the AP coats and it appears that I don't have the "knack" for this job! Did I say that NOTHING is flat? :vs_mad:Now there is the tape and Durabond "bump" to deal with as well. I am finding it very difficult to estimate the buildup thickness. Complicating matters further is that most of these are repairs and are constrained by a door frame, ceiling, or electrical outlet where there is no room to get tools into or to feather out compound.


The first coat of AP is on but the result is far from flat. I have begun to figure out that the best approach is to just apply the mud, smooth it out ONCE and cross your fingers. Trying to fix imperfections at this point seems to make things WORSE. :vs_mad: I think that fixing areas like these has to be the HARDEST and requires the most skill. I think that I would much rather work on new construction (like all of the YouTube videos that make it look easy) than try to fix what was a pretty poor drywall job to begin with.


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