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There
are several methods of applying and completing an acid
stain project, and this is by no means the only way to
complete the task. This is the method I prefer and use
for most applications.
How
Acid Staining Concrete Works
Concrete
acid stain is water based liquid bearing minerals and acid.
The acid mixes with the cement to force a chemical reaction,
which changes the color of the cement similar to a forced
rusting. When highlighted with the proper sealer, this effect
gives the natural rock glow that attracts so many people
to acid stained concrete.
Surface
Preparation
Surface
preparation is one of the most important steps of the acid
staining process. The concrete must be free of debris, dirt
and oils. For old concrete, or exposed concrete, be sure
the surface of the concrete is intact, and aggregate is not
exposed. Acid stain will only work on the cement portion
of the concrete, and will not stain rocks and sand. Concrete
that has been acid etched or washed with muriatic acid CANNOT
be acid stained.
Often,
surfaces inside an existing house will have dry wall mud,
paint, wood stains, tile adhesives, carpet adhesives, grease,
pet stains, etc on the concrete. Acid stain is not an over
coat, it is an opaque re coloring of the concrete. These
spots will show through if not removed, especially mastic,
dry wall mud and paint, as these get into the pores of the
concrete and block the staining process. There are several
products available at a local hardware store such as adhesive
removers and lacquer thinners that can be used to clear these
products from the surface. A fine sanding pad on a floor
buffer can even the surface and re open the pores of a distressed
concrete in this circumstance. These types of distressed
floors will nearly always yield a varied character of finish
with a high degree of color difference area to area across
the surface, and the distressed sections lend character and
depth to your floor. Cleaning one of these floors to a stainable
level is a considerable amount of work, but it is not impossible.
If you desire a more even finish, you should consider an
overlay resurfacing, especially on a floor that has had glued
tile or glued plastic carpet.
Using
an organic degreaser (such as DCI Orange, Simple Green, etc)
at a medium concentration, scrub the surface thoroughly with
a nylon brush and rinse with clear water. For an interior
project where water run off is not available, you may use
a shop vacuum and mops or squeegees to contain the water
and aid in drying. As a final step, you may rinse the surface
with water and ammonia to fully neutralize the surface and
insure a balanced ph for staining. Be sure all soap and cleanser
residue is removed from concrete before staining and that
the surface is adequately dried.
Applying
the Stain
The
appearance of the finished product is very much influenced
by the manner in which the acid stain is applied. The stain
can be sprayed, mopped, brushed, rubbed, etc. I prefer to
spray the stain on using an all plastic pump sprayer, and
brush with an acid brush in even circular strokes. When the
residue dries, spray a second coat on top of the residue
to eliminate any brush strokes in the stain, unless the strokes
are desired in the finish. Brushed acid stain applies darker
and more evenly. For a more diffuse look, you may wish to
spray the stain onto the surface without brushing. Every
slab of concrete is different, and acid staining is an artistic
process, so when available, do small test patches on the
surface in corners or where furniture will be to find the
look you like the best.
 
Acid
stain can be cut with water to lower the ratio of minerals,
thus making the color lighter in shade. The best option is
to test patch the concrete using straight stain and stain
cut two or three parts water to one part stain. If the water
content is too high, the acid won't facilitate the chemical
reaction required to make the color. This can be corrected
by raising the acid content or using stain extender. Some
colors vary more by adding water content and many factors
determine how dark the stain will take such as age of concrete,
cement content and weathering. This is another reason to
do as many pre stain tests as the job site will allow.
As
the acid stain dries and processes, a residue of alkali and
minerals will form on the surface of the concrete. This is
natural and part of the reaction. Different stains need different
times to activate and fully color the concrete, generally
from one to eight hours. Be sure and check your stains activation
time before starting the job to insure full coloring of the
surface. If you are going for the most color from a given
stain, spray another coat of stain over the dried residue.
Do not walk on wet residue. When the residue is wet, before
it has been neutralized, the stain is active and can retain
impressions of your feet or other marks from your feet or
tools.
Removing
the Residue
When
the residue has dried and the stain has been given the proper
time to process, the residue should be neutralized and all
acidic properties removed. Properly removing the residue
is important for obtaining the best possible acid stain appearance.
Here are the steps I've found to be most effective in removing
the residue and preparing the floor for sealing.
1)
Prepare a base solution using either baking soda or sodium
bicarbonate at about half a cup of soda per gallon of water.
Pour this on the residue, scrubbing with a mop handled nylon
scrub brush and shop vacuum the residue while it is wet.
2)
Repeat the process, using straight water. After this step,
all but a light residue should have been removed. Let the
floor dry and some lighter coloring may still be visible
indicating residue.
3)
Apply a clean, damp mop to the surface, wiping away any remaining
trace of residue. The floor should now be ready to seal.
Sealing
the Surface
"This
is for Direct Colors ac 1315 sealer"
After
the floor has dried from the residue removal, the acid stain
must be sealed with a proper decorative sealer. The sealer
may be brushed, sprayed or rolled on. I prefer spraying for
most non textured applications, but I've included three different
methods here for the DCI 1315 sealer.
To
spray the sealer on, use a good all season deck sealant pump
sprayer. These usually come with three different nozzles.
For spraying the sealer straight, use a medium sized nozzle
and thoroughly coat the surface. DCI 1315 sealer dries very
smooth and flat to the surface, so the most important aspect
is complete coverage. A thick coating of sealer can sometimes
take 48 hours to cure enough for foot traffic, depending
on humidity, etc. You can decrease the thickness of the application
and the drying time by adding no more than 25% xylene to
the sealer in the sprayer. This product can be obtained at
most paint stores in gallon cans.
To
brush the sealer on, use a good quality brush so the bristles
do not fall loose on the surface as you apply. This is recommended
for very rough surfaces or touch up work. In a sprayed or
rolled surface you can come across areas of a floor that
are more porous and absorb sealer, causing an uneven finish.
You can touch these areas up, feathering the brush strokes
without brush marks, as the sealer cures to the concrete.
Rolling
is a popular method for applying the sealer. Be sure to use
a very short napped roller with no texture, as the texture
of the roller can impress into the sealer. It is much harder
to get an even, thick coating of sealer with a roller and
is the method most likely to have unpredictable finish results.
If applied carefully, this is the easiest of the methods.
You
may also use an oil or water based wax applicator depending
on the type of sealer you are using for perhaps the smoothest,
easiest method of applying the finish. This is the method
I most recommend for home owners or DIY ers. Applying the
sealer in two or three even, thin coats with this method
is very, very reliable for achieving a high quality trouble
free application.
To
maintain the gloss of the surface, a good mop on acrylic
wax is a good idea for any acrylic sealed surface, especially
surfaces with high stress from pets or children, etc. These
products are water based and even out the finish after a
fresh seal or revitalize the look of a scratched surface.
They can also be buffed for a deeper glow. This is, in my
opinion, the best look for a medium gloss finished floor,
and the look you see most often in commercial applications.
Thank
you for your time and enjoy your new concrete!
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Direct
Colors - "How to Acid Stain" Volume
1
