Observatory on concrete slab

[David at Bythel Obs]

About to lay base for installation of Pulsar dome. How to prevent water ingress under dome wall? Any thoughts or experience of solving problem sealant beneath dome wall doesn’t seem adequate.

thanks

[Franklin]

We use CT1 in the building trade.

[MikeP]

It is what I used with a new installation earlier this year and it has worked perfectly so far.

Mike

[inFINNity Deck]

Hi David,

where reasoning stops, sealants start... 😉

Most important in avoiding the ingress of water is simple: avoid it getting there in the first place! If the concrete slab has yet to be pored, try to make it in a way that water will not want to go to the inside of your observatory. There are multiple solutions for this, but in basic principle they are all quite alike, the next image shows four variants of it (dimensions are exaggerated):

So the red and blue lines are the surface of the concrete slab. The basic principle is that the surface outside the footprint of the observatory is sloped by at least 5mm per meter. In above figure profile A represents the most basic version of that profile. Ingress is even further prevented by having a raised floor inside the observatory as in profile B. Profile C has the raised floor all the way to the outside of the wall, which helps to keep torrential rains out, but is not as good against ingress as profile B. Profile D is even better as it combines all three defences: the outside slope, a raised edge along the outside of the wall and a further raised floor inside the observatory.

Once again, the dimensions are exaggerated: the slope 5mm per meter minimum, the raised edges 10mm should normally suffice, but the higher the better.

Nicolàs

PS: of course the pier should have a separate concrete foundation that is not in contact with the slab.

 

Edited December 17, 2021 by inFINNity Deck

[David at Bythel Obs]

Thanks Nicolas great clear diagrams