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james 08-30-2007 10:42 PM

Smooth coat over existing drywall texture
To kick things off, I have a question on drywall. I want to apply a smooth, skim coat for gypsum joint compound over an existing textured drywall finish (a knock down coat circa 1980), on both the walls and ceiling. It is painted with satin latex paint.

Will standard joint compound stick to it? Or, do I need to sand it, or hit it with TSP?

Also, what is the best way to get a smooth finish. A plaster trowel, or a wide taping knife (14")?

It can be difficult finding good answers to real questions.


Unofornaio 08-31-2007 06:05 AM

Re: Smooth coat over existing drywall texture
It will probably be just fine with no prep work at all. There are so many binders in the joint compound that stuff sticks to most any surface. If you already have one I would go over it in one pass with a screen on a pole sander, just for insurance.

For the finish a plaster trowel is the only way for the novice to make an attempt. At your local store in the masonry section get a "pool" trowel, this is a finishing trowel with rounded edges. Pick though them and check the edges by taking one trowels edge and placing it up against another's bottom lengthwise the gap or non gap should be consistent and there should be no ripples or you will NEVER get your wall smooth. Go for the best quality this will pay you back in application. Next if you are going to coat the whole surfaces you might as well get a hock in the drywall or stucco area. Working off of the hock will take some practice but its much easier than getting back down and putting material on the trowel or directly to the wall with a separate knife.

Also pick up a good quality hand held spray bottle you can use this to get the surface really smooth and it helps with the troweling.

Its gonna be much easier if you mix the compound before you apply it, use a good size drill or you will burn it up. Get the buckets of compound the boxes are not worth it. Besides if you do not use it all, just scrape the sides clean, put about an inch of water over the top and put the lid back on.

DO NOT GET THE LIGHT WEIGHT STUFF for your application I have found it doesn't work as good as the reg stuff for skim coating. I did my whole house like you describe only I added washed sand to the mix to give it a old world plaster look still smooth but not, American smooth.

Good luck. One bucket will more than do the average room stay thin and keep the edges of the trowel clean. You can also have a bucket of fresh water in the room with you to just dip the trowel in.

asudavew 08-31-2007 06:12 AM

Re: Smooth coat over existing drywall texture
What he said!


james 08-31-2007 08:51 AM

Re: Smooth coat over existing drywall texture
Wow. Jeff, that is incredibley helpful. Thanks.

Couple of quick questions:

1. What's a hock (sorry)?
2. What is the best was to get the compound to the wall? Small trowel from the 5 gallon tub to the plaster trowel?

Thanks again,

Unofornaio 08-31-2007 09:22 AM

Re: Smooth coat over existing drywall texture
Hock- I misspelled it its Hawk- is the square board or piece of metal attached to a handle with the material piled on you see stucco or plaster guys using.

Loading this with material-just a little bit until you get the hang of it- is how you get it to the wall.

1. Mix your material
2. Load the hock
3. holding the hock in your no dominant hand gently tilt it toward you
4. Take you trowel and use it as sort of a stopper so as you are tilting the hock it flows on to the trowel.
5. In a quick motion flip the trowel up to load it.
6. Apply to surface.

This is gonna be messy at first, mostly for you and the floor while trying to load the trowel. Your material should be not runny but defiantly no where near stiff. You may need to add more water to the mix. each time you add water throughly mix it in before the next addition.

I found this when looking up the spelling its a little better than my description:

"Scoop up and load plaster onto the hawk. Now, holding the hawk in your left hand, if you're right handed, (or visa versa, if you're left handed) at a level between chest and shoulder, set the blade of the float at right angles to the bed of the hawk and push a measure of plaster towards the edge furthest away from you. As you do this, tilt the hawk slightly towards you and follow through with the float in a scooping motion. This movement is carried out in one fluid action. Practice this until you are satisfied with your progress."

RTflorida 08-31-2007 09:24 AM

Re: Smooth coat over existing drywall texture
I believe a hock is the flat, blade like tool used to hold your plaster/joint compound. You remove a big glob (technical term):) of mud from you bucket, placing it on the hock giving you easy access with your knife as you skim along.

Another alternative is what we call a mud pan - about 4 x 15 inches and 4 inches deep. cheap DIY pans are plastic and have a metal blade on the rim for scrapping you knife off...Don't buy this one - those blades fall out and will rust if you don't dry them off after each use. Spend the extra money on the stainless steel (only about $12 or $14) At Depot or Lowes. Available with all the other drywall tools.

It has been my experience that joint compound does not stick quite as well to high gloss finishes, so if there is high gloss enamel on those walls your skimming....hit them with some fine sandpaper or drywall screen first and wipe down with a damp cloth to get the dust.

Thin is better...DON'T apply thick coats. It will probably take 2 coats to skim a knockdown or orange peel finish to get it perfectly smooth (It took 3 in my bathroom to get it the way I wanted) - If you do it right, just a light sanding is needed at the end.


james 08-31-2007 01:39 PM

Re: Smooth coat over existing drywall texture
Got it. I've used a hock before -- so that's OK. The mulitple coat recommendation sounds good -- I have spent time in the past messing around trying to get a single coat smooth.

Thanks all.

james 09-03-2007 12:37 PM

Re: Smooth coat over existing drywall texture
One more quick question. I have three bedrooms with a foil wallpaper. When you take it down, it leaves a lot of wallpaper glue behind.

Do I need to remove that with enzyme solvent, or will the joint compound adhere to it?
Thanks again,

Unofornaio 09-03-2007 01:40 PM

Re: Smooth coat over existing drywall texture
Thats a good question.

You would think, logically, its glue right? it probably would not be a problem. But I do not know for sure sorry.

Here is my thing about drywall compound. I have done many repairs on homes ranging from new to plaster and lath and been in many homes undergoing remodels and I have yet to see de-lamination (or peeling) of drywall compound that is not related to some type of movement or water damage. Others here may have..

RTflorida 09-03-2007 04:33 PM

Re: Smooth coat over existing drywall texture
when you say there is a lot of glue left on the wall, do you mean glue and a thin layer of the paper backing?
I've never removed foil type paper or any antique papers and glue.... I do have quite a bit of experience with the pre-pasted and modern wall paper pastes and their removal.
Usually I peel as much of the vinyl or paper as possible, exposing the inner paper layer and glue...I discovered on accident that joint compound will actually REMOVE this inner paper and glue - VERY efficiently. I've done several rooms that the only chemical used was old lumpy joint compound that I skimmed over the remains that didn't peel of. within 2-3 minutes it all scraps off very easily - them wipe with a damp sponge. The joint compound acts as a stripper. Make sure none of the joint compound sets up...
Seems I always have about 1/3 of a 5 gallon pail of joint compound sitting around; I save it for wallpaper removal. Thankfully, I removed the last wallpaper from our house about 9 months ago- my wife doesn't know it yet, but we will NEVER put up wallpaper again.
Anyway, give it a try, if you can peel the paper to the inner layer of paper/glue


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