Thread: Sealing concrete floor for timber boards

Plenty of good proprietry sealers around.

Does the set of instructions talk about an underlay ? If not then it should.

What , if anything , does your local building authority have to say about the matter .
And ,
is there a DPC under the concrete ?

Thanks Artme and Jock.
Which of the proprietary brands have you had success with?

With regards the local authority requirements, I don't know if there is anything under the slab, that is why I am being cautious. Doesn't take much time, money or effort to slap a coat of sealer on the slab to protect against any possible moisture ingress on a $3,000 floor.

Good investment I would think, but I really need to know what is the best available product eg Bondcrete mix 1:4 parts water as a sealant?

hi jill.

a lot of timber floor companies use sika.

it is a 2 part epoxy which you mix together in a drum.
the mix ratio is 50/50. then mop it straight on to the concrete floor.

it is one of the best quality sealers you can get, hence the expensive price.

another brand i have seen being used on site is bostik aquashield sb40.

justin.

As Justin says Jill.

We laid a floating floor in our lounge/dining area. I didn't seal beacause there is a layer of black plastic under the slab.
BUT as a precaution I laid plastic sheeting down, appropriately tapped along the joins. Over this was placed a ather sheeting of thin, foam like material ( you see it used as packaging). the idea of this layer is to help with any uneven finishing of the floor.

Several years and absolutely no problems.

Don't forget the expansion gap around the walls!

Good luck!!!

Well, I ended up giving the floor 2 coats of Bondcrete 4:1 sealing coat mix just to be on the safe side. The bamboo floor installers put down a layer of 2mm thick foam with polythene backing, so that should make it water proof

Interestingly, the bamboo floor was only tongue and groove board 1800 long , which was glued together and temporarily clamped using PVA glue, and the whole floor was left floating, so you can feel the slight give in it where the floor is uneven.

They told me bamboo expands 2mm per metre with moisture, the expansion being across the board width.

The real problem is that they made a mistake with a longitudinal rip cut, so that in one section of the floor adjacent to the wall there is a 12 mm gap. All the skirting boards are 11mm thick these days - searched all the shops and suppliers.

so I decided to make my own from 12mmx 63mm pine and a 1/2inch roundeover bit on the router table - no such thickness available locally - all 12mm nominal stuff measures 11mm.

In the end found some 19x 63mm bullnose skirting, at Bunnies of all places, and got that machined down to 13mm thick at one of the local timber places - that did the trick.

Thanks for the advice and suggestions you have all made

Regarding the plastic under the slab.
I have heard that teh main reason for this to stop the moisture leaving the slab when it is curing to let it cure slower. Doesn't help much with stopping moiture rising through the slab. The plastic is not generally under the foootings. So some type of sealing the top is a must.
Hope this helps.
Great forum
Cheers
Kurt

Hello GillB

If you are floating your bamboo floor, then the underlay usely will have the moisture barrier incorperated into it, so you don`t have to paint the concrete. Only with the direct stick flooring that the moisture barrier is painted on. I always use Sika.

thanks for this, simply bamboo, and others. The installers put the 2mm foam sheet with plastic sheet backing on the concrete floor, then floated the bamboo floor, which was simply tongue and groove with PVA glued joints, and they clamped for an hour or two. Could walk on on it as soon as they were finished - looks great.

Still glad I put down the Bondcrete sealing mix as double security against damp on the boards

Also they said the board expand 2mm per metre width of boards with moisture ingress during summer up here in the tropics