Dumb painting question

Nix143

Hi guys, I've had some MDF shelves built and have just undercoated them - my question is should I now give them a coat of eggshell paint or should I undercoat them again? The undercoat is really patchy and I don't know whether you need the undercoat to perform as a key for the top coat and give that two coats OR whether the undercoat needs to be done twice?


Does that make sense? Basically I suppose I am asking whether it's under or top coat that gives the finish - and if undercoat is patchy will it effect the final finish?

I am on a tight budget so don't want to get it wrong.

Cheers

GottaGetSortedOut

I would give it another coat of undercoat (as it should have had a coat of 'primer' No harm done though :-) )

Give it another coat of undercoat, what is happening is the wood is drinking the paint

hth

Nix143

Ah LOL that would explain why it's sucking up the paint then!

Cheers GGSO!

misgrace

I have just finished a big job, painting MDF wardrobes and cupboards, and my goodness I had to do quite a few coats to get the perfect finish.
You dont need to prime MDF, just apply a thin coat of Undercoat, and make each coat slightly thicker, rubbing down in between, I had quite a bit of furring with the wardrobes.

I will be very suprised if you get away with 2 coats, I did 3 undercoat, and 3 satinwood topcoat,the third coat of satinwood gave it the finish I was after, they do look the business though I say so myself BTW, all oilbase, and Dulux.

never_enough

If I have to do something like that I usually do 2 coats of undercoat, then 2 coats of eggshell.

Nix143

Well so far they have had 2 coats undercoat and are gonna be sanded again tomorrow - I can see them never being finished as I'm looking for an ultra smooth finish as well

kat21

you should have used watered down pva glue for your sealant first then let that dry, it creates a shiny barrier
kat21

Mikeyorks

kat21 wrote:

you should have used watered down pva glue

Much as people appear to despise PVA these days - that's absolutely right. It seals the fibres and a good sandapering after the PVA leaves it just right for the finish coats. Which. on MDF, normally looks best if eggshell

handyman.

never heard of sealing mdf with pva........ever thought of using mdf primer? I might just be a silly sausage, but i thought this was the right stuff to use

Mikeyorks

That's what it's sold for .. as it's much more expensive. But PVA works a treat - and particularly if the MDF surface has been cut in any way (eg routed) or an end grain is exposed. The PVA seals it in one go and makes it easy to get a surface that's immediately ready for a final coat.

Worth mentioning - that you should use a mask if working with MDF in a manner that creates dust / fibres. It's pretty obnoxious stuff if breathed in.

handyman.

what about the issue of pva 're activating' (ie, becoming liquid again when wet), as it does when you plaster with it

does this not mean you are putting your top coat on a thin layer of pva, instead of a primer that has penetrated deep into the fibre

The primer lifts the fibre (furr) for a reason you know, its going deep into the fibre, whereas pva will just coat the surface.