Sealing, varnish and finishing MDF


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Old 08-07-14, 03:38 PM
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Sealing, varnish and finishing MDF

I have a little MDF project but now its about time to varnish it but not quite sure how to seal MDF properly; I have 2 pieces of scrap mdfs and sealed it with PVA glue mixed with water turns out okay I guess but it doesn't seems to fully seal the edges.

So the first sample, I varnished it already but few coats and sanded in between coats which turned out pretty okay and smooth but I don't quite like the feel of it when it gets warm because it feels a little rubbery. Was wondering how to properly finish a varnished project and remove the rubbery feel.
 
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Old 08-08-14, 03:31 AM
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but I don't quite like the feel of it when it gets warm because it feels a little rubbery.
I'm having a hard time comprehending that can you better explain it?
What is causing the heat? sanding? or is there a heat source? Did you use oil base or waterbased varnish? How long ago was it applied?
 
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Old 08-08-14, 04:42 AM
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well its more likely sticky sorry for choosing the wrong word. Well by just placing my hand on top of the varnished wood really and the varnish is a water-based one. Well its been two days now, I left 4hrs apart before applying another coat.
 
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Old 08-08-14, 05:21 AM
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I don't often use water based poly/varnish so I don't know a lot about them Latex enamels are prone to 'blocking' which means when pressure is applied to them they tend to get sticky. I don't know if the same is true for water based varnish. Waterbased coatings often take a week or so to fully cure.
 
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Old 08-08-14, 05:24 AM
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I see I guess i'll just have to wait and see, but is pva glue diluted with water okay to use to seal the edges? Also can you give me some tips to properly or get nice smooth finish.
 
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Old 08-08-14, 05:29 AM
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I don't know a lot about using glue to seal the edges, I normally use multiple coats of the poly/varnish.

You need to sand the varnish smooth with 180 or 220 grit sandpaper, remove the sanding dust and apply the next coat of varnish. A good quality brush works better than a cheap one. Sometimes it's beneficial to thin the coating slightly so it will flow better, eliminating or at least reducing brush marks.
 
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Old 08-08-14, 05:36 AM
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The thing about the edges of mdf it soaks the varnish very quick and it turns the edges very dark and won't match the surface. Any particular type of brush or just good quality ones? How can I thin a water-based varnish? It says on the tin just to add clean water then others on the internet says mineral spirit (is white spirit the same as mineral)?
 
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Old 08-08-14, 05:48 AM
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Mineral spirits is for thinning oil base coatings, you'd use a small amount of clean water to thin water based varnish.
I've always been partial to the Purdy brand of brushes but there are quite a few other brands that have quality brushes. You'll want nylon, polyester or nylon/polyester blend bristles - I prefer the latter. The main thing is to stay away from the cheap bargain basement type brushes. A good brush kept clean and stored in it's wrapper will last a long time. Natural bristles [usually hog hair] are only for solvent based coatings - water makes those type of bristles swell and become useless for painting.
 
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Old 08-09-14, 06:36 AM
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What is the exact product you are using? Some finishes will feel like that if they are applied really thick.

Sealing the edges of MDF works well for painting. Never put clear finish on MDF before, so I don't know if it's a good idea. Where I work now, we mix about 30-40% glue to water. Apply one coat, scuff, then apply a second coat. Since you are using clear, you should use white glue as it will dry translucent.
 
 

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