I’m in the middle of finishing some wainscotting and crown molding using a 50/50 wipe on oil poly. I was able to get two coats on the entire project before I had to let it go for a week. I am ready to apply some more coats and per the instructions started to sand to facilitate adhesion of the new coats. I decided to use 320 grit sandpaper (based on info in Jeff Jewitt’s book). The can of poly didn’t say what grit to use. Anyway, I started on a small section sanding with what i thought was very light pressure. Well you might have guessed what happened. I sanded thru the finish and stain on the edge of one of my boards.
So my question is. What grit of sandpaper should I be using? Or should I be using abrasive pads instead (and if so what color)? How much pressure do I need to apply? I definitely don’t want any adhesion problems in my subsequent coats but then again I don’t want to sand thru my finish.
One further question. Though the can of poly (its VARATHANE) says each coat should dry for 4 hours before further coats are applied can I actually apply the coats quicker since it’s diluted 50/50.
Thanks for any help and sorry for the wordiness!
Dan
Replies
Yes, you can apply sooner.
I think the 320 grit is okay--you just want to scuff the surface for adhesion, as you know. I guess you just applied too much pressure on the edge. I think just sort of "wiping" it with the paper is sufficient.
If you use non-poly varnish, this would not be an issue.
For the most part all you want to do when sanding between coats is to remove the "nubs" The raised dust particle. Having a lighter hand will come with practice and experience.
I would agree that just removing the nubs would be sufficient if I was able to recoat within the 12 hour period where sanding is not required. Due to the size of the project and time constraints (watching my 3 kids) I'm not always able to apply more coats within the 12 hour time frame. Proper adhesion is my main concern. I've been working on this project for months and I would be sick to my stomach if my top coats of poly began to peel off in a week, month or year.
So would your recommendation change given these specifics or not? When I called the company's technical service line (Varathane) to see what grit of sandpaper to use they actually suggested 220. But on the other hand they also brought up the point that if I was sanding through my finish with 320 grit paper the layer of poly is probably pretty thin (and hence rough) and therefore might not require much sanding at all. Does this ring true to you?
Dan
It does sound correct. And the 220 grit would give more "bite" for the next application.
It is probably fine. The poly isn't completely cured in a day. Just "wipe" with the sandpaper. I have even used worn out sandpaper for this step. And I believe I have read that some use a brown paper grocery bag.Gretchen
I'm in the midst of a similar problem. For the size of your project I would recommend using the scotchbite type sanding pads that are out there everywhere now. They fit into cracks well, and it is much easier to control the 'bite' due to the thickness of the material.
On the other hand, I personally have never had a problem with poly peeling off. Has anybody out there had an adhesion problem? I think if you start mixing finishes and applying them really thick, maybe you will get into trouble.
I have been using steel wool between coats. I can feel the "rough" dust particles through the steel wool and I am less prone to oversanding.
I use the bown scuff pads by 3M. They are made for automotive clearcoat scuffing.
Garry
I've used wipe-on poly (mostly Minwax) on quite a few things. That stuff goes on pretty thin so I was always concerned about the same problem you ran into. I made a conscious decision to not follow directions and scuff between every coat. I typically end up scuffing with 320, 400, or 600 grit between every 2 or 3 coats - depending on how smooth the finish feels and whether I'm putting another coat on as soon as allowable or whether it's sat for a while and cured hard since the last coat. I usually end up with 6 or 7 coats. So far I've never had any problem with finish not bonding and then flaking off (Knock on wood). For the top coat I've been using rubbing compound rather than sandpaper or steel wool.
"00" Steel Wool works best in my opinion. Be very light on the edges and corners.
Have Fun!
Why are you diluting the mix 50/50? You are going to have to apply more coats to build up the finish.
Diluting the finish will not change the amount of time that you have to wait between coats, in fact the diluted mix might need more time since more solvent will need to evaporate, in addition to the reaction between oxygen in the air and the varnish.
John W.
Why are you diluting the mix 50/50? You are going to have to apply more coats to build up the finish.
Diluting the finish will not change the amount of time that you have to wait between coats, in fact the diluted mix might need more time since more solvent will need to evaporate, in addition to the reaction between oxygen in the air and the varnish
The 50/50 wipe on varnish finish is a well recognized and useful finish technique. It obviates the problem of drips, runs, and sags of brushing varnish. You wipe it on with a rag. Also, it dries quickly enough so that any ambient dust or trash does not settle into the finish. The finish film is, of course, much thinner. It dries to the touch within an hour usually and another "coat" can be applied, without the need for any sanding between coats. Four or more coats can sometimes be applied in a day. A total of 8 coats for tabletops is usually sufficient. Try it--you'll like it.You can make your own cheaper by mixing your own varnish and mineral spirits instead of buying an already diluted product.Gretchen
Gretchen, I know this is going to sound as though I'm kidding, but please, define "rag".
I want to use this technique but I don't know what kind of cloth to use, nor how thick, nor what size, nor how to fold it.
Also, when you use this technique.. do you wipe it on as though you were brushing it on? How do you get a uniform coat?
What about when you're covering a large surface.. like a 36"X60" tabletop?
I know.. lot's of questions.. but if you could help I would appreciate it.
Bill
See if this helps:The number of coats in a given day is not important. Important is to apply a wet coat with an applicator and merely get it on. Think of a 16 year old kid working as a busboy at Denny's you have sent over to wipe off a table. The applicator should be wet but not soaked. The applicator can be a paper towel, half a T-shirt sleeve or that one sock left after a load of washing. Then leave it alone. The surface should not be glossy or wet looking. If you have missed a spot, ignore it - you will get it on the next coat. If you try and fix a missed spot you will leave a mark in the finish.Timing for a second coat involves the pinkie test. Touch the surface with your pinkie. If nothing comes off you are ready for another coat. It was tacky 5 minutes ago but not now. Apply your next coat just as you applied the previous coat. Remember, you are wet wiping not flooding. After applying the second coat, let it fully dry for 48 hours. Using 320 paper and a sanding block ligthtly sand the surface flat. Now, begin applying more coats. Do not sand between coats unless you have allowed more than 24 hours to elapse since the prior coat. Keep going till you are tired of it. The number of coats is not critical - there is no critical or right number to apply. For those who need a rule, four more coats on non-critical surfaces or six more coats on surfaces that will get abraded seems to work.After your last coat has dried at least over night you will have boogers in the surface. You should not have marks in the surface because you ignored application flaws. You may have dust, lint and, if you live in Texas, bug legs. Use a utility knife blade at this point. Hold it between your thumb and forefinger, near the vertical, and gently scrape the surface. Gentle is the important word - no harder than you would scrape your face. If you start scraping aggressively you will leave small cut marks in the surface. After you have scraped to the baby butt stage gently abrade the surface with 320 dry paper or a gray ScotchBrite. Clean off the surface. Now, leave the area for two hours and change your clothes. Apply your last coat with a bit more care than the previous coats and walk away.An anal person is going to have a tough time with this process. Missed spots have to be ignored. Wet wipe, don't flood. Scraping to babies butt smooth means scraping no harder than scraping a babies butt. Ignoring any of these will leave marks that are tough to get out. Getting these marks out requires some agressive sanding to flatten out the surface and starting over.Finally, It works better to use a gloss varnish for all coats except the last. The flatteners in semi-gloss and satin tend to rapidly fall out of suspension when the finish is highly thinned. If you want a non-gloss finish, use it only on the final coat or two and be sure to stir the material frequently or you will end up with cloudy streaks.Howie.........
Thanks, Howie. Your explanation is thorough and complete and I really understand what you're saying.
My problem with wipe on in the past has been doing the exact opposite of what you prescribe.
Notably:
Too much poly on the cloth.
Trying to smooth it all on uniformly each time.. and going back if I notice a dry patch.
Getting frustrated when I see lint (from the cloth) on the wet surface and trying to "wipe it away".
I also appreciate the tip about gloss before satin to do away with the cloudy streaks.
I can't wait to try your technique.
What Howie said, but I have put more than 2 coats on in a day. I will also add that the first 2-3 coats will not look good and you will wonder if it ever will. It will.
Gretchen
Edited 11/25/2004 6:47 am ET by GRETCHEN
I thin poly with Naptha and have great luck. It evaporates really fast! Do you have any info on if Naptha causes any problems.
Thanks
Thinning with naphtha is OK but I find that using it to thin some of today's "Fast Dry" polys causes it to flash off too fast. The surface actually becomes gummy too fast to get the finish on evenly. For the "fash dry", standard mineral spirits seems to work better.Howie.........
Thanks for the reply. I do not use fast dry. Naptha seems to work fine without gumming as long as I keep the dehumidifier running.
Great comments. I might make one suggestion for what it is worth.
Do not use a sanding block on such a large piece. Especially anything connected to a wall. Walls are too irregular shaped and you will only sand through the high spots.
Unless you are doing a table top or fine piece of furniture I agree the others. Forget sanding between each coat. Wipe with a soft scotch pad or piece of stiff denim or burlap. Wipe-on is extremely thin and you are not trying to level brush marks etc..
Those dust bumps will probably never be seen and can surely be removed on the third or forth coat (if even needed then). IF I just had to sand I would use 400 or 600 and apply the same pressure I would if I were dusting my desk.
If you are trying to get an extremely smooth and reflective surface I would use something besides wipe-on.
Hope this helps.
Ive never had fgood luck with paper towels, maybe I am using too cheap a towel or trying to use it for too long
never liked the fast dry, again maybe to big an area
but learned a lot from Howies suggestions
No luck using paper towels. Tried them. Went to Lowes and bought a plastic bag of T-shirt material. Actual T-shirt material - white. Works great and cheap. Try them and you will not use paper towels again.
Lots of luck.
Edited 11/27/2004 10:45 pm ET by 81treehouse
This forum post is now archived. Commenting has been disabled