Skim Coat (almost) Like a Pro

Posted by Steve on Sat, 09/02/2006 - 1:33pm


Most people seem to like the flat, clean effect of drywall. Drywall is cheap, goes up easily and doesn't take much acquired skill to learn how to tape, mud and finish the joints. Even drywall repairs are relatively painless. So what's not to like?

Maybe I'm just weird (well, there's probably no contesting that regardless) but I like plaster. I like the way side lights create shadows and textures over the natural unevenness of a plaster wall, giving it density and bulk.

The problem is that I absolutely suck at plastering. My plaster work usually looks more like adobe, with half of it winding up on the floor and the mix setting up before I can work it. What I used to do is use plaster to get the wall in the ballpark then add a finish coat of joint compound with a 12" blade, followed by copious sanding that left me, the room, and much of the rest of the house, looking like the set of The Polar Express. It was a tedious, laborious and dirty business.

Then I ran across a tool with the dubious name of Magic Trowel.

I watched a demonstration at a woodworkers show and it looked so easy. But I've been burned enough times by affable salesmen selling miracle niche market tools to know that my mileage may, and probably will, vary. I've got a box full of Magic Planes and Magic Coping Tools and Magic Drill Bit Sharpeners to attest to that.

But I knew enough about joint compound to know that the concept seemed solid: a wide squeegee blade instead of a hard-edged metal taping knife. It was worth a shot.

The verdict? It works very well! After extensive plaster repairs to my living room I skimcoated it in about two hours. Even better, I only had to give the 200+ feet of mesh tape I used to fix cracks just one coat of compound before skimming the wall with Magic Trowel. The compound lays down so thick that it sinks the exposed tape. It didn't completely eliminate the need for, or the mess of, dry sanding but it reduced it considerably.

So why not just use a garden-variety squeegee? Magic Trowel is different than a squeegee normally used for cleaning windows. The long flexible blade floats over the surface pushing down on high spots. The 30-degree angle on the outside edges reduces tension on the ends of the blade leaving minimal trowel lines. Those that it does create are easily sanded off later.

There's a technique to using Magic Trowel but you pick it up pretty quickly. Texmaster has a how-to video on their web site demonstrating the technique (Windows Media Player only).

Use long strokes, top to bottom. Don't obsess on small divots or gouges. Those can be easily patched later. Instead, work quickly and use consistent pressure.

The video advises adding 8 ounces of water to a five-gallon bucket of joint compound to thin it out for rolling. I found that mixture to be a little too thick. In fact, I experimented with the mix by replacing one gallon of compound with a slightly soupy mix of plaster of paris and a couple of ounces of white vinegar to retard the plaster from hardening. It worked but you have to work even faster.

(Click on the photo to expand it). You'll need a painter's paddle and a torquey, variable speed corded drill to mix the compound. Warning: I damaged the collet on and practically overheated my Milwaukee drill mixing joint compound. Use a sustantial drill for this, not a cordless, not a Target red dot special! And do it at slow speed unless you want to be scraping compound off the dog.

If you do this over an existing old plaster wall, make sure it's clean and degreased. If the wall has anything other than a flat paint on it, scuff it up with an orbital sander. Wash it down with TSP twice and rinse it down thoroughly. I lay down a plastic sheet and cover that with a cotton dropcloth.

Work on vertical sections and don't let the edges dry out. As I said before, don't obsess with making the wall perfect at the expense of letting the compound get crusty. You can always fix it later. Also, keep your compound, the blade and the wall clean! Any foreign matter will create long gouges in the finish.

After the wall has dried, dry sand any high lumps, fill any gouges with a taping knife and give it at least two coats of primer/sealer. The compound will really suck up the paint so you need to seal it well before you roll your finish coat.

I had concerns about the softness of joint compound as a skim coating material but after four years in my entry hallway the finish still looks like the day I primed it. My guess is that the primer sucks into the compound, making it more durable. But that's just a guess.

Just keep your eyes on this tool because once your fellow tyromaniacs see the results they're going to want to borrow your Magic Trowel. Mine has done five houses. Unfortunately, they were casualities in one those houses, which had a bad basement fire. Gotta order some new ones.


Comments

Posted by Anonymous (not verified) on

Hey, read your review of the Magic Trowel w/ much interest. (Just saw a feature on the trowel in "Fine Homebuilding...)

Like you, I also prefer plaster to joint compound. And like you, my plastering sucks. (it's getting better, but still ain't quite perfect...). My problem w/ plaster is I also have some flat spots. Troweling over those is tough as the plaster hardens.

So -- my question is, can the Magic Trowel be used for plastering? ie, use it while the plaster is still soft and hasn't begun to set up yet?

Let me know your thoughts. I'm tempted to give it a try. Thanks! :)

Posted by Steve on

I've mixed plaster with joint compound but I've never tried skimming with 100% plaster. If you use a lime-based plaster it might work because it sets by carbonization so it has a longer working time than gypsum plaster. Gypsum starts to harden almost immediately on contact with a wall. While there are retardants for gypsum plaster, I'm told they also reduce its strength.

I'd also spray down the wall with clean water first before troweling to reduce suction too.

Posted by Howard (not verified) on

Through a lot of web browsing I discovered the idea of thinning down the drywall mud and applying it with a roller. More searching later I came upon the Magic Trowell. It's sold at Sherwin-Williams, just none of the employees knew that. A trowell called Magic Trowell, they really did laugh. I also thinned the mud a bit more. After about 15 minutes of getting the hang of applying, quickly smoothing but getting chatters because of the quickness of the drying, a light bulb went on. I went down to my shop and got a pump up sprayer that I use to apply wall paper remover, filled it with water and after smoothing with the Magic Trowell, misted it completely and ran the Magic Trowell over it once more. Wow, perfect. And so easy.

Posted by Steve on

My only criticism is that joint compound isn't the most durable of finishes. I skimcoated my entryway six years ago and I'm just now getting around to painting it. I have a coat rack on that wall where I hang the dogs' leashes. There are hundreds of little dents where the steel clasp had knocked against the wall. Hopefully, a few more coats of paint over that primer will stiffen it up.

I just tried out the magic trowel, and it absolutely rocks. I used it on old pitted plaster walls that I had stripped of wall paper. I cleaned the surface really well with soap and water (I didn't bother to prime the walls like the directions say). It still looks great. I too had to add more water to the joint compound than the directions said. I can't wait to recommend this tool to anyone and everyone! : ) Our web blog for renovating our house: http://pleasantstreetrestoration.blogspot.com/
Thanks for posting this info. : )

Posted by Anonymous (not verified) on

Nice overview and instrcution! Plastering is not a skill I have but I can do a decent job with drywall so this looks like the best approach. Older (100 yr+) home in need of work.

Posted by Anonymous (not verified) on

Thanks for this info. Using your ideas and tips I used the Magic Trowel tool on the walls and ceiling during remodel a bathroom. It was relatively easy and I am very happy with results!

Posted by Chris (not verified) on

On MT's page they say a bunch of times: "Remember to wet your magic trowel before using" Is this just once per session, every time you start going over a new line, or not at all? Or does it depend on how thin your material (joint compound, paster, etc) is? Thanks!

Posted by Steve on

If you're using plaster I'd probably wet a dry blade so there's no chance of drying plaster gouging the bed.