Concrete pad treatment

[Mark Henthorne]

Last week saw the completion of a 2.4m x 2.4m concrete pad to accommodate an old Pulsar 2.1m dome I have acquired. What did anyone who has already trodden this path do to their concrete pad both before and after the dome was fixed in position? I am thinking in terms of sealant to afford protection against both concrete dust and any damp from below. I am probably less than a month away from starting the build. Any advice is very gratefully received, and thankyou in advance for any advice 😀.

[Tomatobro]

Screw wooden battens to the concrete floor and then board over with the green moisture resistant floor boards. Set the net height 10 mm below the door lip so you and cover with the interlocking floor tiles. Before laying the joists I used Thompson's brush on silicone concrete and brick sealer two coats.

Leave a gap between the dome and floor to allow air to circulate (25-30mm)

[Tomatobro]

[Mark Henthorne]

Many thanks Tomatobro, for taking time out to come back to me.

I had in mind originally to simply seal the surface (thanks for product info) and once the base was sealed to the pad with silicone, tile it with the interlocking tiles. However, there is a deal of merit in having a floor in as you describe, so I intend to pursue that route for better air flow. I was going to use the cable guard used in offices where it has to traverse the top of a carpet, but the raised floor will make cabling internally a lot more flexible. The last owner of the observatory had kitchen carpet directly on the floor with a thin plastic membrane separating it from the concrete. It did look as though perhaps condensation had penetrated, for the observatory suffered condensation internally primarily on the dome. I hope to achieve a rather better air seal between the dome, its sides, and the slot, for I have a descicant dehumidifier I'll be employing to keep the air inside at a reasonable humidity level.

[Swoop1]

Not got experience of an obsy myself but, I have seen much mention of allowing airflow to reduce condensation.

[pmlogg]

My Pulsar dome sits on a stone circle rather than concrete (the pier base is concrete) so I didn't want too many holes drilled into it to support decking. The support framework for my floor has cross members to make it into a single, structure which sits atop the stone rather than screwed to it. Cabling goes under the floor with one section of decking hinged to give access if necessary. I have a gap of around 6 to 7mm between the decking boards for ventilation.  To avoid losing small items down those gaps I have a section of thin matting covering one part of the decking.  I've not suffered from condensation on the dome but do have a dehumidifier for the benefit of the telescope.

[JeremyS]

My Pulsar dome has been sitting on a concrete circular pad for the last 17 years. Before installing it, I sealed with a few coats of garage concrete sealant paint. After installation I filled gaps under the lip and above the concrete with exterior grade silicone sealant. (I should have done this before placing the dome down). I then sealed around the inside of the lip with more sealant. 
I repaint the floor every year or two to keep it looking nice.

The first year I did have some water ingress, which came from the bolt holes that hold the pier in place. I then sealed around the base of the pier and all has been well

[Mark Henthorne]

Thankyou one and all for the many words of wisdom.

I feel inclined to make the raised floor as suggested by Tomatorbro, but with crossmembers as pmlogg has done (but including cable mananagement), without drilling to the concrete base, for each drill hole will break the sealant barrier. Obviously, there will be four holes required for the pier, and another eight for the four observatory quadrants attached to the floor. I am thinking now that once these are drilled, to "paint" the insides of the holes with a suitable bottle brush with a view to re-establishing the seal. How successful that will be I don't yet know, but it has to be berrer than leaving the bare drill hole, again in the light of experience of JeremyS's initial water ingress. My pier is second hand, and was a little rusty when I got it. Having had it sandblasted followed by powder coating, I'll hopefully avoid any rust recurrence that way.

Finishing as I started, thank you one and all for the benefit of your experiences.