Finish stripping is one of those “easy” things that’s a hardware store video favorite. But as I was reminded this last week — it’s not as easy as those store videos make it look. In fact, there’s a lot that’s simply not well known. So, though I originally wasn’t going to write about this little stair stripping job, it seemed a good opportunity for a do-it-yourself entry for the Tips and Tricks section on using chemical strippers.

Introduction & Safety

To Strip or To Sand — That Is The Question
Both have their advantages and disadvantages; both have their place.

Stripping: First, there’s nothing even remotely green and environmentally friendly about chemically stripping a coating. While there are lots of strippers out there, the only ones I’ve found to be worth their time and money are pretty noxious. Some (like the one I’m going to introduce you to below) are down right dangerous!

That said, stripping is sometimes the only viable option for a work piece. Strip sanding that venerable old table might be quick and safe and easy on the environment, but it will also rip the patina right off the table. That venerable old table will look like it just came out of the factory. That’s probably not the effect you want.

Also, sanding an antique will ruin its value as a collectible! (I don’t recommend antique refinishing as a do-it-yourself project. If your appraiser says it needs to be refinished, take it to a professional furniture refinisher.)

Finally, for detailed pieces, sanding the finish out of all the little nooks and crannies is virtually impossible.

Sanding: If the work piece is fairly simple (like our table) strip sanding is a fast and safe solution — assuming you don’t care about the patina. In fact, with a good strip sander, you’ll be done before you’re through cleaning up after your first coat of chemical stripper.

Sanding is really the only way to make a work piece “look like new.” As a furniture refinisher I had jobs where, because of the detail, I first had to chemically strip the work piece to get all the old finish out of the crevices, and then sand it down because the customer wanted “that new look.”

Sanding strips the old patina off of the wood and opens up the grain. If you look at a piece of wood that’s been sanded under a microscope you’ll see little fibers standing straight up, ready to receive and absorb the new finish.

A Few Words About Safety
Most strippers that are going to get the finish off for you with a minimum number of applications are pretty toxic. You’re going to want some safety gear:

• Chemical gloves. Most strippers use solvents that are readily absorbed by the skin, and you’re going to get some stripping solution on your hands. Count on it. You can either get the surgical style nitrite gloves (they’re the green ones) which are great for fine work, or the orange dish washing style gloves (just make sure they’re chemical safe). In the pictures below you’ll see I’m using the latter.
• Saftey glasses. Remember, no matter how “safe” or environmentally friendly the chemical you choose is, it still has to be strong enough to destroy the finish you’re stripping. It’ll do the same thing to your eyes!
• Good ventilation or a respirator. The VOCs in some of these strippers (including the one I’ll introduce you to below) are so potent that breathing them will make your lungs hurt, and make you sick in short order. If you can’t work outside, wear a respirator.

Speaking of respirators, those paper masks are worthless for this kind of thing. In fact, they’re worse than worthless because people use them for all kinds of things for which they were not designed.

Those paper “surgical masks” were originally designed to keep the water vapor of the surgeon’s breath inside the mask, not to protect the surgeon from the patient. On the job site they’re classed as “dust masks”, meaning they help protect you from saw dust and so on. But they’re not even designed to be used around fiberglass, never mind asbestos or paint vapor.

At right is a picture of my mask. It’s one of the models made by the Mine Safety Appliance Company (MSA). Obviously, since I need my mask to work in a lot of different environments, the filters on this mask are good for everything from toxic dusts (including asbestos) to chlorine and sulfur dioxide environments. You might not want something so complete, but you’ll at least want one that’s rated for paint vapors.

How do you know what your mask is rated for? Well first, it’s not the mask, it’s the filters on the mask. On my mask, the filters come off. I can put a lower rated filter on the mask if I want. In fact, I can put a filter on the mask that won’t protect me from the paint stripper VOCs. So if you borrow a mask, check the filters! Make sure they’re rated for the environment you’re going to be in.

In the picture at right you can see the label on the bottom of the filter. The bottom half is green and shows the filter part and lot number. The red top half says “GME-P100″, meaning the National Institute of Occupational Safety and Health (NIOSH) has approved the filter at the P100 level.

In general filters come with one of three different ratings:

P100: Particulate filter; 99.97% efficiency level effective against all particulate aerosols.
N95: Particulate filter; 95% efficiency level effective against all particulate aersolols free of oil; time use restrictions may apply.
R95: Particulate filter; 95% efficiency level effective against all particulate aerosols; time use restrictions may apply.

MethylamineFormaldehydeMercury vapor

AM	Ammonia
HS	Hydrogen sulfide
CD	Chlorine dioxide (escape)
CL	Chlorine
MA
FM
MV
HC	Hydrogen chloride
OV	Organic Vapor
HF	Hydrogen fluoride
SD	Sulfur dioxide

To help you remember the filter codes, “N” means No protection against oils, “R” means Resistant to oils, and “P” means Proof against oils. The number is the percentage of protection afforded by the filter. So an N100 would provide 99.97% (or better) protection against all particulate aerosols that are free of oil. In general, the “N” and “R” filters are designed to last one work shift (8 hours continuous or intermittent exposure) and then should be changed. The “P” filters should be changed when it becomes difficult (more difficult, actually) to breath.

Below the P100 rating on the filter label is a list of what the filter is effective against. My filter says: “P100/OV/CL/HC/SD/AM/MA/CD/HS (escape)/FN/HF”. Again it reiterates that it’s a P100 rated filter. Referring to the table above, we can see that my filter is rated for OV=Organic Vapor; CL=Chlorine; HC=Hydrogen chloride; SD=Sulfur dioxide; AM=Ammonia; MA=Methylamine; CD=Chlorine dioxide (escape), meaning the filter is only good for escaping from an environment poisoned by chlorine dioxide and cannot be used for working in that environment; HS=Hydrogen sulfide (escape), again only for emergency escape of the environment.

As a final note: Respirators are not military gas masks. They are not design for environments so toxic they’re immediately dangerous to life and health! NIOSH publishes regulatory data on maximum workplace concentrations for all the chemicals listed above (and more, actually). Those are the maximum concentration levels in which these types of respirators are designed to protect you. Exceeding that concentration level is not only stupid, it could cause you permanent lung damage or be fatal!

In practical terms that means: Open the doors and windows in the area you’re working.

The tools and Chemicals

The tools you’ll need for your job depend on the complexity of the work piece and the wood it was made out of. I’m simply stripping stair treads made of redwood, so I really don’t need a great plethora of tools for fine work. For this job I’ve chosen two different sized putty knives, a 5-in-1 tool, and steel wool (not shown). I’ve also got my cat’s paw handy because there are nails sticking out of the treads that I’ll need to pull as I go along. Rags are also essential. Don’t bother with reusables. Once contaminated with chemicals they have to be thrown away, so stick with the disposable paper type.

If you’re working on something more complex than flat stair treads you’ll also find dental tools handy for gently scraping finish out of grooves and other hard to reach places. (Available at Harbor Freight for a few dollars, amongst other places.) Tooth brushes and/or acid brushes are also helpful for detailed work.

There are lots of chemicals on the market to choose from. For this job I chose Greens. The blue can on the left is a “semi-paste”. Jellied chemical that not only sticks to vertical surfaces (which I don’t have), it also evaporates more slowly and so keeps air away from where the chemical contacts the paint for a longer period of time. The can on the right is the liquid form, which penetrates the wood better, and is also handy for cleaning tools. It also evaporates quickly, and so is not as useful for “heavy” stripping.

The downside to Greens is what also makes it so useful: It’s powerful and it’s dangerous! Greens chemicals have no antidote and no thinner. Which is why I spent so much time on safety. If you get it in your eyes, you’re going to lose an eye. If your skin is sensitive and starts to burn, it’s just going to burn (and turn red and all that stuff) until the chemical evaporates — which takes about 15 minutes.

So if you decide to use Greens, please use appropriate safety gear and be careful.

Stripping

The first step in stripping is to clean your work piece of dirt and loose debris. The second is to apply the first coat of chemical. At right you can see me applying the first coat of Greens semi-paste with a chip brush.

Put the chemical on fast and even. Going over and over the area with the brush only breaks the chemical bond between the stripper and the finish, preventing it from working. Quickly coat a workable sized area (one tread, in this case) and the leave it alone. Let the stripper do it’s thing.

It could take quite some time — as long as 30 to 45 minutes for some products — for your stripper to loosen the paint. You’ll know it’s done its thing when the finish is all crinkled up. On this job Greens cut through most of four coats of old paint in about five minutes. Whatever you do, don’t let the chemicals dry on the finish. This, in fact, is the best sign of a poorly designed product. It evaporates before it loosens the paint. That said, if you’ve got a known good product (like Greens) and it’s not doing a good job, recoating is appropriate. Use the same technique as the first time. Put it on evenly and quickly and let it sit.

Once the stripper has loosened the paint, scrape the bulk of it off with an appropriate tool. Since I’ve got a nice big, flat surface, I’m using a four inch putty knife to do the rough work. Clean the scraped up finish off your knife with your 5-in-1 tool. I usually line a paint roller tray with rags and scrape the goo off into it.

Use smaller tools to clean the spent chemicals and loosened finish out any crevices and detailed areas before proceeding. Don’t hurry and apply another coat of stripper before removing all of the first application. Not because you’ll hurt something, but because you’ll be wasting your time. The fresh chemicals won’t be able to reach the left over finish, and so will do virtually nothing.

Take your time. Clean up after your first application, then move on.

On this job I had to apply two coats of the semi-paste to get all the crusty old paint off. But because I did a good job of cleaning up the first application, the second coat cut through the remaining paint almost as fast as I put it on.

Now it’s time for the finishing touches.

I’m working redwood. Redwood is a very soft, porous wood — as are all the conifers (fir, pine, cedar, and so on). Believe it or not, it’s harder to strip a softwood than a hardwood. First, the stripping chemicals are so strong they soften the fibers of the wood. You can’t use detail tools like dental tools and hard bristled brushes on soft woods. You’ll simply cut into the wood without removing any finish. Second, the pigments from paints and stains penetrate the grain and wood fibers, “bleaching” them to the color of the pigment. Unless you sand away the bleached wood fibers, you’ll never get rid of them, no matter how many chemicals you use. (Actually, that’s not entirely true. For white woods you can literally “bleach” the wood back to something resembling its original color, but that’s a different article.)

After the second coat is scraped off I do even more detail work than I did after the first coat — including back scraping with my 5-in-1 to get all the gunk off the wood. Note the angle I’m holding the 5-in-1 at. The last thing I want to do is cut into the wood. Also, you can’t see it, but beveled edge of the tools is facing away from the pull — again to help prevent cutting into the soft wood.

Now I’m down to the wood itself. There’s almost no paint left sitting on the surface of the wood. So now we turn to the liquid. Pour it on, swish it around quickly with the chip brush and let it sit for a few minutes. Then it’s time to scrape it off. Notice in the picture how it’s really a mud. The Greens liquid is literally pulling the paint (the primer coat) from the wood fibers.

All that leaves is the stuff deeply ingrained in the grain and the fibers. More liquid Greens is applied and is worked in with the steel wool. I’m working softwood, so I have to be careful to go with the grain lest I scalp the wood. The picture at right shows what the tread looks like after I’ve thoroughly scrubbed it with the steel wool.

Once this last coat is worked in it’s wiped off with the rags almost immediately, pouring more Greens liquid over the surface to “lift” the gooey grime off the wood. Finally, I apply Greens directly to the rag and go over the wood to lift the film away. Then the work piece is left to dry.

The picture at left shows the finished stair tread (and my tools and rags). Note the “bleached” center of the tread where people have been stepping for a hundred years (that’s how old these stair treads are). Another characteristic of soft woods is that as they wear they “open their grain”, which just makes them wear faster.

On the other hand, the property owner wanted the antique look, and that’s certainly what this will be after a good quality oil finish is worked into this aged redwood. (If it was me I’d put tung oil on it, but I’m not the finisher on this job.)

Enjoy your stripping and refinishing projects! (And if you have any questions, don’t hesitate to write.)

Technorati Tags: paint stripping, finish removal, safety, respirators, chemical stripping

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This entry was posted on Sunday, March 23rd, 2008 at 5:33 pm and is filed under Projects, Tips & Tricks. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.