Painting wood and wood warping

[rogerg (Roger)]

G'day all,

Very basic question I have.

I'm creating somewhat of a cradle in the box I carry my Losmandy GM8 in to hold the mount securely. The "cradle" consists of a plywood base with some pieces of pine screwed to it with correct groves cut out of them for the mount to sit nicely in. That all then sits in the bottom of a plastic box I cart the mount in. The plywood base is about 35cm x 30cm, to give you an idea of size.

1) I want to paint the wood. Do I need to prime it with anything or can I just paint standard interior paint directly on to it? (I have some of a suitable colour in the shed).

2) since buying the plywood I've noticed it's warped somewhat. I haven't screwed the pine pieces to it yet. do I need to somehow un-warp it before putting it together and painting it? I am quite confident that screwing on the pine pieces will flatten it out nicely in the short term and likely hold it well for ever, but I'm not sure if I'm going to end up with it tearing its self apart with stress from warping?

Thanks,
Roger.

[merlin8r]

G'day Roger,
How thick is the plywood? I'm surprised it would warp at all.

As for your solid timber pieces, timber expands and contracts across the grain. So long as your pine pieces are relatively narrow (40-60mm) that shouldn't really be a problem. However, when you screw the plywood to it, make the holes in the pine oversize, since the pine will try and move but the plywood won't. If you don't let it move, it will crack somewhere.

You can paint straight over the timber if it's just for general use.

[rogerg (Roger)]

Originally Posted by merlin8r

G'day Roger,
How thick is the plywood? I'm surprised it would warp at all.

Interesting. I haven't got it in front of me now to know for sure, but I would day 5mm or there abouts, perhaps 6mm.

Thanks,
Roger.

[garymck (Gary)]

You need to undercoat the surface before coating it with an interior paint. Undercoat serves a couple of purposes: firstly is seals the surface so that later coats do not penetrate the substrate, in the case of tannin rich timbers it also prevents the tannins leaching out through the surface coat, secondly it provides a high level of adhesion for the surface coat so that it sticks properly. Not using an appropriate undercoat is the single biggest cause of poor paint performance.......

cheers
Gary
(and yes I do work in paints...)

[solissydney (Ken)]

Or you could just use a few coats of Varnish
Ken

[rogerg (Roger)]

Thanks Gary and Ken... Varnish isn't a bad idea if I'm going to have to buy undercoat anyhow. I'll think about it. Will probably get to it this coming weekend.

Thanks,
Roger.

[solissydney (Ken)]

You don't need u/coat if you intend using Varnish.
Just apply a few coats. Either oil based or water based.
Ken

[rogerg (Roger)]

Originally Posted by solissydney

You don't need u/coat if you intend using Varnish.
Just apply a few coats. Either oil based or water based.
Ken

Yeap, got that, what I was meaning is if I'm going to have to buy undercoat, buying varnish instead is probably similar cost. As opposed to doing neither and just using the spare interior paint I have at home for free

[Lumen Miner (Mitchell)]

Originally Posted by rogerg

Yeap, got that, what I was meaning is if I'm going to have to buy undercoat, buying varnish instead is probably similar cost. As opposed to doing neither and just using the spare interior paint I have at home for free

I am a bit shocked Gary didn't pick up on the fact that you said "interior" paint. Although his description of the undercoat is adequate, unfortunatley the under coat is not the main reason for painting defects. It is the top coat used. No undercoat will fix, the wrong topcoat.

I would be more concerned about the paint you have left over...
I would assume it is water based wall paint. Do not use that.
You need to use an oil or water based enamel for hard wearing surfaces.
Water based acrylic will just peel off, when it touches/taps something..
Dulux Aqua-enamel would be suitable, or a good old oil based is best.
Although an undercoat is recommended, it is not necessary. Paint bonds perfectly well with almost all timber / metal / masonary surfaces, given proper preparation. It needs something to "bite" onto and a dust / grease free surface, to not peel away from. An undercoat just means you don't need to prep so much, still needs to be dust free though.


I would varnish it. Cheaper and looks better IMHO

(I also work in paints. )

[bmitchell82 (Brendan)]

roger, ide just use a spray can of clear varnish. criky if every second year you have to give it a quick rub back and spend 10 bucks on a can of spray who gives a rats just don't go full gloss scratches too easy!

on the upside to it there isn't a brush so you don't have brush marks and a stuffed brush by the end.!

my 2 bobs worth

ps i painted my son's block trolly/blocks with interior paint samples then did the same thing coated it with clear varnish spray. worked a absolute treat. 4 years down the track they still look as good as new (apart from the dents and kidz ware)

[garymck (Gary)]

[QUOTE=Lumen Miner;486018]I am a bit shocked Gary didn't pick up on the fact that you said "interior" paint. Although his description of the undercoat is adequate, unfortunatley the under coat is not the main reason for painting defects. It is the top coat used. No undercoat will fix, the wrong topcoat.

Hi,
As to cause of painting defects - I respectfully disagree, poor preparation and no top coat will ever be any good. Certainly the choice of top coat must be correct, but put the right top coat on an incorrectly prepared substrate and your screwed.
I didn't worry about the topcoat as his question was about whether he needed a primer. I also reasoned that since it was not going to be left outside and subjected to UV day in and out using a bit of interior would be Ok. Same as most spray can varnishes are interior rated and hence if going down that path and being picky choose an exterior one.

cheers
Gary