Wood Finishing Question?

[Kevin Gerstenecker]

A budding Woodworker friend of mine asked me a question today, and I have no idea the answer. Here is the dilemma: He has completed a project, and stained it using Minwax Red Mahogany Stain. He want's to use Minwax Polycrylic for a durable, protective finish. (The item is a table). Anyway, the instructions on the Polycrylic say that it is not recommended for use over Red Mahogany Stain. I remember seeing this on the can, and we were wondering what the difference is with the Red Mahogany Stain? I have used Polycrylic over Minwax Red Oak and Dark Walnut Stain before, and the results were excellent. Personally, I don't see much difference it the 3 Stains. For Grins, we stained some scrap, and let it dry for 24 hours, and then put a coat of Polycrylic on it. I haven't seen it, but he says it dried well, and it looks OK to him. Any ideas on the restriction for Polycrylic for this one particular Stain Color? I can't think of any thing, other that it may be an issue with the pigment used for Red Mahogany Stain? Just curious what anyone else thinks. Thanks in advance for any ideas or insight. :)

[Todd Burch]

I don't know exactly what it is that warrants the disclaimer, but I have some other professional finishing products that also have similar disclaimers over their very heavily pigmented stains.

I suspect part of it is amount of pigment in suspension, and the solvents in the polycrilic wanting to "pick up the pigment" by redisolving the stain. I had this issue with brushing Pratt & Lambert #38 satin varnish over Minwax #225 Red Mahogany. First coat was a bear to brush, as the pigment kept moving around. My varnish brush actually was stained red and I REALLY had to watch for lap marks and tip off quite a bit. Also, curing was an issue. The first coat too several days to lose its tackiness. I finally got tired of waiting and applied the second coat of varnish, and it hardened up just fine overnight.

I bet if you call Minwax tech support they would tell you exactly why.

Todd.

[Kevin Gerstenecker]

Thanks Todd. I think you are on the right track with the Pigmentation issue. I checked out the sample we applied the Polycrylic to this evening, and the Poly. completely wiped out the Red Tint the stain had. The test piece looks fine, it now looks like a Walnut Stain.........compared to the stained, Un Poly'd work, it looks like 2 different stains! Wildest thing I ever saw. The Polycrylic was applied to the test piece using a foam brush, and the brush ended up clean.........no pigment was evident, but the Red sure is gone now! I guess we will have to go with an Oil Based Poly, unless I can talk him into an Oil Finish. Oh well, at least we both learned something..............the label really does mean what it says about using this product with Red Mahogany.

[Bob Lasley]

Kevin,

Tell your buddy to put a coat of shellac over the stain and then he can use the WB poly without problems. The other solution is to just use oil base poly for all the top coats.

Bob

[Eric Apple - Central IN]

Seems like I heard this has to do with the type of pigment rathen then the amount. I think the red might be iron based (a type of iron oxide maybe ?) and cause a possible problem with the WB top coat.

[Jason Roehl]

Seems like I heard this has to do with the type of pigment rathen then the amount. I think the red might be iron based (a type of iron oxide maybe ?) and cause a possible problem with the WB top coat.

From what Kevin said about the color change to brown, you may be on to something there, Eric....

[Howard Acheson]

Todd has the answer. Minwax's cherry stain if very heavy in pigments. Pigments are not absorbed into the wood, rather they sit on the surface. The solvents in polyacrylic will partially dissolve the small amount of binder holding the pigments on to the wood. As you then brush back and forth you muddy up the stain leaving a blotchy and uneven appearence when it dries.

What many will do is spray on a coat of shellac or lacquer. This will "fix' the pigment and allow subsequent coats to be brushed on.

In most cases I have seen, brushing on shellac will be problematic. The alcohol can dissolve the binder also. However, you can sometimes get away with just flowing on a coat of shellac with a single brush stroke. It's the back and forth that causes most of the problem.

[Kevin Gerstenecker]

I have to respectfully disagree with the Cherry Stain being a problem with Polycrylic. I have stained many of the Slot Car Boxes I build using Minwax Cherry Stain, and have top coated all of them using Polycrylic. It has worked very well, with no blotching or streaking. I am staining Red Oak Ply, and it really takes the Cherry Stain well. I have also used the Polycrylic over Minwax Red Oak, and Walnut Stain with no problems. I think it is whatever is used to add the red pigmentation to the Red Mahogany that is affected by the water based Poly. Eric's theory about the Iron Oxide make perfect sense to me. Oh well, we both learned something before it was too late. Thanks for all the advice and comments, we appreciate it! :)