Painting shuttering ply

[fraser]

Hi
I am currently painting some shuttering ply and have given it 3 coats of slightly thinned down matt emulsion. The ply is quite knotty, and one piece is quite resinous, both of which are both still showing through the paint. However there is also some yellow patches now showing, which I keep painting over between coats but can't seem to get rid of.
What is this and what's the best way to paint over it now it is 'primed'
I'm not looking for a perfect finish as it's only to line the shed but would like a good solid final coat to get rid of the knots, resin and yellow patches. I am coming to the end of the tin so should I get something else to use for the final coat. Whether I need more emulsion coats I haven't decided yet
Any help would be great

 

[jasonB]

You really need some oil based paint to stop the bleeding, bit of oil eggshell will do then go over with another emulsion. You may also find all the knots start bleeding resin if you didn't treat with knotting first.

J

 

[fraser]

Hi thanks very much for the reply
Ok will go and get an oil based paint to go over the emulsion, then another emulsion to go over that. Would any b and q oil based interior paint do? Also, it is touch dry very soon after I paint it, do you think I would be ok putting the oil based paint over today? Or should I wait til it is properly dry tomorrow?

 

[jasonB]

Leave it overnight

You don't want a gloss oilbased as the emulsion will just crack and come off.

J

 

[fraser]

Thanks again. I have just looked on the b and q website and there is so much paint to choose from, I am not sure which one would be best. do you know which one I would be after off hand? Also should I key up the emulsion before the oil based paint and then again after ready for the final emulsion. Will the one coat of the oil based be enough to cover over the knots and stop them from showing do you think!?

 

[deserter]

You really need some oil based paint to stop the bleeding, bit of oil eggshell will do then go over with another emulsion. You may also find all the knots start bleeding resin if you didn't treat with knotting first.

J

Whoa, steady on. Don't paint water based products over oil based, really bad idea. The oil based paint will always try to float on the oil, resulting in cracking.

Sorry to contradict you Jason but its a real pain to try and correct this later.

 

[fraser]

What do you suggest mate?

 

[deserter]

Sorry, obviously I meant oil will try to float on the water.

You can use knotting still but you would need to sand the emulsion from the area. As for the yellow areas I would use a water based primer probably a multiple surface one, any if the big brands will do one with stain blocking properties but the best one I know of is zinser 123.

 

[jasonB]

The OP wanted a quick cheap fix for a shed wall, A can of Zinzer is not exactly cheap.

Also the waterbased emulsion does not "Float" on the oil based, there is a risk - more so with gloss than eggshell - that the emulsion will not bond well and as it dries it crazes, it certainly wont bead as its applied. This was the old way to block out a slight stain if it was bleeding through emulsion long before Zinzer cam onto the scene.

J

PS I doubt B&Q stock much in the way of oil based particularly eggshell as the VOC is a bit high and all the makers are slowly taking it out of their ranges.

 

[deserter]

The OP wanted a quick cheap fix for a shed wall, A can of Zinzer is not exactly cheap.

Also the waterbased emulsion does not "Float" on the oil based, there is a risk - more so with gloss than eggshell - that the emulsion will not bond well and as it dries it crazes, it certainly wont bead as its applied. This was the old way to block out a slight stain if it was bleeding through emulsion long before Zinzer cam onto the scene.

J

PS I doubt B&Q stock much in the way of oil based particularly eggshell as the VOC is a bit high and all the makers are slowly taking it out of their ranges.

I never said it would beed on the eggshell at all, floating is the term people like ICI and Akso Nobel use to describe the lack of adhesion of water based products over oil. You are right that on times gone by this was accepted practice but until recently the water based emulsion was made using formaldehyde as a binder instead of the modern polymers.

 

[fraser]

To be fair a 1L pot of zinser is £12, hopefully I can get a coat the whole way round the walls on my 12 x 8 shed on that. If that is going to do the job in covering up the stains and knots in one coat, (qnd keeping them that way) rather than just doing endless coats of emulsion, that would be great. A coat of emulsion to finish. That sounds good to me?

 

[deserter]

You only need zinder on the stains and knotting on the knots, so you'll have loads left over for other jobs.

 

[fraser]

Would I need to sand the emulsion back from the knotted areas? There are quite alot!

 

[deserter]

That's something I can't answer I'm afraid, I wouldn't of thought so as emulsion is micro porus, however someone else may no better.