Painting without sanding?

[Dolly Varden]

How long can you safely go between coats of an alkyd enamel paint without needing to sand for adhesion? if i put on one coat today ( sprayed) and the temp stayed below 65 degrees, would a coat that was put on tommorrow "melt" into the paint I applied today?

[garland reese]

I have only limited experience with painting, but what I've done, I've found that it's better to spray coats fairly close together, when it gets tacky and dry enough not to cause a run.

I've waited until the next day before, and nearly every time, I get that orange peel effect that happens when the new paint softens the coat underneath. I've heard that you should do your coats close together, or wait a few days in between. I guess you'd have to sand at that point though.

Sorry, I know that's not much help.....just what I've experienced with some of the repair work I've done on modern rowing shells.

[Ron Williamson]

It should stick, but take exactly forever to dry.
It takes about as much time to let it dry properly,then sand.
My experience is with B-M Impervo almost exclusively.
R

[Ken Hutchins]

This is a means of getting more work done let's say if only weekends are available. Sand and paint on Saturday second coat on Sunday. Then let sit until the following weekend before doing anything else. It will definitely need the extra drying time, might even need 2 weeks.

[Wild Wassa]

Dutch G'day. I sprayed 4 coats of exterior oil based enamel (I view alkyd as similar) onto a 14 ft hull in an afternoon last November. It was not my choice of medium or my modus operandi but the boat owners. He wouldn't listen to what I had to say, about what he really needed, which was a marine enamel for his boat. I was happy to do what he wanted.

The boat was sprayed in a booth with heat lamps so each coat tacked up well. The exterior enamel was diluted with 40% thinner by volume and each new coat was applied when the paint tacked up, which was about 45 minutes to an hour per coat. It was the way the boat owner wanted it, so I did it. Even my suggestions on how long the boat should sit after painting without being moved, were ignored.

Shortly after I left him he and his mate moved the boat and left handprints in the boat they wanted to spray another boat after they got the hang of what was needed, :D . The boat could have sat for a month before it had to move to help it cure well, again he wouldn't listen and the following morning he and his mate turned the boat upright and trailored the boat. He told me it felt dry.

Don't go there, I totally agree with Ron W. Let each layer cure well before moving on to the next. Key lightly between coats and you will be delighted with your result. The paint will have an increased longevity as well. After a light sanding to aid keying, wipe each layer with Prepsol and then give it a light swiff with a tack cloth.

If you are spraying on an enamel that isn't a marine enamel do allow at least a month to 6 weeks or to even 8 weeks for the paint to cure at 22C. The paint will stay soft with sprayed on enamel. You must allow the solvents in each layer to dissipate and allow each layer to polimerize before proceeding. That is the optimum.

Two weeks later I visited the owner and took a few photos. This is one of the best, after the trailering. I was really happy with the paint job ... but I'm even happier with this photo in my collection.

http://www.imagestation.com/picture/sraid195/pe1cd49a7ba0a01e8fabf94f015d28214/f144e558.jpg


Warren.

[ 02-26-2006, 04:47 AM: Message edited by: Wild Wassa ]

[Lew Barrett]

Warren,
Pardon my ignorance, but what do you mean when you say "key" the coat?
Lew

[Dolly Varden]

i believe keying is the positive effect that the tiny scratches left by very fine sanding does for the adhesion between coats.

im sure it wasnt fun warren but it makes for a fun storey. nice picture. reminds me a bit of a few saggy old gals i know :D

[hoz]

That's some paint creep there Warren. So did the owner try to blame you for the defect? Or did he "Man up" and accept responsibility?

The old adage comes to mind,"If you don't have enough time to do it right the first time, you'll have to find time to do it right the second." (Third and fourth...)

[Dolly Varden]

not needing to sand between coats of paint is the primary reason i stick to 2 part urethanes almost exclusively - there as you know is the window of opportunity depending on temperature and humidity of overcoating after 24 hours without sanding, and wet on wet coats are the rule for good coverage. i had a us paint (awlgrip) representative tell me that even after 24 hours but prior to 48 hours, their paint can be keyed via a good scrubbing with a scotch bright pad

i have less recent experience with traditional enamel and alkyd coatings- ive always sanded between coats before, but am always looking for an easier way if it doesnt reduce the quality of the finished product

[Wild Wassa]

Lew B, there are two ways a new coat of paint can adhere to the previous coat. By chemically keying which is what Dutch is after. This saves a lot of time and a bit of work, or if a period of time has passed between coats the ability of the medium to chemically key may have passed. The only way to then guarantee that the new coat will stick is to put a scratch pattern in the existing coat ... a physical key.

Instructions for use on the tin will read, "sand well between coats with #180-220" after a certain number of hours have passed. I think that this a bit harsh and necessitates the use of more paint than is required because with such coarse grits more paint than necessary can be removed. I'm not one for sanding off hard work. Also with the coarser grits any rough keying can be telegraphed through to the top coats. That is something that I notice on the boats at the yacht club a lot.

When you are keying by sanding you are also fine fairing. If you are brush painting or rolling, a good consistent scratch pattern will allow the paint to draw more uniformly from the brush or roller. If you haven't got a uniform scratch you can sometimes see the paint wanting to bead slightly.

Painting many thin coats is a better practice than painting a few thicker coats. So that is why I usually key with #400. If grits finer than #400 are used (with the brush or roller) you get into a situation where the scratch is too fine to even allow a physical grip.

When spraying, it is common to key with #560-600, or slightly finer. After that nothing much will grip. Call #800 the absolute upper limit for spraying.

Dutch, with alkyds and oil based paints you have a few days of latitude ... but read your manufacturer's instruction. They should give you the advised outer limit between coats in the application instructions on the can or in data sheets ... for a chemical key.

With the polyurethane that I use, I have to physically key the material after 4 1/2 hrs on hot days (say above 26C) and after 6 hrs at normal room temperatures (about 20-22C) ... otherwise it can come off in sheets.

I'd like to stay and chat but I have to continue doing the prep prior to painting a Catalina 26 called 'Maxximus' she was called 'Wendy's'. The anti-foul etched the surface to a depth of 1-2 mm. That is after the paint was stripped off. It is a radical surface, it looks like the surface of the moon. Glass bubbles will fix it. I'll photograph her this afternoon and post a shot for those into astronomy or for the average fibre glass loving lunatic. If the glass macros don't work, I'll buy some of that acne treatment you see on TV ... 'Pro Formula'?

Warren.

[ 02-26-2006, 07:01 PM: Message edited by: Wild Wassa ]

[Bob Cleek]

Warren's advice is dead right. I have had good results using Scotch-Brite pads (which come in different grits) for keying. They do not remove much, don't clog up, last a lot longer than a sheet of sandpaper, and are much cheaper. Get 'em at the paint store.

[Lew Barrett]

OOPS AGAIN.....

[ 02-27-2006, 12:54 AM: Message edited by: Lew Barrett ]

[Lew Barrett]

Thanks guys. I understand the processes, just never in all the years I've been painting and varnishing heard the term "keyed" before. I've heard, fairing, sanding, scratching, (putting on a scratch is something people say hereabouts) or the various ways people talk about chemical bonding, which I intrinsically understand (though not via any brilliance or knowledge of chemistry, mind).....you have some "heat" in the solvent and the new stuff coat bonds with the old by "melting" into it so to speak. I'd call that "hot coating" and you can do it, if you're brave, with many products, including most regular varnishes, though as a rule I don't. I usually like to sand between coats mainly to clean the inevitable schmutz off, and because I like the brush feel that way. I am hot coating my decks at the moment using an Epiphanes product specifically developed for the job to get some build going though.
I agree on your choice of grits, though I commonly sand with 320 until I reach the top coat and rarely beyond 320 when varnishing, but sometimes finer for paint, just as you described. Last time I painted Rita it rained on the first day, so i took out the wet/dry and stood there in the downpour sanding away with 600 grit on a block, Best paint job I ever got.
http://www.imagestation.com/picture/sraid197/p0ec89b1d701f44e4a0290242102e8589/f10d306e.jpg

Lew

[ 02-26-2006, 09:53 PM: Message edited by: Lew Barrett ]

[Wild Wassa]

Lew, nice boat. I didn't have to have a rave then, to you Skipper. I thought that you were a young bloke who might be just starting out painting a boat. Thanks for letting me indulge Sir.

Dutch, here is the boat that I'm fairing prior to painting, I hope your boat is in better nick. It is very appropriate to put these shots on your thread, I'm jealous of anyone who can paint with out sanding ... there will be days of sanding on this beauty when I finish fairing her.

I'm trying to get as much done as possible before she goes up on the hoist again. She is coming on. She had blue anti-foul when I first met her. Her owner has done an awesome amout of work, so I'll just dress her up a tad and give her a nice skin and get all the credit ... life can be cruel. She will look a treat at the end of next week. The brown is an epoxy filler which has shrunk nicely and she is being faired with glass macros now, I like fairing hulls ... I don't always get to work on wooden boats in fibre glass boat city but working on this boat is inspirational because of her owner's dedication.

http://www.imagestation.com/picture/sraid201/pfc1ca0c4dcc9615378651b581f92f3c1/f005e181.jpg

The boot stripe is a gel coat.

http://www.imagestation.com/picture/sraid201/p6377c84f374746e0d2731bbd8d5bf167/f005e172.jpg

Spiders. The filler has shrunk well, perfect for the glass bubbles ... I mean, 5 micron hollow glass spheres in epoxy which I have just started applying. In the top photo.

http://www.imagestation.com/picture/sraid201/p5a40833e5746d587a137720e37035beb/f005e165.jpg

Sitting under this boat filling holes is good practice for dinghy racing ... the zen of looking up.

Warren.

[ 02-27-2006, 05:21 AM: Message edited by: Wild Wassa ]

[Dolly Varden]

Sitting under this boat filling holes is good practice for dinghy racing ... the zen of looking up i bet you have a neck like a bull mooose too :D

what do you use to chase out the spider cracks? I usually use a dremel tool, but look for suggestions.

do you use a mechanics creeper at all?- ive threatened to buy one but never have

I absolutely despise sanding boat bottoms

[ 02-27-2006, 09:19 AM: Message edited by: Dolly Varden ]

[maa. melee]

Wonderful work, Wild Wassa! I only wish I had the wonderful weather you have. Wouldn't it be advisable to drill a small hole slightly into the gelcoat at the ends of the 'legs' of the spider cracks? This way the stress concentration is dropped way down, stopping future cracking, going back to fillg the cracks and holes. Personally, I love fairing a fiberglass boat, bottom or topsides. I love the results. I'm in the process of fairing a ~17 year old outdrive that has only been painted once...kind of a rescue mission, as well as a fiberglass boat bottom. Feeling the surface get smoother, despit the different colors, is amazing. People often stand around wondering what I'm doing or have done all day under this boat...with nothing but unsightly patches of different color fillers, flash coats, and primers. I've even heard someone say the boat looked better before I started working, but I'm confident all this will change when the blotches of color are covered in topcoat, shining and smooth as glass. :D

PS: I have pics somewhere...

[ 02-27-2006, 10:52 AM: Message edited by: maa. melee ]

[Dolly Varden]

ive heard of drilling at the ends of the gelcoat cracks also melee, but if you chase the crack out further than where it ended, wouldnt it have the same result?

[Lew Barrett]

Thanks Wild One, and you're welcome! ;)
Lew

[maa. melee]

I guess if you get the drill point right on the end of the crack, it'd stop it from spreading. I doubt a drill is even needed, maybe even a countersink to break the gelcoat alittle. Backfill with epoxy.

On another note, I've read many spray paint cans, paint cans, and specification sheets. All or most say that a sanding is needed to proper keying. In the case of my bottom paint, 80-100 grit is recommended, and in my opinion, the scratches will show through the glossy epoxy paint. Is this a ploy to get us to apply more paint and buy more of their product?

[Wild Wassa]

Dutch, I use the Dremel with their cutting/ engraving bit 124. I only use the 124 (which is a larger bit and similar to 121), because if I'm opening up a spider it might as well be openned up to 3mm or better. The point of the 124 is fine mostly but as you roll the tool to the centre of the bit you can cut a 5mm chanel, just from the shape of the high speed cutting bit. All the cuts become feathered and circular. It is the tool for the job.

Dutch and maa melee, with drilling out the end of each spider (all fine cracks in the gel coat are spiders to me) as you both so correctly mention, I'm putting a plug in the end of each spider leg. I'd better photograph the bits that I've done ... not just the interesting bits that the owner has cleaned up. As I wrote earlier, the owner has done the hard work, he cleaned them up with a screwdriver sharpened as his chisel ... and I get all of the credit. So I'm not looking at this fix from a painter's point of view ... this fix needs the closer eye of a dermatologist.

All the spiders were attacked by the owner, I'm just the payed help who fixes them with plugs of compression strength filler. Using epoxy just by itself is too brittle as plugs and eventually shrinks too much. Using a sander filler is also a tad brittle. That is why I use either the glass macros if the colour base is important under a lighter coloured flow coat (for a small fix) or I use the red compression strength filler (from Boatcraft Pacific) if the boat is having a serious paint job and not just a touch up. I'll take a few more shots today of the work that I've finished.

The weather is here, I wish you were beautiful.

Warren.

[ 02-27-2006, 04:44 PM: Message edited by: Wild Wassa ]

[Wild Wassa]

Originally posted by maa. melee:
"Is this a ploy to get us to apply more paint and buy more of their product?"

I think so, I think the manufacturers are really rude and very ordinary with their general instructions. They don't give a toss about how much extra paint their advice causes the painter to use. In the hands of non painters it would be tragic for some at times.

I use Holt's, made in the USA, if a simple spray is needed to colour match over old fibre glass. The vast automotive colour ranges in a can, fit old fibre glass fixes very well (that is after T-Cutting with the appropriate coloured T-Cut not before, so you know what colour to actually match). I'm talking small fixes only.

I like Holt's which I water bath to 30C (even in warm weather) this gets back to Lew's comments on hot coating, to aid getting an even coverage. This is too simple to include in the advice to painters but sanding their paint off isn't too simple. At 30C the coverage is so good you dont have to sand. You will notice on the cans they say, "sand," it is not possible to sand the stuff for a simple key without taking it off ... and they know it, without committing the painter to buying lots of paint.

Every now and again I need to use a spray from a can on a small fibre glass fix because of the ability to colour match ... it is the affordable option for some, if you don't sand. All of the manufacturers say "cut after one week of curing before polishing" ... that will guarantee that you will buy more paint. If you wait a month after painting you might just need to polish ... the manufacturers don't tell you that.

Warren.

[ 03-03-2006, 04:12 AM: Message edited by: Wild Wassa ]

[Wild Wassa]

"Painting without sanding?"

I'm trying out your minimalist technique Dutch ... and I think I like it.

Yesterday, I walked up to a keel and a bit of leftover anti-foul.

http://www.imagestation.com/picture/sraid201/p07ae6b35a553f15761beaa5d532be425/eff8d30e.jpg

Today I walked away from the keel. Not a touch of sanding has been done as I prepare to paint ... but about 3 hours of scraping with a carbide scraper after an hour and a half of circular wire brushing, about 2 hours in total of high velocity water jet squirting, 7 acid baths of hydrochloric acid with a squirt between baths, 5 coats of metal primer and so far 4 coats of glass macros in epoxy including re-fairing the leading edge ... but not one joule expended on sanding.

http://www.imagestation.com/picture/sraid201/p526afd871d25aa4063098b10ac12aac4/eff8d30b.jpg

Dutch you could have hit on something with your minimalist thoughts for painters. Minimilists rule OK ... well they have in the last two days.

Warren.

ps, unfortunately tomorrow, the whole gig gets a good sanding and then the foil will be sheathed in glass cloth ... two days out of three of not sanding 'ain't bad.

[ 03-03-2006, 05:36 AM: Message edited by: Wild Wassa ]

[Dolly Varden]

one of my mentors once told me " 90% of boat building is sanding, and the rest is really hard work"

he was right smile.gif

[capt jake]

FWIW, I painted a tender last spring with an alkyd enamel. Sprayed four coats in a day, allowing 1 to 1 1/2 hours between coats (thin). Instead of mineral spirits, I thinned with Naptha. Naptha shortened the drying time a bit which allowed for multiple coats in a day (no sanding in between). The subsequent coats went on well and blended well with the prior coats.

The next day it was dry enough to handle, turn over and spray the outside.

The paint representative stated that Naptha would thin the paint too much and spread the molecules too far away from each other. But when I explained my painting 'plan' he agreed that it would not be a problem with the multiple coats.

Though I haven't had it out and about yet, the paint cured very hard, no blemishes or overspray problems (the overspray melted right in). It has been bumped into many times in the shop this winter and I am (thus far) impressed with the 'toughness' of the paint job.

Benjamin Moore M22

[Dolly Varden]

thanks jake. i was almost scared off by wassas experience, but i just sprayed my latest project with a marine alkyd enamel - also thinned with vmp naptha probably about 30-40%. i usually go by viscosity rather than a strict percentage. also waited about 45-60 minutes between coats. 3 covered quite nicely and the paint set up hard overnite in a 60 degree shop.

[ 03-03-2006, 12:50 PM: Message edited by: Dolly Varden ]

[Wild Wassa]

Dutch that wasn't my experience, I knew what the result was going to be ... it was a warning. Which was obviously not needed in your case.

The 40% thinning was to achieve the required viscosity. It just so happenned to end up at 40%. It isn't a regular figure that I subscribe to, but what the owner and his mate were comfortable with, with the quality of their gear. They didn't have the best of compressors.

Warren.

[ 03-04-2006, 03:48 AM: Message edited by: Wild Wassa ]

[Dolly Varden]

what is up with elevating the air line wassa? ive never heard of doing that, though i could see where it would help keep the line out of the wet paint

[Wild Wassa]

Dutch, to stop condensation, if your condensation trap overflows and as you have mentioned the high lines are easy to manage for sure ... but to stop water is the reason.

Some painters will go straight from the compressor, into a condensation trap then the line is elevated to the ceiling then down to another trap and back up to the ceiling again. Fitting two traps can be better than one to be on the safe side if you are doing custom finishing.

Warren.

[ 03-06-2006, 01:40 AM: Message edited by: Wild Wassa ]

[Dolly Varden]

thanks warren- im not too old to learn some tricks

[Wild Wassa]

Dutch, with one of your mentor's comments about "90% sanding" this trick can reduce that figure considerably when fairing. When fairing, change the colour of the filler between coats. One passer bye asked me if this foil was marble (I said no but not wanting to disapoint her, I told her it was a pink granite). When using filler, there can be a tendency to go over good work when using the same colour between coats. When a concave is spotted, I fill it with a different coloured compatible epoxy filler ... filler indicator.

I've spent one week fairing this foil (about 20 minutes work each day). If I had used the one colour of filler only, I could have spent a huge amount of time getting it right. I would have had trouble finding the problems and possibly doubled the amount of filler that I used, due to wastage. Already I've used 3lts of epoxy and 3 lts of filler on this foil. The sanding to a fine fair and to unify the scratch pattern before painting will hopefully only take a further hour's work.

http://www.imagestation.com/picture/sraid202/p61acf4b0b1621ef566c151751a8f2a5e/efe01bf0.jpg

The white is glass macros, the pink is a compression strength filler and the brown is a sander filler.

After I sand the foil this morning, I'll take some close-ups. That will show the different colours. I'm doing this post now because I'll be too weary tonight ... or too drunk. John Tracy the Australian Flying Fifteen Champion is not racing today so we might have a win at last. If we have another second or third, I'll spit the dummy and finger paint this foil a high visibility tangerine.

Warren.

ps, Orange it is, we had another second this afternoon.

I hate coming second so does my Skipper. Some pretend sailors in a plod boat, caused us drama on the first leg by cutting in front of us, Sunday salors have little to no road sence. My Skipper read the riot act to them. Then a Hobie 16 stalled at the first mark and to avoid a collision with a third boat who failed to give way, and who we'd actually cut slack to, after we took evasive action, and then had to go around the cape to pass that muvver's melee, claimed we hit something when they pushed us into it ... so we did a seven-twenty to be on the safe side (we don't go to protest Bernard and I, we would rather go drinking and crucify them when they least expect it. They're targeted for later) and that cost us the bloody match. I hate coming second ... I get real dark when we do, :rolleyes: .

http://www.imagestation.com/picture/sraid202/pcea935d5086d013bddcc5b1639661dcb/efdd6441.jpg

The sanding happened, the trailing edge of the foil, about 1cm wide.

http://www.imagestation.com/picture/sraid202/p9e05fb96058f5d06e1f86d41528aadc6/efdd4d82.jpg

At the start of the fairing.

http://www.imagestation.com/picture/sraid202/pc9b1b7c8769a8b407a0644af6aaa4578/efdd4d6a.jpg

Now nearly ready for painting, underneath the foil is still to be sanded. You just can't paint without sanding. I'll raise the foil and sand the rest with a Dremel.

[ 03-12-2006, 12:33 PM: Message edited by: Wild Wassa ]