Fixing MDF panels to the side of kitchen units

My partner wanted our new kitchen to have that classic look - so we bought some MDF tongue & groove panels and I trimmed them to size and and had them sprayed up to match the colour of the units.

Now I've come to fixing them, and not sure of the best approach. Some of the boards are slightly curved so it would need a strong fix to prevent them bowing. I can see three options -

1. Glue them
2. Nail them
3. Both glue and nails

I'm not an expert on adhesives, but some internet research has suggested gripfill or similar. However, this is described as 'gap-filling', but the sides of the kitchen units and the back of the MDF are really smooth and they would need to bond with virtually no gap at all, or it would look odd from the front. The glue can't just disappear so will this leave me with a few mm of gap between them? What about contact adhesive or something else?

Alternatively, I can borrow a nail gun from a friend, but I'm a bit worried that this would leave fairly conspicuous holes in the panels, or if I nailed through the grooves it might just rip straight through the boards since they're only quite thin.

Has anyone done anything like this?

Cheers

 

Thanks both.

Wouldn't foam create the gap I'm trying to avoid? Though I guess good clamping should minimise it.

What's an example of a polymer grab adhesive? I wondered about screwing from the inside but wasn't sure I'd get enough thread engagement to hold them well enough.

 

Cheers Bob, were yours 9mm MDF?

 

Thanks all

Sorry I had meant to state up front that they were 9mm. OK thanks it's looking like I'll go with this method, though some of the units will be tricky to strut - see photo.

Not had the backs painted except for a short distance to make sure the edges are covered. Was going to score the backs with a knife or something to add a bit of key - good shout on sanding the melamine.

Any suggestions for a grab adhesive that is fairly thin? I've never used the stuff before. I'll probably try a test one with some spare boards to compare foam to grab.

 

Do you mean something like this - https://www.screwfix.com/p/evo-stik...O0ZtxWOUAlDMTyNVKDAaAiMbEALw_wcB&gclsrc=aw.ds

 

I looked at that but didn't know if it would stick too fast with no adjusting time, or indeed if it would be sticky enough.

 

Thanks for everyone's help - if anyone has the same question in future, I glued with Gripfill then clamped the fronts and braced the backs as suggested. Then (very carefully) screwed through from inside to try and pull them tight. There wasn't much thread engagement, maybe 5-6mm but it definitely helped. Some of the units were impossible to brace so the screws saved the day there.

I don't rate gripfill, doesn't seem sticky at all so switched to the Geocell that was suggested which seemed better, though I think slower drying. Having said that the gripfill ones haven't fallen off so I guess it's alright.

Cheers!