Office Trailer Roof Recoating

Good day everyone, could anyone steer me in the right direction? Trying to recoat an office trailer roof that has seen better days. There is a bunch of pin holes caused from rusting. Roof is flat and made of thin metal and coated with a silver rubberized membrane. The trailer is probably 20 to 30 years old. There is a fair bit of surface rust as seen in the pictures.

Currently going over with a wire brush to loosen up the rust spots. Not looking at spending an arm and a leg. Just trying to make it last another 5 years or so.

I was thinking of coating with rustoleum type paint to seal the rust and then coating it with Henry 107… any thoughts or a better way to do this?

Thank you!

Find out what’s on there first. Paint thinner will tell if it is asphalt based. Rinse it off and scrub it with a street broom at the same time. Spray it down with phosphoric acid with a little soap in it to kill the rust, power wash it, and coat it.

Thank you! I rubbed it with Kleen-Strip Acetone and nothing happened. Just surface dirt and a little color rubbed off the membrane.

Just so I understand correctly, I already scrubbed it with a degreaser and powered washed it. I can now spray it with phosphoric acid and soap, scrub it, Power wash again, let dry and apply coating?

Which off the shelf coating do you recommend?

Thanks again

Phosphoric acid kills the rust. soak a rag with paint thinner or mineral spirts and let it sit for an half an hour to see if it blisters up. If it’s an acrylic/latex you’re kinda stuck with that.

Hi Darkthirty, It blistered a bit and definitely softened it. I can scrape it off quite easily.

So Latex/Acrylic based coating it is I gather. Any recommendations?

Thank you

look at Gaco. I like Gaco roof for a recoat on a good surface. I like Gaco Tape to roll on a roof like this, because of the fiber in it. The only drawback is all these coatings will mildew.
Just my opinion.

Gaco Liquid Tape… got it. Stuff looks amazing.

Would i be ok with using Gaco 100% silicon or am I limited to using Gaco acrylic A4600 or A4700?

Both acrylics warn against pooling. The roof on the office trailer is on a very slight angle so the water does run off slowly for the most part, and whatever pools a bit can dry off pretty quick in a hot sun…but being in Seattle, our winters are horrible rain wise.

I read that they recommend two coats for the acrylic, but only one coat for silicon… does that sound correct?

Apologies if I am overthinking it… I just dont want to have to do the work twice.

Thank you

I shy away from silicone. If you only need 5 years, about any acrylic latex will do …

:+1: thank you! Always a pleasure talking to you guys. You helped me out 2 years ago when i was doing a complete reroof on my double wide… happy to report No Leaks and No Problems… only thanks to you and your compadres on this site.

Cheers and Gob Bless

True roofers are very intelligent. The con men give the whole business a bad name.

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Good day, The can says to dilute 25 to 50%. Nothing else. What dilution ration do you suggest and how long do I let sit?


What are you diluting? What system/coating are you using? Brand and product # would help!

Phosphoric Acid. I was in a bit of a time crunch to get this roof done this weekend and went ahead with a 1:1 ratio thinking what could go wrong? Sprayed the diluted phospheric acid onto the roof, brushed it, let it sit for about 30 to 45 min, brushed it again then rinced it and let it dry over night… it rained a bit this morning so had to wait until now for it to dry and this is what I came to… surface rust everywhere.

Any idea what i did wrong? And how do I fix that?


Spray the acid on the rusted areas, let it sit for 24 hours, the rust will turn black (iron oxide II) when the oxygen is out of it. Power wash, let it dry, and coat it asap.

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Flat roof leak repair can be accomplished through the use of liquid roof coatings such as Butyl Liquid Rubber. Butyl Liquid Rubber conforms to any shape surface, flashing protrusion, vertical or horizontal, and can be applied easily with a paint brush or roller. It is catalyst based and cures by chemical reaction forming a self- leveling seamless membrane as it dries.