Metal Prep FAQ

No, you do not rinse the metal prep off. Allow Metal Prep to air dry once rust is removed and surface is etched. If you introduce moisture, the surface may re-rust.

Usually only a few hours, but it is important to make sure the Metal Prep has dried thoroughly before applying Mastercoat Permanent Rust Sealer. It is best to wait overnight and then check it.

Metal prep is a very good step to take but not necessary in every application. It is highly recommended to use to dissolve surface rust, etch the surface, and ensure a toothy surface for adhesion for our permanent rust sealer. However the rust sealer will still adhere to surfaces that have been cleaned of oil and grease (use mineral spirits), and loose scale removed. If our metal prep is unavailable, other brands of metal prep can be used. We recommend phosphoric acid, preferably with zinc as an ingredient.

Yes, sometimes this happens and it is normal. Metal Prep is a rust remover, but it is also an etch. It removes the rust, but it also creates a chemical reaction and the result depends on things like how much rust was present. 

Sometimes when there is heavy rust, the Metal Prep will not get the surface entirely clean. It is always good to start as clean as possible, but the rust sealer was made to adhere to marginally prepared surfaces. Even if the surface still has rust, the rust sealer will adhere and encapsulate the rust, keeping it from spreading.

If gummy residue is present after applying Metal Prep, neutralize Metal Prep with water and clean with a scuff pad until it is no longer gummy.

This is unusual, but all rust does not need to be removed to apply the rust sealer. Two coats of rust sealer and a topcoat will encapsulate any flash rust or light rust.

No, do not apply Metal Prep to a painted surface. Metal Prep is made for metal surfaces only. If Metal Prep comes in contact with paint, just neutralize with water to wash it off.

Just neutralize with water as quickly as possible.

First of all, try your best not to do this. Metal Prep will damage concrete. If you spilled it on concrete, wash it off with water as soon as possible.

Yes, this is what it's supposed to do. The white powder is zinc for adhesion for the rust sealer. If there is excess white powder, just wipe some off with a dry rag.

This happens when too much Metal Prep is applied and the surface is oversaturated. Re-wet with Metal Prep, and using a scuff pad and a dry paper towel, scuff the surface and dry with paper towel. Repeat until surface has dried.

No. Always let Mastercoat Metal Prep dry and do not rinse, no matter what other brands' instructions say. Our Mastercoat Permanent Rust Sealers won't be affected by the dried acid leftover on the surface after the Metal Prep dries, and the zinc film left by our Metal Prep is great for adhesion purposes. It is still better to start as clean as possible with the surface; if you rinse the Metal Prep and let it rust again, there is no point in using Metal Prep in the first place.

No, it is not recommended to use Metal Prep on paint. Use a wire wheel or grinder to remove as much paint as you can, and only use Metal Prep if you can completely get it down to bare metal. If not, scuff up any leftover paint and proceed with two coats of rust sealer and one coat of AG111, Chassis Black Finish, or your own topcoat. It should encapsulate the leftover paint just fine. However, if you have large areas of bare metal after removing the paint, you can spot treat them with Metal Prep. Just wash off any paint with water that may come in contact with Metal Prep.

We recommend wiping the surface with mineral spirits. Disclaimer: some pre-paint cleaners may not be compatible with our products and may cause issues.