Priming over paint ?

[Dick Wynne]

I just painted the topsides on the whaler, Epifanes dark blue over "Pusser's" white. 2 coats is fine, except there are many tiny lines where the paint hasn't 'taken', eg around some fasteners, along some plank seams etc, it's as if some of the white was a bit chalky, or even filler of some kind. I don't really want to remove all the blue, it may as well stay on for its protection value, but I intend to prime the whole already-painted boat and paint her again to get a uniform colour. Question: Prime with what?

[Wild Wassa]

The word prime has me a bit confused? Compatible paint bases do not need priming. They need keying.

Prime in reference to paint, means first, as in the first coat. A primer might not be the best coat to link the paint with.

Also if you can take the fittings off it will make painting easier and allow for better uniform keying. Good thorough prep is the most important part of painting. Applying paint is the easy part of painting ... getting there takes the real time.

What did you clean the old paint with?

What grit did you cut back and key the original/old paint with?

Is the scratch pattern uniform?

Is your new paint the same base type as the old paint?

There sounds like there could be a bedding compound or a seam sealant or contamination from wax that is causing the new paint to not key to the old paint, if your paint bases are compatible and the scratch pattern was uniform.

I would wash with acetone firstly, that is for any residual wax, then I'd lightly scrape the bad areas with a tungsten carbide scraper looking for sealant residues like silicon skins and then I'd sand back the areas again to attempt to unify the key, then wash again with acetone (being careful of the acetone on the new paint if the paint is still not hard ) and I'd try to blend the touch-up as much as is possible ... being sure that the paint bases are compatible.

Then re-key the lot with #280-320 and recoat to get a uniform coat. If you are spraying re-key with #400.

Warren.

[Dick Wynne]

Thanks WW


The word prime has me a bit confused? Compatible paint bases do not need priming. They need keying. Also if you can take the fittings off it will make painting easier.

Prime in reference to paint means first as in the first coat. A primer might not be the best coat to link the paint with.

Understood, but there are so many areas of poor adhesion that I guessed it was easier to treat the whole hull with something which would cover the troublesome parts, and read somewhere that primer can be effective between old & new paint anyway.

What did you clean the old paint with?

Nothing, just sanded it.

What grit did you cut back and key the original paint with?

#80

Is the scratch pattern uniform?

More or less

Is your new paint the same base type as the old paint?

Both thin with turps or white spirit so I guess so

There sounds like there could be a bedding compound or a seam sealant or contamination from wax that is causing the new paint to not key to the old paint, if your paint bases are compatible and the scratch pattern is unifom.

I would wash with acetone firstly, then I'd scrape the bad areas with a tungsten carbide scraper looking for sealant residues/skins and then sand back the areas again, then wash again with acetone (being careful of the acetone on the new paint) and I'd try to blend the touch-up ... being sure that the paint bases are compatible.

Then re-key and recoat to get a uniform coat.

Warren.

She's clinker built, and rubbing down between coats its all to easy to remove paint from the plank edges altogether. In domestic painting, instead of sanding I wash between coats with sugar soap (not to be confused with the American cosmetic product of same name!) which cleans & degreases and provides key without being too aggressive. It seems to work fine This might work on the boat and replace both the acetone and the sanding, but I'll try a patch first.

[Wild Wassa]

Dick, you can use Sugarsoap as part of the cleaning process but I will not advise it as the total cleaning process.

Emulcifying cleaners like Sugarsoap are only strong detergents. Contaminents like waxes need solvent or spirit cleaning agents like acetone to break them down. Acetone will help to soften residual sealants which will make scraping them off easier. Sugar soap will only clean their surfaces. Any surface for painting sould be squeeky clean. Nothing finishes off the cleaning process like acetone or Prepsol or Prepsole Wipes.

Sugarsoap doesn't cut through the surface to reveal fresh paint. Paint that hasn't been exposed to the elements is important in the keying process. Keying doesn't just create a microscopic crevice for paint to lock into it exposes fresh paint to the new paint.

I honestly do not feel there are shortcuts to be taken once problems have arrisen. I think it is too great a gamble to take shortcuts ... go for the ultimate result straight away now, ... unless you are a gambler?

When it comes to doing the edges of the planks take time and go slowly, if you do cut through in spots then re-prime. Do the edges with #280 - 320 that will provide enough key without cutting back too much old paint. I will not even recommend using a rough Scothbrite pad on the plank edges in an attempt to preserve the paint because a Scotchbright pad is only a cleaning pad and it will not reveal enough fresh paint on the edges of the planks to benfit their painting.

Good luck.

Warren.

[Dick Wynne]

Thanks Warren, sounds like good advice, and I have too much time invested to take any chances

Dick

[mike hanyi]

Dick you seem to love to paint topsides, is it that the raid number keeps pulling off the paint again!?!