Hi to all members from the UK!

I have always loved the look and finish of a good hardwood floor and as such decided to run with it in our lounfe and kitchen.

I completed the lounge about 6 weeks ago and am about to start the kitchen.

I opted to use a glue down method as it is concrete floors throughout.

I approached Mapei for a full specification to prepare and install the engineered 20mm thick flooring that we had chosen. Firstly i was advised to flatten the concerete using a moisture to.erant levelling compound then coat it with a two part epoxy liwuid damp membrane. I could then complete the job by glueing the flooring down with one if their wood flooring glues.

Everything went well and it seemed i had carrid out a successful installation.

However since finishing I have noticed a few hollow sounding areas. As a wall and floor tiler to trade i know this is not good.!!

Could anyone advise what this could be and also if there is any remedy at all to rectify this without lifting the floor? Ive noticed somewhere else talk of an injection resin that can be pumped under the wood floor??

What i am really scared of now is that i end up with the same problem i. The kitchen when i do that area...

Any advise would be greatly appreciated.

Not all the boards in an engineered floor are completely flat. Some have a little stiffness and will lay flat for a few minutes, but eventually want to spring back into the relaxed shape which can pop up a small area. With a board that doesn't lay flat on the floor I use a circular saw and set the blade so that when you put the board face down your saw kerf only goes part way though the board as you cut across. Sometimes it takes back cutting every couple of inches along the board to help the board lay flat. Setting the saw depth so that it just cuts to the top of the tongue when it is laying flat and upside down when you make the kerf cuts will limber up difficult boards so they lay flat when you turn them over. The kerf cuts will never show through if you don't go too deep and will help the glue grab and hold better. If you can get a general purpose two part epoxy, you can make the repair. Mix the epoxy together in a separate container then pour into a syringe and inject it into a hole the size of the syringe tip drilled through the flooring to the slab. The epoxy will hold the flooring where it sits, so you may need to weigh it down with a bucket filled with water as it sets up.

Thats superb, thanks Pete.!

I dont recall any of the boards looking out of shape when i was installing them but i will make sure to check when i lay the kitchen floor.

With regards to the glue skinning over, how much floor area do you tend to trowel onto the floor before fixing the boards in?

Also, what methods do you adopt to make sure the floor is flat enough? I have to work to a tolerance of+/- 3mm over 2m when tiling but am sure it has to be near perfect for engineered flooring? The boards are 2.2m long

I like to cover 2 feet wide or about 600mm so I can cover before any skinning.
One of your flat boards will make a great straight-edge using a good light source as you work away from where you are inspecting.

Thanks again Pete, ive just opened one of the boxes of flooring to i spect their ‘flatness’... the first full length is definitely slightly curved like a banana...

Is it worth me opening all boxes and carrying out your back cutting exercise before even thinking about installation.

When you say cut ‘to the top of the tongue’ does that mean right through the plywood and reach the oak veneer? The wood we have is 14/6

We really love the oak flooring but i am very nervous about future hollowness so really want to be metocullous how it goes down

With solid wood which is pretty stiff, I cut to the top of the tongue through the bottom of the plank. The plank is definitely more limber and the kerf cut will allow more contact for the glue. With a plywood backing it will not be necessary to cut so deep and still have the flexibility because plywood cross layering of the veneer will make the plank more flexible as plywood is not as stiff as solid wood. Cutting to the top of the tongue should not diminish the possibility of as many re-sands. The glue will hold the plank to the sub-surface for strength. I don't know if you will need to cut all the way to the veneer to get enough flexibility. I don't think that the glue should need to hold the plank down, just hold it in place.

Cheers Pete.

If its OK with you I will send you photos when i am about to start to see what you think of the kerf cutting depth.?

Send pic's if you like. I like to keep track of the lengths of the flooring and open a couple of boxes so I don't end up with a lot of shorts that I cannot use for starters or finishing up a row, so I group them in piles by length. You could back kerf the ones that need it then get cleaned up before the glue goes down to get some production. Once you have some flooring laid you can work over the new floor, carefully.

Thanks Pete.

Im guessing the glue will work into the saw cuts to help with grip?

Do you ever install an epoxy DPM over concrete?

I haven't before, but I am going to put some down this next week, Sika "green ".