Sanding the Bottom

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TritonSailor
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Sanding the Bottom

Post by TritonSailor »

Hello everyone,

I am starting my bottom sanding this next week. The previous owner has pretty much sanded down through all the previous paint layers. Some areas though, there are chips or patches of area that a layer of paint is clinging to. My question is if I should start with an 80 grit on just those spots or just resand the whole thing with 80 grit. I will be using a PC 7335 orbital sander for the job.

thanks

Jeff
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Post by Tim »

You pretty much need 80 grit to even begin to touch bottom paint. One thing you will find is that 80 grit is not particularly coarse paper when working with fiberglass.

Although I don't know what the bottom of your boat looks like, I don't see any problem sanding everything with 80 grit, if that's what it needs. If you only have to sand painted areas, then do just that, but you'll find that 80 grit clogs quickly with bottom paint.

Hopefully you have good heavy-duty, quality sandpaper for the job.
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Post by Rachel »

Good point, Tim.

I found that after spending a bit of time grinding/filling through hulls, and then doing some rudder work (my, I do need to get caught up on photo posts), I started thinking of 80 grit as "fine finishing paper"! At that point, 40-grit was more the "everyday" paper, and I even went grittier that that a few times. (Of course start with higher grits, but just be prepared to go lower rather than spend all day with a grit that's too wimpy.)

When Tim talks about getting good sandpaper, well, if you want to read up on that, go to this thread:

http://tinyurl.com/cjneoo

On an only slightly disturbing note, the search terms I used to find that were "Mcmaster" and "fun." Hee -- it popped right up!

I ordered a selection of these discs, and one mistake I made was to not "decant" them from the plastic they came in. What happened was the plastic shrank over time and as a result the discs became slightly taco-shaped. They still work but they are less enthusiastic about sticking to the sander (PSA pad). I should try putting them under a bucket of water and some boards, or something, to flatten them.

Rachel
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Post by Tim »

Actually, the curling problem happens with or without the plastic overwrap--it's a function of the discs, not the plastic. It doesn't seem to happen on 40 and 80 grits, but 120 can curl right up like a cannoli.

I find even the curled ones are easy to press onto the pad successfully. If you're finding a problem with discs sticking, give the PSA pad a wipe with alcohol to clean it (only alcohol, not any other solvent).

The McMaster cloth-backed discs, details of which you can find in the thread that Rachel linked, are simply the best, ever. Ever. Expensive, and totally worth it; nothing comes remotely close.
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Post by Figment »

mmmmmmm cannoli.
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Post by TritonSailor »

Thank you Tim and Rachel, I have found where they put the disks in the newest catalog. HERE. But I am unable to find the correct backing pads. I found a couple HERE, but I don't know if they are the right ones for the porter cable 7335. As far as some pictures are concerned, I know You love pictures:) here are a couple:


Image

Image

Image

Image

Image[

Image

Image

Sorry Tim if that's to much, I wanted to provide as mush information as I could.

Thanks.

Jeff
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Post by Quetzalsailor »

I use a 12" disc sander, well, actually two (one on my Shopsmith in the basement and the other a Delta in the barn where the FD is). Either way, there's plenty of humidity to curl fabric-adhesive-backed discs. I clamp the collection between squares of plywood: easy cheap and works.

I oughta' do the same for the 4 1/4" grinders' paper. And the drywall paper.

OK OK, I bought the Shopsmith for $25, solely for the disc sander attachment. It's a wonder of 'does everything, but nothing well'. It's very decorative, though.

Back on point: does anybody think an air-powered sander and lots of water would be dandy for sanding the bottom? I've never liked the dust and mess of hand- or palm sander. Wouldn't it be fine for adequate power and for staying clean, keeping the discs from filling?
David

Post by David »

Two things that come to mind from your photos Jeff: The pads for your jack stands seem very small to me and I would consider adding a larger plywood pad that goes against the hull to each (similar to the jackstands on the boat next to yours). Second: is that the correct shape for the rudder? I would think the top edge would follow the line of the bottom.

For your bottom paint, I have found a sharp carbide tipped scrapper, the sort that you pull, to be fast and very effective against old layers of bottom paint.

David
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Post by TritonSailor »

Yes Dave, talking with Brian of Jollyboat, he mentioned that piece of the rudder is missing or it could have been rebuilt that way. He was looking at the same photo and I didn't know enough to look while I was there. I also don't know if I should leave the rudder as is or rebuild per the factory specs.
Those pads you mentioned were put on by the marina, it used to be their boat, you would've thought they would know...
thanks

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Post by Rachel »

The taco problem I'm having is with the 40 and 80 grit dics, actually. I think the reason they don't like to stick is that -- in this grit range -- the backing is so thick, and high-quality and stiff that the "taco-ness" has quite a bit of power to it. The PSA pad seems clean and fine, although I'll give it another going over; can't hurt. Good to know they curl with or without the plastic; I think if I ever order more I'll store them in a hydraulic press or something before they curl (because they are great discs).
TritonSailor wrote: Those pads you mentioned were put on by the marina, it used to be their boat, you would've thought they would know...
You would've... Although there are some fabulous yards, with very knowledgeable and conscientious crew, there are (sadly) just as many who will block the boat incorrectly, refuse to not block under the false keel, etc. etc. There are definitely many people you should trust and take advice from, but just know that that won't always be the case, so don't take it for granted that everything is done right, or that you should follow all suggestions just because they are pros.

I'd say that looks like a rudder off of another boat, "re-purposed" for your Triton. The general shape looks off, especially at the top, and the prop aperture is a slightly different size that the one on the boat.

David's recommendation to scrape is one I'd try. Less of the noxious dust, and plus, you just never know what's going to work best in a given situation until you try a few methods.

Rachel
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Post by Tim »

Rachel wrote:The taco problem I'm having is with the 40 and 80 grit dics, actually.
Maybe you just don't use them up fast enough. ;<)
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Post by Rachel »

I'm aging them, like a fine wine.

R.

PS: Jeff, I just noticed that your Triton is covered and in a shelter. Don't you think you ought to share the wealth there? ;)

Also, I looked up those backing pads you linked to. I'm not familiar with those, and they may work (?) but I know you don't need them. My PC 7335R came with a hook-and-loop pad, but I ordered the Porter Cable PSA pad at the same time, and exchanged them immediately. The hook-and-loop paper is much more expensive.
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Post by Tim »

TritonSailor wrote:But I am unable to find the correct backing pads. I found a couple HERE, but I don't know if they are the right ones for the porter cable 7335.
You don't need those backing pads. The 7335 comes with a soft PSA pad that is just what you want, and need.

With the amount of paint shown on your bottom in the photos, I second (third?) the suggestion for a carbide scraper. Scrape the bulk of the paint off, then finish with the sander. It'll take you a few minutes to get used to how much pressure, etc. to use with the scraper, so be careful at first not to gouge. If you really want, you can grind the sharp corners off the blades first to prevent them from digging in. I don't do this, but it's a good idea in many cases.

Sanding bottom paint tends to heat it up, which quickly clogs discs. Discs are expensive, and so is your time. Scrape first, then sand. It's a back breaker, but you'll manage. It's a great time of year to strip your bottom this way, as the cold weather prevents you from getting too overheated, but you'll soon warm up and be comfortable as you work.
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Post by Tim »

By the way, order some 40 grit discs too. You'll need them.
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Post by TritonSailor »

Hey Rachel, I would if I could, but I'm losing the covering. The marina owned the Triton I bought so it was on their own dime. Good news is that since I bought the boat from them they will let me store outside without cover until june 1st for $276.00. What a bargain!!! Concerning the sanding, Tim, that's exactly what I'll do, is scrape first. Question is though, with all the paint off, won't 40 or 80 grit be too much for what's left?

Thanks

Jeff
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Post by Tim »

No. Particularly the 80. 80 doesn't cut nearly as fast as you think it will on fiberglass or bottom paint. Use the 40 at your own judgment. I know what it does; you may not yet. It's not like using these coarse grits on wood.
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Post by kendall »

may not be relevant, but I recently sanded the bottom of my Ariel, and the paint was very resistant to sand paper, but I played around and found out that using a regular single edge scraper allowed me to get nearly all the paint off one side in a couple hours.

Took two hours to sand a roughly a 2x2ft section, then after trying the scraper I managed to do the rest of the hull in the same time.

Had at least three layers of paint, not sure of coats per layer.

Won't say it's a sure thing, it may have been an error in one of the first coats that made it so easy, but I'll grab the scraper first next time I have to do it.

Ken.
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Post by Rachel »

kendall wrote:Took two hours to sand a roughly a 2x2ft section, then after trying the scraper I managed to do the rest of the hull in the same time.
Sweet! And now that's done :)
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Post by Peter »

I swear by the carbide scraper too. The one I use is only 2" wide and the blade is reversable. The narrow blade doesn't cut such a wide swath, but needs less horsepower to move it.
I used three double blades to do the Vega.
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Post by Tim »

This is a good one. Mine are just like this, but without the knob.

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Post by TritonSailor »

I've started looking at them, I balked at the first few when they were only 1.5"-2" long, I thought no way this will take me forever. I quickly found out that the longest one so far is 2 3/8". But as far as the job it does, it's not a b ad price for between $12-15

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Post by Duncan »

I've heard that if you combine a heat gun with the scraper, the old paint comes off very smoothly.
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Post by cmartin »

Some of this depends on what you plan to do with the boat. Are you racing and every week and need to be as slick as possible? Looking for to be the best boat possible? Or, do you like sailing more than sanding/scraping?

There is nothing wrong with scraping off the stuff that comes off quickly then sanding the rest, assuming you are in the last camp. I found after 1 go around with the scraper most of the loose stuff comes off. Take another pass with the sander then paint.
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Post by jollyboat »

Jeff, I might wrap the boat in skirt to work under or get the boat out of the shed that you are in before starting a sanding project of any kind with other boats in the shed. The sanding dust will go everywhere unless you are planning on using a vacume recovery system too. Just a thought.
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Post by TritonSailor »

Hey Brian,

Depending on if they leave me under cover or not, I was thinking of hanging a tarp and working on the inside of it with a respirator. I don't think the marina will send a welcome committee if I let loose a dust storm in the enclosure!

Jeff
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Post by Figment »

Hey, at least you don't need to scrape/sand this monstrosity...

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Post by TritonSailor »

Yesteice rday I went to Lowes's and found a nice 2 3/8" Kobalt scraper with a carbide tip. What I found out though, which is par for the course, Lowes's doesn't carry replacement blades for the tool...Why sell it then!!!
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Post by Hirilondë »

TritonSailor wrote: Lowes's doesn't carry replacement blades for the tool...Why sell it then!!!
They probably make enough money selling the tool to people who don't notice that they don't carry the replacement blades until too late.

I don't mean this to simply rub salt into the wound. One should always locate replacements, be it blades, bits, paper etc. for tools before buying them. Even great tools that will eventually be supported by the retailers often start off with replaceable items not being available. And this will continue until the buyers demand better by their consumer habits.
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Post by cmartin »

Yesteice rday I went to Lowes's and found a nice 2 3/8" Kobalt scraper with a carbide tip. What I found out though, which is par for the course, Lowes's doesn't carry replacement blades for the tool...Why sell it then!!!
They just sell more tools, no need to bother with replacement parts.
David

Post by David »

These replacement blades should work just fine:

http://www.amazon.com/Bahco-Heavy-2-Inc ... y_hi_img_c

Jamestown Dist also sells them.
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