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 Post subject: WHY DOTS ON GLOSS PAINT?
PostPosted: Fri May 04, 2018 1:47 am 
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Any Pro. Decorators advice - Primed a new timber banister handrail with `Wilko Quick Dry Stain Blocker - White` (water based) followed by `Wilko One Coat Gloss Paint Pure Brilliant White` (self undercoating gloss) prior to surface preparation : light sanding followed by dust brush. Unfortunately the result was an imperfect finish - hundreds of tiny dots in the paint, all approximately uniform in size (1mm-2mm), WHY?. Note - 3yr old gloss, but on opening looked absolutely fine & new tin of primer.....also gloss brush was rinsed with clean white spirit and shook out and wiped on newspaper before commencing. Thanks.


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PostPosted: Fri May 04, 2018 6:54 am 
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Personally, I would have used better quality paints - prime, then undercoat, then two gloss topcoats. However, that wouldn't explain those "dots".

The cause is most likely either dust, either dust on the rail as you painted it or, more likely, dust settling on the rail after you cleared up, either from lifting the dust sheets off the floor or from your vacuum cleaner if you vacuumed.

I have had it happen to me twice. The first time was my fault for not being careful enough when lifting my sheets, and the second time was when a customer vacuumed the hall, stairs, landing and all the other rooms in the house immediately after I left, despite me telling her to wait until the next day. Now I paint everything apart from the banister rail, lift all the dustsheets and take them along with all my gear outside, vacuum the hall, stairs, and landing, have a cup of tea while the dust settles, wipe the rail with a damp cloth, lay a very clean smaller dustsheet under where I am working, and then paint the rail. A bit of a faff but I've not had a "spotty rail" since!


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PostPosted: Fri May 04, 2018 7:21 am 
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Are the dots raised or are they pinholes in the finish? Dots (raised) are likely airborne dust, while pinhole dispersion (cissing) is a surface contamination which the paint won't adhere to. You can see this effect if you try to paint silicone.

I would sand the rail with wet and dry sandpaper (180 grit used wet), wash off the rail with clean water. Once dry, degrease with methylated spirit and re-paint. Given the tin of paint was 3 years old, I'd be inclined to get a fresh tin to be sure it wasn't something in the original tin.

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PostPosted: Fri May 04, 2018 6:27 pm 
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dynamod wrote:
Are the dots raised or are they pinholes in the finish? Dots (raised) are likely airborne dust, while pinhole dispersion (cissing) is a surface contamination which the paint won't adhere to. You can see this effect if you try to paint silicone.

I would sand the rail with wet and dry sandpaper (180 grit used wet), wash off the rail with clean water. Once dry, degrease with methylated spirit and re-paint. Given the tin of paint was 3 years old, I'd be inclined to get a fresh tin to be sure it wasn't something in the original tin.
Yeah, sounds more like silicone contamination, but also cleaning brushes in white spirit and using in water based paint isn't the best plan. Spirit and water don't go well together.

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PostPosted: Fri May 04, 2018 7:36 pm 
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Not sure if the Wilko gloss is water-based or oil-based, but if there was cross-contamination between different paint bases on the same brush, it certainly wouldn't help.

Oil-based top coats over a water-based under/base coat shouldn't really cause any issues, provided everything is clean, dry and you use separate brushes for each coat.

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PostPosted: Fri May 04, 2018 8:25 pm 
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The second coat (gloss) is OB given what the OP wrote first time. I think you are correct on cissing Dyna (been there done that wiping something in between coats after sanding with a dodgy cloth) but took a few years to figure out the problem.


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PostPosted: Sat May 05, 2018 10:21 pm 
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Thank you to everyone who posted a response, appreciated. However, I am still baffled as to why the paint finish was imperfect - as I applied the water based primer with a clean quality synthetic bristle brush and for the oil based gloss used a quality natural bristle and dry sanded with a 120 grit outside and as stated earlier brushed off thoroughly with an old paintbrush - then painting the handrail indoors - no other painting was undertaken or DIY projects at the time. And the dots were raised not dimpled: could the paint formulation have broken down despite looking fine? Thanks.
PS.
Did not vacuum either.


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PostPosted: Sun May 06, 2018 9:30 am 
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Raised dots, may have been raised grain leaving aside that the paint itself may have been faulty.


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