Why did plywood go mouldy? And what should I do?

[Norfolkandchance]

Hi,

During the summer I made a work top and some shelves from 18mm plywood and installed them in my garage. I didn't put any finish on. It has developed black mould in spots. Its not an especially damp garage but it isn't as dry as the house. I keep books and magazines for example, without problem. Also lots of other bare pine and MDF, which hasn't gone moudy and has been in there for years. Any idea why the mould came on the ply and not the other wood (or paper etc?)

Today I did my best to clean it off with bleach solution and got to a point where it won't really show once I varnish it. Will a coat of floor varnish stop it coming back?

Ta

[anonymous-user]

Was it birch plywood? If so birch loves to go mouldy. Sand it down and varnish it, that will act as a barrier and should prevent future mould growth.

[xyz123]

U need to send it before varnish as said....

[Norfolkandchance]

Out of interest, why does it need to be sanded - I've removed most of the mould by scrubbing with bleach and they are only garage shelves / work tops.

[singlecoil]

Osmo Poly-x oil is a good alternative to varnish and easier to apply, although it takes longer to dry. Neither particularly need sanding unless there are traces of the mould remaining, though I've never applied finish over mould so don't know whether it absolutely needs to be removed.

[jakesmith]

singlecoil said:

Osmo Poly-x oil is a good alternative to varnish and easier to apply, although it takes longer to dry. Neither particularly need sanding unless there are traces of the mould remaining, though I've never applied finish over mould so don't know whether it absolutely needs to be removed.

This is a great suggestion, I used it on our doors and oak staircase it brings it up beautifully and really emphasises the grain, it even makes plain plywood look great. You can slap it on too. It's not the cheapest but it's so easy to use and looks great

[Norfolkandchance]

jakesmith said:

singlecoil said:

Osmo Poly-x oil is a good alternative to varnish and easier to apply, although it takes longer to dry. Neither particularly need sanding unless there are traces of the mould remaining, though I've never applied finish over mould so don't know whether it absolutely needs to be removed.

This is a great suggestion, I used it on our doors and oak staircase it brings it up beautifully and really emphasises the grain, it even makes plain plywood look great. You can slap it on too. It's not the cheapest but it's so easy to use and looks great

I've ordered some, then remembered it was just for garage shelf and cancelled it and bought £8 worth of varnish instead. Thanks for the tip though!

[227bhp]

Given it's just a ply shelf in the garage it's less of a worry, but I wouldn't be coating anything I cherished or was any good that had been stored in there in Winter, the MC is too high at this time of the year hence the mould.
Alternatively (in this case) i'd be using a water based product.

[singlecoil]

Norfolkandchance said:

jakesmith said:

singlecoil said:

Osmo Poly-x oil is a good alternative to varnish and easier to apply, although it takes longer to dry. Neither particularly need sanding unless there are traces of the mould remaining, though I've never applied finish over mould so don't know whether it absolutely needs to be removed.

This is a great suggestion, I used it on our doors and oak staircase it brings it up beautifully and really emphasises the grain, it even makes plain plywood look great. You can slap it on too. It's not the cheapest but it's so easy to use and looks great

I've ordered some, then remembered it was just for garage shelf and cancelled it and bought £8 worth of varnish instead. Thanks for the tip though!

I hope you bought water based varnish, not polyurethane.

[Norfolkandchance]

singlecoil said:

I hope you bought water based varnish, not polyurethane.

Yes, the truth is that it isn't cherished. Interesting that its even gone mouldy as pine and paper in the same garage didin't. So I'm only varnishing to stop the mould coming back after the bleach killed it.

Edited by Norfolkandchance on Thursday 17th January 07:23

[Norfolkandchance]

Interestingly, the (water based) varnish I bought says "do not use below 10 degrees C". I first read this as "do not apply below 10" but am now wondering, because it also says "do not use on decking and floors" if it is unsuitable for the garage, which is below 10 quite often.

What might happen if I apply it and then temps go below 10?

thanks

[MJNewton]

Warnings about cold application of liquids usually relate to 1) being too thick to apply, 2) slow evaporation of the solvent leading to a poor finish or, particularly for water-based products, 3) the risk of freezing and the damage caused by ice crystals forming.

The warning about decks and floors is probably more to do with how resistant (or not) it is to abrasion and wear from foot traffic.