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Deft Finish on African Mahogany

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Blog entry by hokieman posted 2327 days ago 3592 reads 1 time favorited 6 comments Add to Favorites Watch

I had something very strange happen on a pair of end tables I am finishing up. They are african mahogany with a lot of inlay. Due to the inlay, I did not fill the grain for fear of messing up the inlay. The first three coats of deft went on fine on both tables with no problems but on the fourth coat, some severe bubbles formed on the areas with the most open grain. AND it happened ONLY on one table top. The other is smooth after the fourth coat. Does anyone have any idea what could have caused this? I am stumped.



6 comments so far

View Scott Bryan's profile

Scott Bryan

27251 posts in 2405 days


#1 posted 2327 days ago

I am not sure what is going on here but one problem with open grained woods (and why they need to be filled) is that air trapped within the grain can come out and become trapped in the curing finish. Although I would have expected this to happen early in the finishing process rather than at the end. But this is a possibility. Letting the finish cure followed by light sanding and another coat should take care of it.

-- Challenges are what make life interesting; overcoming them is what makes life meaningful- Joshua Marine

View GaryK's profile

GaryK

10262 posts in 2571 days


#2 posted 2327 days ago

I have had that happen before. I think I didn’t wait long enough between coats. Not sure though.
I was using oil poly.

-- Gary - Never pass up the opportunity to make a mistake look like you planned it that way - Tyler, TX

View Todd A. Clippinger's profile

Todd A. Clippinger

8705 posts in 2683 days


#3 posted 2327 days ago

I finished my mahogany sofa table without filling the pores. It is not absolutely necessary to fill the pores.

Mahogany Sofa Table

I have had the bubbles occur before and I have found that it is caused by a couple of things.

#1. If the finish is put on too thick it will skin over on the surface and trap air underneath in the deep pores. I spray my finish now, brushing a finish on inherently applies it thicker than spraying.

#2. If you apply the finish and set it in the sun to aid the drying process it will do the same thing with a solvent or waterbase finish. The finish surface skins over, the board warms up and the air tries to get out.

These are the things that I have experienced personally. The solution is to put the finish on thinner and let it dry without trying to force it with solar gain, a fan, or setting it close to a heat source like a wood stove. Yep, I have done all of these.

Fortunately they can be removed with sanding and more coats of finish.

I like the look of the open pores depending on the style of the piece, but you do take a bigger risk of air bubbles.

-- Todd A. Clippinger, Montana, http://americancraftsmanworkshop.com

View Karson's profile

Karson

34841 posts in 2984 days


#4 posted 2327 days ago

Interesting problem. I’ve never have had the problem, but as todd says. I guess it’s not a proble,. Just sand and add another coat.

-- I've been blessed with a father who liked to tinker in wood, and a wife who lets me tinker in wood. Southern Delaware karson_morrison@bigfoot.com †

View Greg3G's profile

Greg3G

815 posts in 2668 days


#5 posted 2326 days ago

I have this same problem with oak sometimes. I think my problem came with tempature changes. I put the finish (it has happened with stain as well) when the shop is cool (in the 60’s). During the course of the day, the shop warms and the air and or excess stain traped in the heavey grain expands and comes to the surface. The staining causes more headaches than the air bubbles. For the air bubbles, I just lightly sand down and apply another coat. Removing the stain takes more care, I have to be very careful not to make the color uneven cleaning it up.

I don’t spray too often (mainly because my old gun was a peice of junk) so I thin down my finish and apply mulitple coats. this helps reduce the air bubbles. It does take a couple of extra coats but since it drys a lot quicker, time wise it doesn’t take much more time.

-- Greg - Charles Town, WV

View tomd's profile

tomd

1716 posts in 2353 days


#6 posted 2326 days ago

I agree with Gary. I have had the same problem before and I found it to be spraying too soon over the last coat.

-- Tom D

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