Preventing Blotching?

[Paul Zonneveld]

I have a couple of projects nearing the finishing stage and I need some advice on how to deal with the Birch ply used in the pieces. In the past when finishing or staining the plywood it would blotch badly and I need to know how to avoid this. I know there are some pre-stain conditioners out there, but I usually use a gel stain to match the plywoods up with the hardwood combinations in projects. Anyone got advice on what to use here. I have the ability to spray finishes if that helps.

[glenn bradley]

I use Zinsser's Seal Coat (dewaxed shellac) for that purpose. I find that on lighter woods (which is usually where I need to stop blotching) I thin is a bit with DNA.

[Paul Zonneveld]

Appreciate the response Glenn.

To all again would I get the same level of blotchiness if I used a gel pigment instead of a stain. With the pigment sitting on the plywood surface I was wondering if the same level of blotch would be seen.

[Randy Denby]

Paul.....I want to piggyback here, if its ok. I too am nearing completion of a soft maple bar unit and I am going to spray Transtint Dark Mission Brown dye.Should I use a sealer as well?
Thanks,
Randy

[Steve Schoene]

Gel stain tends to blotch less than oil based pigment stains. And, dyes tend not to show blotching very much.

Pre-stain conditioners, including shellac wash coats, tend to make the potential color from the stain a lot lighter. If that's too light, then start with a dye to get the basic shade right, and then use a conditioner followed with the pigment stain to add depth.

It's important to make tests on scraps of the same wood before starting, and those tests should go through all the steps. Dyes, in particular, look very different when they dry compared to what they will look like when a top coat is applied.

[Joe Chritz]

It's important to make tests on scraps of the same wood before starting, and those tests should go through all the steps. Dyes, in particular, look very different when they dry compared to what they will look like when a top coat is applied.

That is the most important thing right there.

If you have spray gear, spray on a sealcoat, I thin mine to 1.5# cut, then stain. Dyes will also avoid the blotch problem some.

It adds a very small amount of work for a lot of reward.

Joe

[Jack Young]

For whatever it's worth, there is a book, sold round and about in the such as Woodcraft on Guitar finishing, in which there are a few pages of color charts, with ratios and combinations of primary and secondary colors (with each other in combination as well as ratios of dye to carrier) to get nearly any shade one might desire. It is the only thing of its kind I have seen or heard of. It is particularly useful in getting close to some shade or tone with either oil or water soluble dyes.

I have become a firm believer in watersoluble dyes. Blotchiness is nearly removed entirely and uniformity of intensity is much easier to achieve. It is surely more trouble, but, to me, ultimately worth it. Most ply has sufficient thickness in the face veneer to allow a bit of sanding at 220 or 180 grit after spraying a tad of water to raise the grain. Watersoluble dye will not significantly raise the grain again. Then glazes (wipe-on/off types) can be added after the first finish coat to tweak the color as you wish, and blotchiness will not be an issue unless you don't wipe uniformly. It has worked well for me on pine, birch and maple, as well as more exotic hardwoods.

That's my two cents worth. Hope it has some relevance for you.

Jack

[Paul Zonneveld]

Steve correct me if I am wrong, but I thought that pigment stains gel or not, due to containing a pigment vs. a dye stayed on top of the wood and did not pentrate it. I thought pigments work by filling in the tiny voids in the wood. Dyes actaully penetrate the wood and hence can blotch more?

[Steve Schoene]

What happens, as I understand it, is that pigmented stain penetrates more porous areas (where grain swirls to the surface, for example) more heavily, hence darkening them more relative to hard dense areas where it penetrates much less due to its pigment size. Gel stain does more to keep the pigment from penetrating the more porous areas and reduces blotching in that way.

But dye has very very small, molecular size coloring, and can penetrate dense and porous alike, reducing blotching compared to the oil based pigment.

[Larry Fox]

Paul.....I want to piggyback here, if its ok. I too am nearing completion of a soft maple bar unit and I am going to spray Transtint Dark Mission Brown dye.Should I use a sealer as well?
Thanks,
Randy

Randy, I just completed a project in soft-maple where I sprayed a dye stain on. I did some tests with and without a wash coat and decided to go without one. The washcoat I tried was a 1# cut of dewaxed shellac sprayed on. Given that I (we) are spraying it I think that blotching and uneven application are less of an issue than if wiping it. Spray light coats and sneak up on the color you want. The only place that I was not 100% satisfied with the results was on end-grain involving an edge treatment (like a roundover). There I noticed some uneven absorbtion that showed up like a dark line. For these areas I think a washcoat might be in order. Fortunately my project involved very little exposed end-grain.

Another thing a washcoat will do for you is that you won't need to pre-raise the grain if you are spraying dye suspended in water.