Temporary fix for rust spots on steel deck

[UNCIVILIZED]

Could you maybe:
- Apply your coatings
- Cover & seal the area with a piece of plastic & some duct tape
- Affix some heat tape in place
- Cover all of the above with some insulation. Be it fiberglass home insulation, blue or pink board foam, bubble pack etc. And then if you're real concerned about condensation, seal over and around the above with more plastic & duct tape.

[Hudson Force]

Ospho is a brand name for one of these phosphoric acid wash treatments. I don't no how many brands are on the market, but I've been using "Jasco" as a rust treatment and I've been pleased with it.

[Wotname]

Being as this is a temporary fix to get through winter, I rather like Warby12's idea (post 3).
Using a quick setting epoxy (during a short weather window as described by the OP) and some gentle heat should see the epoxy cure to a stage where more weather won't upset the curing process. It would certainly far faster than paint product.

Easy enough to grind off when the spring paint job is undertaken.

[mike d.]

Use an infrared heat light on the inside about 45-60cm from the foam! The infrared penetrates the foam slowly with out damaging the foam. It will take a while! We use this process to dry fiberglass encapsulated wood transoms. With those it takes about 5-6 weeks to dry out the wood, before you can do other repairs!

[phipseml]

Hi again,

All good tips. I agree that having something that cures quickly is crucial in this case. I saw a Jotun one pack quick curing primer the other day and might go for something like that. Not sure about curing times of the Rustoleum primer, anyone knows?

I did some research on Ospho and it has 45% phosphoric acid as active ingredient (see their website). As said we don't get that product here. One product I found here states it has 15 - 25% phosphoric acid (not sure why it states a range), so less than the praised Ospho, but claimed by the seller the thing used most here. All the other products don't say anything about their composition. I have a work colleague working in the lab and will ask her if there might be a supplier of pure phosphoric acid.

I also saw a cold galvanizing, zinc rich primer (also Rustoleum), suggested a bit earlier in this thread. It says on the package that the area to be painted has to be rust free as opposed to slightly rusty, and I read in the DIY book that although this might be the best and preferred primer to use, it is very hard and in practice impossible to prepare the steel in a suitable way without blasting and hence cold galvanizing won't last long, i.e. fall off quickly. Any opinions on that?

Warming and keeping dry with sealing the area sounds weird: how will the paint dry? But if you have experience with it, I suppose it'll work and would be a good option for us. It starts to be below freezing during the nights with a lot of condensation. I should really prioritize this now, but have a lot of job things to do, too. Hopefully this weekend...

Cheers,
Phil

[Wotname]

A couple of points:

Don't worry too much about getting it perfect if you are still planning on just doing a temporary pre-winter repair. The next summer job will sort out any developing problems.

The phosphoric acid actually requires some rust present to work properly.

Don't use a zinc rich primer over a phosphoric acid treatment.

The zinc rich primers that I am aware of, require another primer coat (non zinc) before topcoating; however your coating may vary.

I have used zinc primers over light rust will no obvious ill effects.

[hpeer]

Wot name,

What's the issue with using zinc rich primers over phosphoric acid treatment?

[sparrowhawk1]

This is your answer. Turns rust back into metal.
There are other brands that work just as well. I've never had good results with ospho. Edit it cleans easily with water ( or just wipe off with a paper towel) but if you let it dry on fiberglass its really hard to get off .almost like a stain

[sparrowhawk1]

Hmmm. My photo seems to have gone blank. Its called extend rust neutralizer by locktite. Comes in an 8oz bottle.

[Wotname]

Originally Posted by hpeer

Wot name,

What's the issue with using zinc rich primers over phosphoric acid treatment?

Disclaimer: I'm not a paint chemist, just a DIYer who once had a steel boat

As I understand it, a zinc rich primer provides galvanic protection and in order to do so, must be in direct electrical contact with the base steel i.e. applied directly to a clean bare steel surface. Phosphoric acid reacts with rust (Fe2O3) and converts it to FePO4 (ferric phosphate) which is in effect an insulating layer between the steel and the paint. In addition, anywhere the phosphoric acid was applied to clean steel, no reaction occurs and unless the acid is completely removed, the remaining acid will react with the zinc content of the paint.

You might find a better explanation here Frequently Asked Questions - Galmet.

All the info I have read on zinc primer application suggests it is not a good idea but I am always open to a well reasoned dissenting viewpoint.

[SailFastTri]

The temperature issue is easily addressed. Any 300-500 watt halogen work light will warm the area if positioned within a few feet of the surface. You can leave it for a few hours until your coating patch hardens. Don't allow it too close, because you can overdo it. Check on it frequently with a non-contact thermometer until temperature stabilizes.

[hpeer]

Wot name,

Thanks. That makes more sense than some answers I got from some professionals.

[Mao Ta 74]

Ospho it let her dry and prime her that should do the trick captain

Sent from my HTC6500LVW using Cruisers Sailing Forum mobile app

[Cheechako]

I'd clean it up good. maybe a wire brush and put rapid drying rustoleum on it until the weather clears up.
I don't think there's any point in acid etching etc for a temp fix to get you thru winter.

[phipseml]

Hi there everybody,

Just a quick follow up that we did finally get plus 5degC days and were able to do some work on the rust spots. Angle grinder with brush, then 75% phosphoric acid (from the pharmacy) for ten to twenty minutes, then a proper rinse with water, then drying with a hair dryer, then Rustoleum.

It was interesting to see different progression stages, some spots with pits, and some with just some surface coloration. Makes me wonder if it's worth putting an effort into the superficial rust spots.

The acid treatment was cool - even though it seemed like we removed all rusty bits, some areas and piths turned black after all. We figured we'd do that, since it only is a little bit of extra effort and might make the temporary fixes permanent (whatever permanent means in this context).

Anyway, we'll see how the Rustoleum holds up.

Cheers and thanks for your help. I'll write a separate post with questions filler material now.

Cheers,
Phil