I'm staining cherry to use as door and window casings, and blotchiness is an
on and off problem. I understand that cherry is inherently problematic with
uneven staining. I'm using a liberal coat of Minwax wood conditioner, and
about a half hour following up with the first coat of a light shade of
stain. The first 2 boards turned out fine, the third is unusable (Extremely
blotchy). I tried again, with only one board turning out well. Is there a
better way to condition cherry prior to staining. I read an article in the
current American Woodworker about cherry, and they pretty much advocate
using a couple coats of a gel topcoat from General finishes, followed by a
coat or two of gel stain. Before I start going through a lot of cherry
trying to fine tune the finishing process (and yes, I tried it on a piece of
scrap first, which looked fine), any ideas out there on sealing the cherry?
Maybe a wash coat of shellac cut with alcohol? Ideas??? Many thanks to
anyone able to help, Mark
I hope the following blather is of use.
P D Q
How to Prevent Blotching Using a Washcoat
What is a Washcoat?
A washcoat is a coat of thinned finish that's applied to bare wood to partially seal the surface before a stain is applied. It keeps the stain from soaking into the wood and causing blotching. It works well on woods like alder, aspen, birch, cherry, and pine. The washcoat is usually made with shellac, vinyl sealer, or glu-size; but you can use other finishes as long as the stain does not dissolve it. To avoid problems, don't use an alcohol reduced dye with a shellac washcoat; a solvent based stain (e.g., lacquer stain) with vinyl sealer (oil-based stain is okay); or a water-soluble dye or stain with glu-size.
Thickness of the Washcoat
Depending on the effect you want and the type of wood and stain you're using, you will want to vary the thickness of the washcoat by controlling the solids content. Using shellac as an example, the approximate solids content (by volume, not weight) of a 2 lb. (2#) cut is 16%, a 1# cut is 10%, and a 1/2# cut is 5%. The lower the cut, the thinner each coat of shellac will be. The thinner the washcoat is, the less it fills the grain and pores of the wood which allows the stain to accentuate these features better. On wood with fine grain and pores, limiting the thickness of the washcoat is very important to the final look.
Some woods are more porous than others and some stains are more likely to cause blotching. By managing the solids content of the washcoat, you can account for and control these variables. Thick oil-base stains (e.g., gel stains) and glazes don't soak into the wood and penetrate very much so a thin (low solids) washcoat works well with them. Thin, penetrating stains soak into the wood deeper and the washcoat needs a higher solids content to keep them from blotching. But small variations in the solids content can make a significant difference in the appearance of the stain. If it's a little too thick, the blotching is gone, but the grain and pores aren't accentuated very well and the stain doesn't add much color (which may be the look you want!). To get the desired look, and be able to repeat it consistently, we have to intentionally control the exact solids content of the washcoat.
Calculating & Adjusting the Solids Content
To make a washcoat, start by finding out the solids content, by volume, of the finish you're using for the washcoat. The manufacturer of the finish can provide this information. Don't use the "solids content by weight" number that the manufacturer supplies, you need the "solids by volume" number.
To be effective, the solids content of a washcoat will generally range between 3% and 10%. To get good grain and figure definition while using a washcoat with a thick oil-base stain, the solids should be around 5%. To change our 20% solids finish to a 5% solids finish, we need to add the right amount of the proper thinner. For shellac, the thinner is alcohol; for vinyl sealer the thinner is lacquer thinner; and water is used with glu-size.
Applying the Washcoat
Pad, brush, or spray a regular wet coat of the thinned finish on the bare wood (after sanding), let it dry, then sand very lightly with a very fine grit (e.g., 220, 320, or 400)to smooth the surface. Excessive sanding will remove too much of the washcoat and allow the dye or stain to soak in and cause blotching. Your application technique will affect how much material you deposit on the surface; for example, spraying will lay down more than padding. Adjust the solids content to work with your application technique.
Preventing Blotching on End Grain (including raised panel doors)
End grain on table tops, dressers, cabinets, raised panel doors, etc. can absorb a lot more stain than the rest of the wood. That's because the end grain exposes the channels that the water that fed the wood used to flow through. To keep the end grain from getting EXTRA dark, just use a washcoat on it.
Start by sanding the end grain up to 220 grit. This will make it smoother and help limit how much it absorbs.
You can apply the washcoat just to the end grain if that's the only area that you need to control stain penetration. Don't worry if the washcoat gets on the flat surface of the wood when you apply it to the end grain... just let it dry and then sand the flat surfaces using a sander or sanding block to remove the sealer. Sand the washcoat very lightly with very fine grit paper or a sanding sponge, just enough to smooth it, and then stain the entire surface all at once.
As always, do a LARGE sample of your finish from start to end before starting on your actual piece(s). Small samples can look deceivingly good, but on a larger surface it's a disaster! Use the bottom of a table top, shelves, or the back of doors if you don't have sufficient scrap to work with. In the sample above showing the 2 washcoats, I used the back of a door and then sanded it off before I applied the final finish. Make sure everything works the way you expected and looks the way you want it to. If you're getting blotching, increase the solids content a couple percentage points at a time until it goes away.
How to Pop the Curl in Cherry
A fail-safe finishing method, when you want some blotchiness to accentuate the grain
Begin by sanding only to P150.
Seal endgrain areas with a thin washcoat of shellac.
Then flood the wood with oil.
Let it cure for a week, then brush or spray on several coats of lacquer.
Once the lacquer is fully cured, rub out the finish using very fine wet-or-dry sandpaper followed by polishing compounds.
Don't look for those products at a hardware store or home center, though. You're much more likely to find them at an auto-supply store.
....A washcoat is a coat of thinned finish that's applied to bare wood to
partially seal the surface before a stain is applied......
I use a washcoat of shellac prior to *clear* finishing of cherry. Here's the
rub.. if I just applied it like any other layer of clear finish I would get
blotchiness. What works for me is to use a very thinned batch (1/2 cut) and
wipe (rag) on as little as possible. A brush would lay down way too much
material. The idea is to *not* give it enough liquid to soak in. Soaking in
= more in some areas (more porous) than others = blotchy. After dry, wipe
lightly with fine sandpaper to knock off any dusticles; repeat.
FWW had an article on mitigating cherry blotchiness recently. They had a
couple other suggestions: Sanding to a 600 grit, and wiping with DNA or MS
prior to finishing to at least identify problem boards.
IME, experience this exactly what the OP does *not* want to do. Curl has
grain going in an out of the surface. The wood fibers which are not parallel
to the wood surface will soak up more oil and look darker. This can be a
great look when you want to accentuate the curl. Not so good (blotchy), when
you have subtle, irregular density changes and meandering grain reversal.
YMMV, but at the end of the day there is only one finishing absolute:
Test on scrap (or the back side of your trim)...
There's an article on exactly this topic in the current Popular
Woodworking. Basically, there's no easy answer. Cherry blotches. Not
all boards blotch the same way, sometimes it looks good, sometimes not.
You can use a washcoat of shellac or a conditioner to reduce the
blotching, but that also makes any stain less effective.
Blotching tends to reduce itself over time...the lighter areas darken
with exposure to light.
On Sun, 25 Jan 2009 20:30:58 -0600, Chris Friesen wrote:
I'm coming in late on this topic, so I apologize if someone else has
already covered what I'm going to suggest.
My favorite method of avoiding blotching is to apply 2 or 3 thin coats of
dewaxed shellac with a pad and then add an alcohol based dye to the next
coat or two of shellac. No pigment particles, therefore no blotching
from that source. And the dye never touches the wood, so no blotching
And since I've used dewaxed shellac, I can then, if I want, topcoat with
varnish or poly with no problem.
This is probably 'way out, but:
has anyone ever tried to darken cherry by heating it? Heres my
When I turn a cherry bowl, the wood seems to darken up as I am hand
sanding with the finer grits. The more heat I feel on my fingers, the
more pronounced it seems to be.
So, what might happen if one used a high speed buffing pad on the
boards pressing hard enough to heat and darken them? Might this blend
the "whatever it is that makes the cherry blotchy" spots?
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