Thread: Bleaching (or lightening) plywood

Bleach will do the job BUT can strong bleach really knock the stuffing out of wood OTOH that might be just what you are looking for.

The bleaching effect is usually proportional to the pH of a solution so some experiments with some mild through to strong caustic solutions might be needed.

As a guide
Sodium bicarbonate 0.1 mol/L (8.4g/L) has a pH around 8.4
Sodium carbonate 0.1 mol/L (10.6 g/L) is around 11.6
Sodium Hydroxide (caustic soda) 0.1 mo/L 94 g/L) is around 13.6

Sodium Carbonate as washing soda is usually a dehydrate ie has 10 water molecules attached to it, so you will need about 30g/L to make a 0.1N sodium carbonate solution.
FWIW I use 0.3N ~100g/L in my electrolysis tanks.

You might also want to try some Oxalic acid (Diggers rust and stain remover).

Originally Posted by Midnight Man

I've had a crack with a couple of applications of Feast Watson Liming White - it's a pain to apply, and fairly inconsistent.

I've seen bleaching kits available overseas, but they don't ship here, and from my limited knowledge are incredibly nasty in terms of application and so on.

Has anyone some advice to lend on how I might go about achieving the desired results here? An example of the timber we're working with, to give you an idea:

Bleaching timber is very messy work so Im thinking if you think applying liming white is a pain your going to Freak trying to bleach a rooms worth of wall lining .

Would you be bleaching before its installed ? You'd want to be although doing it while on the walls is possible .

Oxalic acid wont change a thing on that stuff . It has good effect on oxide stains like the grey black staining from iron oxide and dirt like stains sometimes . But it wont change the colour of clean natural new wood .

I like what Bob is saying about the PH of those three liquids . Makes sense as to what Ive seen when bleaching . Ive used a lot of Amonia from strong 25% to 3 % house cleaning stuff and strong hydrogen peroxide . 25 Vol . Never had a clue what 25 vol meant but its strong stuff . You apply the amonia then the peroxide, the efffect of 3 % Amonia seems to give almost exactly the same as 25% . Itl turn dark Red Mahogany or Red Gum Yellow straw colour . If I want less bleaching I water down the Peroxide.

The problem with Amonia , specially 25% stuff is the fumes will just about kill you if your not extremely well ventilated so Ive stuck to the household cleaning 3% stuff from the supermarket for that reason .
I like using Caustic soda and peroxide sometimes . As Bob said about more PH having an effect and it shows ! With the same peroxide it bleaches the wood to a more extreme level . Something like a bit of silver white driftwood can be had the longer the Caustic is left to soak on some woods.
I did a Cherry table once using Caustic, and as it was applied it sent it as Black as the inside of a dog at first ! Just as the Owner walked it to see what we had done with her table . She was great about it , nice girl , she left us saying that "You know what your doing, I'm sure you'll get it right " We spread the Peroxide on and the whole thing foamed up and hissed at us and ended up like drift wood . Which was what she wanted .

The easiest way to apply for large coverage is spraying on a windy day outside . Don't mix the two parts together in any sealed containers or you will blow yourself up and get covered in bleach at the same time .
The two solutions must come together and mix on the wood .

Originally Posted by BobL

Bleach will do the job BUT can strong bleach really knock the stuffing out of wood OTOH that might be just what you are looking for.

The bleaching effect is usually proportional to the pH of a solution so some experiments with some mild through to strong caustic solutions might be needed.

As a guide
Sodium bicarbonate 0.1 mol/L (8.4g/L) has a pH around 8.4
Sodium carbonate 0.1 mol/L (10.6 g/L) is around 11.6
Sodium Hydroxide (caustic soda) 0.1 mo/L 94 g/L) is around 13.6

Sodium Carbonate as washing soda is usually a dehydrate ie has 10 water molecules attached to it, so you will need about 30g/L to make a 0.1N sodium carbonate solution.
FWIW I use 0.3N ~100g/L in my electrolysis tanks.

You might also want to try some Oxalic acid (Diggers rust and stain remover).

Bob . Is the Sodium Carbonate with 10 water molecules attached a similar thing to Hydrogen Peroxide, and used the same way I use Hydrogen Peroxide ? Is it the other part needed with one of the high PH solutions?

Originally Posted by auscab

Bob . Is the Sodium Carbonate with 10 water molecules attached a similar thing to Hydrogen Peroxide, and used the same way I use Hydrogen Peroxide ? Is it the other part needed with one of the high PH solutions?

Sodium Carbonate with 10 water molecules attached is Na2CO2.10H2o.
Hydrogen peroxide is H2O2 - they are quite different chemicals.

Na2CO3 is an alkaline agent or "base" and has a pH above 7 (neutral)
H202 is the opposite, its a weak acid and has a pH of a around 5.

The bleaching property of H202 will be enhanced by adding a base like ammonia.
To get any from the toxic fumes generated by ammonia you could always use sodium carbonate.
Washing clothes in a solution of washing soda and H2O2 will act as an effective bleach.

I didn't realise you wanted to do this in place on a shed wall and are thus likely to get these chemicals all over the place.

I reckon you're better off just painting it white: far safer, less mess and better reflectivity for light

Many thanks for the input everyone - the thinking here seems to run in line with some further research and searching around I've done - essentially pointing to it being a potentially dangerous and messy process.

Time to rethink my plans, I think - appreciate all the input and advice!