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Glue line showing through finish

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Forum topic by CWWoodworking posted 02-26-2020 02:11 AM 583 views 0 times favorited 18 replies Add to Favorites Watch
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CWWoodworking

659 posts in 850 days


02-26-2020 02:11 AM

I have a glue line that keeps showing through the finish. Precat lacquer.

Any tips or techniques? Tried burn in and that was a disaster. Was thinking of filling with CA glue?


18 replies so far

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bilyo

1030 posts in 1774 days


#1 posted 02-26-2020 03:41 AM

can you provide a photo?

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CWWoodworking

659 posts in 850 days


#2 posted 02-26-2020 03:49 AM

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Rich

5346 posts in 1260 days


#3 posted 02-26-2020 04:09 AM

Keep going with the lacquer and sanding until it levels out. It looks like it won’t take much. It also looks like you have a couple of other issues besides the glue line that are more of an issue.

If it keeps showing up, you can run a streak of lacquer down it with an artist’s brush. Build it proud of the surface and then use a denibber or cabinet scraper with no burr to level it. Then sand with 320 or 400 and give it one final coat.

Finally, as I look at the photo, it appears that you’ve build a good layer. It’s hard to tell from just a photo though. But if you have, you might be able to wet sand it level just as it is. Start with 400 and go until you get the sheen you want, probably around 1500, but that’s up to you. Again, without knowing the details and seeing it up close, I’m just tossing out ideas.

-- Half of what we read or hear about finishing is right. We just don’t know which half! — Bob Flexner

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LeeRoyMan

744 posts in 398 days


#4 posted 02-26-2020 05:18 AM

With pre-cat I don’t like to build too many coats because of the fear of the finish cracking later down the road. It’s not like nitrocellulose lacquer which you can spray as many coats as you want. Pre cat only burns in to itself during the first 3 or 4 hours or so, after that it’s a mechanical bond. (So I have read, I use SW Brand)

That being said, what I do with these is 1 of two things. Sometimes I will use a fine paint brush and try to fill the crack with 3 or 4 coats until it’s filled, sanding flush after each coat. But more times than not it still shows a slight blemish in the finish even though the crack is filled.

The other thing I will do is to spray the whole area of the crack/seam then sand the whole area down as much as possible as to not build extra coats in that area, being careful not to sand through the surrounding area that wasn’t sprayed.
Spray on, sand off. Usually 3 or 4 coats, sometimes less, just depends.

After the seam is filled, I sand the entire surface, to satisfaction, and then spray the final coat, maybe 2 coats depending on how much is already on the table.

I’m not good at explaining so YMMV, but I seem to be able to w

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Rich

5346 posts in 1260 days


#5 posted 02-26-2020 05:53 AM


With pre-cat I don t like to build too many coats because of the fear of the finish cracking later down the road. It s not like nitrocellulose lacquer which you can spray as many coats as you want. Pre cat only burns in to itself during the first 3 or 4 hours or so, after that it s a mechanical bond. (So I have read, I use SW Brand)

That being said, what I do with these is 1 of two things. Sometimes I will use a fine paint brush and try to fill the crack with 3 or 4 coats until it s filled, sanding flush after each coat. But more times than not it still shows a slight blemish in the finish even though the crack is filled.

- LeeRoyMan

I hadn’t thought about the cracking, or crazing, like you mentioned. I’m sure you’re right since SW mentions it with respect to temp changes. However, my understanding regarding pre-cat is that there is a re-coat window. You can keep building and it will burn in, as long as you don’t go past the point where it’s started to become reactive (versus evaporative).

We agree about the artist’s brush build up to fill it, but I find scraping it flush works better than sanding. Sanding affects the surrounding area, whereas a denibber or scraper simply flattens it. Generally after that, a light finish coat to even it out (or sometimes just some blush remover) is enough to smooth it out.

So, LeeRoy, what do you think about what you see in that photo? It looks thick to me, like it might be better to wet-sand it rather than trying to build it up.

-- Half of what we read or hear about finishing is right. We just don’t know which half! — Bob Flexner

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CWWoodworking

659 posts in 850 days


#6 posted 02-26-2020 12:51 PM

Rich your right it is getting thick. I need to get this right with next coat. Not to mention it’s holding up delivery.

Have anyone tried the CA glue?

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OSU55

2596 posts in 2661 days


#7 posted 02-26-2020 01:36 PM

CA will be harder than the new precat making leveling more difficult and will leave a line. I agree with Rich and LeeRoy – fill with precat. Appears to be pretty thick. I would drop fill the 2 dents and the hole, scrape down, then wet sand the whole area with the glue line. You could lay a drop line out of the gun on the glue line and scrape it down. Sand the whole top down a bit to keep from getting too thick, then a finish coat over the whole thing.

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DS

3419 posts in 3091 days


#8 posted 02-26-2020 01:59 PM

I’ve always understood that PVA glue shrinks as it dries.
If you sand your piece too early after a glue up, it can create the line you are trying to eliminate.
(Since the glue continues to shrink after you’ve smoothed the surface)

Allowing enough cure time after gluing and before sanding usually takes care of this line problem for me.
My 2 cents.

-- "Hard work is not defined by the difficulty of the task as much as a person's desire to perform it.", DS251

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Robert

3655 posts in 2152 days


#9 posted 02-26-2020 02:22 PM


I ve always understood that PVA glue shrinks as it dries.
If you sand your piece too early after a glue up, it can create the line you are trying to eliminate.
(Since the glue continues to shrink after you ve smoothed the surface)

Allowing enough cure time after gluing and before sanding usually takes care of this line problem for me.
My 2 cents.

- DS

@CWW
I can’t address correcting its going to be a tricky task.

I would say the problem started with jointing. Either boards not jointed well enough or , when a slight bow is clamped out, you have to leave clamps on a full 24 hours. If there is a defect in the glue line, when the glue shrinks you get this result usually not detected until finish applied.

-- Everything is a prototype thats why its one of a kind!!

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LeeRoyMan

744 posts in 398 days


#10 posted 02-26-2020 02:49 PM


We agree about the artist s brush build up to fill it, but I find scraping it flush works better than sanding. Sanding affects the surrounding area, whereas a denibber or scraper simply flattens it. Generally after that, a light finish coat to even it out (or sometimes just some blush remover) is enough to smooth it out.

So, LeeRoy, what do you think about what you see in that photo? It looks thick to me, like it might be better to wet-sand it rather than trying to build it up.

- Rich


To be honest I have never tried scraping.
What I find when filling with the artist brush is that it leaves a hard line at the edges of the fill. For me this is harder to remove than just spot spraying the area. I’ve never wet sanded, so no comment on that.

Like I said above, I respray the whole surface after I’m done filling anything so the “affected surrounding sanding area” gets blended back in with no problem.
This is just what works for me, lots of variables for everything, so I’m not discounting any other methods.

The total recommended (for SW, I use T77- F58 dull rubbed) film thickness is only 4 mils. I’m sure there is some leeway, but I wouldn’t feel good going over 5.

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Rich

5346 posts in 1260 days


#11 posted 02-26-2020 03:34 PM


To be honest I have never tried scraping.

- LeeRoyMan

Everyone knows I’m a real nerd, so you shouldn’t be surprised that I have an assortment of things to deal with issues like this. The first one below is super-fine. It’s for those times where you can run your hand over the finish and just feel a nib or two. It’ll knock them right off and generally no final touch up is needed. The second one is what I use most often to level any runs or things like that. It’ll shave it flush with the rest of the surface and a final spray will leave a flawless finish. The last one is the first one I bought. It’s a very high quality tool and I still use it often, however at the current price, I’d probably pass on it. The first two though, I’d recommend for anyone who sprays lacquer. I find that leveling a run or drip is easier with it than sanding and doesn’t affect the thickness of the finish in the surrounding area.

I will say though that LeeRoy’s finishes look flawless in his project posts, and he’s probably a far superior finisher than I am, so whatever he’s doing clearly works.

I have one of these:

One of these:

And one from König which TungOil reviewed here. (Heads up, the König is now $55 and their shipping is pretty high, so that could set you back $70 or so.

(Dang, those images are big. Sorry for being such a screen hog…lol)

-- Half of what we read or hear about finishing is right. We just don’t know which half! — Bob Flexner

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LeeRoyMan

744 posts in 398 days


#12 posted 02-26-2020 03:48 PM



The second one is what I use most often to level any runs or things like that.

I find that leveling a run or drip is easier with it than sanding and doesn t affect the thickness of the finish in the surrounding area.

- Rich

What are these so called runs and drips you speak of? .... lol

I may have to get me one of those, maybe the second one you posted to start?

I used to spray lacquer with an airless, learned real fast what a run is,
actually learned more about what a sag is.

The hardest thing to remove is where a drop landed.

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Rich

5346 posts in 1260 days


#13 posted 02-26-2020 05:01 PM


I may have to get me one of those, maybe the second one you posted to start?

I used to spray lacquer with an airless, learned real fast what a run is,
actually learned more about what a sag is.

The hardest thing to remove is where a drop landed.

- LeeRoyMan

Wait…what? LeeRoy…sags…drops? Cue my look of utter disillusionment.

Another advantage these have over sanding that I forgot to mention is that, while you do need to let the lacquer harden enough that the teeth of the denibber don’t dig in, you can use it much sooner than you can sand.

Wow. LeeRoy. Sags. I haven’t felt this way since I found out Alan Ladd was only 5’6”.

-- Half of what we read or hear about finishing is right. We just don’t know which half! — Bob Flexner

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LeeRoyMan

744 posts in 398 days


#14 posted 02-26-2020 05:07 PM


Wow. LeeRoy. Sags. I haven t felt this way since I found out Alan Ladd was only 5 6”.

- Rich


It’s like Nascar, you don’t know how fast you can go until you hit the wall.
Even after hitting the wall, you push the limit every once in a while. ;)

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CWWoodworking

659 posts in 850 days


#15 posted 02-26-2020 05:20 PM

Definitely rushed the glue up. Closer to 24 minutes. Lol

Thanks for all the help. Hopefully get it knocked out tonight.

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