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Update: What is this blotched look?

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Forum topic by gko posted 1220 days ago 674 views 0 times favorited 4 replies Add to Favorites Watch
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gko

77 posts in 1829 days


1220 days ago

I ran into a problem and hope someone can help me with this. I stripped a conference table using stripper and then lightly sanded the surface. I noticed a strange blotchy look. I thought maybe it wouldn’t show if I stained it but it was obvious the blotch was there. Stripped it again and sanded but it still remains.

-- Wood Menehune, Honolulu


4 replies so far

View Sawkerf's profile

Sawkerf

1730 posts in 1653 days


#1 posted 1220 days ago

Blotching happens because wood isn’t uniformly porous and stain goes deeper into the more porous areas.

When you’re using a wiping stain, wiping it removes more of the pigments from the high density areas leaving them lighter than the less porous areas where the pigments have gone deeper into the wood.

When you strip old stain/finish, the stripper doesn’t get deep enough to remove all of the stain from the more porous areas and they’re darker than the less porous areas. Unless you can sand really deep, you’re probably stuck with this problem.

You can try bleaching your piece to lighten the darker areas, or use a conditioner which evens up the porosity and gives a more uniform stain color.

-- Adversity doesn't build character...................it reveals it.

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gko

77 posts in 1829 days


#2 posted 1220 days ago

I know this is not normal blotching because it was already like this before staining. This is also the second half of a large conference table and the other half didn’t do this. I have a feeling one of the strippers I used had ammonia which sometimes darkens wood but I read the label to see if it had ammonia and it didn’t say. When I got to this half I ran out of the stripper I normally use and the local Ace ran out of that stripper so I went to another store and bought a different brand. I stripped it several times and just when I barely got to bare wood I ran out of that one. At that point Ace had brought in the stripper and I finished it with the one I usually use.

So I think that is what happened. I thought I read this somewhere and after posting last night read through stripping section of Flexner’s book and it did say ammonia darkens some wood. I used the first stripper until most of the old varnish was gone but there were areas where there was islands of the old varnish. That’s when I bought my regular stripper which must have not darkened the wood.

Sorry didn’t think about it before posting. It was 1am and I just wanted to post it. Anybody have any ideas? The top is veneer and is pretty thin so I can’t sand it too much. Learned this when I sanded the first half. Bleaching? Never done it before and worried that it will all lighten but there will still be the blotched look. It might also not match the first half.

-- Wood Menehune, Honolulu

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gko

77 posts in 1829 days


#3 posted 1198 days ago

Ok, here’s an update in case it might be helpful to someone. I’m pretty sure it was the ammonia in one of the strippers I used. Here’s what happened. I stripped most of the finish with the stripper with ammonia but there were still some islands of finish left. Went and found my usual stripper that doesn’t contain ammonia and got rid of the last bits of finish. The islands were lighter in color because the ammonia hadn’t reached it. That’s when I wrote the above. I stained it thinking it wouldn’t show. It came through clearly. Very noticeable that most of the table was darker but there were islands of light spots. Stripped everything off. Tried sanding as much as I dared but the dark areas didn’t lighten. It’s a veneer so I can only sand a little. Stained again but it didn’t seem to make any difference.

Then I tried Oxylic Acid as suggested by Flexner. Made a solution as instructed. Wore chemical gloves and scrubbed it with a bristle brush. Washed it down with water three times. After it dried it looked the same, maybe a tiny bit lighter but a terrible disappointment. I thought well that was it I’m just going to finish it. So I stained it and lo and behold it was really even! I’m a bit confused about why the staining looked so even when it still looked messed up underneath but I’m a happy camper.

By the way, be careful with the acid. I wore gloves but after rinsing the acid off I took off the gloves to move the table not realizing some of the acid was still under the table. Fingers hurt for a week.

-- Wood Menehune, Honolulu

View peterrum's profile

peterrum

135 posts in 1263 days


#4 posted 1197 days ago

Good update, thanks for the info. Glad it all worked out for you.

-- Carpe Diem

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