need to glue small area of wood floor to concrete

[6tap]

Hi all
I am laying a solid oak floor directly onto floorboards, using the secret nail technique, however there is an area about 4'x2' of concrete where a herth used to be.
I had planned on just gluing the boards to that area but the only glue I can find comes in a 5L tub and is £30, which is a lot considering I only need a small amount - Does anyone know of any alternate ways of solving this issue or recommend a less expensive glue option please?

Thank you

 

[WoodYouLike]

Grip fill - but no guarantee

 

[6tap]

Thanks I'll give that a try