Nestor_Kelebay

If you can't get a longer working time by increasing the lime content, the fail-safe fall back situation would always be to simply add sand to drywall joint compound, and use that. It would just take a bit of experimentation to find the mixing ratio to get the right roughness.

Msupsic

Funny you should mention that... before I consulted this forum, I had bought a bucket of joint compound and a bag of sand and that was going to be my approach.

Let's see if adding the lime helps first. If not, it's on to plan B.

Msupsic

Well, Nestor, seems I figured out the problem: Apparently, I just suck at plastering. The good news is, I'm getting better.

I was mixing this like you would mix concrete: thinking I wanted it the consistency of cookie dough. No wonder it was drying up on me so fast.

Last night I tried adding more water, and used a paint mixer attached to my drill. There's a balance point where the base coat mix becomes liquified enough to spread nicely with a trowel, but not so wet that it runs down the wall. More the consistency of mortar or joint compound, than concrete.

It makes a big difference in the application and my ability to texture the surface. It also took most of the night to dry.

I only hope that the previous area I did with the drier stuff was wet enough to reconstitute the glued drywall and adhere properly. It's holding fine for now, but no telling how it will stand up over the years. Only time will tell.

Thanks again.

Nestor_Kelebay

But, when it dries, does it match the surrounding base coat plaster?

Msupsic

Sure... aside from the color, of course. The original stuff is so old that it's gray in color, whereas the new stuff is ivory-white.

The texture itself is a pretty good match. I even brushed in strokes that match the strokes of the original texture, so in most places it's hard to find where the patch is.

Nestor_Kelebay

That's great.

You don't need to know this, but...

The hydrated lime you're spreading on to your walls is going to gradually turn into limestone. There's something in nature called "the lime cycle" whereby limestone that comes from marine reefs that formed millions of years ago can be heated to form "hot lime" or "quick lime". That hot lime or Calcium oxide can then be mixed with water to form the hydrated lime that you're mixing with gypsum (Plaster of Paris) and sand to form your base coat plaster.



But, over the next several years, that hydrated lime (Ca(OH2)) will react with the carbon dioxide in the air to form calcium carbonate (Ca(CO3)), or the primary constituent in what we call "limestone". The purer the calcium carbonate, the whiter it is, and limestone that is quarried will typically be at least 90 percent calcium carbonate.

The above is important because until the hydrated lime in your plaster patches transforms into limestone, it's going to be highly alkaline because of all those -OH groups in the hydrated lime. The high alkalinity of that lime will cause any oil based primer or paint to basically turn into soap if you paint it on your base coat plaster. If you're planning to paint over your base coat plaster within the next couple of years, then you should buy a latex primer made especially for fresh concrete (called a "concrete primer".)

What you might want to do instead is skim coat over your base coat plaster with drywall joint compound, sand that smooth, and prime and paint with whatever primer and paint you like over that. Drywall joint compound consists of gypsum, and so it's neither alkaline nor acidic.

PS: The reason why the cement based grout used in bathroom ceramic tiling won't mildew in the first year or two is because the grout is a cement based product made with lime. Until the lime in that grout transforms into limestone, then the grout will be too alkaline for mildew to grow on it. This is why ceramic tiling contractors can guarantee their work for one year. They know that it takes about two years for the lime to transform into limestone, and it's only then that mildew will begin to grow on the grout.

Msupsic

Thanks for the education, Nestor. I'm actually almost done doing my patching, and it's going swimmingly. Haven't yet decided if I'll skim coat the whole thing, or just paint it.

Some of the old base coat was already painted. I'm not sure if that affects how a layer of skim coat would stick to it. I have no idea how old the paint is - it's olive green. It appears to be a lead paint from the old days.

I just installed the replacement door last weekend. Getting the old door out wasn't as bad as I had expected.

Thanks for all of your help thus far.

Nestor_Kelebay

Then it won't have very much lead in it.

You see, prior to titanium dioxide becoming the hiding white pigment used in paints in the mid-1970's, paint companies used the white pigment "lead carbonate" (also called "Flake White" or "Lead White") as the high hiding white pigment in house paints. You can still buy lead carbonate in artist supply stores... just ask for "Flake White". Paint companies aren't allowed to use it in house paints anymore, but artists are still allowed to use it in their paintings.

So, the "lead" in "lead based paints" was the white pigment "lead carbonate", and just as you'd expect, the whiter the paint, the more lead carbonate pigment is probably in it, and the more of a health risk it could pose to young children.

To make an olive green, they probably started with a "medium" tint base and added green and brown. That medium tint base wouldn't have had nearly as much lead carbonate pigment as a white tint base or a pastel tint base.