Some years ago, an idiot who was just starting out in DIY painted a wall in my apartment so badly and unevenly that it's funny. Looks like a scale model of the Rockies on its side. It was such an appalling job that I would have fired the painter, but I can't really fire myself, can I?

So the time has come to make amends. I have seen a few videos on YouTube about skim coating, so i'm ready to make a complete hash of that too. My only relief is that i can hardly make it worse than it already is.

Question: the existing paint is a latex semi-gloss. Might there be any problem with adhesion of the mud? I'd plan to wash thoroughly with TSP, but do you reckon it would help to roughen the surface with steel wool as well, before applying the skim coat?

 

TSP needs to be rinsed well! TSP residue can cause adhesion issues.
Scuff sanding the walls with 80 or 100 grit will allow the joint compound to adhere.

Use the green lid [all purpose] j/c as it has better adhesion properties than the lightweight mud.

 

If you want to be real sure, I would do all the above and then prime the walls with Zinsser Gardz before skimming.

If you do use the Gardz, you can skip the TSP, just scuff up the walls and wipe clean.

 

Thanks v much. Will surely look for the grren lid mud.

As to the sanding, the reason i thought of steel wool instead of sandpaper is that my prior paint jon is so uneven (blush!) that there are 'lands and grooves', hills and valleys. I'm concerned that sandpaper being flat, it will only sand the high points and miss the grooves/valleys. Of course, I could grind it right down flat with a very coarse grit, then smooth off with finer, but then I wouldn't need to apply the skim coat, which I'm only doing to flatten the surface (that I messed up before).

What do you think?

Re. the TSP - you've just taught me something new. I thought the whole purpose of TSP was to remove any grime, specifically to aid adhesion. It sounds from what you say though that I should sponge over the surface a second time with plain water to rinse. I'll do that. Thanks!

 

Thanks for that. Given marksr's comments re TSP, I'll happily switch to the Zinsser Gardz.

Per my reply to marksr, do you think there is any merit in doing the scuffing with steel wool rather than sandpaper, in this case, because of the uneven surface of the existing paint?

 

Stick with sandpaper, steel wool can leave bits behind which could rust later on. As Mark said, use a pretty coarse sandpaper.

 

The sanding job doesn't have to be perfect. I'm not sure steel wool would scratch the paint up sufficiently and as SS stated, any specks of steel wool left behind will rust after it contacts latex paint.

 

Great thanks. Will nix the steel wool (wasn't looking forward to it). I've got some excellent Rambo-esque 60-grit sandpaper I got on eBay that should give my dreadful earlier paint job a good roughening.

 

marksr, embarrassed just to be getting going on this job now after some serious procrastination.

Approx how much mud would you guess I'll need for my small 45 sq ft of wall?

Thanks,

 

Depends on how think you have to apply it. I've never bought anything other than the 5 gallon pail (4.5?), what sizes are available to you?

 

1.75 pt
3.5 qt
4.5 gal

Search Results for pre-mixed joint compound at The Home Depot

 

I've always bought the 5's [4.5] because it costs marginally more than the 1 gallon. I've never really had to estimate how much mud I'd need because I mostly just do patches or small jobs. As SS said a lot depends on how thick or how many coats of mud the wall will need.

 

I just don't know whether that almost gallon would be enough. As Mark said, it's pretty cheap so I think I'd still get the big pail.

 

Gottit -- thanks, All.

I think i should perhaps have realized that my question was a bit, 'how long is a piece of string?' The good point is that the stuff if like paint inasmuch as, now i look, the price plummets with the bigger buckets, so it's hardly worth being frugal, then finding you're a cup short of finishing the job.

 

Those that do drywall work everyday are better able to estimate how much mud it will take for most any given job

Joint compound can keep for a long time. Obviously you don't want to introduce any grit/trash back into the bucket from leftover j/c in your mud pan but other than that if you put a little water over the mud [or plastic] tightly seal the lid and store in a cool [but never freezing] area it will last a long time.

The 2 biggest issues with storing an opened bucket of mud is heat drying it out and mold.