Filling gap in floor

[Tywais]

Due to an underground water leak and the need to run new PVC above ground they cut a section out of the floor in the utility room which was a cover for the drainage system to see if they could spot the leak. Wasn't there so this is what the did to put the concrete slab back on. Large gaps around all edges and no match of the tiles. Now I've got roaches, much more than normal, in the back room. I suspect it is due to the large gaps around the cover as it is a large dark damp area underneath.

What is a good way to seal these cracks? Instant concrete, caulking? Want it to be simple and easy to smooth out to get an even surface. Is instant concrete, if suitable, available in Thailand, specifically Chiang Mai?

[eyecatcher]

These drain covers are common; we had them also, open drains 6 inch below the surface.

Its not clear from the photo that the new lid consists only of 4 tiles i.e 600x600.?

It does appear that there is no grout fill between the 4 tiles and these tiles are simply bed on an old base raised maybe an inch above the floor and with a slight overhang. i assume also there is no support for the tiles in the centre so any weight would collapse them.

On that basis my first choice, if it was me would be to remove the 4 small tiles and replace with a 600x600 tile, replacing the existing mortar bed with new. a continuous bed of mortar will seal the 4 edges of the tile.

Uness you can salvage a 600 tile, maybe ex display or buy a new box of 4 costing you 300bt this is the best but not necessarily the easiest solution for a non diy -er

If youare happy with the integrity of the 4 small tiles, then you need to flush up the 4 edges with a sand cement mortar mix. You lterally only need 1/3 bucketful but with means buying a bag of sand for 30bt and bag cement. i havent seen readymixed mortar here, but i dont care for it so would never look for it but as a quick diy solution its ok. you will need a small trowel to push the mortar in and flush it to the tile edge but be careful not to push too hard or it will simply find its way back into the drain.

the joints on the top should be filled with a mastic/silicone sealant. grout will simply dry out and eventually fall through (again i am assuming this area is raised and unsupported)

finally, if you think you will need access to the open drain in the future then a better solution would be to forget the tiles and screw down a 2x1 timber frame around the opening and then screw down a plywood lid onto the frame. i suppose it depends on the location aswell whether it would be a hindrance.

As with all diy, not often such a thing as quick easy and simple unless you have a shed full of tools, and odds and sods materials.

[Tywais]

Thanks eyecatcher, useful information. The patched on grey tiles are flush in height with the original blue tiles. The whole room has the blue tiles so this is an eyesore. The new tiles are mortared to the cement lid which is probably 12+ cm thick and very heavy, probably a hundred kilograms as two big guys were pressed to lift it with an iron tube. You can see in the top right corner the iron 'hook' to lift it out. The open area below the lid is probably a half meter deep with another round drain cover at the bottom. This utility area is an extension to the house and goes all the way across the back and across one side, so one very large utility area.

They used a concrete saw to cut along the edges of the lid, there were lines that sort of defined the lid otherwise with the original tile it looked continuous.

So, the replacement tile is flush in height with the original blue tile so just a mortar mix to fill in between the new tiles, the joints and out to the edge of the new tiles?

The workmanship for the whole job was piss poor. When they added new brick and concrete to the wall where the cut out a large hole to get to the main PVC pipe, they left the concrete rough and never came back to paint it. So, I bought my own paint and roller and did it myself, as I'm going to have to do with this.