The hidden secret to sanding - Is there one?

[lowkee]

Is there one? Because I can't take another day wasted to sanding this tub of a hull.

I royally screwed up the paint job with drips and sags galore, so I now need to sand it all back to ready again.

Is there a certain method to sanding which works better, easier, faster?
Is there a certain sand paper which lasts longer?
Is there a certain sander which sand more efficiently and contours to the curve of the hull?

This thing has chines everywhere and concave sections where I need to use the edge of the sander, which makes a nice even sand nearly impossible, and certainly impossible for me.

Any help from the experts?

Also, anyone willing to make a how-to video of using an HVLP gun? I can't seem to find a video which goes through what does what and how to actually use the gun to apply the paint. And I certainly haven't seen any which look reputable enough to trust. Most are "Look at me paint this pane of glass which has nothing to do with vertical and inverted surfaces of freshly sanded primer.. NO, I won't zoom in to show the final result! Buy this video for $7,000 and I'll show you on a much bigger pane of glass from further away".. yes, I am frustrated in my search

 

[Tail_Gunner]

Re: The hidden secret to sanding - Is there one?

Been there done that...What type of paint did you use?

 

[proshadetree]

Re: The hidden secret to sanding - Is there one?

Which hvlp gun do you have?I have one of the harbor freight ones the purple one to be exact.You need to have enough pressure at gun I use 40 psi for mine.Adjust the gun so you have a good spray pattern.I have not sprayed any kind of boat paint but automotive paint is thin.If you are using thick paint and cant thin it you must use a gun with a bigger tip.I just bought a 2.5 for gel coat and plan on spraying house paint out of it to.Most hvlp ar automotive use and have a 1.4 tip.Im going to check your thread and see if there is more info there.I lik Air DA sander but youll still have to do the chines by hand or longboard.Use a wet/dry paper and sand wet it will last loner.Knob on the bottom of gun is air pressure.Knob on the back of gun is flow/How much paint is put out at one time.Should be one on the side that is Spread on patern.Set gun up on plywood or card board.Not enough flow to run about 7 to 9 inch wide pattern or spread.Enough air to get it to atomize. Lap 1/2 of next spray over first.Thats where you get coverage.1st run start moving pull triger make a pass.Let off trigger before you stop.Drop down 1/2 of spray IE 4 inches and make next pass.I wish I was there to show you rather than typeing it.Try on ply wood or scrap first.Youll get it.

 

[Numlaar]

Re: The hidden secret to sanding - Is there one?

Is there one? Because I can't take another day wasted to sanding this tub of a hull.

I am right with you there Lowkee...

I took a break from sanding and shingled my shed in 95 degree heat, just to not have to sand again today LOL

I haven't found any "trick" to it, but I am using 3m wet/dry paper and wet sanding which seems to be going pretty good... Just cut a sheet up into about 8 small squares and use little pieces at a time and doing it by hand... I used the most getting the orange peel down, but after that, I can use a single sheet to sand the entire hull...

Its slow, but the results are pretty good...

Now I just need to find some 800 and 1000 grit wet/dry paper...

 

[bigbad 4cyl x2]

Re: The hidden secret to sanding - Is there one?

its all about the prep work , go buy an orbital sander a nice palm makita . buy lots of sand paper at a cheap store 80 grit , hook and loop, sand till the paper loads rip it off then get a new paper on there , grind it way into the glass . no light sanding here .epoxy prime, now go get some long boards from an auto paint supplier and buy there sticky rolls of sand paper dont bother with the flat stuff from the store , use 80 grit tear off a 4 inch piece and fold it in half sticky side to stickey side . do detail work , use long boards to shape high build epoxy. reapply . all straight with the longboards ok now use 180 grit on some finnish primer , however many coats it takes , check it with your long boards flat ok , now 320 the finnish or leave it at 180 to 220 stickey rolls , any other way and your messin around to long , i had a bad asssssssss machine the orbiatled and force randomed by makita ;http://www.makita.com/en-us/Modules/Tools/ToolDetails.aspx?ID=315 ;the badboy of sanding right there ; if you have air your in luck cause you can wet sand and make evryones life easy plus the air sanders are a lot lighter

 

[oops!]

Re: The hidden secret to sanding - Is there one?

the secret to sanding is elbow grease.....my elbows needed more gresae because the were so sore that i could move for a day or two after.

the real tool besidses the sander is a foam 6 inch pad.....you use the hook and loop to attach the pad.....then put your sand paper on the foam.

it will help in the crevice areas.....but fot really tight work.....you have to finger fiddle with it.

remember.....you can remove dry sand marks....but not wet sand marks.

as mentioned in the post above.....knowing when to shop sanding is crutial......or you just add filler and take it off over and over.

all the scratch marks must be taken out.......the paint will hide nothing.
use the primer and sand it till its right or you wont be happy.....

cheers
oops

 

[drewpster]

Re: The hidden secret to sanding - Is there one?

Can you wet sand the runs out scuff the whole thing and shoot another coat? Is it necessary for you to sand back to primer?

 

[lowkee]

Re: The hidden secret to sanding - Is there one?

Thanks for the advice guys, especially the HVLP lesson. After all, this wouldn't be too bad if the priming went smoothly.

I'll check into buying the foam intermediary pad. I don't think I'll be ablt to just scuff and add coats, as the primer is already orange pealed, so extra coats will make it worse anyhow. Although I suppose then I can use a course grit and tear through it faster.

I've been using 220-320 grit since the initial sanding in the hopes of getting to a point where I can finally add paint instead of primer, but I just go through more paper and sand longer. I think that may be the 'secret'.. knowing what grit to use and when. Tomorrow I'll step down to 80 for a while and breeze over everything, then shoot a layer of primer and (if all goes well shooting it) begin with the less gritty paper.

 

[proshadetree]

Re: The hidden secret to sanding - Is there one?

When you mix the primer bump up your air pressure at the knob at bottom of your gun.Screw flow all in then out about 3 rounds.Adjust so that you have a fair coat not full.That will come in second pass.Point at scrap and pop the trigger to see your spray pattern.Mix primer thin so it will flow out.Kind of like milk maybe a bit thicker but not much.

 

[lowkee]

Re: The hidden secret to sanding - Is there one?

When you mix the primer bump up your air pressure at the knob at bottom of your gun.Screw flow all in then out about 3 rounds.Adjust so that you have a fair coat not full.That will come in second pass.Point at scrap and pop the trigger to see your spray pattern.Mix primer thin so it will flow out.Kind of like milk maybe a bit thicker but not much.

Ah! Not one single site told me it wasn't supposed to cover on first pass. That'd certainly make a big difference, since I was gong slow enough to get full coverage and still overlapping 50%.. drip city.

Assuming it is pretty humid (50%) and hot (90F), should I be using mineral spirits or acetone to thin? I bought both, as I pretty much have no idea what I'm doing. Spraying stuff seemed much easier when i was younger.. maybe I just cared less about it looking like crap.

 

[erikgreen]

Re: The hidden secret to sanding - Is there one?

Hmm... sounds like you're new to spraying.

Here's my advice: Sand the hull smooth, make sure your prep work is done completely. Make sure you have a clean surface (wash with a solvent and wax remover if needed).

Then prime with a spray or whatever. First coat just to get even coverage, second coat heavier to opaque. Try to keep it even, and leave enough time between coats that the first one gets very tacky... basically leave it as long as you can but still stay within the window for recoating.

Final coat... if you don't have experience spraying then reconsider... use roll and tip with a quality paint (actually, use a quality paint period) and you'll get better results than with spraying if you're not practiced with the sprayer.

Really, roll and tip with any of the better one part or two part paints looks amazing, better than a lot of spray jobs I've seen. It's also safer than spraying and actually easier.

If you're going to spray, practice first. Get a 4x8 of plywood and seal it, then cut it in half and practice your whole sequence of prime, sand, and paint on it. Learn the settings on your sprayer that work for you, learn how much to spray and how long to wait between coats, and learn how much sanding you have to do before and after each coat.

Once you've painted the first half, do the second. The final result should look better than the first half. If you're satisfied with the improvement, then paint the boat, or else cut another plywood sheet and practice more.

Erik

 

[Rickairmedic]

Re: The hidden secret to sanding - Is there one?

Lowkee you will have to ask Mr. Miagi the secret its been to long since I have seen that movie I cant seem to remember the secret either other than a random orbit sander does seem to make it quicker .


Rick

 

[ringmaster72]

Re: The hidden secret to sanding - Is there one?

Your best bet is to buy a how to manual. There are so many tips and tricks involved with painting that you will learn the hard way, like you hav already started. First things first, I would not apply paint over anything more coarse than 400 grit sandpaper. If you are going to prime, then use 180 or 220 grit to remove the old finish. If you go more coarse than 180, you will have sand scratches in your finish, even with the use of primer.

What brand materials are you using? Whatever it is, you need to get the directions for their products as far as mixing and spray technique. Most manufactureres have tech manuals to follow for each product.

As far as gun adjustment, for HVLP you need 8-10 psi at the tip, which translates to about 28-32 going into the gun. From there you need a football shaped pattern that is the same size as the distance from the object. For example, if you are sraying six inches from the surface, you should have a six inch tall pattern in the football shape. it is important that you check your spray pattern frequently.

 

[berry79]

Re: The hidden secret to sanding - Is there one?

When using the spray gun I set my regulator to 30 psi. Also, make sure you drain all the moisture out of the compressor tank before starting and have a good water separater filter in line. Moisture can realy mess up a paint job too.
I alway test the sprayer on a scrap peice first. You never know what happens to the gun in storage. Setting the hvlp is quite easy, just read through the manual and figure out which knob is flow and which is for the spray pattern. I agree with ringmaster72 a football shaped pattern is a good way to describe what you are looking for. If you are spraying in a horizontal motion you will what the football pattern vertical (). Good luck

 

[allpoints360]

Re: The hidden secret to sanding - Is there one?

Is there one? Because I can't take another day wasted to sanding this tub of a hull.

I think if there is a secret it is to use the most aggressive grit you can for your job. Nothing wastes more time than sanding with too little grit.

Also, are you sure you have to take it all off? Just get the sags and runs off and rough up the rest and repaint.

I like my DA sander.

 

[lowkee]

Re: The hidden secret to sanding - Is there one?

Thanks everyone for the HVLP tips. I'll be sure to try out a piece of plywood first, as I just can't do this again.

I figured out I never sanded correctly the first time, so it all had to be sanded smooth anyhow. I learned a trick to making sure you get everything completely smooth, and that is to spray some flat black rattle can paint (a light sprinkling) all over the surface you intend to paint. Then when you sand it, it is obvious what parts need more sanding, as the pits will becomes apparent, having black paint still in them. Works a treat and makes obvious tiny dips I would have never seen (and didn't see) without that trick.

I know this sounds scary, since you just finished painting the darn thing, but you need to sand it anyhow, so you will sand all the black off no matter what (and it makes sure you don't get lazy and skip a section or two).

 

[WesMason]

Re: The hidden secret to sanding - Is there one?

Lowkee,

Tons of great tips above. My experience with a spray gun was automotive...and something I got very good at. I applied my "prep work" principals to prepare my boat for paint but opted for the roll/tip method using Interlux Brightside Polyurethane. I took several peoples advice on this method and glad I did. SCARY at first, but it went on really well and is simply beautiful. Roll/tip also seems to do a better job of dealing with light scratches as it will flow out. Spray simply lays it on.

Marine grade primer is very dense and will eat up tons of sandpaper no matter what grit. It works great though.

Using a guide coat of rattle-can paint is helpful, but will stick to your paper like crazy. You'll eat up more. Wait a looooong time before sanding after guide coat. Not saying don't use it, just be prepared.

Totally agree with ringmaster on the grit choice. Personally I wouldn't go below 120 and I'd use that only where you have the biggest issues. If you need to cut something down...do it qucikly and get back to a higher grade grit.

My $.02

Have fun...and post pics!

Wes

 

[bigbad 4cyl x2]

Re: The hidden secret to sanding - Is there one?

yea the boat yard had me use a pencil to make a guide coat marks . cause the rattle can would gum the paper . i think i liked the rattle can better though ,gotta get the long boards though

 

[lowkee]

Re: The hidden secret to sanding - Is there one?

I guess here is the best place to ask.. is there an equiv steel wool for each sandpaper grit? I have a ton of steel wool, and it never clogs or wears out to any degree.. would that be worth using as the finishing once-over or will it ruin the smoothness of it with finger-dent shaped curves?

 

[erikgreen]

Re: The hidden secret to sanding - Is there one?

Pretty sure there's not. Also the problem with steel wool is that it tends to break off little bits and embed them in the surface to cause problems later on.

I'd recommend you use sandpaper, and pay for the good stuff, it'll both last longer and make the job easier.

The other thing to mention is that long boarding is for fairing.. making your surface level. It's not for making it smooth.

To prep a hull (or any boat surface) for paint, I build or fix it as smooth as I can, grind down any projecting cloth or whatever. Then I smear an even layer of fairing putty on, usually glass microbubbles. Only as thick as I think is necessary to get a level surface.

Then long board. Use the board held diagonal in a sideways motion (hard to describe, but know you're not pushing it back and forth like a scrubber). If you work it right it'll cut and level without a lot of force. Use that to get your surface level, ignoring rough spots. Your first task is to get the surface even, so the long board hits all spots when it moves across the surface.

Once you've gotten it as level as possible first pass, you'll also have marked a bunch of low spots or dips that you can't long board out because there's not enough filler there. Fill them with "patches" and let 'em harden, then use the long board again to level the spots.

Once you have the whole surface level, then you can put the long board down and start smoothing. Use whatever sanding technique you like, just try not to remove much material... you're smoothing, not leveling.

Once the surface is smooth, prime it and check using low angle lights for defects. You'll find some. Sand some more, go back to leveling if you have to and re-apply filler as needed.

Once your surface is as perfect as you can make it, prime again and check with low angle lights.

After a couple checks after priming your surface should be close to ready for paint. You can do a final prime coat if you want, then start the paint job.

The real trick with fairing and painting a hull is to recognize the steps... it's not like a car where you're sanding for smoothness.. you have to do the fairing first, then smooth sand, then the painting.

At least that's how I do it.

Erik