Oxalic Acid Dilution Calculator

How much oxalic acid to dissolve for a 2–8% solution, weighed as sold (dihydrate crystals), for any batch size.

Chemical

Strength you have

Target as

% 1:X ppm

Strength you need

Batch size

Reviewed by Andre Taki, Chief Commercial Officer, Alliance Chemical. Densities: Laliberté (2009) and the CRC Handbook; bleach strength from Alliance's TDS. Check the SDS for your lot before mixing.

02

Understand The Oxalic Recipe Pattern

Oxalic is sold as solid dihydrate crystals, not liquid. Real-world recipes are gram-per-gallon, but the math still maps cleanly to the percent-dilution model once you treat a 10% w/v solution as the starting stock.

Buying Guide

Two ways to mix oxalic. Option A: dissolve the target grams of crystals directly into your final water volume — simplest when you already know the target percentage. Option B: make a 10% w/v stock solution once and dilute from it — useful when you batch recipes frequently and want consistent math.

Typical grams-per-gallon recipes. A 5% wood-bleaching solution is roughly 190 g of oxalic dihydrate per gallon of water. A 4% deck wash is ~150 g/gal. A 2% gentle solution is ~75 g/gal. The calculator above uses the stock-and-dilute model, but these direct weights work identically.

Which product. Dihydrate is the standard crystal form — what most wood-working and restoration recipes assume. ACS Grade is the purer laboratory form, useful when you need reproducibility or documentation for analytical work.

Filter the stock. Oxalic crystals dissolve well in warm water but leave fine particulate that can clog sprayer nozzles. Strain the stock solution before loading a pump-up sprayer or HVLP gun.

Oxalic Acid, Dihydrate - Ethanedioic Acid

Standard crystalline dihydrate for wood bleaching, deck restoration, and rust removal recipes.

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Oxalic Acid ACS Grade

Higher-purity laboratory grade when documentation and reproducibility matter more than price.

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Oxalic acid dihydrate product image from Alliance Chemical — Oxalic dihydrate ships as crystalline powder. Dissolve target grams into water directly, or make a 10% stock and dilute from there.

03

Common Oxalic Dilution Targets

Working strengths depend on substrate and severity. Start at the lighter end and step up only if the first pass is under-performing — oxalic will lift wood color permanently.

Common recipes

Starting Stock	Target	Typical Use	Notes	Calculator
Powder, as sold	5%	Wood bleaching and tannin stain removal	Standard target for raw-wood restoration and iron-reaction stain removal. Typical recipe: ~190 g oxalic per gallon water.	Open
Powder, as sold	4%	Deck cleaning before refinishing	Common concentration for greyed or mildew-darkened deck boards. Apply wet-on-wet, dwell 15 min, neutralize and rinse.	Open
Powder, as sold	2%	Gentle wood or composite refresh	Milder entry point when aggressive bleaching is not wanted or the substrate is soft, painted, or composite.	Open
Powder, as sold	1:1 water	Intermediate step-down from stock	Halves the stock to 5% in equal-parts-water mode, matching SOPs written as parts rather than percent.	Open

04

Oxalic Handling Reality Check

Oxalic acid is toxic if swallowed and aggressive on eyes and skin despite the mild-sounding wood-bleach marketing. Dust inhalation during weighing is the most overlooked hazard.

Guardrails

Dust matters more than liquid. The most common oxalic exposure is inhalation during weighing and mixing. Wear a dust mask rated for fine particulates (P100 or equivalent) when handling the dry crystals; switch to liquid-phase handling once dissolved.

Neutralize and rinse, always. Residual oxalic left in wood grain or sprayer lines will continue reacting. Neutralize with a baking-soda wash after treatment, then rinse thoroughly. Especially important on decks before sealer application.

Compatible with most woods; variable on stone. Oxalic is the standard wood-bleaching acid. On stone, it is excellent for iron-stain removal but can etch calcium-rich materials (limestone, marble, some concrete). Test a hidden area first.

Store dry and sealed. Oxalic crystals are hygroscopic — they will cake in open containers exposed to humidity. Keep the bag sealed between uses, or transfer to a tight-sealing plastic container.

Questions

How much oxalic acid do I use per gallon of water?

Approximately 190 grams of oxalic dihydrate per gallon makes a 5% wood-bleaching solution. For a 4% deck wash, use ~150 g/gal. For a gentle 2% solution, ~75 g/gal. The calculator on this page converts any target percentage to an exact batch.

Does oxalic acid bleach wood color permanently?

Yes, when it works it removes the pigment rather than covering it. That is why it is the go-to for tannin stains and iron-reaction darkening. Neutralize and rinse thoroughly after treatment to stop ongoing reaction.

What is the difference between dihydrate and ACS oxalic acid?

Dihydrate is the standard commercial crystal form assumed by most wood-working and restoration recipes. ACS Grade is higher purity — the same chemistry but with tighter spec on trace impurities. ACS is worth it for analytical or documented work; dihydrate is fine for restoration.

Can I use oxalic acid on stone or concrete?

For iron-stain removal, yes — oxalic is the standard choice. For general cleaning of calcium-rich stone (limestone, marble), avoid it: the acid will etch the surface. Test on a hidden area before committing to a full application.