Bottom paint failure cause?

woodster · Nov 28, 2015

You must have not sanded very well in those spots I for one think that every surface needs etching (read priming) before painting especially when coating with unlike paint products might be a good time to soda blast it to gel coat and Put on a barrier coat and then new bottom paint ...I think enterlux has a barrier coat that also acts as a primer then a bottom paint ...e2000 or something like that

Davidasailor26 · Nov 28, 2015

The gray color that's showing looks to me more like barrier coat than gelcoat. I'm guessing that the PO applied the barrier but then let it dry for too long before applying the paint. Not sure I have a good answer for what to do about that now though.

JamesG161 · Nov 28, 2015

I can only guess at the cause. I spent 25 years making pigment for every paint manufacture world wide and was involved in hundreds of paint failure analysis.
Picture one, DSC01293
The lighter blue paint never bonded to the gel coat or maybe grey paint ( can't tell which) in the scabbed area. Plus any similar type failures.
Picture 2, DSC01294
I guess is abrasive action caused by your propeller ( on the edge) and not a bad bond. I would guess the side abrasion is on both sides of your rudder in about the same spot. If not, you are mainly on a Port tack

. I would guess that is prop wash abrasion.
Picture 3&4
They look like a mixture of bonding and abrasion.

All a paint is, is pigment (wear and hiding power), tint (eyes only ) and a vehicle ( the liquid carrier that carries the pigment to the surface, helps spread, and helps protect the embodied pigment when hardened).
Tips:
1) Read and follow the Architectural/Application specifications for prep and application, to the letter for your paint. They are available for reputable paints.
2) You would have to sand the poor bond areas until you have a "feathered edge" exposing all layers and a hand smooth feel. See Tip 1 for sanding, primer and thickness of a coat.
3) The abrasion areas, sand in Tip 2 and apply an extra coat to give more pigment to wear.

Jim...

seadaddler · Nov 29, 2015

Sounds like more aggressive sanding on the old paint making sure
all old buildup of paint is in good condition to apply new bottom paint to.
My last bottom job I changed from Pettit SR60 which is a very soft ablative and
was just not lasting and few years before used SR40 and lasted a lot longer.
But wanting to race and wanted to use a diver I switched to Sea Hawk Biocop
which is a harder harder self polishing boosted ablative.
But after contacting both Pettit and Sea Hawk for the best way to apply there paints they both told me we should always do a aggressive sanding but not down to the gelcoat for a good adhere to with the new paint and so far on 2 years my diver reports the bottom paint is working very good and in great shape.
Nick

rgranger · Nov 29, 2015

Related I promise but first a back story....I have purchased and restored 7 very old and badly neglected sailboats. One of the first things I do is a peel-away (home made) to expose the hull. I have found that bottom paint can hide a lot of cracks and gouges in the bottom. Anyway, every time I have done the peel-away thing, most of the paint just sloughs off but there is always a few spots where the bottom paint is stubborn and nothing short of 60-grit sand paper will get it off the hull. I wish I knew why! If I could reverse engineer that adhesion, I would be rich. There must be something about the bottom of the hull (in those spots) when the paint was applied. Either it was completely free of dust and wax.... or maybe the bottom coat was still curing. I would not sand blast the entire hull. I would focus on the spots giving you trouble. If a good sanding doesn't work, then maybe apply a patch of barrier coat on those spots and then put your bottom coat on while it is still relatively young.

JamesG161 · Nov 29, 2015

JamesG161 said:
2) You would have to sand the poor bond areas until you have a "feathered edge" exposing all layers and a hand smooth feel. See Tip 1 for sanding, primer and thickness of a coat.

Also get the applications specs. If you give me your paint brand, I will get them for you.

rgranger · Nov 29, 2015

Home made peel away is very easy.....

Go to Lowes or Homedepot and get a 3 lb bag of garden lime. There are several things people call lime...You want the calcium hydroxide or calcium oxide (strong and nasty stuff be careful with your eyes).... It is a white powder much like baking flour.....then you need either sodium or calcium hydroxide... (about 4 cups)....I'm a chemist so it is easy for me to get but you can also find it as drain-o or other pipe cleaners... or if you have a seed co-op or tractor supply, you can find it there.... Put all of that in a 5 gallon PVC bucket and SLOWLY add water until it is the consistency of thick pancake batter (melted peanutbutter).

I use a roller on a pole to apply... put it on thick... I also lay burlap on the ground and once I've applied, I pull the purlap up and tape it in place. I've also done this with plastic sheeting. This just keeps it moist so it works longer. Let it sit overnight and lay the burlap back on the ground then pressure wash your hull. The paint will come off in big sloughs and the burlap will catch it for disposal. This recipe will make a lot more than you need ... just put the lid on the PVC for use later. Reapply to the stubborn spots and do it all over again. After that, any spots that won't come off will need to be sanded. But this will get more than 90% of the bottom paint off and leave your gel coat untouched. Total cost of ingredients is about $10.... maybe $20 if you have to buy a PVC bucket and a roller + pole.

JamesG161 · Nov 29, 2015

rgranger said:
You want the calcium hydroxide or calcium oxide (strong and nasty stuff be careful with your eyes).... It is a white powder much like baking flour.....then you need either sodium or calcium hydroxide... (about 4 cups)....I'm a chemist so it is easy for me to get but you can also find it as drain-o or other pipe cleaners.

I would by some full eye goggles, rubber gloves and have a standby water hose to emergency wash every thing that mix comes in contact with. This mix will BURN your skin!
Take care!
Jim...

bffatcat · Nov 29, 2015

rgranger said:
Home made peel away is very easy.....

Go to Lowes or Homedepot and get a 3 lb bag of garden lime. There are several things people call lime...You want the calcium hydroxide or calcium oxide (strong and nasty stuff be careful with your eyes).... It is a white powder much like baking flour.....then you need either sodium or calcium hydroxide... (about 4 cups)....I'm a chemist so it is easy for me to get but you can also find it as drain-o or other pipe cleaners... or if you have a seed co-op or tractor supply, you can find it there.... Put all of that in a 5 gallon PVC bucket and SLOWLY add water until it is the consistency of thick pancake batter (melted peanutbutter).

I use a roller on a pole to apply... put it on thick... I also lay burlap on the ground and once I've applied, I pull the purlap up and tape it in place. I've also done this with plastic sheeting. This just keeps it moist so it works longer. Let it sit overnight and lay the burlap back on the ground then pressure wash your hull. The paint will come off in big sloughs and the burlap will catch it for disposal. This recipe will make a lot more than you need ... just put the lid on the PVC for use later. Reapply to the stubborn spots and do it all over again. After that, any spots that won't come off will need to be sanded. But this will get more than 90% of the bottom paint off and leave your gel coat untouched. Total cost of ingredients is about $10.... maybe $20 if you have to buy a PVC bucket and a roller + pole.

bffatcat · Nov 29, 2015

about bottom paint
My 2 C Down thru the years Ive used different kinds of paint. Experience has taught me to stick with the tried and true. In the 70`s I used pettit unipoxy a hard paint that needed a lot of prep work every season As soon as the ablative paint came out I began using that. Today I use Donovan marine ablative B Prep work is easy a little sanding on the rough spots in the spring and one fresh coat One thing I did learn: friends that switch around from soft to hard, water base to oil seem to run into problems I use the same paint every year No problems

rgranger · Nov 29, 2015

JamesG161 said:
I would by some full eye goggles, rubber gloves and have a standby water hose to emergency wash every thing that mix comes in contact with. This mix will BURN your skin!
Take care!
Jim...

Yeah! What he said!!!!!!

uncledom · Nov 29, 2015

If it was actually barrier coat that you scuffed and painted it will have an adhesion issue. I believe you need to lay the first coat of anti-foul over the barrier before it has cured.

JamesG161 · Nov 29, 2015

njlarry said:
Each of the past two years it was Pettit Hydrocoat applied after vigorous scotch brite sanding applied over a thin coat ablative that should be ok with the Hydrocoat. After the first season it came out looking showroom new.

http://www.pettitpaint.com/fileshare/product_pds/Hydrocoat.pdf
This the link to the application specs.

This from just part of the info.
Previously Painted Surfaces: To paint old, hard antifoulings, thoroughly wipe down the surface with 120 Brushing Thinner, paying particular attention to waterline areas, then sand painted surface with 80 grit sandpaper. Wipe clean of sanding residue with water and apply Hydrocoat. Old tin or copper copolymers or Teflon based antifoulings should be sanded thoroughly with 80 grit sandpaper to remove the chalky outer surface, wiped clean of sanding residue, and then may be over coated directly with Hydrocoat. Traditional, soft antifoulings should be removed before applying Hydrocoat.

Read completely the section titled SYSTEMS. Another partial quote from that section.

Fiberglass bottoms potentially can form osmotic blisters within the gelcoat and into the laminate. To render the bottom as water impermeable as possible, prepare the fiberglass surface as mentioned above (sanding method) then apply three coats of Pettit Protect 4700/4701 Gray High Build Epoxy Primer or three coats of Pettit Protect 4100/4101 White High Build Epoxy Primer per label directions. Apply two or three thin finish coats of this product.

I can confirm the hours of technical testing done to make these detailed instructions.

If you would like an explanation of the how's and why's of this document. Send me a private message and we can make a phone contact.

It more than sanding to complete a good bottom protection.
Jim...

Maine Sail · Nov 30, 2015

njlarry said:
We scuffed the prior bottom paint not the barrier coat. I am thinking that it is not a barrier coat issue as the bottom paint was in good shape for the PO when hauled before I purchased it and was also good after our first season. Other application issues, too thick????

Merely scuffing the paint is often not enough when switching paint types. The directions needs to be followed to a tee..

If the original paint (what you painted over) was not applied properly over a barrier coat it will eventually fail to bond and can look exactly like your photos. It can take a few years but once it starts it just tends to get worse until massive chunks are literally flaking off..

I have seen this numerous times with a lack of adhesion/bonding to a barrier coat and in nearly every case it has been caused by an improper application of the first layer of paint over the barrier coat..

Paint over barrier really should be "hot coated" for the best chemical bond. If you do this correctly the first layer of paint will not flake off as it physically bonds to the barrier coat..

Hot coating involves two people, one applying the last coat of barrier and a chaser applying the first layer of bottom paint, when you can leave a thumb print but not get any barrier on your thumb. Proper application and the correct & compatible products are critical in this stage. If the barrier was allowed to cure beyond thumb-print then judicious sanding & washing needs to take place and even then the paint will usually not adhere as well as when hot-coated.

Barrier coats are often incorrectly applied & used. Done poorly the results can be a real PITA a few years down the road......

rgranger · Nov 30, 2015

njlarry said:
Thanks Rgranger! If I read correctly sodium hydroxide, calcium hydroxide and calcium oxide are all equally good. Would it be safer to put the water solvent in first and then add the stronger hydroxide solute to the water? Also do you think I could use up some landscaping fabric instead of burlap?
Anyway I owe you my thanks and my secret Limoncello recipe;
Put the zest of 6 to 8 lemons in 750 ml of 100 proof vodka (two mason jars are perfect) for 3 weeks to two months. Shake about one a day. When ready, strain twice into a bowl and mix in 750 ml of simple syrup ( 2 cups sugar stirred into 2 cups hot water on the stove). Promise kept.

I just put the garden lime in the PVC bucket, add water with stirring... then add the KOH... about two to three cups worth. Probably could just dump two cans of drain-o....I don't think it matters what you use to keep the paste moist. I have even let it dry without a cloth and just re-wet it with a light mist using the "thumb over hose end" approach a few times before blasting it off. And I have used plastic sheeting and once an old tarp. I think the commercial stuff uses sheets of wax paper.... so maybe an old news paper would work also. The nice think about burlap is that it strains the mess when you blast it off... so you can catch all of this toxic paint for proper disposal.

One mistake I did make (once!).... on one of my boats, I applied and then got busy and didn't get back to it for several weeks. This is nearly the same chemical mix as brick mortar.... and brick mortar slowly converts into calcium carbonate (lime stone). I ended up with a hard, insoluble layer of mortar on my boat that then required scrapping. Don't leave it on the boat for more than a day or two... maybe three but then GET IT OFF before it sets all the way. Otherwise, you will have made a lot of work for yourself.

What is "zest"?

Bottom paint failure cause?

.

Attachments

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.