I was sanding a piece of sheetrock, but the paper covering is rough and I can't get a smooth finish. What do you recommend? I was thinking of painting the paper with shellac to get it harden so that I can sand it smooth. Or do I sand past the paper down to the plaster? Will it crumble or split if I try that?

On 07/09/2013 08:21 PM, Deodiaus wrote:
I was sanding a piece of sheetrock, but the paper covering is rough
and I can't get a smooth finish. What do you recommend? I was
thinking of painting the paper with shellac to get it harden so that
I can sand it smooth. Or do I sand past the paper down to the
plaster? Will it crumble or split if I try that?


Skim it with a setting type joint compound, then sand that.

nate

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On Tuesday, July 9, 2013 7:21:11 PM UTC-5, Deodiaus wrote:
I was sanding a piece of sheetrock, but the paper covering is rough and I can't get a smooth finish. What do you recommend? I was thinking of painting the paper with shellac to get it harden so that I can sand it smooth. Or do I sand past the paper down to the plaster? Will it crumble or split if I try that?

Like Nate says, you have to skim coat it and then sand. You will never be able to sand the paper smooth so you have to completely coat it and then sand the coating.

If you apply a skim coat and use regular non-setting drywall compound (lets you work slower, compound can be made soft again by spraying it with water), you may be able to get by with no sanding.

No, you want to put something on that sanded paper to prevent it from absorbing moisture from the joint compound skim coat. Not only will the rough paper absorb moisture from the joint compound, it'll absorb it fast enough that he's going to have trouble getting the joint compound smooth when he's spreading it.

I would go over your rough paper surface with an alkyd primer first, and give that time to dry. Once that alkyd primer is dry, then you can skim coat over it with a joint compound and sand that joint compound smooth without having to be concerned that the moisture from the skim coat is going to cause more problems.

ALWAYS ALWAYS ALWAYS spread your joint compound and sand it smooth with the aid of a bright light held close to the wall but some distance away from where you're working. This will illuminate your work at a sharp angle, thereby creating "critical lighting" that exagerates the roughness of the wall, making it easy for you to see where you need to add joint compound or remove it to achieve a smoother surface. When your wall looks like it wasn't done by a monkey under such critical lighting, it'll look "not all that bad" under normal lighting. When it looks "good" under critical lighting, it'll look perfect under normal lighting. In my building, I'll work with a trowel or hand sander in one hand and a mechanic's trouble light in the other, and I'll fix any imperfections I can find under critical lighting before I prime and paint.

Zinsser also makes a product especially for priming over damaged drywall face paper. It's called "Gardz" and it's a water based product. I've never used the stuff, so I can't say if or how well it works. But it is made specifically for prepping drywall with torn face paper before priming and painting.

http://jackpauhl.blogspot.ca/2009/01...ce-sealer.html

You should also be aware that premix joint compound comes in three flavours:

1. "Regular" or "Taping" - This kind of joint compound has the most glue in it so that it sticks to drywall the best. But, that glue also makes it dry hard and difficult to sand smooth. Only use this one when you're intending to cover it with a softer drywall joint compound anyhow.

2. "Finishing" or "Topping" - This kind of joint compound has the least amount of glue in it so that it sand smooth very easily. It still has enough glue in it that you don't have to worry about it not sticking well. However, never mist the surface of your joint compound with a spray bottle and keep trowelling to get a smoother surface when using this kind of joint compound because the resulting joint compound can dry so powdery that your primer and paint might bubble cuz the surface they're trying to stick to isn't holding together well. (Modern joint compounds spread smooth much more easily than the old lime putty based plasters, and so when spreading real lime putty based plaster, the old timers used to dip a brush in water and fling a water spray onto the fresh plaster and keep troweling to get a smoother finish. You can do the same thing with a spray bottle and joint compound, but it's risky to do that when using Finishing joint compound cuz it'll dry TOO powdery soft with the result that your primer and/or paint bubble.)

3. "All Purpose" - This kind of joint compound is about half way between the first two, and it's meant for drywall contractors who don't want to have to carry two pails or boxes around everywhere in their truck. It sticks well, but isn't a bear to sand smooth either.

Also, I mix my own joint compound from a powder, but I understand the convenience of buying a box or pail of premixed joint compound. My limited experience with premixed joint compound is that you need the arms and wrists of a mountain gorilla to spread it smooth straight out of the box or pail. They mix it super thick at the factory because no one wants to pay to transport water. So, even if you choose to use a Finish joint compound, don't be scared to thin it with water to make it EASY for you to spread smooth. Lots of newbies presume it's supposed to be as thick as pottery clay, and try to work with it the way it comes, and that's just plain stupid. Working with joint compound that's too thick to spread smooth easily is fighting an uphill battle. Mix in some water so that you find it much easier to spread, and that'll go a long way to your doing better work.

Also, go to any place that repairs small appliances in your area and ask them to save any old stripped kitchen mixer blades for you. Kitchen mixer blades have a notch cut out of their ends that eventually wears out so that the blade slips and won't work properly. However, you can put stripped kitchen mixer blades in the 3/8 inch chuck of a cordless drill to make mixing water into your joint compound to thin it to a spreadable consistancy a breeze. Watch your fingers! When mixing water into your joint compound, do the mixing inside a cardboard box or something so that the spinning mixer blade doesn't throw wet joint compound all over the place.

If you choose to mix your joint compound from a powder as I do, then be aware that powdered joint compounds will often come with "chemical sets" of 30, 60, 90 or 120 minutes. That means that 30, 60, 90 or about 120 minutes after the joint compound is mixed with water, a chemical reaction will occur that makes the compound get stiff. When that happens, it will very quickly become unworkable. (ie: unspreadable) However, you can always scrape the "kicked" compound smooth with a sharp paint scraper and apply another coat of fresh joint compound over the stiff stuff.

Also, mixing your compound from a powder allows you to mix in as much white wood glue into it as you want to make it stick like he11 and dry hard as a rock, or mix no glue at all into it so that it practically falls off the wall when it sees you pick up your sanding screen, or mix it anywhere in between. You can also add white wood glue like Weldbond or Bondfast to premix joint compounds to make them stick better and dry hard if you want. Some people will scoff at that suggestion, but I've been repairing the plaster walls in my building with joint compounds for well over 20 years, and have not had any problems doing things like that. So, scoff if you will, but it's good advice whether you chose to follow it or not.

Hope this helps.

On 07/09/2013 10:03 PM, wrote:
If you apply a skim coat and use regular non-setting drywall compound
(lets you work slower, compound can be made soft again by spraying it
with water), you may be able to get by with no sanding.


that would require an artistic touch that I don't have

But yes, I have seen talented drywall guys use a non-setting compound
and smooth it with a damp sponge.

nate

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