Rule of thumb for cloth, thickened epoxy or just fairing in abundant blister repairs?

[Prairie Schooner]

We glassed all the deeper blisters where we had ground beyond the chop layer. Some of those covered a relatively big area. We finished that part a while ago. Now it about how to get the final layers of fairing on most efficiently and deciding how much fairing is enough. I don't think we are there yet.

Ditto everything Ray (Pete the Cat) said, above. I found the following long board very helpful. I'd locate and rough down the high spots with it, then move to a power sander.

https://www.amazon.com/Tool-Aid-89890-Flexible-Sanding/dp/B000HHGOOM/ref=sr_1_2?crid=7MZR3OFO5Q8F&keywords=tool+aid+s%26g+%2889890%29+flexible+sanding+board&qid=1667681249&sprefix=%2Caps%2C162&sr=8-2

I had visions of a perfectly fair surface. Before I reached perfection my 66 year old arms ran out. Fatigue determined how far I carried it as much as desired finish. If I were going to do an entire boat bottom, I'd look into a pneumatic long board.
I liked Total Boat fairing compound. It adhered really well and sanded quickly.
It's a long, exhausting job. Keep moving the rock forward. Good luck.
Jeff

 

[PANorth]

i am not sure what equipment and process you using to fair the hull--or of what specific issues you are encountering with your current approach, but--in my experience--technique and equipment matters. A dual action sander (larger is better, but increased weight comes with size) with the capability of vacuuming aggressively through the paper is required so that you can keep going. Personal protection is really really important--the guys who so this professionally use positive pressure suits because the dust is really awful. And you have to keep the DA moving widely over the surface--technique matters. It is exhausting overhead work that I could not do at 75 anymore. I recall that when we faired the bottom of my Tartan 37 the we had about 80 hours in the effort using West System. I liked System 3 but the shelf life of the stuff was so poor (is it still?) that we stopped using it at the yard where I worked--makes a gooey mess if it gets past its useful time. Just thoughts about the process. My experience was 25 years ago and things might have changed. The bottom of my Tartan still looks perfect.

We have a Bosch random orbital sander with 6" discs. I think it's the fancy kind. Is that the type of sander you are talking about?

 

[Gaviate]

An observation without really seeing....somewhere in this thread I read that you're using drywall tools, aka knives, to spread the fairing compound with resulting "dimples" showing where more compound is needed. These dimples may be caused by using a straight blade on a curved surface. When I redid my bottom, I used a 6 inch steel drywall knife which I bent to match the curve of area I was working on (it'll never be straight again). This left the fairing compound high in the middle and nearly flush at the edge and easier to sand down to fair. This will work with any size knife. I suspect that by now, you have enough experience with your tools that you could do a side by side comparison (straight blade/bent blade) and observe whats happening. Drywall knives are bendy but if you don't intentionally bend them to suit you, they always want to be straight, even when running across a curved surface.

 

[PANorth]

An observation without really seeing....somewhere in this thread I read that you're using drywall tools, aka knives, to spread the fairing compound with resulting "dimples" showing where more compound is needed. These dimples may be caused by using a straight blade on a curved surface. When I redid my bottom, I used a 6 inch steel drywall knife which I bent to match the curve of area I was working on (it'll never be straight again). This left the fairing compound high in the middle and nearly flush at the edge and easier to sand down to fair. This will work with any size knife. I suspect that by now, you have enough experience with your tools that you could do a side by side comparison (straight blade/bent blade) and observe whats happening. Drywall knives are bendy but if you don't intentionally bend them to suit you, they always want to be straight, even when running across a curved surface.

These too are bendy knives. I did the same as you but tried to match the curve of the hull. I will make the next application a little high in the middle. I also think that the cured fairing is soft enough that it sands more quickly where its thicker, i.e. over the divot, than over the hard intact hull material. The soft pad on the random orbital sander probably conforms to that surface softness. That's my guess.

 

[Pete the Cat]

We have a Bosch random orbital sander with 6" discs. I think it's the fancy kind. Is that the type of sander you are talking about?

If it is the type attached to a vacuum it will work. The pros use a larger DA that I think makes the smoothing a bit easier but the machine is heavy. Keep it moving all the time.

 

[PANorth]

If it is the type attached to a vacuum it will work. The pros use a larger DA that I think makes the smoothing a bit easier but the machine is heavy. Keep it moving all the time.

Yes, it attaches to a vacuum. I am pretty sure its the type of sander the pros use. There was so much sanding to do, I decided to buy a good one. I hooked it up to a DIY dust collector between the sander and the shop vac. The dust collectors catches some of the dust but most goes through to the shop vac. It was difficult to set it up so the vac didn't collapse the plastic bucket I was using as the barrel of the collector.

 

[Loren Beach]

Check out a powerful bag-type vac made for pulling dust thru hose from a sander. There are larger and alternative brands, but the Fein product is excellent. I have been using the previous model for years. (The 'little' one that looks a bit like a Dalek...!)

 

[Nick J]

It took a while for me to realize how important a good sander with dust collection is when you own a boat, especially an older one that needs work. When i finally came to my senses, I bought this one (recommended by the Sail Life Youtube channel):

https://www.amazon.com/Bosch-Power-Tools-Aggressive-Woodworking/dp/B07WK42NC5/ref=asc_df_B07WK42NC5/?tag=&linkCode=df0&hvadid=385272107002&hvpos=&hvnetw=g&hvrand=7473860846972713312&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9033347&hvtargid=pla-826243574532&ref=&adgrpid=78829231656&th=1

The dust collection is awesome when you use mesh sanding discs. Don't get me wrong, sanding is still horrible, but this makes it a little less horrible. It fills the gap between a grinder and a regular orbital sander allowing you to take more material off while limiting the risk of going too deep.

 

[PANorth]

It took a while for me to realize how important a good sander with dust collection is when you own a boat, especially an older one that needs work. When i finally came to my senses, I bought this one (recommended by the Sail Life Youtube channel):

https://www.amazon.com/Bosch-Power-Tools-Aggressive-Woodworking/dp/B07WK42NC5/ref=asc_df_B07WK42NC5/?tag=&linkCode=df0&hvadid=385272107002&hvpos=&hvnetw=g&hvrand=7473860846972713312&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9033347&hvtargid=pla-826243574532&ref=&adgrpid=78829231656&th=1

The dust collection is awesome when you use mesh sanding discs. Don't get me wrong, sanding is still horrible, but this makes it a little less horrible. It fills the gap between a grinder and a regular orbital sander allowing you to take more material off while limiting the risk of going too deep.

That's the one we have.

 

[PANorth]

Check out a powerful bag-type vac made for pulling dust thru hose from a sander. There are larger and alternative brands, but the Fein product is excellent. I have been using the previous model for years. (The 'little' one that looks a bit like a Dalek...!)

Did you intend to include a link? I'm not sure I'll like this, the Daleks creep me out.

 

[Loren Beach]

Turbo I | FEIN Power Tools, Inc.

Compact wet and dry vacuum cleaner with connection for power tools during workshop and installation use. Product number: 9 20 35 236 09 0

fein.com

This seems to be their current base model. It does incorporate a tool plug in, which would be handy. Our prior base model does not have that feature. Shape is now more boxy so you will not be bothered by references to Daleks... !
The 'secret' to the usefulness of this model (or its competitors) is that inside is a large bag trapping the dust.

 

[Gaviate]

inside is a large bag trapping the dust.

Its true, I will not run a vacuum without a proper bag installed in addition to the filter on the motor. The fine particles produced by power sanders easily escape the motor filter and the plastic drum/container of the vacuum by itself, is in no way an air tight assembly. A vacuum bag is needed to achieve adequate containment.

 

[PANorth]

Its true, I will not run a vacuum without a proper bag installed in addition to the filter on the motor. The fine particles produced by power sanders easily escape the motor filter and the plastic drum/container of the vacuum by itself, is in no way an air tight assembly. A vacuum bag is needed to achieve adequate containment.

I watched some Youtube videos for DIY dust traps. The primary method is to create a cyclone in a container where the dust is supposed to lose momentum and settle to the bottom. I found that it worked pretty well, at least for the courser dust, as long as it was air tight. But that eventually also caused the five gallon bucket being used as a barrel to collapse. So I let a little air leak in around the vacuum hose in the top. But then the amount of dust retained in the barrel was greatly diminished. I wonder if there is a material that can cover the exit hose, containing the dust in the barrel but allow for sufficient air flow to keep drawing dust from the work site. Any ideas?

 

[Pete the Cat]

I watched some Youtube videos for DIY dust traps. The primary method is to create a cyclone in a container where the dust is supposed to lose momentum and settle to the bottom. I found that it worked pretty well, at least for the courser dust, as long as it was air tight. But that eventually also caused the five gallon bucket being used as a barrel to collapse. So I let a little air leak in around the vacuum hose in the top. But then the amount of dust retained in the barrel was greatly diminished. I wonder if there is a material that can cover the exit hose, containing the dust in the barrel but allow for sufficient air flow to keep drawing dust from the work site. Any ideas?

I have never used anything but a ShopVac for connection to my sanders. I use the special expensive bags that are meant for trapping drywall dust. I the dust from sanding fiberglass is really not good for you and is ridiculously fine. The guys who do the big jobs in the yard where I have worked dress in positive pressure suits to prevent breathing the stuff.

 

[PANorth]

I have never used anything but a ShopVac for connection to my sanders. I use the special expensive bags that are meant for trapping drywall dust. I the dust from sanding fiberglass is really not good for you and is ridiculously fine. The guys who do the big jobs in the yard where I have worked dress in positive pressure suits to prevent breathing the stuff.

The health aspects of the work are not usually emphasized except in general terms. Or maybe it just takes a while to sink in. This is important information.

 

[tenders]

Something else to consider about sanding in this project: epoxy in whatever form you’re using it is MUCH MUCH easier to sand within 24 hours of application, as I learned on my 2021 bottom job and had to relearn in my 2022 topsides paint job.

The difference is vast between laying it down one day and abrading it the next day, vs. putting it down Sunday afternoon and coming back to sand it the next weekend (or even Wednesday).

Fairing compound in particular is a walk in the park this way. When fresh it is softer than the surrounding polyester resin and yields nicely without clogging the sandpaper. When cured it is the same hardness as the surrounding polyester, and it is much more work to slough.

 

[Prairie Schooner]

Something else to consider about sanding in this project: epoxy in whatever form you’re using it is MUCH MUCH easier to sand within 24 hours of application, as I learned on my 2021 bottom job and had to relearn in my 2022 topsides paint job.

The difference is vast between laying it down one day and abrading it the next day, vs. putting it down Sunday afternoon and coming back to sand it the next weekend (or even Wednesday).

Fairing compound in particular is a walk in the park this way. When fresh it is softer than the surrounding polyester resin and yields nicely without clogging the sandpaper. When cured it is the same hardness as the surrounding polyester, and it is much more work to slough.

Indeed.
In fact, if you catch the fairing compound when it's still just a little bit rubbery, you can knock the high spots down with a Surform file. Keep a wire brush handy to clean it out.

 

[PANorth]

There are so many tricks to this trade that are not included in the West Systems fiberglass repair guide. Who wants to write the definitive how-to book?

 

[Pete the Cat]

BTW: If you do a whole bottom with a household (not commercial steel of Fein tool type) Shop Vac, you should consider the vacuum expendable with the job--it will not last a very long time. The dust is so fine that some of it will get in the vacuum's motor and I have destroyed four of them in the last 25 years on my own boats despite using the drywall dust capturing bags. The vacuums are not expensive, but it underscores the need to use the best bags you can find and protect yourself from the dust (and the microfibers in the epoxy fillers and adhesives while mixing) that you cannot see. I think first quality 3M mask suitable for paint spray might be OK for short exposure and wear a Tyvek suit, but I am sure I have compromised my lungs significantly over the years of building and rebuilding numerous boats despite my efforts to protect myself.

 

[Kenneth K]

but I am sure I have compromised my lungs significantly over the years of building and rebuilding numerous boats despite my efforts to protect myself.

I've wondered about that too. Then again, with all the $$ I burn on the boat, I can't afford to live forever. Maybe it all works out..