Too dark Merbau Screen

Merbau-Kwila is naturally a dark red brown timber with sulphur colored flecks running with the grain. The best way to lighten its lightest stage prior to coating is too sand the oxidised -coated layer. After sanding just hose with fresh water and look at the colour of the timber. Water is clear and reveals the timbers true colour when a clear liquid is applied. Now coatings are not clear (because they need to block UV) but man made products given names in factories. Nearly all coating products have a natural in their range. You could put 6 different naturals on your screen & see 6 dfferent shades.

Napisan(sodium percarbonate) PH 12 is just a detergent but does not brighten timber. Oxalic acid based products PH 1 slightly brighten timber. Sanding bypasses all of this quickly and gives you the best starting position prior to coating.

Thanks jimj, because the screen is hinged and not fixed at both ends, together with the fact that it has been up for a few years with the oil based finish, I guess you can only clean the timber as best you can. I hand sanded as best I could, but given the screen was “wobbly” and a machine sand would probably have been better, but not practical, I probably have the best I can expect. Not disappointed, but curious since both screens (with different finished colours) are both in the same area. Thanks for your advice.

Sounds like you have it figured out. Exterior timber can be fraught with so many issues.