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So without further ado- here is one typical Groopmail discussion and what it looks like, except that in a real Groopmail you would see the person’s real name used and what State they are from.
In an average day you would get 10 to 15 mails like this on the different topics under discussion.
~~ Original Message Subject Title: "Problem- Pinholes in Mahogany ~~
Member KE writes:
I've been having problems with pinholes and hope you can help.
Its a mahogany table top, not looking for filled grain. Here's the scenario:
Mahogany dining table
NGR dye sprayed
Wash coat sanding sealer
Sealcoat coat straight from can
Mohawk aerosol glaze
Tack coat then wet coat of precat straight from can, pinholes show up Cut back with 220/320 Blow and tack Thin material 20% standard thinner, spray thinnest wet coat possible, pinholes reappear Wait a day for weather to warm so shop is 70/70 temperature/humidity Cut back 220/320 Thin 20% standard thinner, spray thinnest coat possible, pinholes come back Throw hands up and open a beer ; )
What next? Add retarder? Thin with AER like LOL? Other suggestions?
<link is provided to view pictures of the problem>
Member KE, USA
~~ Day 2 Replies ~~
> Member KE asked:
>I've been having problems with pinholes and hope you can help. Its
>a mahogany table top, not looking for filled grain. Here's the
Member SM replies:
I experienced a similar problem; however, there were only a relative few "pits". I too had thrown up my hands. My eureka moment was to use thin CA and apply it into each hole. From then on the lacquer filled the holes and I did end up with a very uniform finish. This might not be a practical approach for you, but I thought I'd share this anyway.
Member SM, USA
Member LH suggests:
I'd suggest better thinner. Not necessarily retarder, but a higher grade thinner. Plenty of drying time too.
Member LH, USA
Member ER speculates:
Have you tried a fish eye prevent treatment added to your lacquer? I have had success by adding that. not sure if the problem is some sort of contamination issue, but it always looked that way to me, especially on mahogany. a capful to a quart and lightly spray should do the trick.
Member ER, USA
Member KA replies:
Quite a few years back I worked for a guy that always put wood filler in his oil base stain and it seemed to work very well for the oaks and mahogany in regards to reducing the pinholing on the standard finish schedule
It did not close the grain but it reduced pinholes
~~ Day 3 Replies ~~
Member SB suggests:
Pinholes are caused by air escaping from the pores. If not porefilling, then do not apply more than a 1-2 mil coat wet.
Mohawk also produces flow out additive which will help.
Also, make sure the wood and finish is not too cold. Wood surface temperature can be 10 degrees colder than air and finish can be 15-20 degrees colder.
Member SB, USA
Member BN writes:
I would think the lacquer sealer wasn't completely dry. Trapped thinner is what causes pin holes. You sealed in the lacquer thinner contained in the sealer with the coat of shellac so, when you shot on the nitro cellulose lacquer it caused the release of the thnner trapped below which shows up as pin holes. Better to use the seal coat (shellac) first. And you should always allow adequate drying times for your finishes. Especially in cold weather.
Member BN, USA
Member CK replies:
Looks like silicone contamination problem trying to produce fish eye.
~~ Day 4 Replies ~~
Member EM writes:
Pinholes at one time were a big problem for us here as well. I found the issue to be mainly on tops- and the advice you're getting so far lines up with that observation. When you're spraying lacquer on tops, you naturally apply more coating than you would on the surface that is vertical, and so the trapped air, solvent or what have you causes the nagging little dimples right on top of an open pore.
What worked for us in eliminating these pinholes is to paste fill all your top surfaces. Even if it is a quick slush-fill step. The paste filler will close the pores enough to virtually eliminate pinholes from your life altogether.
Member EM, USA
Member OC replies:
I have run into this and think even brought it to GROOPs attention once. The problem with this type of issue is you may be dealing with a couple of issues such as solvent entrapment within the pores and contamination. I say this because upon looking at your picture, some of those "craters" look more like contamination than pin holes created by solvent release. I will try and not duplicate some of the great information all ready provided and am going to mentioned something I noticed in your procedures that has not been touched on. I noticed you did not wash or neutralize the table after stripping.
Sanding will not help getting any stripper still embedded in the pores. This needs to be washed out, preferably scrubbed with a course pad or brush. Additionally, as you probably know, heavy grain is a favorite place for all types of contamination to hide. Here I will duplicate some information. After washing you need to seal the surface with a wax free shellac. For better or worse, on severe cases, I have padded the shellac on, forcing it into the pores as it dries. After allowing plenty of time for drying, as not to trap solvents in the pores, you need to apply light coats of vinyl sealer or coating of choice before applying a heavier coat.
I hope this helps somewhat.
Member OC, USA
Member OS writes:
I think that this problem could be resolved with a series of VERY light seal coats, as these would not bridge the pores like a heavier coat. This coat should be no more than 2 or 2.5 mills thick wet. Just my experiences....
Member OS, USA
Member GL troubleshoots:
(1) Drafts which cause surface drying before the solvent can break through the surface film in order to evaporate.
Solution is to eliminate the cause.
(2) Fine drops of moisture coming through the water separator into the spray apparatus.
Solution: clean up the system and make sure the air is dry and clear.
(3) Air trapped in the pores of the wood.
Solution: Spray a very thin wash coat......(I use finish that has been thinned 50/50 with Acrylic enamel reducer).
These are (almost) quoted out of MLCampbell hand book.."COMMON WOOD FINISHING PROBLEMS" they are free for the asking from your dealer.
Member GL, USA
Member KE (who started the discussion) reports:
Thanks to all that replied. And thanks for the call, Member S
Don't know why I didn't view this as possible contamination but think that's what is was. Some drying, sanding and thin coats got it where it needs to be.
Member KE, USA