Solid Hardwood, Engineered and Laminate Flooring - Uneven Subfloor with Drain Covers?!

I have pulled up carpet in a basement room of our house, which has a concrete floor that is below ground level, with the intent to install laminate click type flooring. However, I have now found that the room has two areas where the concrete dips down around what appear to be thin flexible plastic drain access covers (the dips are around 2 to 3 feet in diameter and are graded gradually down towards the plastic covers - I would guess that they are around 1/2" down at the deepest point). I do not know what these are for or what is under the covers. I have no choice but to cover these areas with laminate as they are well into the room (they were previously covered with underlay and fitted carpet and the dips were very apparent when walking in the room).

I need to fill these dips to provide a solid level floor for the laminate to be laid on. However, to ensure that these access points could be opened in the future I have been trying to find ways to fill these dips with something that can be easily removed. I was wondering if trying to make a rubber mould of the area could work. Alternatively, I have also thought of lining the areas with thin plastic sheeting and then pouring in self-levelling compound. Are these ideas way off base? Grateful for any other suggestions?

These slopes are meant for draining in the event of a flood. Seeing this room is below grade, I would worry about excess moisture and water penetration. Both these would be very bad for a laminate floor.

Have you done a moisture test yet? Most laminate manufacturers will not warranty the material if you install it in high moisture areas.

Yes, I realise the slopes are for draining but I am unsure as to where the source of the water would come from. I assume it would be from rising groundwater coming up the through the plastic access covers. We have a sump pump in our furnace room so hopefully this would reduce the risk of the laminate floored room being flooded.

I intend to put down plastic sheeting as a moisture barrier and to run this up the walls a few inches so that it is sealed behind the baseboards. However, I have NOT yet done a moisture test and so should probably do this first. Is this best done with a moisture meter and if so can these typically be rented from tool rental shops? Are there alternative to moisture meters? I do not want to buy one as this will be a once only job for me (I hope).

Well, if you're determined to do this, here are some suggestions. Test for moisture by taping a one foot square piece of plastic to the floor with duct tape. A plastic trash bag will do fine. Leave it there a week or so and then pull it up. If you have moisture issues, the concrete will do any thing from turning a darker color for less moisture to being very wet with standing water with lots of moisture. What many folks don't realize is concrete is a huge sponge and will wick an amazing amount of water up through it. With any luck at all, the concrete will still be the same color as the floor that had no plastic taped to it. If it turns color, imagine what you'll have under the moisture barrier growing in a year or so after installing the laminate? Don't try the plastic film and leveling compound. The leveler needs to get a good bond to the floor or it forms this weird looking dish, shrinks away from the concrete, and is easily broken when stepped on. Care to guess how I know THAT one? It was embarrassing to say the least. One idea would be to set an old coffee can with both ends cut out, so it is a tube, over the cover and tape it down so the leveler can't get under it or move it. Then level the area around it. That should leave the cover exposed in the case of a flood of some sort or as access to the clean out that it may actually be. Once the leveler sets up, build a lid over the hole so your laminate doesn't tend to break when the hole is stepped on. Doing this at all is not really a good idea. I have a friend who does flood restorations for a living and he's told me some really wild stories of what caused someones place to flood.

Smokey49, thanks for the very useful reply - you certainly bought a smile to my face regarding your unfortunate experience with the leveler (laughing with you and NOT at you). Great to learn from others and not repeat mistakes - so thank you for putting me off that idea. Your coffee can idea is interesting and could certainly work, I could even rig up a small wooden frame as one of the covers is rectangular. However, I want to err on the side of caution - I don't want to be one of those wild flood stories you refer to - and so I'm going to try the following first:

1. Moisture test - will try your plastic bag approach for starters. Is this method okay on its own or should I be considering a moisture meter or calcium chloride dome test as well?
2. Remove access covers and determine what they are there for.

I will report back once I have the answers to the above and then plan my way forward from there (based on the excellent help from this forum).

Many thanks.

The plastic test will tell you IF you have a problem. The more professional tests will determine the extent of the problem, if one exists. Have fun and we'll look forward to progress reports.

Okay, I have applied three plastic sheets in various locations around the room and will leave them for a week as suggested.

I have also checked under both plastic access covers:

Cover 1 - This cover is around 8" x 12" in size and it is recessed below the concrete level by about 1/2". Under the cover is a platsic lined rectangular pit around 18" deep. At the bottom of the pit is a 4" diameter plastic pipe and a Fullport Backflow Preventer. The pit also contains what I assume to be groundwater to a depth of around 6", i.e. at least 12" below the level of the concrete level.

Cover 2 - This cover is circular, around 6" in diameter and flush with the concrete floor. It is in line with the pipe leading to Cover 1 and so is sure to be related to it. The plastic cover dips down in the middle and so I'll probably put some roofing felt in this area to provide some coarse levelling before I lay the floor. Under the cover the circular hole has been filled with large pebbles, covered in thick clear plastic and then a mess of solid gunk has been splattered over the top of this. The hole is essentially full of these pebbles and gunk. Any idea what this hole could have been for?

I am confused why this valve access pit would have been located in the middle of a room that is identified as an office on the building plans. The room was carpeted when we moved in with a double layer of underlay over Cover 1.