I'm fairly new to foam adhesive and don't yet completely trust it. I need to fix some oak door thresholds to the concrete sub-floor and I'd prefer not to have visible brass screws. I could counterbore and use plugs but am wondering whether Everbuild Constructa-pro adhesive foam would be up to the task - anyone here any experience of using it?
Not that brand, but used Soudal Low Expansion foam for several sheets of plasterboard to a brick well, it's not let go after a few years ...
If the gap is of the order of mm rather than cm the MS polymer stuff (Stxall and similar) may be more satisfactory. Certainly more solid, and less likely to expand ten times bigger than you expect. The latter often applies if you are not used to using foam. Obvious how I know that.
And whichever you use, but especially the foam, arrange a way to immediately clamp in the right position in all three axes when you have applied the adhesive, don't rely on just adjusting it and leaving it unclamped - it will rock, twist or whatever to its own preferred position.
hence the "low expansion" versions ...
The issue is if its trod on repeatedly does this affect the bond? Brian
"Gorilla" is a pretty good variant. Never let me down. The job will need securely clamping in position. Note all these adhesives need moisture to make them set.
Since posting on here about boarding a wall and someone suggested foam as an adhesive (I thought they were taking the piss), the amount of stuff i've mounted with foam is nobody's business, it's become a running joke.
I put a door casing in a brick wall, I propped it and secured it temporarily, filled the gap with foam, the plan was to put some screws in later but i've yet to get around to it. It's a solid door, relatively heavy, i even left a small gap between the casing and the floor to allow for flooring and it's stayed put for about
6 months now. I can't see it budging.
I've used both foam and polyester to fix wood frames to masonry. By far and away the most reliable route is polyester resin loaded with a stable filler.
Car Body Filler in fact. It has far higher strength than foam especially in gap filling situations.
I have found all the 'sticks like shit' gapfilling foams and polymers useless by comparison. They, in fact do stick just like shit and a good tug finishes them
You may want to drill holes in the concrete to key it.
Caution: Wood moves relative to concrete especially in terms of annual humidity cycles. The resin will not accommodate that much. Having said that the expansion of wood longitudinally - along the grain -- is very small and a thick bed of filler should be OK
Of course countersunk holes with oak plugs rammed home looks nearly as good.
Many double glazing installers used to foam the frames in and only use a couple of fixings to hold it while it set.
SteveW
The problem with foam is that it fails in tension.
Its ok for a rigid frame where all the forces are in shear, but for just a cill or threshold it likely that a good kick will put it in tension
the OP could screw some brass screws into the concrete to provide a solid non-rockable support for the wooden threshhold which just sits snuggly on top.
In fact he could bore some shallow holes into the underside of the timber so that the brass screws fit into each of them, thereby preventing any lateral movement too.
then attach with the foaming PU adhesive.
Andrew
This is what I did (FWIW). For one threshold in a high traffic area, and which has a short ramp to change levels, I decided to screw and plug. I used the adhesive foam on the other threshold and, so far, it's not showing any signs of being anything other than solid. Both got a light Georgian oak stain and then a good oiling with Osmo 3032; they look good, and it was particularly satisfying to make them from some naff oak skirting that I stripped from the kitchen. Thanks, as always, for the replies.
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