Thomsons one coat seal drying time?

RrogerD · 25 Oct 2025

How long should a 'thicker than 1mm' coat of Thomsons one-coat take to dry, before being safe for rain?
I applied according to the instructions; "can be applied to moist surfaces" and "is rain-proof immediately".
However, what I didn't appreciate was; "ponded water should not be allowed to stand on newly applied roof seal".
I applied the stuff. Rain 'maybe' in about 6 hours. Came back the next day and the whole lot had lifted, like a skin on custurd. When prodded, it was full of water underneath and of course, not adhered. The only option was to scrape it all off and start again.
I think that I hadn't realised quite how uneven the roof was.

Wayners · 25 Oct 2025

If I'm reading the same product data sheet online it says 24h to dry.
Start early as you can.
If rain is likely cover up if not dry...

Have you read the data sheet online?

RrogerD · 25 Oct 2025

Wayners said:
If I'm reading the same product data sheet online it says 24h to dry.
Start early as you can.
If rain is likely cover up if not dry...

Have you read the data sheet online?

Not read the online data sheet, I will look at this. I was just going off what was on the side of the tin.
I think the problem is, that I'm laying it on thicker than the 1mm. Also, covering it up isn't possible unless I can make it totally water-tight. It's a 'very' flat roof and puddles everywhere. I don't think 24hrs will be enough. I'm thinking 48hrs min without forecast rain and hopefully, won't be scraping the whole lot off again, again.

Wayners · 25 Oct 2025

It sold says don't apply over silicone based roofs.
What was the original roof?

RrogerD · 26 Oct 2025

Wayners said:
It sold says don't apply over silicone based roofs.
What was the original roof?

Oooo. Good point, not noticed that.
It was previously coated in Thompsons 10 year roof seal. I'd put a couple of coats on a couple of years back but they'd started to blister.
I did however have a a couple of areas where I'd tried to resolve the suspected leaking at board edges, by using an all-weather silicone sealant. I'd pulled most of it off. Thinking about it, maybe this is what and where the issue is.
I'll have closer look at this.
Thank you for your observation and suggestion.

RrogerD · 27 Oct 2025

Wayners said:
If I'm reading the same product data sheet online it says 24h to dry.
Start early as you can.
If rain is likely cover up if not dry...

Have you read the data sheet online?

@Wayners do you have experience of using the product? Thank you very much for your tips re applications and drying etc.
I've just re-visited the property and had a prod at the product. It's been some 5 days since I applied it originally and 3 days since I scraped the excess / non-stuck stuff off. It is still tacky. I would have thought that it would have gone off by now. We haven't had that cold weather. I'm beginning to think I may have had a dodgy tin of the stuff....

Wayners · 27 Oct 2025

I have use similar products but not that one

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Thomsons one coat seal drying time?

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