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PostPosted: Fri Oct 13, 2017 11:55 pm 
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Hi. Really hoping someone could give me a quick solution to this!

I bought some mdf letters to go on the wall in my sons bedroom and wanted to paint them with some left over emulsion that was used for one wall in his room. Rushing a bit, not researching enough and trying to use what I already had in the garage, led me to use 2 coats of pva, sanding in between coats, to seal both the edges and face on. I have just put the emulsion on to find it cracking terribly as soon as it started drying :( Is there a quick and easy way to rectify this without having to spend more money?!

Thank you


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PostPosted: Sat Oct 14, 2017 12:16 am 
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I'm no expert on paint but emulsion paint is happier on porous surfaces than non-porous materials, but like I say, I'm no expert and I'm sure someone will come along later and advise... :dunno:

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PostPosted: Sat Oct 14, 2017 9:57 am 
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The problem you have is that PVA is water soluble so using emulsion will reactivate it and that is what has happened. PVA sealing will work with an oil based paint but it is not ideal. For MDF I always use Zinsser BIN which is a shellac based primer and this really need two coats. Work quickly, first coat looks crap but comes good on second. As it dries in a very short time you can get the two base coats on in an hour and, in this instance the emulsion top coat on shortly after.

By this time you will probably have lost the impetus to do the work you need, and the cost of the paint (£20 for a litre of BIN) all the rubbing back etc. If you follow this plan then it will come good. :thumbright:

DWD

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PostPosted: Sat Oct 14, 2017 10:02 am 
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Thanks for your reply. So get some of this BIN and just go over the pva coats I've done already? Or do I need to sand the pva down first?

Also do I need to sand between coats of BIN? Thanks again


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PostPosted: Sat Oct 14, 2017 10:13 am 
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Yes, sand it flat first but no need to try to remove. First coat of BIN, it looks streaky and goes off very very quickly so use a 2" brush and get it on. After an hour you can sand it back lightly to get rid of any ridges and nibs. The second coat reactivates the first slightly and it levels off nicely. Very light sanding an hour or so after this and then your top coat (s) You can tell if BIN is dry if it sands and does not drag at the paper. Use some used sand paper, nothing too aggressive.

You can get BIN at Screwfix see https://www.screwfix.com/p/zinsser-b-i- ... /29661#_=p

Good luck :thumbright:

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PostPosted: Sat Oct 14, 2017 12:14 pm 
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Thanks so much. I will def do this. So hope it works!


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PostPosted: Sat Oct 14, 2017 12:47 pm 
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would love to know what made you think of putting 2 coats of pva on the mdf to start with.


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PostPosted: Sat Oct 14, 2017 6:06 pm 
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Might be worth getting a spray can of BIN at half the price and saves you needing to knacker a brush or by meths. Sits a bit nicer too.



For this message the author Desmondo15 has received thanks - 2: dewaltdisney, OchAye
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PostPosted: Sat Oct 14, 2017 6:07 pm 
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Might be worth getting a spray can of BIN at half the price and saves you needing to knacker a brush or by meths. Sits a bit nicer too.


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PostPosted: Sat Oct 14, 2017 6:32 pm 
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I didn't know they did spray cans if it Des, I will check that out for small jobs.

Cheers

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PostPosted: Sat Oct 14, 2017 7:42 pm 
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Thanks so much. I did see that when I looked online earlier but I wasn't sure it would be suitable. Sounds easier so perhaps I'll give that a go :)


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PostPosted: Sat Oct 14, 2017 9:37 pm 
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I much prefer it for spot priming and knots. They do cover stain and a few others now. Small projects like a stool or sill it's ideal. It also IMO don't need rubbing down so much.


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PostPosted: Sun Oct 15, 2017 9:05 am 
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Desmondo - do you think one can would be enough for me to cover 8 letters 20cm tall? Just wondering whether to pick up one or 2 cans today. Thanks again


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PostPosted: Sun Oct 15, 2017 9:17 am 
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Yes 1 should do it - give it a good shake and then some more, have a bit of a test area to get the feel of it too.


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PostPosted: Sun Oct 15, 2017 9:35 am 
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The knack in spraying is to start spaying before you hit the work and keep moving at an even pace and stop spraying after you leave the work. Gauge the next run to allow for minimum overlap so it does not develop 'bands' Do not try to get it perfect with the first cover. The object is not to overcover, just a nice even coat without build ups that might cause runs. Spray obliquely on the edges not straight on with gentle bursts and steady movement.

I hope it all goes well and post a picture when you have done :thumbright:

DWD

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