In This Issue of The Acid Staining Newsletter

I have recently received three inquiries which run something like this one:

We just bought a house with a bare concrete floor…except the fellow before us painted it a flat gray color and it is wearing off in spots. Would this have to be removed to stain the floor?

The simple answer is, “You betcha!” With acid staining, you are trying to get stain to penetrate the pores of the original concrete slab so that a chemical reaction can take place between the metallic salts in the stain and the lime in the concrete. The very top surface of the concrete itself will be colored permanently in this process.

This is not a matter of laying a coating of new color on top of whatever is on the floor now. The acid stains are translucent (think of wood stains) and this is what gives them their depth and interest. Just as the natural grain patterns of hardwood glow through the oily wood stains which are rubbed into them, so it is with the natural curing patterns, rain spots and tiny cracks in your concrete slab. There are all kinds of random imperfections in a concrete slab which will glow through your stain application and help to give the effect of a natural stone floor – IF you can get every speck of paint off the floor first.

It is unfortunate, but blobs of carpet pad glue, old tar, and light paint do not make marks which blend in well with acid stains or look the least bit natural. If you leave any of these behind, your work will look as though you took shortcuts.

You have two possibilities for paint removal: mechanical (abrasive) removal and chemical stripping. They each have advantages and disadvantages which you will need to weigh.

The quickest way to remove coatings, especially if they are multiple, is to hire a shotblaster to come into your home with his walk-behind machine and remove everything on the floor, including the “cream” (the smoothest part of the concrete) at the top of the slab. He pushes a machine about the size of a lawn mower which pelts the floor with round steel b-bs. When he is through, he passes a large magnet over the floor which picks up the steel shot so he can use it again. Shotblasting will create an overall pitted texture, but if it is fairly even it does not matter much to the finished look of the stained floor. You will never get a polished-marble look on such a surface, but you can get a warm, sandy look which is more earthy than formal.

Very often a shot blaster will leave “corn rows” behind where the machine overlaps itself (just like a lawn mower), so you would be wise to lay plastic or rags down into the wet stain to distract the eye from these linear patterns.  The shotblast machine cannot usually get right up against the walls, so those areas may have to be ground down by hand with a rotary grinding wheel which leaves a different sort of pattern. If you can find a shotblaster who is patient enough, his crew can pass the same grinder over the central areas of the floor, so that the swirl patterns are somewhat unified across the floor.

What if you are a do-it-yourselfer who has more time than money? In this case paint removing chemicals might be the way you would want to go. You will have to do some test areas with various materials to determine the easiest way to remove the type of paint which is on your floor. If it was painted with cheap latex paint, you are in luck.  A 40-minute soak with a strong solution of Tri Sodium Phosphate crystals (found in boxes at most paint stores) followed by vigorous scrubbing with a rotary floor buffer fitted with a black abrasive pad might be all that is needed. If some spots remain on the floor, you could use TSP in another soak, or let the floor dry and rent a heavy sander. We have sometimes increased the abrasion of our black scrub pad by throwing a handful of sandbox sand under it during the scrubbing phase. It thickens the TSP solution into slurry, and works quite well.

Oil-based paints and urethanes are what are most commonly sold as “concrete floor paint.”  If the word “enamel” is on the label, the paint is most likely an oil-based product. Even though paint thinner or turpentine is the solvent for new oil paint, it does not work to strip dried enamel paints. You could go to a heavy-duty solvent-based paint stripper (used in furniture stripping) like methylene chloride, but this is extremely toxic and would require great caution in its use. In states with strict air quality laws, you might not be able to purchase the many gallons you would need to strip an entire floor, in any case.

Fortunately, Franmar Chemical makes Soy Gel, which is purported to remove difficult layers of paint.  It costs about $115 for 2.5 gallons and can be ordered from their website at www.franmar.com.  I have not yet tried this product, but their Bean-e-Doo mastic remover, is non-toxic, non-odiferous and works like a champ. I have some Soy Gel on order and have high hopes for it.  

In a web forum I just read about yet another method of paint removal. A sticky-backed paper is adhered to the surface, left for awhile to bond, and then peeled up, carrying with it the paint you wish to remove. The forum writer recommended Dumond Chemicals, Inc.  A check of their website, www.dumondchemicals.com, showed a long list of “pull-away” papers for various types of paint.  If anyone reading this newsletter has had experience with this type of product, please e-mail me at gaye@fauxrealfloors.com.  Just off hand, I would think that this form of removal would only work if there were a fairly weak penetration of the slab by the first paint layer and the upper layers of paint were very well bonded to each other!  Dumond also sells a type of poultice remover. You spray the paint remover on the floor, press a porous fabric into it, let it set, and then peel everything off.

A proper job of chemical paint removal will not be cheap in either time or materials, but it will leave the smooth surface of your slab intact. Be sure to scrub the slab with a TSP solution prior to staining. Very often the product you use to do the stripping will act as a resist to the stain, itself, and must be removed with a strong detergent or base such as TSP. 

If your floor coating is fairly new and appears to be adhering well, a decision to strip and stain the floor should not be taken lightly. It will not be a week-end task, but a job of several weeks. You will be taking a leap of faith and will need to desire stained floors with an intensity bordering on religious fervor, in order to see the whole process through to the end.