ALL: Have a problem w/ some setting type wallboard mud. It’s NGC Sheetrock brand grade 90 lightweight mud. Used it last week to repair a rather large joint in LR ceiling. Stuck bag in closet anticipating needing it this week for a job in laundry room; house is air conditioned & humidity controlled at about 50%. It cured fine in LR. But… in laundry room, it set splotchy. Some areas didn’t set for over 24 hrs; some set in about 3 hrs. None set in the normal range 85-130 min. The areas that took longest to set are hard as a rock and smooth as a baby’s butt; the areas that set fastest are sandable, but are pockmarked like it had smallpox.
Any clues as to what could have gone astray? One thing I can suggest is that since I didn’t need a whole bag for the laundry room, I put the dry stuff in a bucket , added water and mixed the Heck out of it w/ a big ole honking drill & a paddle, Second, the splotchy areas appear to be related to the successive applications to build up/ smooth out the wall. Put less than 1/8 inch on it, but some of the globs from the bucket seemed to go on smoother than others; some didn’t want to stick to the wall as well.
Thanks.
Don
Replies
If you had lumps it was not well mixed and this could effect the distribution of what makes it work. The little air bubble holes usually happen due to holding the trowel or knife too flat. You can always skim coat any defects with ordinary compound. 1/8" is a very thick application for drywall work. Not sticking to the wall could be due to dust on the wall, too dry a mix or poor trowel technique. The material does not like to be overworked either, you need to apply it correctly with just a few strokes. The DIY method of glob and grind doesn't work well with with the stuff. If you sand between coats of mud, you have to get the dust off for a good job. It is much easier to knock off ridges with a joint knife. Your goal when finishing drywall is to keep the final surface as flat to the board as possible. Butt joints are harder and require a wide tapered application. Make sure when sanding that you create a taper that is transparent on the edges. Primer and paint will deal with any color differences. The good part is that you can scrape it out and start over if you really have to.
Hammer: Thanks. I'm afraid that my problems were a little bit of everything you said. Of course, that is in retrospect. won't make those mistakes again. This was a narrow band of mud to blend up against the edge of a tile backsplash I did in a laundry room. Was 1/8 inch only at a few spots where the wall was low. I hate sanding, so I try to keep the globs to a minimum.
Between your's & Jeff Buck's comments, I can see how I wound up w/ some spots that didn't cure well; I had spots that didn't have the right proportion of whatever makes it set up fast. Won't make that mistake again, either.
Only way you learn is to do it, screw up & redo it till you get it right!
Thanks.
DonThe GlassMasterworks - If it scratches, I etch it!
the only tip I can give is ...
when mixing dry powders ...
water or liquid goes into the bucket first ...
then the dry mix ....
makes for a much better and easier mix.
also ... don't dump in all what you think you'll need at once ... pour in and mix slowly ... helps for a more uniform mix .... less chance of big dry chunks ...
Jeff
Buck Construction, llc Pittsburgh,PA
Artistry in Carpentry
Jeff: thanks - you confirmed my suspicions. When I mixed it last week I added the water first then the powder. Wound up w/ a lot more mixed mud than I needed - but that is what the dumpster is for. Re-read Myron Ferguson's article on drywall mud work, & I suspect that I didn't have the mix wet enough. Recently I did an entire bathroom for a daughter w/ a skim coat and had none of these problems.
DonThe GlassMasterworks - If it scratches, I etch it!
I put the dry stuff in a bucket , added water and mixed the Heck out of it w/ a big ole honking drill & a paddle
Don, here are my 2 cents.
Jeff got it right on, always powder to water not the other way. I suspect it's not that you didn't mix enough but with a drill on fast and mixing the heck out of it would create a heterogeneous mixture of over mixed and under mixed globs.
When you over mixed, little pockets of plaster set up really fast which acted as seeds to set the surrounding plaster so the smooth and hard areas were the ones that were almost set and you were just burnishing the plaster. And the under mixed areas were splotchy and bubbly.