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rubecula

Leaking base seal

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I have a Pulsar fibre glass observatory sitting on a home built concrete slab.  A couple of months ago I noticed that the observatory floor was getting squelchy.  On lifting the flooring I found a thin film of water sitting on the slab.  On doing a bit of research I found that the sealant that I had used became acidic when curing and so had probably eaten away the concrete thus forming a poor seal.

Since then I have tried twice to seal the base without success.  I have used sealants that were neutral when cured, could be applied under water, and applied it to the inside and outside edges of the base flange.  The rate of water ingress has slowed but I have not been able to stop it completely.

I'm wondering if anyone has encountered this problem and if they had any success in solving it.

I have emailed Pulsar but had no reply.

Thanks,

Robin

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Did you treat the concrete before placing the observatory on it? i.e., a waterproofing sealant?

ChrisH

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You could try Sikaflex (from any yacht chandlers) its a very good sealant - sets flexible and can be painted and its inert ie it wont eat concrete. Best applied when everything is dry - its available in black, white and brown.

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Chris, no i didn't but I have since treated the inside (except where the pier is) and the concrete slab on the outside with a Sika concrete waterproofing compound.  Maybe bolting the stable door after...........

Thanks Skipper, I'll look into that

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Hi,

Sikaflex is the business for sealing around the base periphery, however, it is possible the water is coming from beneath the concrete slab, especially if you did not install a waterproof membrane beneath the slab.

If this is the case then you will need to  coat the entire slab with a waterproofing sealant and one of the best is: -

http://aquron.co.uk/aquron-products1/aquron-2000-waterproofing-for-concrete/guaranteed-waterproofing

You will, of course, need to allow the concrete to fully dry out before you apply the sealant.

Good luck.

Best regards.

Sandy. :grin:

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Hi Robin,

I used generous amounts of CT1 sealant/adhesive to seal around the base of my 2.2 meter Pulsar. I put the sealant on the inside and outside of the base flange and I also put a bead along all the quadrant joins.

So far, so good. The observatory is completely waterproof apart from rain that gets in under the dome in extreme weather conditions - special North Devon rain that travels upwards!

I can certainly recommend CT1 - I have used gallons of it and it does work!

Regards, Hugh

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Another vote for Sikaflex, wonderful stuff.

Huw

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Make sure it is Sikaflex 512, as it is not affected by UV light.

Derek

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The other thing you could try if you think its a very small gap that's letting the water in is 'Captain Tolleys Creeping Crack Cure' - available from any yacht chandlers.

Its a very searching liquid that finds its way into cracks and voids then turns into a jelly and expands slightly.

It also repairs itself if the joint it is sealing moves.

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Thanks for your input guys.  Seems its a race between Sikaflex and CT1, I'll read up about them.

I was thinking of trying to jack the obsy up and lay a 10mm thick neoprene strip bedded top and botton on sealant.  That's obviously a lot of work so I think I'll try one of your recommended sealants first.

Just a couple of questions:

1) did you treat the concrete before sealing or did you apply straight onto the concrete as laid?

2) did you apply the sealant from the tube and leave it or did you tool it into the joint somehow?

Thanks again,

Robin

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I have always had the best success by getting the Sikaflex into the joint rather than around it.

If you are going to trowel the Sikaflex into the joint (which is a good idea) then mask around the area or it will end up everywhere (you can guess how I know !!)

The good news is that ordinary white spirit removes it whilst its uncured. Once its cured nothing will shift it but you can paint over it - paint sticks very well to it (unlike silicone).

If you dont have a supplier near you I can post you as many tubes as you need (I have a chandlery) at cost price plus postage.

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I'm guessing here but it sounds like the base is LARGER than the obsy forming a 'shelf' for rainwater to collect and seep under the obsy walls. If so this is a classic error of construction and no sealant will give a permanent solution - excuse the pun. You only have to look at the perimeter of a house for example and note there's no base overhang and for good reason.

Sorry guys - just take a gander at basic building construction :-)

Nytecam - architect with 50+yrs experience

Edited by nytecam
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Hi Robin,

1: No pretreatment of the conctrete, the CT1 was applied direct to the concrete and glass fibre.

2: Straight from the tube - BUT - I used a 'high pressure' gun type applicator that makes it much easier to get a nice even bead.

http://www.sealantsonline.co.uk/Products/Resin_guns/KRO3711

CT1 is fairly flexible when cured so resists cracking off due to thermal expansion and other types of differential mechanical movements. 

I have used Sikaflex for doing stuff on boats and it was fine but very pricey and a with very large product range it was difficult to know what the best grade was.

Hope this helps,

Regards, Hugh

Just a couple of questions:

1) did you treat the concrete before sealing or did you apply straight onto the concrete as laid?

2) did you apply the sealant from the tube and leave it or did you tool it into the joint somehow?

Thanks again,

Robin

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Thanks again for your help guys. It seems the best plan is to replace the sealant. For that I'll need some dry weather to give me time to remove the old sealant and apply the new.

The forecast for next week looks dreadful so,I'll use the time to order materials and then wait for a reasonable dry spell. Still undecided as to which sealant to get.

Cheers,

Robin

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For our own internal use (we are boat builders) we have stopped using Sikaflex - mainly because they had a 45% price increase in one unannounced jump but partly because it cures in the tube surprisingly quickly.

We still sell Sikaflex to the public but for internal use we now use Sabatak which is an identical product but doesn't cure in the tube, is half the price and performs exactly the same.

We also use CT1 when the items are damp.

Both are good but Sabatak lasts longer - CT! degrades eventually if exposed to UV.

I am happy to supply any of the above to you at cost plus VAT and postage.

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I use Soudal Fixall inside as it will degrade in UV, but it is very cheap and every bit as good as Sikaflex.  I only use Sikaflex 512 on the caravan and external jobs. Mine never gets the chance to go off in the tube as it is used so quickly. Yes it is not cheap but does work. Soudal  gives a very strong  bond. I think I pay about £4.50 a tube, cannot be sure. I will look out for CT1 and try it sometime internally.

Derek

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Now this is getting even more complicated. I can't see getting the concrete completely dry till summer and I don't really want to wait that long. So now I need something that will adhere to damp concert and is also UV resistant.

Would that be Sikaflex 512?

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Now this is getting even more complicated. I can't see getting the concrete completely dry till summer and I don't really want to wait that long. So now I need something that will adhere to damp concert and is also UV resistant.

Would that be Sikaflex 512?

No. No. definitely No. :) I do not think Sikaflex would work on wet cement or concrete very well.(never tried it anyway).

Sikaflex is good but I would go with Skipper Billy. Try CT1, But I would use Sikaflex externally some time afterwards to cap the joint. I.e. Stop UV getting to the CT1. You will be able to do this in the summer when dry conditions prevail. I had a look at the CT1 website and their adverts, very informative. CT1 looks to be a fair bit thinner to apply as well. But that could be because it was in warmer conditions than when I usually get to apply it. I usually put the Sikaflex or Soudal in a sink filled with hot -ish water for half an hour before application. If you don't it is a sod to apply even with a good gun. You hand will get knackered quite quickly if it is cold, as it firms up with cold temps. The CT 1 website videos show it being applied under water, very impressive if true. It also has a much better stretch/flexibility from their adds. I don't doubt that as Skipper Biily is promoting it, he can't afford to give us duff info, now can he? ;). ;)

I will have to try it shortly if for no other reason than his say so. I am always on the lookout for something better and easier to use.

Derek

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I'm guessing here but it sounds like the base is LARGER than the obsy forming a 'shelf' for rainwater to collect and seep under the obsy walls. If so this is a classic error of construction and no sealant will give a permanent solution - excuse the pun. You only have to look at the perimeter of a house for example and note there's no base overhang and for good reason.

Sorry guys - just take a gander at basic building construction :-)

Nytecam - architect with 50+yrs experience

I've learned this, too, and totally agree. A 'water shelf' is the last thing you want and flagging this up on observatory builds would be a good idea. Trouble is, if you are buying a preformed fibreglass observatory then it's going to be quite a challenge to pre-form your own concrete circular base at just the right diameter and perfectly round - assuming that the incoming fibreglass structure is also perfectly round... If you can do it then do it, I would say.

Perhaps what the fibreglass observatory builders should do is offer a a moulded rain shedder which goes around the circular walls near the bottom, slopes downwards, and would overhang a slightly oversized circular concrete base.  This would reduce the precision needed for the construction of the circular base.

My last two sheds have been just the same size as the concrete. This is a very, very good idea.

Olly

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I've learned this, too, and totally agree. A 'water shelf' is the last thing you want and flagging this up on observatory builds would be a good idea. Trouble is, if you are buying a preformed fibreglass observatory then it's going to be quite a challenge to pre-form your own concrete circular base at just the right diameter and perfectly round - assuming that the incoming fibreglass structure is also perfectly round... If you can do it then do it, I would say.

Perhaps what the fibreglass observatory builders should do is offer a a moulded rain shedder which goes around the circular walls near the bottom, slopes downwards, and would overhang a slightly oversized circular concrete base.  This would reduce the precision needed for the construction of the circular base.

My last two sheds have been just the same size as the concrete. This is a very, very good idea.

Olly

You are absolutely right.  But the advice from Pulsar is to construct a slab that has a radius 150mm larger than the observatory. Had I known what I know now.......

I'm just desparate to find a solution so that I can start using the obsy again.

Robin

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Hmmm, what about attacking the problem form the inside? I'm not a builder, so just thinking out loud. Inside the observatory, using waterproof cement, lay a ring of shallow bricks round the perimeter, not quite up to the fibreglass wall. These need not be full size bricks, nor even bricks in the normal sense at all. They might be more like decorative brick strips or path edgings or whatever, maybe only two inches high. Once down you could fill the gap between this brick ring and the fibreglass with a waterproof mortar or a resin of some kind. Take advice on what would be best.

Olly

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Further to Olly's idea, google "curved bricks" they do make them........

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Hi Robin,

I wouldn't  stress too much about this. My Pulsar sits on a concrete slab that extends about 300 mm past the base so quite a large 'shelf'. But - no problems at all with water getting in!

However, if I lift the Pulsar rubber flooring tiles and polythene sheet, the floor concrete inside the observatory is definitely damp. This is nothing to do with water coming in from outside and eveything to do with the slow, slow release of water from the concrete itself. I have always used a dehumidifier in my observatory for exactly that reason. 

I think that unless you have the patience to let the concrete slab cure completely - no idea how long but probably years - you will have to find a way to deal with the water coming from the concrete. Ventilation would be one way but that would still give a fairly humid internal environment. I just did what many others have done and installed a dessicant type dehumidifier - Ela type DD822. This is very effective. I left an uncoated mild steel counterweight in the observatory and it had very little surface rusting even after 6 months. This was good enough for me to stop worrying about a fairly damp floor under the rubber tiles and polythene sheet.

Regards, Hugh

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Thanks all again.  I've decided to try CT1 in three strips on the inside, middle and outside of the base flange.  Advice from Hugh and Skipper Billy plus watching a video on the CT1 site convinces me that its worth a try.  I don't mind it being a bit damp in there but I'm getting puddles on the south and west sides at present.

If that fails then I'll think about using a circular brick wall.  I did find a manufacturer for radial stretchers that are just about the right radius for the observatory.  However this as well as being more expensive would raise the observatory by about 75mm which would rob me of a bit of sky. I dont fancy the thought of having to raise the pier.

Thanks for your info on the dehumidifier Hugh.  The one I have keeps icing up even in these relatively mild conditions.

Best wishes,

Robin

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