bathroom sealant

Hi,
I've recently renewed the sealant in my bathroom as the old stuff was covered in mould.
However, although I filled the bath with water before using the sealant and left it for almost 24 hours before emptying it and using the over-bath shower, it seems that every time weight is applied to the bath, a large open crack appears in the sealant.
Similarly, when I run my finger along the sealant above the sink that was renewed a few days earlier, bits of it come away on my finger.
Should I have left the bath sealant a lot longer before emptying the bath and using the over-bath shower (it *seemed* dry to me) or is it possible that the sealant (although advertised as for kitchens and bathrooms) is just plain rubbish? - It was a B&Q branded sealant.
FWIW, both areas were stripped of the old sealant, cleaned and dried before the new sealant was applied.
cheers, RM
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It sounds to me as if your bath isn't supported properly - if it moves enough to disturb the sealant when you stand in it. Are you sure that all of its supporting feet are properly wound down onto something solid?
In addition, the surfaces to which you apply the sealant must be clean and dry for it to stick properly. This can be difficult to achieve - if there was old sealant there previously, and in the presence of water and steam - but it is still essential!
Roger
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Roger Mills wrote:

I'd aggree with that. .

Maybe a highly elastic sealant (low modulus) would help but in my opinion the movement should be minimised before sealing. i.e. support the bath underneath with e.g. bricks and build a decent timber frame to support the dge. This is another point where steel baths are better; the edges are squarer so they are easier to seal and they don't flex like the plastic ones
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Sounds to me like the sealant you've used is acrylic or partly acrylic rather than silicone. You need to use "sanitary grade silicone", you will recognise it because it's the most expensive stuff on the rack! It is very flexible and should take up a lot of movement. Stinks of vinegar while curing.
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Tim Mitchell wrote:

failing that - order from screwfix and it is usually cheaper than the naff acrylic offerings from the sheds!
http://www.screwfix.com/app/sfd/cat/pro.jsp?id 329&ts014
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Tim Mitchell wrote:

The unibond one I used says it is water based acrylic kitchen/bathroom sealant. Says it is waterproof when dry. And shows a picture of someone applying it around a bath on the tube.....
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writes

Well, all sealants are waterproof, but all are not created equal. If you use the expensive silicone you will not have the problem. Some of the cheaper ones are OK too but it's such a pain scraping it off, you may as well spend a few quid more and use the best stuff. Your choice...
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<snip>
Quite - I apply the rule of thumb of dividing the "Guaranteed for X years" figure by 5 to get the true figure. "Guaranteed for 25 years", for example, means it may last 5 if you're lucky, and so on.
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Tim Mitchell wrote:

Well, yes, but the expensive silicone is what I thought I was buying!
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I used an acrylic one about 3 months ago, said it was for bathrooms. It is still soft, and you can put permanent dents in it with your fingernail. Part of it is coming away with mould growing behind it. That is in the shower end of the bath, the sink I did at the same time is OK (less water around).
At least it will be easy to scrape off so I can put silicone on, it seems to have the consistency of putty. Is cheap silicone any good, or is 6-7 the minimum you should pay?
Bob
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I've used the acrylic one in the past and found it to be a dead loss as well.
Nowadays I always buy a decent silicone and never have any problems. Considering that it is only a couple of pounds more than the cheap brands, I don't think it is worth messing about.
Another thing that I have found really useful, since I have an air compressor, is a pneumatic mastic gun. These are really cheap but very effective - Axminster have them as stock code B41CG at 9.40
There is an adjustment knob on the side to control the delivery rate and the gun then produces very clean and consistent runs of silicone completely repeatably. I found that my success with the spring and trigger type was not that great, but this does a really good job. It's also very effective for other materials such as Gripfill or anything else that comes in a cartridge.
.andy
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Reestit Mutton wrote:

I've just had EXACTLY the same problem with unibond sealant.
It appears to have set much more brittle and coarse on the surface than kitchen/bathroom sealant I've used before, what would cause that?
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OK - I've read the thread and as I'm about to seal my newly installed bath I need advice.
What is the best sealant to use (brand please)? Cost no problem - I want to do a good job.
TIA.
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Troy the Black Lab.
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Dow Corning
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