Painting polystyrene fish boxes

[John85]

With what kind of paint can you make those boxes (low density) "rootproof"?
I use those boxes for several jobs but the roots grow inside the polystyrene quite easily.I'd like to make a kind of a liner with a NON phytotoxic paint.
What should I use?
May be our paint specialist knows the answer?Polystyrene is used a lot by artists...isn't it...

[Ian Y]

John

You may not need a paint, try using PVA a white glue mostly used in the building trade. As well as sticking things together it waterproofs and seals surfaces so coating the inside of the boxes with two coats should prevent the roots penetrating.

I use a lot of PVA as a binder in my art mixing it with dry powder pigments to make paint.

As an alternative any waterproof acrylic based paint should also help.

[John85]

Thank you Ian,I'll try it

[brianw]

I may be remembering wrongly but I thought PVA was only any good, as a bonding agent, away from damp. I tried to use it many years ago to bond a layer of render over some crumbling concrete and it only lasted a couple of seasons. Maybe it never cured properly in the first place under those conditions.

[John85]

Brian,
You are right:on a pot of white wood glue that I have in the shed is written:use only in a dry environment.For glueing in damp conditions use a polyurethane based glue.
I wonder if a acrylic brick paint would do the job.
Anybody more ideas?

[Darren]

You could try one of the pond coating paints such as TAP ipaint. Designed for concrete so  don't know how well it will stick to polystryrene. Water based so should not, at least, melt your trough!

[Ian Y]

There are different types of PVA some of the woodwork types of white glue are not fully water proof but the builders multi purpose PVA that I use is recommended for sealing cement as well as an adhesive is full waterproof when dry.

I have used it to mend polystyrene boxes that got broken in two and the repairs have lasted around 10 years.

You could use the same exterior masonry pain that you use to paint the outside - just apply two coats.

 

[ChrisB]

I've always just used masonry paint in those sample jars, just enough to do a trough... I get the chocolate colour then coat it, while wet, with sharp sand....